# Aerospace Science & Technology Dictionary

M

m
(Space Flight Glossary - JPL)
Meter (U.S. spelling; elsewhere metre), the international standard of linear measurement..
M
(Space Flight Glossary - JPL)
Mega (million).
M
(Space Flight Glossary - JPL)
Mass.
Mögel-Dellinger effect
(NASA SP-7, 1965)
M-curve
(NASA SP-7, 1965)
A plot of values of M-units (modified index of refraction) as a function of height in an atmosphere. M-curves are frequently used in ray tracing studies.
M-display
(NASA SP-7, 1965)
In radar, a display in which target distance is determined by moving an adjustable blip along the baseline until it coincides with the horizontal position of the target signal deflections. The control which moves the blip is calibrated in distance. Also called M-scan, M-scope, M-indicator.
M-indicator
(NASA SP-7, 1965)
= M-display
M-region
(NASA SP-7, 1965)
See M-region magnetic storm, note.
M-region magnetic storm
(NASA SP-7, 1965)
A magnetic storm that is independent of visible solar disk features; it begins gradually and shows a strong tendency to recur within a period of 27 days.
The hypothetical region on the solar disk assumed to be the source of the incident corpuscular radiation is called the M-region.
M-scan
(NASA SP-7, 1965)
= M-display.
M-scope
(NASA SP-7, 1965)
= M-display.
M-unit
(NASA SP-7, 1965)
See modified index of refraction.
M0
(Imagine the Universe Dictionary - NASA GSFC)
A representation of the mass of an object in terms of Solar mass. The average mass of the Sun is about 2x1033 grams. Astronomers often express units for other objects in terms of solar units-- it makes the resulting numbers smaller and easier to deal with.
Mach
(NASA SP-7, 1965)
= Mach number.
Some writers use Mach as a unit of speed equivalent to a Mach number of 1.00, as a speed of Mach 3.1.
Mach angle
(NASA SP-7, 1965)
The angle between a Mach line and the direction of movement of undisturbed flow. See Mach wave.
Mach cone
(NASA Thesaurus / NASA SP-7, 1965)
1. The cone-shaped shock wave theoretically emanating from an infinitesimally small particle moving at supersonic speed through a fluid medium. It is the locus of the Mach Lines.
2. The cone-shaped shock wave generated by a sharp-pointed body, as at the nose of a high-speed aircraft. See Mach wave.
Mach indicator
(NASA SP-7, 1965)
= Machmeter.
Mach line
(NASA SP-7, 1965)
A line representing a Mach wave; a Mach wave.
Mach number
(NASA SP-7, 1965)
(symbols M, NMa)
(Pronounced mock, after Ernst Mach, 1838-1916, Austrian scientist). A number expressing the ratio of the speed of a body or of a point on a body with respect to the surrounding air or other fluid, or the speed of a flow, to the speed of sound in the medium; the speed represented by this number. See Cauchy number.
If the Mach number is less than 1, the flow is called subsonic and local disturbances can propagate ahead of the flow. If the Mach number is greater than 1, the flow is called supersonic and disturbances cannot propagate ahead of the flow with the result that shock waves form.
Some authorities use
mach number but engineering practice is to use a capital M in all words and combinations employing Mach.
Mach reflection
(NASA Thesaurus)
The reflection of a shock wave from a rigid wall in which the shock strength of the reflected wave and the angle of reflection both have the smaller of the two values theoretically possible.
Mach wave
(NASA SP-7, 1965)
1. A shock wave theoretically occurring along a common line of intersection of all the pressure disturbances emanating from an infinitesimally small particle moving at supersonic speed through a fluid medium, with such a wave considered to exert no changes in the condition of the fluid passing through it.
The concept of the Mach wave is used in defining and studying the realm of certain disturbances in a supersonic field of flow.
2. A very weak shock wave appearing, e.g., at the nose of a very sharp body, where the fluid undergoes no substantial change in direction.
Mach-Zehnder interferometers
(Plasma Physics and Fusion Energy Glossary)
This is a variation of the Michelson interferometer which is used mainly in measuring the spatial variation in the refractive index of a gas (or plasma). A Mach-Zender interferometer uses two semi-transparent mirrors and two fully reflective mirrors located at the corners of a rectangle. The incoming beam is split in two at the first semi-transparent mirror, and the two halves of the beam travel along separate paths around the edge of the rectangle, meeting at the opposite corner. Typically one beam is a control, and the other travels through the system under study. The two beams meet at the second semi-transparent mirror, after which they are mixed together and interfere.
machine error
(NASA SP-7, 1965)
See error, note.
machine language
(NASA SP-7, 1965)
1. A language, occurring within a computer, ordinarily not perceptible or intelligible to persons without special equipment or training.
2. A translation or transliteration of sense 1 into more conventional characters but frequently still not intelligible to persons without special training.
machine word
(NASA SP-7, 1965)
For a given computer, the number of information characters handled in each transfer. This number is usually fixed, but may be variable in some computers.
Machmeter
(NASA SP-7, 1965)
An instrument that measures and indicates speed relative to the speed of sound, i.e., that indicates the Mach number. Also called Mach indicator.
MACHOs
(NASA Thesaurus)
See massive compact halo objects.
Maclaurin series
(NASA SP-7, 1965)
See Taylor theorem.
macroscopic
(NASA SP-7, 1965)
Large enough to be visible to the naked eye or under low order of magnification.
macrosonics
(NASA SP-7, 1965)
The technology of sound at signal amplitudes so large that linear approximations are not valid.
Magellan project (NASA)
(NASA Thesaurus)
A Venus exploratory mission to acquire radar imagery and topographic profiles of the planet surface and determine the characteristics of the Venusian gravity field. (This term is used to designate general project reviews, chronologies, and project management and planning.) Used for Venus Radar Mapper Project.
Magellan spacecraft (NASA)
(NASA Thesaurus)
A Venus probe incorporating Voyager and Galileo hardware designs equipped with a synthetic aperture radar system to acquire surface imagery, altimetric profiles, and surface radiothermal emissivities. Earth-based Doppler radio tracking of the spacecraft will be used to derive gravimetric data. (This term designates the spacecraft intrinsic and support hardware, instrumentation acquired data.) Used for Venus Radar Mapper.
Magellan ultraviolet astronomy satellite
(NASA Thesaurus)
This ESA mission will provide high resolution spectra of celestial sources down to sixteenth magnitude over the extreme ultraviolet wavelength range (between 50 and 150 nm). This mission is still in the study phase. Used for Magellan Mission (ESA).
magic tee
(NASA Thesaurus / NASA SP-7, 1965)
A compound waveguide or coaxial tee with four arms which exhibits directional characteristics, when properly matched, so that a signal entering one arm will be split between two of the other arms but not the third. A signal entering another arm is likewise split with half the energy entering one of the arms common to the other input but not its second arm and the other half of the energy entering the arm not used by the other input.
magma
(Photoglossary of Volcanic Terms - USGS)
Magma is molten or partially molten rock beneath the Earth's surface. When magma erupts onto the surface, it is called lava. Magma typically consists of (1) a liquid portion (often referred to as the melt); (2) a solid portion made of minerals that crystallized directly from the melt; (3) solid rocks incorporated into the magma from along the conduit or reservoir called xenoliths or inclusions; and (4) dissolved gases.
magma
(NASA Thesaurus)
Naturally occurring mobile rock materials, generated within the Earth and capable of intrusion and extrusion, from which igneous rocks are thought to have been derived by solidification and related processes.
magnesium cells
(NASA Thesaurus)
Primary cells with the negative electrodes made of magnesium or its alloy.
magnesyn
(NASA SP-7, 1965)
(A trade name, from magnetic + synchronous; often capitalized). An electromagnetic device that transmits the direction of a magnetic field from one coil to another, used to transmit measurements electrically from a point of measurement to an indicator in a remote-indicating system.
magnet
(NASA SP-7, 1965)
A body which produces a magnetic field around itself.
magnetars
(NASA Thesaurus)
Highly magnetized neutron stars believed to emit quasi-steady x-rays along with bursts of soft gamma rays-- emissions powered by their magnetic energy. According to the magnetar theory, these stars form in some fraction of all supernovae. When they are young (with ages less than about 10,000 years) magnetars may be observed as soft gamma repeaters (SGRs) or anomalous x-ray pulsars.
magnetic
(NASA SP-7, 1965)
1. Of or pertaining to a magnet.
2. Of or pertaining to a material which is capable of being magnetized.
3. Related to or measured from magnetic north.
magnetic axis
(Plasma Physics and Fusion Energy Glossary)
the location of the innermost flux "surface" in a toroidal device, the one which encloses no volume and has therefore degenerated from a flux surface into a single field line. Roughly, the circle through the middle of the dough of the donut. Additionally, in systems with magnetic islands (see entry below), each island has a local magnetic axis, distinct from the overall magnetic axisof the torus.
magnetic bay
(NASA SP-7, 1965)
A small magnetic disturbance whose magnetograph resembles an indentation of a coastline.
On earth, magnetic bays occur mainly in the polar regions and have durations on the order of a few hours.
magnetic bearings
(NASA Thesaurus)
Any application of the principle in which something capable of rotation and translation is held by the use of electromagnetic force without touching it. Applications range from small instruments to very large forces.
magnetic binary core
(NASA SP-7, 1965)
= binary magnetic core.
magnetic bottle
(Plasma Physics and Fusion Energy Glossary)
Colorful term used to describe a magnetic field structure which confines a plasma "like in a bottle".
magnetic character figure
(NASA SP-7, 1965)
= C-index.
magnetic compass
(NASA Thesaurus)
Compasses whose operation depends upon an element that senses the Earth's magnetic field, e.g., an instrument having a magnetic needle that turns freely on a pivot in a horizontal plane and that always swings to such a position that one end points to magnetic north.
magnetic compression
(NASA Thesaurus)
The force exerted by a magnetic field on an electrically conducting fluid or on a plasma.
magnetic confinement
(Plasma Physics and Fusion Energy Glossary)
Use of magnetic fields to confine a plasma. (Confinement involves restricting the volume of the plasma and/or restricting particle or energy transport from the center of the plasma to the edge.)
magnetic confinement fusion
(Plasma Physics and Fusion Energy Glossary)
Method of fusion which uses magnetic fields / magnetic bottles to confine a hot plasmauntil fusion occurs.
magnetic cooling
(NASA Thesaurus)
Keeping a substance cooled to about 0.2 K by using a working substance (paramagnetic salt) in a cycle of processes between a high-temperature reservoir (liquid helium) at 1.2 K and a low temperature reservoir containing the substance to be cooled.
magnetic core
(NASA SP-7, 1965)
= binary magnetic core.
magnetic crotchet
(NASA SP-7, 1965)
A sudden change in the earth's magnetic field due to an increase in the conductivity of the lower ionosphere. See sudden ionospheric disturbance.
magnetic current sheath
(NASA SP-7, 1965)
See plasma sheath.
magnetic declination
(NASA SP-7, 1965)
(symbol D, )
In terrestrial magnetism; at any given location, the angle between the geographical meridian and the magnetic meridian; that is, the angle between true north and magnetic north. Also called declination , and in navigation, variation.
Declination is either east or west according as the compass needle points to the east or west of the geographical meridian. Lines of constant declination are called isogonic lines and the one of zero declination is called the agonic line.
magnetic deviation
(NASA SP-7, 1965)
The angle between the magnetic meridian and the axis of a compass card, expressed in degrees east or west to indicate the direction in which the northern end of the compass card is offset from magnetic north. Also called deviation. Compare variation.
magnetic dip
(NASA SP-7, 1965)
(symbol i)
The angle between the horizontal and the direction of a line of force of the earth's magnetic field at any point. Also called magnetic inclination, magnetic latitude, inclination, dip.
magnetic dipole moment
(NASA SP-7, 1965)
= magnetic moment.
magnetic disturbance daily variation
(NASA SP-7, 1965)
(symbol SD)
A periodic variation of the earth's magnetic field that is in phase with solar (local) time. It is the difference between the solar daily variation (or the disturbed-day solar daily variation) and the quiet-day solar daily variation. This variation is primarily an effect of enhanced electromagnetic radiation during increased solar activity.
magnetic disturbed-day solar daily variation
(NASA SP-7, 1965)
(symbol Sd)
The solar daily variation of the earth's magnetic field obtained from the 5 most disturbed days of the month.
magnetic domains
(NASA Thesaurus)
Small areas on the surface of the body of thin films of a magnetic medium, each of which maintains a descrete magnetic field orientation relative to the others around it.
magnetic double refraction
(NASA SP-7, 1965)
The splitting, into two components, of a radio wave traveling in a region of free electrons. This is due to the interaction of the earth's magnetic field and the alternating field of the radio wave. Except for waves near the gyrofrequency, the components of the split wave, the ordinary ray and the extraordinary ray, will travel with slightly different velocities and be reflected at different heights. See magneto-ionic theory.
magnetic drum
(NASA SP-7, 1965)
A memory device used in computers; a rotating cylinder on which information may be stored as magnetically polarized areas, usually along several parallel tracks around the periphery.
magnetic element
(NASA SP-7, 1965)
1. In terrestrial magnetism, any of the following measurements: the vector magnetic field, also called total field (symbol ); the scalar intensity of the total field ( symbol F); declination, also called variation ( symbol D); the intensity of the horizontal component of the earth's field ( symbol H); the intensity of the vertical component ( symbol Z), taken as positive downward; the inclination or dip ( symbol I); the angle between and H; the intensity of the component of the horizontal field in the geographic north direction ( symbol X); and the intensity of the component of the horizontal field in the geographic east direction.
2. That part of an instrument producing or influenced by magnetism.
magnetic equator
(NASA Thesaurus / NASA SP-7, 1965)
That line on the surface of the earth connecting all points at which the magnetic dip is zero. Also called aclinic line. See geomagnetic equator.
magnetic equivalent amplitude indices
(NASA SP-7, 1965)
A linear measure of geomagnetic disturbance activity, based on the K-indices that gives an equivalent amplitude of the magnetic disturbance for the 3-hour period denoted by ap. A daily index Ap is defined as the average of the ap value over the 8 values of the day. See magnetic K-indices.
magnetic field coil
(Plasma Physics and Fusion Energy Glossary)
Coiled current-carrying wires used to generate magnetic fields.
magnetic field intensity
(NASA SP-7, 1965)
The magnetic force exerted on an imaginary unit magnetic pole placed at any specified point of space. It is a vector quantity. Its direction is taken as the direction toward which a north magnetic pole would tend to move under the influence of the field. If the force is measured in dynes and the unit pole is a cgs unit pole, the field intensity is given in oersteds. Also called magnetic intensity, magnetic field, magnetic field strength.
Prior to 1932 the oersted was called the gauss; but the latter term is now used to measure magnetic induction (within magnetic materials), whereas oersted is reserved for magnetic force. By definition, one magnetic line of force per square centimeter (in air) represents the field intensity of 1 oersted.
magnetic field lines
(Earth's Magnetosphere Glossary - GSFC)
Lines in space, used for visually representing magnetic fields. At any point in space, the local field line points in the direction of the magnetic force which an isolated magnetic pole at that point would experience. In a plasma, magnetic field lines also guide the motion of an ion and electron, and direct the flow of some electric current.
magnetic field reconnection
(NASA Thesaurus)
A change in topology of the magnetic field configuration resulting from a localized breakdown of the requirement for 'connection' of fluid elements at one time on a common magnetic field line. Alternatively, it occurs when an electric field exists with a component parallel to a locally two-dimensional X-type magnetic neutral line which is equivalent to a breakdown in connection.
magnetic field strength
(NASA SP-7, 1965)
= magnetic field intensity.
magnetic fields
(Solar Physics Glossary - NASA GSFC)
Fields of force that are generated by electric currents. The Sun's average large-scale magnetic field, like that of the Earth, exhibits a north and a south pole linked by lines of magnetic force.
magnetic fields
(NASA Thesaurus / NASA SP-7, 1965)
1. Regions of space wherin any magnetic dipole would experience a magnetic force or torque; often represented as the geometric array of the imaginary magnetic lines of force that exist in relation to magnetic poles.
2. = magnetic field intensity.
magnetic flux
(NASA Thesaurus)
The magnetic force exerted on an imaginary unit magnetic pole placed at any specified point of space. It is a vector quantity. Its direction is taken as the direction toward which a north magnetic pole would tend to move under the influence of the field. If the force is measured in dynes and the unit pole is a cgs unit pole, the field intensity is given in oersteds. Used for magnetic field intensity.
magnetic giant pulsations
(NASA SP-7, 1965)
Magnetic micropulsations having large amplitudes.
magnetic inclinations
(NASA SP-7, 1965)
= magnetic dip.
magnetic induction
(NASA SP-7, 1965)
A measure of the strength of a magnetic field existing within a magnetic medium.
The relation between the magnetic induction and magnetic field intensity is such that the magnetic induction within a small mass of material of magnetic permeability µ is, except for possible hysteresis effects, µ times greater than the external magnetic field intenstiy. Whereas magnetic field intensity is measured in oersteds, magnetic induction is measured in gausses.
magnetic intensity
(NASA Thesaurus / NASA SP-7, 1965)
= magnetic field intensity.
magnetic islands
(Plasma Physics and Fusion Energy Glossary)
A magnetic topology near a "rational surface" (see entry) where the flux surface is broken up into tubes which are not connected with each other poloidally. Islands may develop in non-ideal magnetohydrodynamic fluids, where electrical resistance becomes important and magnetic field lines are no longer "frozen-in" to the fluid. Then magnetic tearing and reconnection may allow field lines to link up and form "islands" with a local magnetic axis (see entry) in a narrow region near a rational surface (see entry).
magnetic K-indices
(NASA SP-7, 1965)
An approximately logarithmic measure of geomagnetic disturbance activity based on the range of the most disturbed magnetic element during each 3-hour interval of the day. The K-indices are assigned integers from 0 to 9.
The K-indices averaged over the observatories of the earth are called planetary indices Kp and divided into 28 grades.
magnetic latitude
(Earth's Magnetosphere Glossary - GSFC)
Geographic latitude of a location, in a system of latitudes and longitudes whose axis is not the rotation axis of the Earth but the magnetic axis, i.e. the axis of the dipole at the Earth´s center which best fits the internal magnetic field. The auroral zone, for instance, is near magnetic latitude 65 degrees.
magnetic latitude
(NASA SP-7, 1965)
= magnetic dip
See geomagnetic latitude.
magnetic lines of force
(NASA SP-7, 1965)
Imaginary lines so drawn in a region containing a magnetic field to be everywhere tangent to the magnetic field intensity vector if in vacuum or nonmagnetic material, or parallel to the magnetic induction vector if in a magnetic medium. See electric lines of force.
As so defined, these lines of force are merely convenient artifices for delineating the geometry of a magnetic field. They are given quantitative significance in magnetic theory by associating one line of force per square centimeter normal to the force for every oersted of field intensity (in vacuum), for every gauss of magnetic induction (in magnetic media).
magnetic local time
(Earth's Magnetosphere Glossary - GSFC)
(MLT)--in the a system of latitude and longitude whose axis is the dipole axis, magnetic local time is the longitude, measured not in degrees but in hours (1 hour = 15 degrees).
magnetic lunar daily variation
(NASA SP-7, 1965)
(symbol L)
A periodic variation of the earth's magnetic field that is in phase with the transit of the moon.
This variation is essentially a tidal effect. The amplitude of this variation changes with the phase of the moon, the seasons, and the sunspot cycle.
magnetic mach number
(Plasma Physics and Fusion Energy Glossary)
A dimensionless number equal to the ratio of the velocity of a fluid to the velocity of Alfvén waves in that fluid.
magnetic memory
(NASA SP-7, 1965)
1. The ability of a material to retain magnetism after the magnetizing force is removed.
2. = magnetic storage.
magnetic meridian
(NASA SP-7, 1965)
The horizontal line which is oriented, at any specified point on the earth's surface, along the direction of the horizontal component of the earth's magnetic field at that point; not to be confused with isogonic line. Also called geomagnetic meridian. Compare isoclinic line, magnetic equator.
magnetic micropulsations
(NASA SP-7, 1965)
Oscillations in magnetic records having periods of between a fraction of a minute and a few minutes, lasting for an hour or so.
magnetic mirror
(NASA Thesaurus / NASA SP-7, 1965)
A magnetic field so arranged that it will theoretically confine a hot plasma.
magnetic moment
(NASA Thesaurus / NASA SP-7, 1965)
1. The quantity obtained by multiplying the distance between two magnetic poles by the average strength of the poles.
2. A measure of the magnetic flux set up by the gyration of an electric charge in a magnetic field. The moment is negative, indicating it is diamagnetic, and equal to the energy of rotation divided by the magnetic field.
3. (symbol m). In atomic and nuclear physics, a moment, measured in Bohr magnetons, associated with the intrinsic spin of the particle and with the orbital motion of the particle in a system. Also called magnetic dipole moment.
magnetic monopoles
(High Energy Astrophysics Dictionary- GSFC)
A hypothetical particle which constitutes sources and sinks of the magnetic field. Magnetic monopoles have never been found, but would only cause fairly minor modifications to Maxwell's equations. They also seem to be predicted by some grand-unified theories. If magnetic monopoles do exist, they do not seem to be very common in our Universe.
magnetic north
(NASA SP-7, 1965)
The direction north at any point as determined by the earth's magnetic lines of force; the reference direction for measurement of magnetic directions.
magnetic nozzles
(NASA Thesaurus)
Nozzle devices used in some nuclear and plasma propulsion systems that utilize magnetic fields to direct and accelerate plasma flows, thereby providing thrust for propulsion.
magnetic number
(Plasma Physics and Fusion Energy Glossary)
A dimensionless number equal to the squareroot of the magnetic force parameter.
magnetic pole
(NASA Thesaurus / NASA SP-7, 1965)
1. Either of the two places on the surface of the earth where the magnetic dip is 90 °, that in the Northern Hemisphere (at, approximately, latitude 73° 8 N, longitude, 101° W in 1955) being designated north magnetic pole , and that in the Southern Hemisphere (at, approximately, latitude, 68° S, longitude, 144° E in 1955) being designated south magnetic pole. Also called dip pole. See geomagnetic latitude, geomagnetic pole, magnetic latitude.
2. Either of those two points of a magnet where the magnetic force is greatest.
3. In magnetic theory, a fictitious entity analogous to a unit electric charge of electrostatic theory. In nature only dipoles, not isolated magnetic poles, exist.
magnetic pressure
(Plasma Physics and Fusion Energy Glossary)
Pressure which a magnetic field is capable of exerting on a plasma; equal to the magnetic energy density.
magnetic pressure
(NASA SP-7, 1965)
The energy density associated with a magnetic field.
In a very real sense, there is energy stored in a magnetic field, and since energy per unit volume is equivalent to force per unit area or pressure, one may speak of the pressure exerted by a magnetic field. For plasma containment in a thermonuclear device, the magnetic pressure must be greater than the kinetic pressure of the plasma. See beta factor. A pressure of 1 atmosphere corresponds approximately to 5,000 gausses, and the pressure is proportional to the square of the field.
magnetic probes
(Plasma Physics and Fusion Energy Glossary)
A conducting coil (sometimes insulated and inserted into the plasma) will have an induced voltage due to changes in the magnetic flux through the coil, and can therefore be used to measure changes in magnetic field strength. Small coils used to measure the local field strength are known as probes. Magnetic probes placed outside a toroidal plasma which are used to measure the poloidal magnetic field are also called Mirnov coils.
magnetic properties
(Galileo Project Glossary - JPL)
The property of a material to attract iron, cobalt, or nickel.
magnetic pumping
(Plasma Physics and Fusion Energy Glossary)
Form of plasma heating where the plasma is successively compressed and expanded by means of a fluctuating external magnetic field.
magnetic quiet-day solar daily variation
(NASA SP-7, 1965)
(symbol Sq)
The magnetic solar daily variation obtained from the 5 most quiet days of the month.
magnetic reconnection
(Earth's Magnetosphere Glossary - GSFC)
In a plasma, the process by which plasma particles riding along two different field lines can be made to share the same field line For instance, following reconnection, solar wind particles on an interplanetary field line, and magnetospheric ones on a field line attached to Earth, may find themselves sharing the same "open" field line, which has one end anchored on Earth and the other extending to distant space.
magnetic sails
(NASA Thesaurus)
Devices that provide low thrust spacecraft propulsion by deflecting plamsa winds with a superconducting cable-generated magnetic field.
magnetic solar daily variation
(NASA SP-7, 1965)
(symbol S)
A periodic variation of the earth's magnetic field that is in phase with solar (local) time.
The primary source of this variation is the ionizing effect of solar electromagnetic radiation on the atmosphere coupled with the earth's rotation. The amplitude of this variation changes with the seasons and the sunspot cycle.
magnetic storage
(NASA Thesaurus / NASA SP-7, 1965)
In computer terminology, any device which makes use of the magnetic properties of materials for the storage of information.
magnetic storm-time variation
(NASA SP-7, 1965)
(symbol Dst)
A nonperiodic variation determined from the onset of a magnetic storm. This variation is characterized by a rapid increase of the magnetic horizontal intensity above the normal value, remaining so for a few hours and then rapidly decreasing to below the normal value and remaining so for periods up to several days. The intensity then returns slowly to the normal value.
magnetic storms
(NASA Thesaurus / NASA SP-7, 1965)
Worldwide disturbances of the earth's magnetic field. See M-region.
Magnetic storms are frequently characterized by a sudden onset, in which the magnetic field undergoes marked changes in the course of an hour or less, followed by a very gradual return to normality, which may take several days. Magnetic storms are caused by solar disturbances, though the exact nature of the link between the solar and terrestrial disturbances is not understood. They are more frequent during years of high sunspot number. Sometimes a magnetic storm can be linked to a particular solar disturbance. In these cases, the time between solar flare and onset of the magnetic storm is about 1 or 2 days, suggesting that the disturbance is carried to the earth by a cloud of particles thrown out by the sun.
When these disturbances are observable only in the auroral zones, they may be termed polar magnetic storms.
magnetic stress tensor
(Plasma Physics and Fusion Energy Glossary)
A second-rank tensor, proportional to the dyadic product of the magnetic field (B) with itself. The divergence of the magnetic stress tensor gives that part of the force which a magnetic field exerts on a unit volume of conducting fluid due to the curvature of the magnetic field lines.
magnetic switching
(Plasma Physics and Fusion Energy Glossary)
The use as switches of saturable inductors for producing high power pulses without electrical arcs. This is a principal technology for extending single-shot accelerators in light-ion-beam-driven inertial confinement fusion to repetitively pulsed devices for possible reactors. Three terawatt, 200 KJ magnetic switches have been developed for fusion drivers at Sandia National Laboratories. (Info from the 1985 OSTI Glossary of Fusion Energy; may be out of date.)
magnetic tape
(NASA Thesaurus / NASA SP-7, 1965)
A ribbon of paper, metal, or plastic, coated or impregnated with magnetic material on which information may be stored in the form of magnetically polarized areas.
magnetic variation
(NASA SP-7, 1965)
1. Variation, definition 1.
2. Change in a magnetic element.
magnetic variations
(NASA Thesaurus)
Changes in magnetic fields in time or space.
magnetic viscosity
(Plasma Physics and Fusion Energy Glossary)
A magnetic field in a conducting fluid will damp fluid motions perpendicular to the field lines, similar to ordinary viscosity, even in the absence of sizeable mechanical forces or electric fields.
magnetic wire
(NASA SP-7, 1965)
Wire made of magnetic material on which information may be stored in the form of magnetically polarized areas.
magnetically insulated transmission line
(Plasma Physics and Fusion Energy Glossary)
Used to transport power efficiently in vacuum lines at very high power densities. Although the cathode is a space-charge limited electron emitter, the electron flow is confined by self-generated or applied magnetic fields. MITL's are used extensively in light-ion-driven inertial confinement fusion.
magnetoelectric
(NASA SP-7, 1965)
Of or pertaining to electricity produced by or associated with magnetism.
Electromagnetic pertains to magnetism produced by or associated with electricity.
magnetoelectric transducer
(NASA SP-7, 1965)
A transducer which measures the electromotive force generated by the movement of a conductor relative to a magnetic field.
magnetofluiddynamics
(NASA SP-7, 1965)
= magnetohydrodynamics.
magnetogasdynamics
(NASA SP-7, 1965)
= magnetohydrodynamics.
magnetogram
(SOHO Glossary - GSFC)
A map showing the strength of the magnetic field in different locations.
magnetograph
(NASA SP-7, 1965)
The trace of an instrument recording variations in the geomagnetic field.
magnetohydrodynamic generators
(Plasma Physics and Fusion Energy Glossary)
A device that extracts kinetic energy from a jet of plasma and generates electricity.
magnetohydrodynamic instability
(Plasma Physics and Fusion Energy Glossary)
Class of unstable (growing, not damped) waves and other modes of oscillation which are described by MHD theory.
magnetohydrodynamic wave
(NASA SP-7, 1965)
= Alfvén wave.
magnetohydrodynamic waves
(NASA Thesaurus)
Low frequency waves in an electrically highly conducting fluid (such as a plasma) permeated by static magnetic fields. The restoring forces of the waves are, in general, the combination of a magnetic tensile stress along the magnetic field lines and the comprehensive stress between the field lines and the fluid pressure. Used for Alfvén waves, hydromagnetic waves, and plasma sound waves.
magnetohydrodynamics
(NASA Thesaurus / NASA SP-7, 1965)
(abbr MHD)
The study of the interaction that exists between a magnetic field and an electrically conducting fluid. Also called magnetoplasmadynamics, magnetogasdynamics, hydromagnetics.
magnetoionic theory
(NASA SP-7, 1965)
The theory of propagation of electromagnetic radiation through a medium containing ions in the presence of an external magnetic field.
It applies to the propagation of radio waves in the ionosphere, and provides theoretical relationships among such aspects of the subject as the index of refraction, radiofrequency, free-electron density, electron collision frequency, the earth's magnetic field (components relative to the direction of propagation), the nature of polarization, etc. See magnetic double refraction.
magnetoionic wave component
(NASA SP-7, 1965)
Either of the two elliptically polarized wave components into which a linearly polarized electromagnetic wave, incident of the ionosphere, is separated because of the earth's magnetic field.
magnetomechanics (physics)
(NASA Thesaurus)
Study of the effects which the magnetization of a material and its strain have on each other.
magnetometer
(NASA SP-7, 1965)
An instrument used in the study of geomagnetism for measuring a magnetic element.
magneton
(NASA SP-7, 1965)
See Bohr magneton.
magnetopause
(Earth's Magnetosphere Glossary - GSFC)
The boundary of the magnetosphere, separating plasma attached to Earth from the one flowing with the solar wind.
(NASA Thesaurus)
The study of the dynamics of generating electricity by passing a beam of ionized gas through a magnetic field.
(NASA SP-7, 1965)
= magnetohydrodynamics.
magnetosheath
(Earth's Magnetosphere Glossary - GSFC)
The region between the magnetopause and the bow shock, containing solar wind which has been slowed down by passage through the bow shock. As the magnetosheath plasma streams away from the bow shock, it gradually regains its former velocity.
magnetosphere
(NASA SP-7, 1965)
The region of the earth's atmosphere where ionized gas plays an important part in the dynamics of the atmosphere and where the geomagnetic field, therefore, plays an important role. The magnetosphere begins, by convention, at the maximum of the F layer at about 350 kilometers and extends to 10 or 15 earth radii to the boundary between the atmosphere and the interplanetary plasma.
magnetospheres
(NASA Thesaurus)
Region surrounding a celestial body where its magnetic field controls the motions of charged particles.
magnetostriction
(NASA Thesaurus / NASA SP-7, 1965)
1. The phenomenon wherein ferromagnetic materials experience an elastic strain when subjected to an external magnetic field.
2. The converse of sense 1 in which mechanical stresses cause a change in the magnetic induction of a ferromagnetic material.
magnetostrictive delay line
(NASA SP-7, 1965)
In electronic computers, a device in which a wave is induced by the characteristic, possessed by nickel and certain other materials, of shortening in length when placed in a magnetic field. The wave travels at the speed of sound through the material. See delay line.
magnetotails
(High Energy Astrophysics Dictionary- GSFC)
The portion of a planetary magnetosphere which is pushed in the direction of the solar wind; The long stretched-out nightside of the magnetosphere, the region in which substorms begin.
magnetron
(NASA Thesaurus / NASA SP-7, 1965)
An electron tube characterized by the interaction of electrons with the electric field of a circuit element in crossed steady electric and magnetic fields to produce alternating-current power output.
magnetron sputtering
(NASA Thesaurus)
A deposition method in which a microwave tube is utilized to confine a plasma magnetically to produce high deposition rates and a low working-gas partial pressure.
magnets
(NASA Thesaurus)
Bodies which produce magnetic fields around themselves.
magnification
(NASA Thesaurus)
A ratio of the size of an image to its corresponding object. This is usually determined by linear measurement. Used for magnifiers.
magnitude
(High Energy Astrophysics Dictionary- GSFC)
The degree of brightness of a celestial body designated on a numerical scale, on which the brightest star has magnitude -1.4 and the faintest visible star has magnitude 6, with the scale rule such that a decrease of one unit represents an increase in apparent brightness by a factor of 2.512; also called apparent magnitude.
magnitude
(NASA SP-7, 1965)
(symbol m)
1. The relative luminance of a celestial body. The smaller (algebraically) the number indicating magnitude, the more luminous the body. Also called stellar magnitude. See absolute magnitude.
The ratio of relative luminosity of two celestial bodies differing in magnitude by 1.0 is 2.512, the fifth root of 100.
Decrease of light by a factor of 100 increases the stellar magnitude by 5.00; hence, the brightness objects have negative magnitudes (Sun: -26.8; mean full moon: -12.5; Venus at brightest: -4.3; Jupiter at opposition: -2.3; Sirius: -1.6; Vega: 0.2; Polaris: 2.1). The faintest stars visible to the naked eye on a clear dark night are of about the sixth magnitude (though on a perfectly black background the limit for a single luminous point approaches the eighth magnitude). The faintest stars visible with a telescope of aperture a (in inches) is one approximately of magnitude $9 + 5 log$10 a. The magnitude of the faintest stars which can be photographed with the 200-inch telescope is about +22.7.
The expression
first magnitude is often used somewhat loosely to refer to all bodies of magnitude 1.5 or brighter, including negative magnitudes.
2. Amount; size; greatness. See order of magnitude.
MagSat 1 satellite
(NASA Thesaurus)
A scientific satellite launched by NASA for surveying the Earth's magnetic field. It was launched in October 1979 and reentered in June 1980.
MagSat B satellite
(NASA Thesaurus)
The second in a series of satellites for measuring the Earth's magnetic field. Similar magnetic measurements are proposed as part of the Geopotential Research Mission.
MagSat satellites
(NASA Thesaurus)
A series of satellites used to study the magnetic field.
main bang
(NASA SP-7, 1965)
The transmitted pulse, within a radar system.
main sequence stars
(SOHO Glossary - GSFC)
An area on the Hertzsprung-Russel Diagram containing "middle aged" stars like the Sun.
main stage
(NASA SP-7, 1965)
1. In a multistage rocket, the stage that develops the greatest amount of thrust, with or without booster engines.
2. In a single-stage rocket vehicle powered by one or more engines, the period when full thrust (at or above 90 percent) is attained.
3. A sustainer engine, considered as a stage after booster engines have fallen away, as in the main stage of the Atlas.
maintainability
(NASA Thesaurus)
A measure of the ease and rapidity with which a system or equipment can be retained in operational status through preventive maintenance or restored to operational status following a failure. It is characteristic of equipment design and installation, personnel availability in the required skill levels, adequacy of maintenance procedures and test equipment, and the physical environment under which maintenance is performed.
major axis
(NASA SP-7, 1965)
The longest diameter of an ellipse or ellipsoid.
major lobe
(NASA SP-7, 1965)
See lobe.
major planets
(NASA SP-7, 1965)
The four largest planets: Jupiter, Saturn, Uranus, and Neptune.
malfunction
(NASA Thesaurus / NASA SP-7, 1965)
Improper functioning of a component, causing improper operation of a system.
mammatus clouds
(Glossary of Weather Terms for Storm Spotters - NOAA)
Rounded, smooth, sack-like protrusions hanging from the underside of a cloud (usually a thunderstorm cloud). anvil). Mammatus clouds often accompany severe thunderstorms, but do not produce severe weather; they may accompany non-severe storms as well.
man powered aircraft
(NASA Thesaurus)
man tended free flyers
(NASA Thesaurus)
Intermittently manned spacecraft or platforms designed primarily to carry out experiments in reduced gravity and life science research. They also serve as annexes or components of space stations. Used for MTTF (space station).
man-machine integration
(NASA SP-7, 1965)
The matching of the characteristics and capabilities of man and machine in order to obtain optimum conditions and maximum efficiency of the combined system. See man-machine system.
man-machine system
(NASA Thesaurus / NASA SP-7, 1965)
A system in which the functions of the man and the machine are interrelated and necessary for the operation of the system.
manatees
(NASA Thesaurus)
Large plant eating aquatic mammals living in shallow tropical waters near the coasts of North and South America.
maneuverable reentry bodies
(NASA Thesaurus)
(1) Reentry vehicles capable of performing preplanned flight maneuvers during the reentry phase. (2) Ballistic missil reentry vehicles whose ballistic trajectory can be adjusted by internal or external mechanisms, enabling them to evade antiballistic defenses and.or strike their target with a high degree of accuracy.
manned
(NASA SP-7, 1965)
Of a vehicle occupied by one or more persons who normally have control over the movements of the vehicle, as in a manned aircraft or spacecraft, or who perform some useful function while in the vehicle.
manned maneuvering units
(NASA Thesaurus)
A propulsive backpack device for extravehicular activity. It uses a low thrust, dry, cold nitrogen propellant.
manned Mars missions
(NASA Thesaurus)
Any of several options for manned missions to Mars in which spacecraft are built for a particular mission. A mission is estimated by around 2020 and may last from one year to three years depending on speed and design.
manometers
(NASA Thesaurus / NASA SP-7, 1965)
Instruments used for measuring the pressure of gases and vapors both above and below atmospheric pressure. See vacuum gage.
manometric equivalent
(NASA SP-7, 1965)
The length in millimeters of a vertical column of a given liquid at standard room temperature equivalent to 1 millimeter of mercury at 0° C.
manures
(NASA Thesaurus)
Materials that fertilize land. Refuse of stables and barnyards consisting of mammal and bird excreta with or without litter.
many-to-few matrix
(NASA SP-7, 1965)
= decoder.
map-matching guidance
(NASA SP-7, 1965)
1. The guidance of a rocket or aerodynamic vehicle by means of a radarscope film previously obtained by a reconnaissance flight over the terrain of the route, and used to direct the vehicle by aligning itself with radar echoes received during flight from the terrain below.
2. Guidance by stellar map matching.
Mapsat
(NASA Thesaurus)
A proposed stereoscopic system for mapping the Earth from space to replace Landsat D as defined by the US Geological Survey.
Marangoni convection
(NASA Thesaurus)
Convective flow induced by surface tension gradients. This is important in both ground and space processing where a free surface is present.
March equinox
(NASA SP-7, 1965)
= vernal equinox.
mare (pl. maria)
(NASA SP-7, 1965)
Latin for sea. The large, dark, flat areas on the lunar surface, thought by early astronomers to be bodies of water. The term is also applied to less well-defined areas on Mars.
Marecs maritime satellites
(NASA Thesaurus)
The European Space Agency's system of two satellites provides maritime communications links between ships and coast Earth stations. Originally known as Marots, the system operates with one satellite over the Atlantic Ocean and one over the Pacific Ocean. It was leased to the International Maritime Satellite Organization for five years. Also known as the maritime European communications satellite.
marine biology
(NASA Thesaurus)
The study of marine fauna and flora and related topics.
marine chemistry
(NASA Thesaurus)
The study of the chemical processes in oceanic environments.
Mariner Mark 2 Spacecraft
(NASA Thesaurus)
A NASA concept of a basic planetary spacecraft for studying the outer planets, comets, and asteroids. The first of the series will be a comet rendezvous mission to be launched in 1994.
Mariotte law
(NASA SP-7, 1965)
= Boyle-Mariotte law.
Marisat 1 satellite
(NASA Thesaurus)
The first commercial maritime communication satellite.
Marisat satellites
(NASA Thesaurus)
A class of maritime commercial communication service satellites designed to provide telephone, telegraph, radio, distress messages and facsimile services to merchant ships, etc.
marmon clamp
(NASA SP-7, 1965)
A ring-shaped clamp, consisting of three equal length segments held together by explosive bolts, used to couple the main subsections of a rocket vehicle.
Marots (ESA)
(NASA Thesaurus)
Earlier name for the Marecs maritime satellites. Used for Maritime Communication Satellite (ESA) and Maritime Orbital Test Satellite.
marriage
(NASA SP-7, 1965)
= mating.
Mars
(Space Flight Glossary - JPL)
Fourth planet from the sun, a terrestrial planet.
Mars
(NASA SP-7, 1965)
See planet, table.
Mars 4 Spacecraft
(NASA Thesaurus)
One of a series of Soviet unmanned spacecraft designed for Mars exploration.
Mars Climate Orbiter
(NASA Thesaurus)
One of two spacecraft comprising the Mars Surveyor 98 program; launched December 1998. After obtaining a polar, nearly circular orbit around Mars, the Orbiter will serve as a radio relay during the Lander surface mission, then begin monitoring the atmosphere, surface, and polar caps for a complete Martian year. The Orbiter carries two science instruments: the Pressure Modulated Infrared Radiometer and the Mars Color Imager.
Mars craters
(NASA Thesaurus)
Craters from meteoritic impact on the surface of Mars.
Mars Global Surveyor
(NASA Thesaurus)
Spacecraft and related mission designed to orbit Mars over a two year period and collect data on the surface morphology, topography, composition, gravity, atmospheric dynamics, and magnetic field. Launched November 1996.
Mars Observer
(NASA Thesaurus)
Spacecraft and related mission to study the geoscience and climate of Mars. Launched September 1992. Contact with the spacecraft was lost in August 1993, three days before the scheduled Mars orbit insertion.
Mars Polar Lander
(NASA Thesaurus)
One of two spacecraft comprising the Mars Surveyor 98 program; launched January 1999. After a soft landing near the Martian south pole, the Lander will search for near-surface ice and possible surface records of cyclic climate change, and characterize physical processes key to the seasonal cycles of water, carbon dioxide and dust on Mars. Prior to landing, the Deep Space 2 microprobes will be released as part of a technology-validation mission related to multiple-lander spacecraft.
Mars Surveyor 98 Program
(NASA Thesaurus)
Mars exploration program consisting of two mission spacecraft-- the Mars Climate Orbiter and the Mars Polar Lander. Two surface penetrating microprobes (part of the associated Deep Space 2 mission) for detecting water ice are also piggybacking on the Lander.
Mars volcanoes
(NASA Thesaurus)
Volcanoes on the planet Mars.
marshlands
(NASA Thesaurus)
Transitional land-water areas, covered at least part of the time by estuarine or coastal waters and characterized by aquatic and grasslike vegetation. Used for bogs, coastal marshlands, marshes, and swamps.
martensitic transformation
(NASA Thesaurus)
A phase transformation occurring in some metals and resulting in formation of martensite.
martingales
(NASA Thesaurus)
In game theory, a procedure for recouping one's losses in previous wagers by doubling or otherwise increasing the amount bet.
Marx generator
(Plasma Physics and Fusion Energy Glossary)
A pulsed-power device invented by Erwin Marx. Capacitors are charged in parallel and then quickly discharged in series to produce high voltage, high current (and thus high power) pulses. Used in light-ion-driven and some laser-driven inertial confinement fusion systems.
mascons
(NASA Thesaurus)
Large scale, high density lunar mass concentrations below ringed mare.
maser
(NASA Thesaurus / NASA SP-7, 1965)
An amplifier utilizing the principle of microwave amplification by stimulated emission of radiation. Emission of energy stored in a molecular or atomic system by a microwave power supply is stimulated by the input signal.
mass
(NASA Thesaurus / NASA SP-7, 1965)
(symbol m)
A quantity characteristic of a body, which relates the attraction of this body toward another body. Since the mass of a body is not fixed in magnitude, all masses are referred to the standard kilogram, which is a lump of platinum.
Mass of a body always has the same value; weight changes with change in the acceleration of gravity.
mass drivers
(NASA Thesaurus)
Electromagnetic devices for the linear acceleration of projectiles or payloads. Applications include orbital insertion and transfer, propulsion systems, and hypervelocity accelerators.
mass flow rate per unit area
(NASA SP-7, 1965)
(symbol G)
In aerodynamics, the product of fluid density and the linear velocity of the fluid v or
G = pv
p = lower case Rho
mass number
(NASA SP-7, 1965)
The whole number nearest the value of the atomic mass of an element as expressed in atomic mass units.
The mass number is assumed to represent the total number of protons and neutrons in the atomic nucleus of the element and is therefore equal to the atomic number plus the number of the neutrons. The mass number of an atom is usually written as a superscript to the element symbol, as in O18, an isotope of oxygen with mass number 18.
mass ratio
(NASA Thesaurus / NASA SP-7, 1965)
The ratio of the mass of the propellant charge of a rocket to the total mass of the rocket when charged with the propellant.
mass spectrometers
(NASA Thesaurus)
Instruments that are capable of separating ionized molecules of different mass to charge ratio and measuring the respective ion currents. Used for ion spectrometers and retarding ion mass spectrometers.
mass to light ratios
(NASA Thesaurus)
The ratio of the mass of celestial body to its luminosity.
mass wasting
(Galileo Project Glossary - JPL)
The downslope movement of rock, regolith, and/or soil under the influence of gravity.
mass-charge ratio
(NASA SP-7, 1965)
The ratio of the mass number of an element to the number of electronic charges gained or lost in ionization.
mass-density
(NASA SP-7, 1965)
(symbol )
Mass per unit volume.
mass-energy equivalence
(NASA SP-7, 1965)
The equivalence of a quantity of mass m and a quantity of energy E, the two quantities being related by the mass-energy relation, E = mc2.
This relation was proposed by Einstein as a consequence of his restricted (or special) theory of relativity; it has subsequently received abundant experimental confirmation and is regarded as the conversion factor relating units of energy and mass; various useful forms of this factor are: $c2$ = (2.998 X 1010)$2$ centimeters per second = 8.987 X 1022 ergs per gram = 931.1 million electron volts per atomic mass unit.
See relativity.
mass-velocity ratio
(NASA SP-7, 1965)
A quantity mv /mr expressing the relativistic variation of mass with velocity.
where mv is moving mass, mr is rest mass, v is velocity, and c is the velocity of light.
This ratio becomes important only at speeds approaching the speed of light.
massifs
(NASA Thesaurus)
Massive topographic and structural features, especially in orogenic belts, commonly formed of rocks more rigid than those of their surroundings. These rocks may be protruding bodies of basement rocks, consolidated during earlier orogenies, or younger plutonic bodies.
massive compact halo objects
(NASA Thesaurus)
Objects, such as brown dwarfs, black holes, and massive planets, hypothesized to account for the dark matter in the halo of the Milky Way. The signature of these objects is the occasional amplification of the light from extragalactic stars by the gravitational lens effect.
master station
(NASA SP-7, 1965)
In a hyperbolic navigation system, such as loran, that transmitting station which controls the transmissions of another station or of other stations. See hyperbolic navigation, slave station.
mate
(NASA SP-7, 1965)
To fit together two major components of a system. Also called marry.
Mate (abbr)
(NASA SP-7, 1965)
Modular automatic test equipment.
material coordinates
(NASA SP-7, 1965)
= Lagrangian coordinates.
materials
(NASA SP-7, 1965)
In general, the substances of which rockets and space vehicles are composed; specifically, the metals, alloys, ceramics, and plastics used in structural, protective, and electronic functions.
materials recovery
(NASA Thesaurus)
The treatment of a material to reclaim one or more of its components.
mathematics
(NASA Thesaurus)
The study of the logical relationships among abstract entities. These relationships are expressed in numbers, symbols, and signs and may also be applied to concrete instances such as measures and properties of shapes. The main subdivisions include algebra, geometry, and analysis.
mating
(NASA SP-7, 1965)
1. The act of fitting together two major components of a system as mating of a launch vehicle and a spacecraft. Also called marriage.
2. = interface.
matrix
(NASA SP-7, 1965)
1. Any rectangular array of elements composed of rows and columns; specifically, such an array consisting of numbers or mathematical symbols which can be manipulated according to certain rules.
2. In electronic computers, any logical network whose configuration is a rectangular array of intersections of its input-output leads, with elements connected at some of these intersections. The network usually functions as an encoder or decoder . Loosely, any encoder, decoder, or translator.
matrix management
(NASA Thesaurus)
An organized approach to administration of a program by defining and structuring all elements to form a single system with components united by interaction.
matrix materials
(NASA Thesaurus)
The ingredients used as binding agents to produce composite materials.
matter-antimatter propulsion
(NASA Thesaurus)
Spacecraft propulsion by use of matter-antimatter annihilation reactions.
Matts (abbr)
(NASA SP-7, 1965)
= multiple airborne target trajectory system.
maximum energy density
(NASA SP-7, 1965)
See sound energy density.
maximum entropy method
(NASA Thesaurus)
Procedure used in estimating high resolution power spectra from short data lengths.
maximum evaporation rate
(NASA SP-7, 1965)
The maximum rate at which molecules could emerge from a surface, deduced from measurements of saturated vapor pressure at the same temperature. Also called Knudsen rate of evaporation or Langmuir rate of evaporation.
maximum sound pressure
(NASA SP-7, 1965)
For any given cycle of a periodic wave, the maximum absolute value of the instantaneous sound pressure, without regard to sign, occurring during that cycle. The unit is the microbar.
In the case of a sinusoidal sound wave, the maximum sound pressure is also called the pressure amplitude.
maximum usable frequency
(NASA Thesaurus / NASA SP-7, 1965)
(abbr MUF)
For a given distance from a transmitter, the highest frequency at which sky waves can be received.
Maxwell equation
(Plasma Physics and Fusion Energy Glossary)
The key equations governing electrical and magnetic phenomena. These are a set of four vector partial differential equations relating electric and magnetic fields to each other and to electric charges andcurrents.
Maxwell-Boltzmann distribution
(Plasma Physics and Fusion Energy Glossary)
Distribution function of particle velocities (or energies) corresponding to a system in thermal equilibrium with a temperature value of T.
Maxwellian distribution
(NASA SP-7, 1965)
The velocity distribution, as computed in the kinetic theory of gases, of the molecules of a gas in thermal equilibrium.
This distribution is often assumed to hold for neutrons in thermal equilibrium with the moderator (thermal neutrons).
maypole antennas
(NASA Thesaurus)
A class of antennas which use the deployable reflector concept for large space systems applications.
MBM junctions
(NASA Thesaurus)
Diode devices using metal-barrier-metal layers. Used for metal-barrier-metal junctions.
MC-cubed
(Space Flight Glossary - JPL)
Mission Control and Computing Center.
MCCC
(Space Flight Glossary - JPL)
Mission Control and Computing Center.
McLeod gage
(NASA SP-7, 1965)
A liquid-level vacuum gage in which a known volume of gas, at the pressure to be measured, is compressed by the movement of a liquid column to a much smaller known volume, at which the resulting higher pressure is measured.
Particular designs are named after the inventors or by various trade names.
MCT
(Space Flight Glossary - JPL)
Mission Control Team, Section 391 project operations.
MCW (abbr)
(NASA SP-7, 1965)
= modulated continuous wave.
MDI/SOI
(SOHO Glossary - GSFC)
See Michelson Doppler Imager/Solar Oscillations Investigation
mean
(NASA SP-7, 1965)
= arithmetic mean.
mean anomaly
(NASA SP-7, 1965)
See anomaly.
mean center of moon
(NASA SP-7, 1965)
A central point for a lunar coordinate system; the point on the lunar surface intersected by the lunar radius that is directed toward the earth's center when the moon is at the mean ascending node and when the node coincides with the mean perigee or mean apogee.
mean deviation
(NASA SP-7, 1965)
= average deviation.
mean distance
(NASA SP-7, 1965)
= semimajor axis.
mean Earth-Sun distance
(Global Land Information System Glossary - USGS)
Mean Earth-Sun distance is the arithmetical mean of the maximum and minimum distances between a planet (Earth) and the object about which it revolves (Sun).
mean equinox
(NASA SP-7, 1965)
A fictitious equinox whose position is that of the vernal equinox at a particular date with the effect of nutation removed. Also called mean equinox of date.
mean equinox of date
(NASA SP-7, 1965)
= mean equinox.
mean error
(NASA SP-7, 1965)
= root-mean-square error.
mean free path
(NASA Thesaurus / NASA SP-7, 1965)
(symbol l, , L)
1. Of any particle, the average distance that a particle travels between successive collisions with the other particles of an ensemble.
In vacuum technology, the ensemble of particles of interest comprises only the molecules in the gas phase.
2. Specifically, the average distance traveled by the molecules of a perfect gas between consecutive collisions with one another. It may be determined roughly from either of the formulas
or
where l is the mean free path; u (lower case Mu) is the dynamic viscosity; v is the kinematic viscosity; p (lower case Rho) is the density; c is the molecular speed (a function of the gas temperature); n is the number of molecules per unit volume; and d is the molecule diameter.
Given the mean free path l0 at a level where the pressure is p0 , the temperature is T0 (°K), and the acceleration of gravity is g0, then its value at any other level is
l = l0 p0 Tg / pT0 g0
where p, T, and g are the pressure, temperature, and acceleration of gravity, respectively, at the new level. See mixing length.

3. For any process the reciprocal of the cross section per unit volume for that process.
mean motion
(NASA SP-7, 1965)
(symbol n, µ)
Of an object in orbit, a measure of angular velocity,
n = / P
where P = period.
mean noon
(NASA SP-7, 1965)
The instant the mean sun is over the upper branch of the reference meridian; twelve o'clock mean time.
mean position
(NASA SP-7, 1965)
Of a star, the position on the celestial sphere computed from past observations plus known proper motion but not corrected for short term variations. See Besselian star numbers.
mean sea level
(NASA SP-7, 1965)
The average height of the surface of the sea for all stages of the tide over a 19-year period, usually determined from hourly height readings.
Mean sea level is the datum from which heights are measured. In this sense sometimes shortened to sea level. See geoid.
mean sidereal time
(NASA SP-7, 1965)
Sidereal time adjusted for nutation to eliminate slight irregularities in the rate.
mean solar day
(NASA SP-7, 1965)
The duration of one rotation of the earth on its axis, with respect to the mean sun.
The length of the mean solar days is 24 hours of mean solar time or 24 hours 3 minutes 56.555 seconds of mean sidereal time. A mean solar day beginning at midnight is called a civil day; and one beginning at noon, 12 hours later, is called an astronomical day. See calendar day.
mean solar second
(NASA SP-7, 1965)
Prior to 1960 the fundamental unit of time, equal to 1/86,400 of the mean solar day. Now replaced by the ephemeris second.
mean solar time
(Space Flight Glossary - JPL)
Time based on an average of the variations caused by Earth's non-circular orbit.
mean solar time
(NASA SP-7, 1965)
See solar time.
mean square
(NASA SP-7, 1965)
Referring to the arithmetic mean of the squares of the values under consideration, as mean-square amplitude, mean-square error.
mean square values
(NASA Thesaurus)
In statistics, values representing the average of the sum of the squares of the deviations from the mean value.
mean sun
(NASA SP-7, 1965)
A fictitious sun conceived to move eastward along the celestial equator at a rate that provides a uniform measure of time equal to the average apparent time; the reference for reckoning mean time, zone time, etc. See dynamical mean sun.
mean time
(NASA SP-7, 1965)
Time based upon the rotation of the earth relative to the mean sun.
Mean time may be designated as local or Greenwich as the local or Greenwich meridian is the reference. Greenwich mean time is also called universal time. Zone, standard, daylight saving or summer, and war time are also variations of mean time, specified meridians being used as the reference. Mean time reckoned from the upper branch of the meridian is called astronomical time. Mean time was called civil time in U.S. terminology from 1925 through 1952. See equation of time, mean sidereal time.
mean-square error
(NASA SP-7, 1965)
The quantity whose square is equal to the sum of the squares of the individual errors divided by the number of those errors.
meanders
(NASA Thesaurus)
Freely developing sinuous curves, bends, loops, turns, or windings in the courses of streams. They are produced by mature streams swinging from side to side as they flow across flood plains or shift course laterally toward the convex side of an original curve.
measurand
(NASA SP-7, 1965)
A physical quantity, force, property or condition which is to be measured. Also called stimulus.
measurement
(NASA Thesaurus)
The technical action required to assign values (numbers) to represent certain properties or attributes, using rules based on scientific laws. Used for determination, measuring, and quantization.
mechanical engineering
(NASA Thesaurus)
Branch of engineering dealing with the design, development and operation of machines including mechanical devices and prime movers, vehicles, machine tools, and manufacturing machinery.
mechanical equivalent of heat
(NASA SP-7, 1965)
(symbol J) = Joule constant.
mechanical system
(NASA SP-7, 1965)
In the study of vibration, an aggregate of matter comprising a defined configuration of mass, mechanical stiffness, and mechanical resistance.
mechanoreceptor
(NASA Thesaurus / NASA SP-7, 1965)
A nerve ending that reacts to mechanical stimuli, as touch,, tension, and acceleration.
median
(NASA SP-7, 1965)
The middle term of a series, or the interpolated value of the two middle terms if the number of terms is even. Compare mean.
median lethal dose
(NASA SP-7, 1965)
The amount of radiation required to kill, within a specified period, 50 percent of the individuals of a group of animals or organisms.
medium frequency
(NASA SP-7, 1965)
(abbr MF)
See frequency band.
mega
(NASA SP-7, 1965)
(abbr M)
A prefix meaning multiplied by 106.
megacycle
(NASA SP-7, 1965)
(abbr Mc, mc)
One million cycles; one thousand kilocycles.
The term is often used as the equivalent of one million cycles per second.
megaparsec
(NASA SP-7, 1965)
One million parsecs. See parsec.
mel
(NASA SP-7, 1965)
A unit of acoustic pitch. By definition, a simple tone of frequency 1000 cycles per second, 40 decibels above a listener's threshold, produces a pitch of 1000 mels. The pitch of any sound that is judged by the listener to be n times that of a 1-mel tone is n mels.
melt spinning
(NASA Thesaurus)
A material process by which polymers such as nylon and polyesters and glass are melted to permit extrusion into fibers through spinnerets.
meltdown
(Plasma Physics and Fusion Energy Glossary)
In a fission reactor, if there is insufficient coolant or the fission chain reaction proceeds too rapidly, heat can build up in the reactor fuel, causing it to melt. In extreme cases the whole fission core can melt down to (or even through) the reactor floor. Fusion reactors are not vulnerable to this.
melting points
(NASA Thesaurus)
liquidus and solidus coincide at an invariant point. In a phase diagram, the temperature at which the
melts (crystal growth)
(NASA Thesaurus)
Molten substances from which crystals are formed during the cooling or solidifying process.
membrane structure
(NASA SP-7, 1965)
A shell structure, often pressurized, that does not take wall bending or compression loads.
memory
(NASA SP-7, 1965)
The component of a computer, control system, guidance system, instrumented satellite, or the like, designed to provide ready access to data or instructions previously recorded so as to make them bear upon an immediate problem, such as the guidance of a physical object, or the analysis and reduction of data.
memory (computers)
(NASA Thesaurus)
The component of a computer, control system, guidance system, instrumented satellite, or the like, designed to provide ready access to data or instructions previously recorded so as to make them bear upon an immediate problem, such as the guidance of a physical object, or the analysis and reduction of data.
memory capacity
(NASA SP-7, 1965)
See storage capacity.
memory device
(NASA SP-7, 1965)
See storage.
Men, Mens
(NASA SP-7, 1965)
International Astronomical Union abbreviations for Mensa. See constellation.
Mensa
(NASA SP-7, 1965)
(abbr Men, Mens)
See constellation.
Mercator projection
(NASA Thesaurus)
An equatorial, cylindrical, conformal map projection derived by mathematical analysis (not geometrically) in which the equator is represented by a straight line true to scale. The meridians are represented by parallel straight lines perpendicular to the equator and equally spaced according to their distance apart at the equator. The parallels are represented by straight lines perpendicular to the meridians and parallel with (and the same length as) the equator. The parallels are spaced so as to achieve conformality, their spacing increasing rapidly with their distance from the equator so that at all places the degrees of latitude and longitude have the same ratio to each other as to the sphere itself. This results in greater distortion of distances, areas, and shapes in the polar regions (above 80 deg. latitude). The scale is increasingly poleward as the secant of the latitude. Because any line of constant direction (azimuth) on the sphere is truly represented on the projection by a straight line, the Mercator projection is of great value in navigation. It is used for hydrographic charts, and also to show geographic variations of some physical property (such as magnetic declination) or to plot trajectories of Earth satellites in oblique orbits. It is named after Gerhardus Mercator (1512-1594), a Flemish mathematician and geographer, whose world map of 1569 used this projection.
Mercury
(NASA SP-7, 1965)
See planet, table.
Mercury (planet)
(Space Flight Glossary - JPL)
First planet from the sun, a terrestrial planet.
(NASA Thesaurus)
Compounds of tellurium exhibiting photovoltaic characteristics and used for photodiodes and photodetectors in the 3 to 12 micrometer wavelengths at cryogenic temperatures. Used for cadmium mercury tellurides.
mercury ion engines
(NASA Thesaurus)
Machines providing thrust by expelling accelerated or high velocity mercury ions and often using energy provided by nuclear reactors.
mercury memory
(NASA SP-7, 1965)
The retention of information by the propagation of a sound wave in liquid memory.
Mercury surface
(NASA Thesaurus)
The surface of the planet Mercury.
meridian
(NASA SP-7, 1965)
A north-south reference line, particularly a great circle through the geographical poles of the earth. The term usually refers to the upper branch, that half, from pole to pole, which passes through a given place, the other half being called the lower branch. See coordinate, table.
A terrestrial meridian is a meridian of the earth. Sometimes designated true meridian to distinguish it from magnetic meridian, compass meridian, or grid meridian, the north-south lines relative to magnetic, compass, or grid direction, respectively. An astronomical meridian is a line connecting points having the same astronomical longitude. A geodetic meridian is a line connecting points of equal geodetic longitude. Geodetic and sometimes astronomical meridians are also called geographic meridians. Geodetic meridians are shown on charts. The prime meridian passes through longitude 0°. A fictitious meridian is one of a series of great circles or lines used in place of a meridian for certain purposes. A transverse or inverse meridian is a great circle perpendicular to a transverse equator. An oblique meridian is a great circle perpendicular to an oblique equator. Any meridian used as a reference for reckoning time is called a time meridian. The meridian through any particular place or observer, serving as the reference for local time, is called local meridian, in contrast with the Greenwich meridian, the reference for Greenwich time. A celestial sphere, through the celestial poles and the zenith.
meridian angle
(NASA SP-7, 1965)
Angular distance east or west of the local celestial meridian; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of the local celestial meridian and the hour circle of a celestial body, measured eastward or westward from the local celestial meridian through 180°, and labeled E or W to indicate the direction of measurement. See hour angle.
meridian transit
(NASA SP-7, 1965)
See transit.
meridians
(Space Flight Glossary - JPL)
Great circles that pass through both the north and south poles, also called lines of longitude.
meridional
(NASA SP-7, 1965)
Referring to a meridian.
meridional flow
(Glossary of Weather Terms for Storm Spotters - NOAA)
Large-scale atmospheric flow in which the north-south component (i.e., longitudinal, or along a meridian) is pronounced. The accompanying zonal (east-west) component often is weaker than normal. Compare with zonal flow.
mesas
(NASA Thesaurus)
Isolated, nearly level landmasses standing distinctly above the surrounding country, bounded by abrupt or steeply sloping erosion scarps on all sides, and capped by layers of resistant, nearly horizontal rock (often lava). Less strictly, very broad, flat topped, usually isolated hills or mountains of moderate height bounded on at least one side by a steep cliff or slope and representing an erosion remnant. Mesas are similar to, but have more summit area than buttes and are common topographical features in arid and semiarid regions of the United States. Mesas are often considered broad terraces or comparatively flat plateaus along river valleys. They are marked by an abrupt slope or escarpment on one side.
mesh
(NASA SP-7, 1965)
A set of branches forming a closed path in a network, provided that if any one branch is omitted from the set, the remaining branches of the set do not form a closed path.
The term loop is sometimes used in the sense of mesh.
meson
(NASA SP-7, 1965)
In the classification of a subatomic particles by mass, the second lightest of such particles. Its mass is intermediate between that of the lepton and the nucleon (see hyperon).
Mesons are highly unstable, very short-lived particles; they carry positive, negative, or no charge, and, in a vacuum, move with velocities approaching the speed of light. All of these particles have extremely short lifetimes and the heavier more unstable mesons tend to decay into lighter ones.
mesopause
(NASA Thesaurus / NASA SP-7, 1965)
The base of the inversion at the top of the mesosphere, usually found at 80 to 85 kilometers. See atmospheric shell.
mesopeak
(NASA SP-7, 1965)
The temperature maximum at about 50 kilometers in the mesosphere. See atmospheric shell.
mesoscale phenomena
(NASA Thesaurus)
Meteorological phenomena extending approximately one to a hundred kilometers (mesoscale cloud patterns, for example).
mesosphere
(NASA Thesaurus / NASA SP-7, 1965)
1. The atmospheric shell, in which temperature generally decreases with heights, extending from the stratopause at about 50 to 55 kilometers to the mesopause at about 80 to 85 kilometers.
2. The atmospheric shell between the top of the ionosphere (the top of this region has never been clearly defined) and the bottom of the exosphere. (This definition has not gained general acceptance.)
Mesozoic Era
(NASA Thesaurus)
An era of geologic time, from the end of the Paleozoic Era to the beginning of the Cenozoic Era, or from about 225 to about 65 million years ago.
message
(NASA SP-7, 1965)
1. An ordered selection from an agreed set of symbols, intended to communicate information.
2. The original modulating wave in a communication system.
The term in sense 1 is used in communication theory; the term in sense 2 is often used in engineering practice.
message processing
(NASA Thesaurus)
In communication operations, the acceptance, preparation for transmission, receipt and/or delivery of a series of words or symbols intended for conveying information.
MESUR
(Space Flight Glossary - JPL)
The Mars Environmental Survey project at JPL, the engineering prototype of which is called MESUR Pathfinder.
metabolic reserves
(NASA SP-7, 1965)
The energy source stored in chemical form, such as carbohydrates, that can be efficiently mobilized and utilized by the body, particularly for muscular activity and work beyond the normal level of activity of an individual.
metabolism
(NASA Thesaurus)
The sum of all physical and chemical processes by which living organized substance is produced and maintained and by which energy is made available for the use of the organism.
metabolites
(NASA Thesaurus)
Products of biological synthesis and/or metabolism.
metachemical
(NASA SP-7, 1965)
Pertaining to the chemistry of subatomic particles.
metagalaxy
(NASA SP-7, 1965)
The entire system of galaxies including the Milky Way.
metal clusters
(NASA Thesaurus)
Bonded aggregations of like metal atoms.
metal foams
(NASA Thesaurus)
Foamed materials formed under low gravity conditions in space from sputtered metal deposits. This experimental space processing was completed in the second NASA SPAR flight.
metal vapor lasers
(NASA Thesaurus)
Stimulated emission devices, the active materials of which are vaporized metals.
metal-nitride-oxide-semiconductors
(NASA Thesaurus)
Class of semiconductors utilizing silicon nitride and silicon oxide dielectrics.
metallic fuels
(NASA SP-7, 1965)
Of or pertaining to nuclear fuels which are a mixture, a pressed powder, or an alloy of a fissionable material, such as uranium-235 or plutonium-239, and a metal such as aluminum, zirconium, or stainless steel.
metallic glasses
(NASA Thesaurus)
Amorphous alloys (glassy metals) produced by extremely rapid quenching of molten transition-metal alloys (e.g., iron, nickel, and/or cobalt). These metallic glasses exhibit unique mechanical, magnetic, and electrical properties, superconductive behavior, and anticorrosion resistance, depending on the alloys, their formation and quenching techniques.
metallicity
(NASA Thesaurus)
The abundance index of a metal or metals for a celestial body.
metamorphic rocks
(NASA Thesaurus)
Rocks derived from pre-existing rocks by mineralogical, chemical and/or structural changes, essentially in the solid state. These changes are in response to marked changes in temperature, pressure, shearing stress, and chemical environment, generally at the depth of the Earth's crust. Metamorphic rocks constitute one of the three main classes into which rocks are divided, the others being igneous rocks and sedimentary rocks.
metamorphism (geology)
(NASA Thesaurus)
The mineralogical and structural adjustment of solid rocks to physical and chemical conditions which have been imposed at depth below the surface zones of weathering and cementation, which differ from the conditions under which the rocks in question originated.
metastable atom
(NASA SP-7, 1965)
An atom with an electron excited to an energy level where simple radiation is forbidden and thus the atom is momentarily stable. See forbidden line.
The presence of these metastable atoms in a discharge is the cause of several anomalous effects since in essence they are storing energy which can be released to other particles upon collision. The Penning effect is a result of the presence of metastable atoms.
metastable compound
(NASA SP-7, 1965)
A chemical compound of comparative stability which, however, becomes unstable under a particular set of conditions.
metastable propellant
(NASA SP-7, 1965)
A metastable compound used as a propellant.
Nitromethane (CH3NO2), for example, may be used as a monopropellant at chamber pressure above 500 pounds per square inch. At lower pressure, it requires an oxidizer for stable combustion.
metastable state
(AS&T Dictionary)
An excited stationary energy state, as of an atom, whose lifetime is unusually long.
meteor
(IMO Meteor Glossary)
The bright streak of light that appears in the sky as a result of friction between a meteoroid and the air molecules in our atmosphere. Entering the atmosphere at speeds between 10 and 70 kilometers per second, the friction-generated heat is hot enough to melt the surface layer of the object and ionize the air. The term originated with the Greeks circa 350 B.C. In its original Greek form, the word was meteora/meteoros and meant something raised up high into the air. Most of the meteors that are observed are produced by a meteoroid that is no larger than a grain of sand. The altitude at which the visible streak of light first appears is approximately 110 kilometers, +/- 20 kilometers.
meteor
(NASA SP-7, 1965)
In particular, the light phenomenon which results from the entry into the earth's atmosphere of a solid particle from space; more generally, any physical object or phenomenon associated with such an event. See meteoroid.
meteor path
(NASA SP-7, 1965)
The projection of the trajectory of a meteor in the celestial sphere as seen by the observer.
meteor shower
(NASA SP-7, 1965)
A number of meteors with approximately parallel trajectories.
meteor stream
(NASA SP-7, 1965)
A group of meteoric bodies with nearly identical orbits.
meteor trail
(NASA SP-7, 1965)
= meteor train.
meteor train
(NASA Thesaurus / NASA SP-7, 1965)
Anything, such as light or ionization, left along the trajectory of the meteor after the head of the meteor has passed.
meteor wake
(NASA SP-7, 1965)
Meteor train phenomena of very short duration, in general much less than a second.
meteoric
(NASA SP-7, 1965)
Of or pertaining to meteors and meteoroids.
meteorite
(NASA Thesaurus / NASA SP-7, 1965)
Any meteoroid which has reached the surface of the Earth without being completely vaporized.
meteoritic
(NASA SP-7, 1965)
Of or pertaining to meteorites.
meteoritics
(NASA SP-7, 1965)
The study of meteorites and meteoric and meteoritic phenomena.
meteoroid
(NASA Thesaurus / NASA SP-7, 1965)
A solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom or molecule.
meteoroid showers
(NASA Thesaurus)
Groups of meteoroids with approximately parallel trajectories. Used for meteor bursts.
meteoroid stream
(IMO Meteor Glossary)
Stream of solid particles released from a parent body such as a comet or asteroid, moving on similar orbits.
meteorological optics
(NASA SP-7, 1965)
= atmospheric optics.
meteorological rocket
(NASA SP-7, 1965)
A rocket designed primarily for routine upper air observation (as opposed to research) in the lower 250,000 feet of the atmosphere, especially that portion inaccessible to balloons, i.e., above 100,000 feet. Also called rocketsonde.
meteorology
(NASA Thesaurus / NASA SP-7, 1965)
The study dealing with the phenomena of the atmosphere. This includes not only the physics, chemistry, and dynamics of the atmosphere, but is extended to include many of the direct effects of the atmosphere upon the earth's surface, the oceans, and life in general.
A distinction can be drawn between meteorology and climatology, the latter being primarily concerned with average, not actual, weather conditions. Meteorology may be subdivided, according to the methods of approach and the applications to human activities, into a large number of specialized sciences. The following are of interest to space science: aerology, aeronomy, dynamic meteorology, physical meteorology, radio meteorology.
metering jet
(NASA SP-7, 1965)
A jet in a fuel-injection system.
methanation
(NASA Thesaurus)
The conversion of various organic compounds to produce methane.
method of attributes
(NASA SP-7, 1965)
In reliability testing, measurement of quality by noting the presence or absence of some characteristic (attribute) in each of the units in the group under consideration and counting how many do or do not possess it.
An example of this method is go and no-go gaging of a dimension.
method of characteristics
(NASA SP-7, 1965)
See characteristics.
method of moments
(NASA Thesaurus)
A method of estimating the parameters of a distribution by relating the parameters to moments.
method of small perturbation
(NASA SP-7, 1965)
= perturbation method.
Metis
(NASA Thesaurus)
A natural satellite of Jupiter orbiting at a mean distance of 127,960 kilometers.
Metonic calendar
(From Stargazers to Starships Glossary - GSFC)
Named for the Athenian astronomer Meton, it is based on the moon, counting each cycle of the phases of the Moon as one month. Days are kept approximately in step with the seasons by including 7 leap years of 13 months in each cycle of 19 years. Used by the Chinese and the Jews.
Metonic cycle
(NASA SP-7, 1965)
A period of 19 years, after which the various phases of the moon fall on approximately the same days of the year as in the previous cycle.
The Metonic cycle is the basis for the golden numbers used to determine the data of Easter. Four such cycles form a Callippic cycle.
metric photography
(NASA SP-7, 1965)
The recording of events by means of photography (either singly or sequentially), together with appropriate coordinates, to form the basis for accurate measurements.
metric system
(NASA SP-7, 1965)
The international decimal system of weights and measures based on the meter and the kilogram.
The use of the metric system in the United States was legalized by Congress in 1866 but was not made obligatory.
metric wave
(NASA SP-7, 1965)
See frequency band.
metrication
(NASA Thesaurus)
The conversion on an industry and/or nationwide basis of English units of measurement into the International System of Units, including engineering and manufacturing standards, tools and instruments, and all affected areas in the government and private sectors. Used for metric conversion.
metrology
(NASA Thesaurus / NASA SP-7, 1965)
The science of dimensional measurement; sometimes includes the science of weighing.
Mev
(NASA SP-7, 1965)
= million electron volt.
MGA
(Space Flight Glossary - JPL)
Medium-gain antenna onboard a spacecraft.
MGN
(Space Flight Glossary - JPL)
Magellan spacecraft.
MHz
(Space Flight Glossary - JPL)
Megahertz (106 Hz).
Mic, Micr
(NASA SP-7, 1965)
International Astronomical Union abbreviations for Microscopium. See constellation.
Michaelson actinograph
(NASA SP-7, 1965)
A pyrheliometer of the bimetallic type used to measure the intensity of direct solar radiation in terms of the angular deflection of a blackened bimetallic strip exposed to the direct solar beams.
Michelson Doppler Imager/Solar Oscillations Investigation
(SOHO Glossary - GSFC)
Helioseismology instrument aboard SOHO which analyzes the vibrational modes of the Sun. Also measures the Sun's magnetic field in the photosphere.
Micr.
(NASA SP-7, 1965)
International Astronomical Union Abbreviation for Microscopium. See constellation.
micro (abbr)
(NASA SP-7, 1965)
1. (abbr µ). A prefix meaning divided by 106.
2. A prefix meaning very small, as in micrometeorite.
microballoons
(NASA Thesaurus)
Very small glass spheres (50 to 100 micrometers in diameter) used as targets in the laser fusion programs.
microbar
(NASA SP-7, 1965)
(abbr µb)
The unit of pressure in the CGS system and equal to 1 dyne per square centimeter; the unit of sound pressure.
In British literature the term barye has been used.
The term
bar properly denotes a pressure of 106 dynes per square centimeter. Unfortunately, the bar was once used in acoustics to mean 1 dyne per square centimeter, but this is no longer correct.
microbursts (meteorology)
(NASA Thesaurus)
A strong, localized downdraft that strikes the ground creating an outflow of severe winds near the ground that diverge radically from the impact point.
microchannel plates
(NASA Thesaurus)
An array of microchannels formed into plates and contained in a photomultiplier tube. Used for multichannel plates.
microcomputers
(NASA Thesaurus)
Complete digital computers utilizing a microprocessor consisting of one or more integrated circuit chips as the central arithmetic and logic unit, and added chips to provide timing, program memory, random access memory interfaces for input and output signals and other functions. Some microcomputers consist of a single integrated-circuit chip.
microdensitometers
(NASA Thesaurus)
Image analysis devices for resolving gray-level differences within or between features and for integrating the optical density across scanned images of irregularly shaped objects.
microenvironment
(NASA SP-7, 1965)
The environment created and maintained within a very small space, such as a pressurized capsule or space suit, and sufficient to support life in a reasonably normal manner.
microgravity
(NASA Thesaurus)
A condition in which the acceleration acting on a body is less than normal gravity, between 0 and 1 g. Used for low gravity, reduced gravity, and subgravity.
microinstability
(Plasma Physics and Fusion Energy Glossary)
Instabilities due to particle / kinetic- theoretical effects, typically occuring on small scales, as opposed to those derivable from fluid models valid on larger scales. As with other instabilities, these are driven by various types of available free energy.
microlock
(NASA SP-7, 1965)
A satellite telemetry system which uses phase-lock techniques in the ground receiving equipment to achieve extreme sensitivity.
micromachining
(NASA Thesaurus)
Performing various microscopic scale cutting or grinding operations on a piece of work.
micromanometer
(NASA SP-7, 1965)
A manometer capable of measuring very small pressure changes or differences.
micromechanics
(NASA Thesaurus)
The study of the constraints, the grain size, and their interrelationship in materials.
micrometeorite
(NASA Thesaurus / NASA SP-7, 1965)
A very small meteorite or meteoritic particle with a diameter in general less than a millimeter.
micrometeorite penetration
(NASA SP-7, 1965)
Penetration of the thin outer shell (skin) of space vehicles by small particles traveling in space at high velocities.
micrometer
(NASA SP-7, 1965)
One of a class of instruments for making precise linear measurements in which the displacements measured correspond to the travel of a screw of accurately known pitch.
micrometers
(Global Land Information System Glossary - USGS)
A unit of length equal to one-millionth of a meter. It also is referred to as a micron.
micron
(NASA SP-7, 1965)
(abbr µ)
1. A unit of length equal to one-millionth of a meter or one-thousandth of a millimeter.
The micron is a convenient length unit for measuring wavelengths of infrared radiation, diameters of atmospheric particles, etc.
2. = micron of mercury.
micron liter
(NASA SP-7, 1965)
One liter of gas at a pressure of one micron of mercury.
micron of mercury
(NASA SP-7, 1965)
(abbr µ of Hg or µ Hg)
A unit of pressure equal to a pressure of 1/1000th of 1 millimeter of mercury pressure at ° C and the standard acceleration of gravity; a millitorr (10-3 torr approximately). See torr.
microphone
(NASA Thesaurus / NASA SP-7, 1965)
An electroacoustic transducer which receives an acoustic signal and delivers a corresponding electric signal.
microquasar
(Imagine the Universe Dictionary - NASA GSFC)
Microquasars are stellar mass black holes, that display characteristics of the supermassive black holes found at the centers of some galaxies. For instance, they have radio jets -- something not every black hole has.
microsatellites
(NASA Thesaurus)
Satellites with a total mass between 10 and 100 kg often incorporating miniaturized electronic and mechanical systems.
microscopes
(NASA Thesaurus)
Optical instruments capable of producing a magnified image of a small object.
Microscopium
(NASA SP-7, 1965)
(abbr Mic, Micr)
See constellation.
microscopy
(NASA Thesaurus)
The science of the interpretive use and applications of microscopes.
microsecond
(NASA SP-7, 1965)
(abbr µsec)
One-millionth of a second.
microseisms
(NASA Thesaurus)
Seismic pulses of short duration and low amplitude, often ocurring previous to failure of a material or structures.
microstrip antennas
(NASA Thesaurus)
Antennas which consist of thin metallic conductors bonded to thin grounded dielectric substrates. The metallic conductors generally have some regular shape, for example, rectangular, circular, or elliptical. Feeding is often by means of a coaxial probe or a microstrip transmission line.
microtorr
(NASA SP-7, 1965)
A unit of pressure equal to 10-6 torr. See torr.
microwave
(Global Land Information System Glossary - USGS)
The subset of the Electromagnetic Spectrum encompassing wavelengths between .03 and 30 centimeters, corresponding to frequencies of 1-100 gigahertz.
microwave
(NASA SP-7, 1965)
Of, or pertaining to, radiation in the microwave region.
microwave absorption
(NASA Thesaurus)
The absorption of electromagnetic radiation in the microwave frequency range.
microwave interferometers
(Plasma Physics and Fusion Energy Glossary)
A microwave interferometer uses radio waves in the microwave frequency (or wavelength) range as the electromagnetic signal. Microwave interferometers are used to measure the line-averaged density of a plasma along the path through which the microwave beam is passed, through phase shifts in the propagated beam.
microwave landing systems
(NASA Thesaurus)
A precision instrument approach landing system operating in the microwave spectrum which provides lateral and vertical guidance to aircraft having compatible avionics equipment.
microwave refractometer
(NASA SP-7, 1965)
A device for measuring the refractive index of the atmosphere at microwave frequencies - usually in the 3-centimeter region.
microwave region
(NASA SP-7, 1965)
Commonly, that region of the radio spectrum between approximately 1000 megacycles and 300,000 megacycles. See frequency band.
Corresponding wavelengths are 30 centimeters to 1 millimeter. The limits of the microwave region are not clearly defined but in general it is considered to be the region in which radar operates.
microwave scanning beam landing system
(NASA Thesaurus)
Primary position sensor of Space Shuttle orbiter's navigation system during the autoland phase of the flight. Used for MSBLS.
microwave turbulence
(NASA SP-7, 1965)
Irregular and fluctuating gradients of microwave refractive index in the atmosphere. See optical turbulence.
Microwave turbulence may be due either to blobby distribution of water vapor, or to thermal turbulence.
microyield strength
(NASA Thesaurus)
Stress at which a microstructure (single crystal, for example) exhibits a specified deviation in its stress-strain relationship.
mid-ocean ridges
(NASA Thesaurus)
Continuous, seismic, median mountain ranges extending through the North and South Atlantic Oceans, the Indian Ocean and the South Pacific Ocean. They are broad fractured swells with a central rift valley and usually rugged topography. They are 1-3 km in elevation, about 1500 km in width, and over 84,000 km in length. According to the hypothesis of sea floor spreading, the mid-ocean ridges are the source of crustal material.
midaltitude
(NASA Thesaurus)
The average of many measurements of altitudes as with satellite instruments for the compiling of planetary maps.
Midas
(NASA SP-7, 1965)
A two-object trajectory measuring system whereby two complete Cotar antenna systems and two sets of receivers at each station, with the multiplexing done after phase comparison, are utilized in tracking more than one object at a time.
midcourse guidance
(NASA SP-7, 1965)
Guidance of a rocket from the end of the launching phase to some arbitrary point or at some arbitrary time when terminal guidance begins. Also called incourse guidance. See guidance.
middle atmosphere
(NASA Thesaurus)
The portion of the Earth's atmosphere extending from the troposphere to 100 kilometers.
Midot (abbr)
(NASA SP-7, 1965)
= multiple interferometer determination of trajectories.
Mie particle
(NASA SP-7, 1965)
See Mie theory.
Mie scattering
(NASA Thesaurus / NASA SP-7, 1965)
Any scattering produced by spherical particles without special regard to comparative size of radiation wavelength and particle diameter. See Mie theory.
Mie theory
(NASA SP-7, 1965)
A complete mathematical-physical theory of the scattering of electromagnetic radiation by spherical particles, developed by G. Mie in 1908. In contrast to Rayleigh scattering, the Mie theory embraces all possible ratios of diameter to wavelength.
The Mie theory is very important in meteorological optics, where diameter-to-wavelength ratios of the order of unity and larger are characteristic of many problems regarding haze and cloud scattering. Scattering of radar energy by raindrops constitutes another significant application of the Mie theory.
MiG aircraft
(NASA Thesaurus)
Any of a series of Soviet fighter aircraft, fighter-bombers, interceptors, and air supremacy aircraft, designed by Mikoyan.
migma devices
(Plasma Physics and Fusion Energy Glossary)
Non-thermal, non-pulsed devices in which fusion occurs among the ions of a self-colliding particle beam.
mil
(NASA SP-7, 1965)
1. One-thousandth of an inch.
2. A unit of angular measurement, 1/6400 of a circle.
Milankovich theory
(From Stargazers to Starships Glossary - GSFC)
Theory by which ice ages were caused by slow changes of the motion of the Earth in space, including the coupling between the 26 000 year cycle of the precession of the equinoxes and the annual variation of the Earth-Sun distance.
mile
(NASA SP-7, 1965)
A unit of distance. See statute mile, nautical mile.
military grid
(NASA SP-7, 1965)
Any grid specified for use on a particular map, or series of maps, by military authorities.
Milky Way
(NASA SP-7, 1965)
The galaxy to which the sun belongs.
As seen at night from the earth, the Milky Way is a faintly luminous belt of faint stars.
Milky Way Galaxy
(NASA Thesaurus)
The galaxy to which the sun belongs.
milli
(NASA SP-7, 1965)
(abbr m)
A prefix meaning multiplied by 10-3.
millibar
(NASA SP-7, 1965)
A unit of pressure equal to 1000 dynes per square centimeter, or 1/1000 of a bar.
The millibar is used as a unit of measure of atmospheric pressure, a standard atmosphere being equal to 1,013.25 millibars or 29.92 inches of mercury.
milligal
(NASA SP-7, 1965)
A unit of acceleration equal to 1/1000 of a gal, or 1/1000 centimeter per second per second.
This unit is used in gravity measurements, being approximately one-millionth of the average gravity at the earth's surface.
millimeter
(NASA SP-7, 1965)
(abbr mm)
One-thousandth of a meter; one-tenth of a centimeter; 0.039370 U.S. inch.
millimeter of mercury
(NASA SP-7, 1965)
(abbr mm Hg)
millimetric wave
(NASA SP-7, 1965)
See frequency band.
millimicron of mercury
(NASA SP-7, 1965)
(abbr mµ Hg)
A unit of pressure equal to 10-6 millimeters of mercury or 10-6 torr.
millimicrosecond
(NASA SP-7, 1965)
(abbr mµsec)
= nanosecond.
million electron volt
(NASA SP-7, 1965)
(abbr Mev)
A unit of energy equal to 1.603 X 10-8 ergs.
(Global Land Information System Glossary - USGS)
Unit of angular measure equal to one-thousandth the angle subtended at the center of a circle by an area of length equal to the radius of the circle.
millisecond
(NASA SP-7, 1965)
(abbr msec)
One-thousandth of a second.
millitorr
(NASA SP-7, 1965)
A proposed new unit of pressure equal to 10-3 torr. See torr.
MIM diodes
(NASA Thesaurus)
Junction diodes each consisting of an insulating layer sandwiched between two metallic surface layers and exhibiting a negative differential resistance in its V-1 characteristics conceivably because of stimulated inelastic tunneling of electrons. Used for metal-insulator-metal diodes.
Mimas
(NASA Thesaurus / NASA SP-7, 1965)
A satellite of Saturn orbiting at a mean distance of 186,000 kilometers.
MIMD (computers)
(NASA Thesaurus)
A type of parallel processor that is essentially two or more individual computers with facilities for interaction and work sharing. Used for multiple instruction multiple data stream.
minerals
(NASA Thesaurus)
Naturally occurring inorganic elements or compounds having an orderly internal structure and characteristic chemical compositions, crystal forms, and physical properties.
mini
(NASA SP-7, 1965)
A contraction of miniature used in combination, as in minicomponent, miniradio, minitransistor.
miniature
(NASA SP-7, 1965)
Used attributively in reference to equipment, such as gimbals, gyroscopes, computers, etc., made small to fit into confined spaces, as within an earth satellite or rocket vehicle.
miniaturization
(NASA SP-7, 1965)
See miniaturize.
miniaturize
(NASA SP-7, 1965)
To construct a functioning miniature of a part or instrument. Said of telemetering instruments or parts used in an earth satellite or rocket vehicle, where space is at a premium. Hence, miniaturized, miniaturization.
minimal surfaces
(NASA Thesaurus)
Surfaces for which the first variation of the area integral vanish.
minimum deviation
(NASA SP-7, 1965)
The least total refraction experienced by radiation passing through a prismatic refractive medium.
It is important to note that the refractive deviation is minimal, in general, only with respect to adjacent light paths, for there may exist a number of path directions through a single object, each one of which yields a local minimum deviation. When radiation has undergone minimum deviation, the angular difference in path directions before and after total refraction is termed the angle of minimum deviation.
minimum entropy method
(NASA Thesaurus)
Application of entropy in statistical mechanics.
minimum ionizing speed
(NASA SP-7, 1965)
The speed with which a free electron must move through a given gas to be able to ionize gas atoms or molecules by collision. In air at standard conditions, this speed is about 107 centimeters per second. See electron avalanche.
minitrack
(NASA SP-7, 1965)
A satellite tracking system consisting of a field of separate antennas and associated receiving equipment interconnected so as to form interferometers which track a transmitting beacon in the payload itself.
minitrack system
(NASA Thesaurus)
A satellite tracking system consisting of a field of separate antennas and associated receiving equipment interconnected so as to form interferometers which track a transmitting beacon in the payload itself. Used for minitrack optical tracking system and MOTS (tracking system).
minor axis
(NASA SP-7, 1965)
The shortest diameter of an ellipse or ellipsoid.
minor lobe
(NASA SP-7, 1965)
See lobe.
minor planet
(NASA SP-7, 1965)
= asteroid.
See planet.
minute
(NASA SP-7, 1965)
(abbr min or ´ )
1. The sixtieth part of an hour.
2. The sixtieth part of a degree of arc.
Mir space station
(NASA Thesaurus)
The Soviet space station launched February 20, 1986; its name means peace or world in Russian. It is a manned, modular, permanent, and multi-mission station.
Mira variables
(NASA Thesaurus)
Long-period (80 to over 600 days) variable stars of red giant or red supergiant type, exemplified by the star Mira Ceti. Used for long period variables.
mirage
(NASA SP-7, 1965)
1. (Optics) definition submitted by Andy Young, June 30, 1997
An apparently reflected image of an object, caused by abnormal atmospheric refraction. The most commonly seen is the inferior mirage over heated surfaces, which often looks like a pool of water because it reflects the sky. Superior mirages, which appear above the direct image of the object, are due to strong thermal inversions above eye level. Other mirage-like images can be produced by thermal inversions below eye level, and by hot air adjacent to a wall heated by the Sun (lateral mirage).
2. (Radar) A refraction phenomenon in the atmosphere wherein an image of some object is made to appear displaced from its true position. See radio duct, note.
Simple mirages may be any one of three types, the inferior mirage, the superior mirage, or the lateral mirage, depending, respectively, on whether the spurious image appears below, above, or to one side of the true position of the object. Of the three, the inferior mirage is the most common, being usually discernible over any heated street in daytime during summer. The abnormal refraction responsible for mirages is invariably associated with abnormal temperature distributions that yield abnormal spatial variations in the refractive index.
Mirage aircraft
(NASA Thesaurus)
Collective term for a class of French attack aircraft.
Miran (abbr)
(NASA SP-7, 1965)
= missile ranging.
Miranda
(NASA Thesaurus / NASA SP-7, 1965)
A satellite of Uranus orbiting at a mean distance of 124,000 kilometers.
Miranda satellite
(NASA Thesaurus)
This United Kingdom satellite was launched in 1974 into a sun synchronous, low Earth orbit. Prime objective of the mission was to experiment with satellite attitude control. It ceased to operate the same year it was launched.
mirnov osscillations
(Plasma Physics and Fusion Energy Glossary)
Fluctuations in the poloidal magnetic field (of a toroidal magnetic confinement system) which rotate in the electron diamagnetic drift direction at a speed comparable to the electron diagmagnetic drift velocity and with frequencies due to 5-20 kHz. Mirnov oscillations arise from tearing modes. Poloidal magnetic probes used to measure the poloidal field in order to diagnose Mirnov oscillations (and other MHD phenomena) are often called Mirnov coils or Mirnov loops.
mirror altitude
(NASA SP-7, 1965)
The altitude above the earth at which electrically charged corpuscular radiation impinging upon the earth is reflected by the geomagnetic field.
mirror device
(Plasma Physics and Fusion Energy Glossary)
Generally, linear fusion machines which confine the plasma using the mirror effect. Basically there is a weak field in the center, and strong fields at the ends. Particles are then reflected at the ends by the strong fields, and are confined in the center of the device.
mirror effect
(Plasma Physics and Fusion Energy Glossary)
A charged particle travelling into an increasing magnetic field will (if the field becomes strong enough) reverse direction and be reflected back. This is a direct result of the adiabatic invariance of the magnetic moment. Plasmas can be confined by devices which utilize this effect. The effect also occurs in some toroidal plasmas, since the toroidal magnetic field is stronger on the inboard side than on the outboard side; in this case it gives rise to so-called "neoclassical" effects. The strength of the mirror is determined by the mirror ratio.
mirror fusion
(NASA Thesaurus)
An open-ended configuration which traps low beta plasmas. It is realized by associating two identical magnetic mirrors having the same axis.
mirror ratio
(Plasma Physics and Fusion Energy Glossary)
The ratio between the strongest value of the magnetic field on the mirror's axis, and the value at some other point on the axis. In a mirror confinement device, the "other point" is taken to be the location of weakest field strength between two confining mirrors. The mirror ratio is a key factor in determining confinement properties of the system.
mirror ratio
(NASA SP-7, 1965)
See magnetic mirror.
mirror reflection
(NASA SP-7, 1965)
= specular reflection.
mischmetal
(NASA Thesaurus)
An alloy consisting of a natural mixture of rare-earth metals; used in electrode materials and hydrogen-storage alloys, as a general alloy addition, and in the production of some aluminum alloys and steels.
mismatch (electrical)
(NASA Thesaurus)
Condition in which the impedance of a source does not match or equal the impedance of the connected load or transmission line.
missile
(NASA SP-7, 1965)
Any object thrown, dropped, fired, launched, or otherwise projected with the purpose of striking a target. Short for ballistic missile, guided missile.
Missile should not be used loosely as a synonym for rocket or spacecraft.
missile ranging
(NASA SP-7, 1965)
(abbr Miran)
A trajectory measuring system that measures loop ranges from a transmitter to a beacon to remote slave stations and back to the transmitter through comparison of time differences of pulses.
The transmitter interrogates at 600 megacycles and the beacon replies at 580 megacycles.
missiles
(NASA Thesaurus)
Any objects thrown, dropped, fired, launched, or otherwise projected with the purpose of striking a target.
missilry
(NASA SP-7, 1965)
The art or science of designing, developing, building, launching, directing, and sometimes guiding a rocket missile; any phase or aspect of this art or science.
This term is sometimes spelled missilery, but is then pronounced as a three-syllable word.
missing mass (astrophysics)
(NASA Thesaurus)
A problem related to a cluster of galaxies in which the mass derived from the dynamical stability of its member galaxies, the dynamical mass, is substantially larger than the mass estimated by the mass-to-luminosity ratio of the visible parts of the galaxies, the visible mass.
Mission to Planet Earth
(NASA Thesaurus)
A NASA initated program that uses both space and ground based measurement systems to provide the scientific basis for understanding global change.
mist
(NASA Thesaurus)
Liquid, usually water in the form of particles suspended in the atmosphere at or near the surface of the Earth; small water droplets floating or falling, approaching the form of rain, and sometimes distinguished from fog as being more transparent or as having particles perceptibly moving downward.
mistake
(NASA SP-7, 1965)
An error, usually large, resulting from a human failing or an equipment malfunction.
mixed icing
(NASA SP-7, 1965)
Mixed aircraft icing is composed of both glaze and rime ice. Typically the ice will be clear near the stagnation line of the wing with the remainder rime. It represents about 15% of icing reports.
mixed oxides
(NASA Thesaurus)
Mixture of oxides, particularly of radioactive metals.
mixed reflection
(NASA SP-7, 1965)
mixed-base notation
(NASA SP-7, 1965)
A system of positional notation used in computers in which two or more bases are arranged according to a plan. See biquinary notation.
mixed-flow compressor
(NASA SP-7, 1965)
A rotary compressor through which the acceleration of fluid is partly radial and partly axial.
mixing height
(NASA Thesaurus)
The heights of the layer through which the atmosphere is well mixed. The height will vary with diurnal, seasonal, and regional variations. Used for mixing depth.
mixing layers (fluids)
(NASA Thesaurus)
Fluid layers in which multicomponent mixing occurs.
mixing length
(NASA SP-7, 1965)
A mean length of travel, characteristic of a particular motion in a fluid over which an eddy maintains its identity; analogous to the mean free path of a molecule.
Physically, the idea implies that mixing occurs by discontinuous steps, that fluctuations which arise as eddies with different characteristics wander about, and that the mixing is done almost entirely by the small eddies.
mixing ratio
(NASA SP-7, 1965)
In a system of moist air, the dimensionless ratio of the mass of water vapor to the mass of dry air. For many purposes, the mixing ratio may be approximated by the specific humidity. In terms of the pressure p and vapor pressure e, the mixing ratio w is
w = (0.6222 e) / (p - e)
Compare absolute humidity, relative humidity, dew point.
mixture ratio
(NASA SP-7, 1965)
In liquid propellant rockets, the relative mass flow rates to the combustion chamber of oxidizer and fuel.
MKS system
(NASA SP-7, 1965)
A system of units based on the meter, the kilogram, and the second.
MKSA system
(NASA SP-7, 1965)
A system of units based on the meter, kilogram, second, and ampere. Also called Giorgi system, International System.
mm
(Space Flight Glossary - JPL)
millimeter (10-3 meter).
MMSP--Modular Multi-Satellite Preprocessor
(Global Land Information System Glossary - USGS)
The MMSP is a frame synchronizer designed to provide the interface between bit synchronized Landsat thematic mapper telemetry data and the host computer system. It is used as the front end for a Landsat data acquisition system that accepts raw serial telemetry data from high density tape (HDT), frame aligns, samples user specified fields, and presents these data to the host computer for decommutation and image extraction.
MO
(Space Flight Glossary - JPL)
Mars Observer spacecraft.
mobile communication systems
(NASA Thesaurus)
Any configuration of mobile or transportable voice and data communication equipment which allows for communication between combinations of mobile/fixed points with or without the aid of satellites.
mobility
(NASA SP-7, 1965)
1. The average velocity or drift velocity that a charged particle in a plasma will acquire in response to a unit applied electric field when restrained by collisions with other particles.
2. = drift mobility.
3. = Hall mobility.
In general the electron mobility is considerably larger than any ion mobility.
mock test
(NASA SP-7, 1965)
An operational test of a complete rocket system without actually firing a rocket.
mockup
(NASA SP-7, 1965)
A full-sized replica or dummy of something, such as a spacecraft, often made of some substitute material such as wood, and sometimes incorporating actual functioning pieces of equipment, such as engines.
mode
(Global Land Information System Glossary - USGS)
That value that occurs most frequently within the data sample being taken. In a histogram, it is the data value at which the peak of the distribution curve occurs.
mode
(NASA SP-7, 1965)
A functioning position or arrangement that allows for the performance of a given task.
Said of a spacecraft, which may move, for example, from a cruise mode to an encounter mode; or said of controls that permit the selection of a mode, such as a reentry mode.
mode of vibration
(NASA SP-7, 1965)
In a system undergoing vibration, a characteristic pattern assumed by the system in which the motion of every particle is simple harmonic with the same frequency.
Two or more modes of vibration may exist concurrently in a multiple-degree-of-freedom system.
mode shape
(NASA SP-7, 1965)
= mode of vibration.
model atmosphere
(NASA SP-7, 1965)
1. Any theoretical representation of the atmosphere, particularly of vertical temperature distribution. See adiabatic atmosphere, homogeneous atmosphere, isothermal atmosphere, thermotropic model, equivalent-barotropic model, barotropic model.
2. = standard atmosphere, sense 1.
(NASA Thesaurus)
This deals with three parameters: an ideal adaptive control system whose response is agreed to be optimum; computer simulation in which both the model system and the actual system are subjected to the same stimulus; and parameters of the actual system which are adjusted to minimize the difference in the outputs of the model and the actual system. Used for MRAC (systems).
moderator
(NASA Thesaurus / NASA SP-7, 1965)
A material that has a high cross section for slowing down fast neutrons with a minimum of absorption, e.g., heavy water, beryllium, used in reactor cores.
Moderators are used to improve the neutron utilization by slowing the neutrons to low energies, thereby increasing the probability of fission capture in the nuclear fuel.
MODFETS
(NASA Thesaurus)
Heterojunction field effect transistor device structures in which only the larger (Al, Ga)As bandgap is doped with donors while the GaAS layer is left undoped. This results in high electron mobilities due to spatially separated electrons and donors. Used for modulation doped FETs.
modified index of refraction
(NASA SP-7, 1965)
An atmospheric index of refraction mathematically modified so that when its gradient is applied to energy propagation over a hypothetical flat earth it is substantially equivalent to propagation over the true curved earth with the actual index of refraction. Also called refractive modulus, modified refractive index. Compare potential index of refraction.
The modified index of refraction is usually expressed in M-units; mathematically
where n is the index of refraction at a point in the atmospheric; h is the height above mean sea level of that point; a is the radius of the earth; and N is the index of refraction in N-units. In ray tracing problems, the vertical gradient dM/dh can be used directly to obtain a ray path curvature that is relative to the curvature of the earth, i.e.,
where k is a value by which the earth's radius is multiplied to get the radius of curvature of the ray path; ka is called the
modified refractive index
(NASA SP-7, 1965)
= modified index of refraction.
Modular Integrated Utility System
(NASA Thesaurus)
A joint NASA-HUD concept incorporating various utilities -- electric power plant, water supply, heating and air conditioning, sewage treatment, and waste disposal into a single system having increased efficiency and economy. Use for MIUS.
modulated continuous wave
(NASA SP-7, 1965)
(abbr MCW)
A form of emission in which the carrier is modulated by a constant audiofrequency tone.
modulated wave
(NASA SP-7, 1965)
A wave which varies in some characteristic in accordance with the variations of a modulating signal. Compare continuous wave. See modulation.
modulating wave
(NASA SP-7, 1965)
See modulation.
modulation
(NASA Thesaurus / NASA SP-7, 1965)
1. The variation in the value of some parameter characterizing a periodic oscillation.
2. Specifically, variation of some characteristic of a radio wave, called the carrier wave, in accordance with instantaneous values of another wave, called the modulating wave.
Variation of amplitude is amplitude modulation, variation of frequency is frequency modulation, and variation of phase is phase modulation. The formation of very short bursts of a carrier wave, separated by relatively long periods during which no carrier wave is transmitted, is pulse modulation.
modulation doping
(NASA Thesaurus)
The process of doping only the larger bandgap of a heterojunction device with donors, while the other layer is left undoped. Since the electrons and donors are spatially separated, ionized impurity scattering is avoided and extremely high electron mobilities are obtained.
modulation index
(NASA SP-7, 1965)
= ratio deviation.
modulator
(NASA Thesaurus / NASA SP-7, 1965)
A device to effect the process of modulation.
module
(NASA SP-7, 1965)
1. A self-contained unit of a launch vehicle or spacecraft which serves as a building block for the overall structure. The module is usually designated by its primary function as command module, lunar landing module, etc.
2. A one-package assembly of functionally associated electronic parts, usually a plug-in unit, so arranged as to function as a system or subsystem; a black box.
3. The size of some one part of a rocket or other structure, as the semidiameter of a rocket's base, taken as a unit of measure for the proportional design and construction of component parts.
modules
(NASA Thesaurus)
1, Self contained units of a launch vehicle or spacecraft that serve as building blocks for the overall structure. 2, A one package assembly of functionally associated electronic parts, usually a plug-in unit, so arranged as to function as a system or subsystem.
modulus (plural moduli)
(NASA SP-7, 1965)
1. A real, positive quantity which measures the magnitude of some number, as the modulus of a complex number is the square root of the sum of squares of its components.
2. A coefficient representing some elastic property of body, such as the modulus of elasticity or the modulus of resilience.
modulus of elasticity
(NASA Thesaurus)
The ratio of stress (nominal) to corresponding strain below the proportional limit of a material. It is expressed in force per unit area. Used for compliance (elasticity), elastic modulus, and Young modulus.
modulus of elasticity
(NASA SP-7, 1965)
(symbol E) = Young modulus.
Moire fringes
(NASA Thesaurus)
The bands which appear in the Moire effect.
Moire interferometry
(NASA Thesaurus)
The use of intersecting families of curves as instruments for making precise measurement, the study of indices of refractions, etc. by utilizing the interference patterns.
(NASA SP-7, 1965)
molar
(NASA SP-7, 1965)
Pertaining to a mole, or measured in moles.
moldavite
(NASA SP-7, 1965)
See tektite.
mole
(NASA SP-7, 1965)
(abbr mol)
The amount of substance containing the same number of atoms as 12 grams of pure carbon12 (C12).
The gram-mole or gram-molecule is the mass in grams numerically equal to the molecular weight.
molecular beam epitaxy
(NASA Thesaurus)
Ultrahigh vacuum technique for growing very thin epitaxial layers of semiconductor crystals.
molecular clouds
(NASA Thesaurus)
Thickest and densest interstellar clouds consisting mainly of molecular hydrogen but also a high concentration of dust grains.
molecular drag gage
(NASA SP-7, 1965)
A vacuum gage in which tangential momentum is transported (viscous transport) by gas molecules from a rapidly rotating member (usually in the form of a disk or cylinder) to a nearby movable member restrained by a restoring torque which can be correlated with gas pressure. Also called molecular gage, rotating disk gage, rotating cylinder gage.
molecular effusion
(NASA SP-7, 1965)
The passage of gas through a single opening in a plane wall of negligible thickness where the largest dimension of the hole is smaller than the mean free path.
molecular flow
(NASA Thesaurus / NASA SP-7, 1965)
The flow of gas through a duct under conditions such that the mean free path is greater than the largest dimension of a transverse section of the duct.
molecular flux
(NASA SP-7, 1965)
The net number of gas molecules crossing a specified surface in unit time, those having a velocity component in the same direction as the normal to the surface at the point of crossing being counted as positive and those having a velocity component in the opposite direction being counted as negative.
molecular gage
(NASA SP-7, 1965)
= molecular drag gage .
molecular gases
(High Energy Astrophysics Dictionary- GSFC)
Gas that is composed of atoms that are bound to each other as molecules.
molecular scale temperature
(NASA SP-7, 1965)
(symbol TM )
An atmospheric parameter defined by TM = (M0 / M)T where M0 is the mean molecular weight at sea level, M is the mean molecular weight at altitude, and T is air temperature at altitude.
Up to an altitude of about 90 kilometers, the molecular composition of air is constant; thus M0 / M = 1 and T M = T. Above 90 kilometers, M0 / M is greater than unity, and T M is greater than T.
molecular shields
(NASA Thesaurus)
Furlable devices used in space vacuum research to permit deployment and retrieval of instruments and the performance of experiments without contamination.
molecular weight
(NASA Thesaurus / NASA SP-7, 1965)
The weight of a given molecule expressed in atomic weight units.
molecule
(NASA SP-7, 1965)
An aggregate of two or more atoms of a substance that exists as a unit.
Moll thermopile
(NASA SP-7, 1965)
A thermopile used in some types of radiation instruments. Alternate junctions of series-connected thermocouples are imbedded in a shielded nonconducting plate having a large heat capacity. The remaining junctions, which are blackened, are exposed directly to the radiation. The voltage developed by the thermopile is proportional to the intensity of radiation. See solarimeter.
molten salts
(NASA Thesaurus)
High temperature inorganic salt or mixtures of salts used for thermal energy storage, heat exchangers, high power electric batteries, heat treatment of alloys, etc.
moment
(NASA SP-7, 1965)
(symbol M)
A tendency to cause rotation about a point or axis, as of a control surface about its hinge or of an airplane about its center of gravity; the measure of this tendency, equal to the product of the force and the perpendicular distance between the point of axis of rotation and the line of action of the force.
moment of inertia
(NASA SP-7, 1965)
(symbol I)
Of a body about an axis, , where m is the mass of a particle of the body and r is its distance from the axis.
momentum
(NASA SP-7, 1965)
Quantity of motion.
Linear momentum is the quantity obtained by multiplying the mass of a body by its linear speed. Angular momentum is the quantity obtained by multiplying the moment of inertia of a body by its angular speed.
The momentum of a system of particles is given by the sum of the momentums of the individual particles which make up the system or by the product of the total mass of the system and the velocity of the center of gravity of the system.
The momentum of a continuous medium is given by the integral of the velocity over the mass of the medium or by the product of the total mass of the medium and the velocity of the center of gravity of the medium.
momentum thrust
(NASA SP-7, 1965)
= thrust.
momentum-transport hypothesis
(NASA SP-7, 1965)
The hypothesis that momentum is conserved in turbulent eddy transfer.
This hypothesis is to be compared with the vorticity transport hypothesis, the respective results being identical only if the eddy viscosity is constant.
Mon, Mono
(NASA SP-7, 1965)
International Astronomical Union abbreviations for Monoceros. See constellation.
monitor
(NASA SP-7, 1965)
To observe, listen in on, keep track of, or exercise surveillance over by any appropriate means, as, to monitor radio signals; to monitor the flight of a rocket by radar; to monitor a landing approach.
Monoceros
(NASA SP-7, 1965)
(abbr Mon, Mono)
See constellation.
monochromatic
(NASA SP-7, 1965)
Pertaining to a single wavelength, or, more commonly, to a narrow band of wavelengths.
monocoque
(NASA SP-7, 1965)
A type of construction, as of a rocket body, in which all or most of the stresses are carried by the skin.
A monocoque may incorporate formers but not longitudinal members such as stringers.
monomers
(NASA Thesaurus)
Low molecular weight substances consisting of molecules capable of reacting with like or unlike molecules to form a polymer.
monopropellant
(NASA SP-7, 1965)
A rocket propellant consisting of a single substance, especially a liquid, capable of producing a heated jet without the addition of a second substance.
Used attributively in phrases, such as monopropellant rocket engine or motor, monopropellant rocket fuel, monopropellant system, etc.
monostatic reflectivity
(NASA SP-7, 1965)
The characteristic of a reflector which reflects energy only along the line of the incident ray (incidence), e.g., a corner reflector. See bistatic reflectivity.
monotectic alloys
(NASA Thesaurus)
Metallic composite materials having a dispersed phase of solidification products distributed within a matrix. The dispersed components can be selected to provide characteristics such as superconductivity or lubricity.
month
(NASA Thesaurus / NASA SP-7, 1965)
1. The period of the revolution of the moon around the earth.
The month is designated as sidereal, tropical, anomalistic, dracontic, or synodical, according to whether the revolution is relative to the stars, the vernal equinox, the perigee, the ascending node, or the sun.
2. The calendar month, which is a rough approximation to the synodical month.
month of the phases
(NASA SP-7, 1965)
= synodical month.
moon
(NASA Thesaurus / NASA SP-7, 1965)
1. The natural satellite of the earth.
2. A natural satellite of any planet. See planet,table.
moonrise
(NASA SP-7, 1965)
The crossing of the visible horizon by the upper limb of the ascending moon.
moonset
(NASA SP-7, 1965)
The crossing of the visible horizon by the upper limb of the descending moon.
MOPTAR (abbr)
(NASA SP-7, 1965)
= multiple object phase tracking and ranging.
morphology
(Galileo Project Glossary - JPL)
The scientific study of form, and of the structures and development that influence form. In geology, the external structure, form, and arrangement of rocks in relation to the development of landforms.
MOSO
(Space Flight Glossary - JPL)
Multimission Operations Systems Office at JPL.
motion
(NASA Thesaurus / NASA SP-7, 1965)
The act, process, or instance of change of position. Also called movement, especially when used in connection with problems involving the motion of one craft relative to another.
Absolute motion is motion relative to a fixed frame of reference. Actual motion is motion of a craft relative to the earth. Apparent or relative motion is change of position as observed from a reference point which may itself be in motion. Diurnal motion is the apparent daily motion of a celestial body. Direct motion is the apparent motion of a planet eastward among the stars; retrograde motion, the apparent motion westward among the stars. Motion of a celestial body through space is called space motion, which is composed of two components: proper motion, that component perpendicular to the line of sight; and radial motion, that component in the direction of the line of sight.
motion sickness
(NASA Thesaurus / NASA SP-7, 1965)
The syndrome of pallor, sweating, nausea, and vomiting which is induced by unusual accelerations.
motion simulation
(NASA Thesaurus)
Replication of exact motion or replication of part of a motion to provide the sensation of the motion.
motor
(NASA SP-7, 1965)
See engine.
motor vehicles
(NASA Thesaurus)
Automotive vehicles that do not run on rails, generally having rubber tires.
motorboating
(NASA SP-7, 1965)
Oscillation in a system or component, usually manifested by a succession of pulses occurring at a subaudio or low-audio repetion frequency.
motors
(NASA Thesaurus)
Machines supplied with external energy which is converted into force and/or motion.
moving target indicator
(NASA SP-7, 1965)
(abbr MTI)
A device which limits the display of radar information primarily to moving targets.
moving target indicators
(NASA Thesaurus)
Radar devices that employ a technique that enhances the detection and display of moving radar targets by supressing fixed targets. Doppler processing is one method of implementation. Used for MTI indicators.
MSAT
(NASA Thesaurus)
A joint Canada/United States mobile satellite system which is being developed with a voice and data communication link between mobile units and the switched telephone network or between mobile units and other mobile units via satellite. Each country will have a satellite capable of mutual backup. Launch date is planned for 1994.
MSM (semiconductors)
(NASA Thesaurus)
Semiconductor devices consisting of a semiconductor layer sandwiched between two layers of metal. Used for metal-semiconductor-metal semiconductors.
MSS--Multispectral Scanner
(Global Land Information System Glossary - USGS)
The MSS is a nonphotographic imaging system which utilizes an oscillating mirror and fiber optic sensor array. The mirror sweeps from side to side, transmitting incoming energy to a detector array which sequentially outputs brightness values (signal strengths) for successive pixels, one swath at a time. The forward motion of the sensor platform carries the instrument to a position along its path where an adjacent swath can be imaged. The MSS simultaneously senses radiation using an array of six detectors in each of four spectral bands from 0.5 to 1.1 micrometers.
MTBF
(NASA Thesaurus)
The mean of the distribution of time (or cycles, miles, events) between successive failure. MTBF is often estimated by dividing the total operating time for like items by the total number of failures encountered. Used for mean time bwtween failures.
MTI (abbr)
(NASA SP-7, 1965)
= moving target indicator.
MUF (abbr)
(NASA SP-7, 1965)
= maximum usable frequency.
multi (combining form)
(NASA SP-7, 1965)
More than one. Used in contexts where a category of two or more is distinguished from a category of one, as in a multipropellant fuel system is more complicated than a monopropellant system.
multi-anode microchannel arrays
(NASA Thesaurus)
A family of photoelectric, photon counting array detectors being developed for use in instruments on both ground based and spaceborne telescopes.
multibeam antennas
(NASA Thesaurus)
Antennas that have the ability to form more than one beam from a single radiating aperture.
multicoupler
(NASA SP-7, 1965)
A device for connecting several receivers to one antenna and properly matching the impedances of the receivers and the antenna.
multidisciplinary research
(NASA Thesaurus)
Research by combining several (academic) disciplines or methods.
multigrid methods
(NASA Thesaurus)
A numerical technique which attempts to accelerate the convergence of an iterative process by computing corrections to the solution on coarser meshes and propagating these changes to the fine mesh through interpolation.
multimission modular spacecraft
(NASA Thesaurus)
Future spacecraft to be operated in conjunction with the Space Shuttle orbiter vehicle and serviced by its module exchange mechanism. Used for MMS.
multipath
(NASA SP-7, 1965)
= multipath transmission.
multipath transmission
(NASA Thesaurus / NASA SP-7, 1965)
The process, or condition, in which radiation travels between source and receiver via more than one path. Since there can be only one direct path, some process of reflection, refraction, or scattering must be involved. See fading, Fresnel zone. Also called multipath.
multiphoton absorption
(NASA Thesaurus)
Ionization and dissociation of a molecule under the action of powerful laser radiation. Laser-flux dependent light intensities emitted by different excited states of the molecule indicate the various absorption processes.
multiple access
(NASA Thesaurus)
The allocation of communication system resources (output) among multiple users by means of power, bandwidth, and power assignment singly or in combination.
multiple airborne target trajectory system
(NASA SP-7, 1965)
(abbr Matts)
A long-baseline angle-measuring system consisting of two crossed-baseline angle-measuring-equipment (AME) stations. Each AME station simultaneously tracks three airborne targets by means of frequency sharing.
multiple interferometer determination of trajectories
(NASA SP-7, 1965)
(abbr Midot)
A trajectory measurement system with multiple-object-tracking capability utilizing two or more short-baseline stations and a data output consisting of a series of amplitude nulls that represent direction cosines at given times in the flight.
multiple object phase tracking and ranging
(NASA SP-7, 1965)
(abbr Moptar)
A short-baseline continuous-wave phase comparison, trajectory measuring system, similar to the Cotar which consists of a crossed-baseline angle-measuring-equipment (AME) system and a distance-measuring-equipment (DME) system, wherein time sequencing of the ground station and transponders is used to track multiple targets.
multiple scattering
(NASA SP-7, 1965)
In contrast to primary scattering, and scattering in which radiation is scattered more than once before reaching the eye, antenna, or other sensing element.
multiple target tracking
(NASA Thesaurus)
The process of following movements of several targets simultaneously.
multiple-degree-of-freedom system
(NASA SP-7, 1965)
A mechanical system for which two or more coordinates are required to define completely the position of the system at any instant.
multiple-stage compressor
(NASA SP-7, 1965)
= multistage compressor.
multiple-stage rocket
(NASA SP-7, 1965)
= multistage rocket.
multiple-unit steerable antenna
(NASA SP-7, 1965)
See musa antenna.
multiplexer
(NASA SP-7, 1965)
A mechanical or electrical device for time sharing or a circuit.
multiplexing
(NASA Thesaurus / NASA SP-7, 1965)
The simultaneous transmission of two or more signals within a single channel.
The three basic methods of multiplexing involve the separation of signals by time division, frequency division, and phase division.
multiplier
(NASA SP-7, 1965)
1. A device which has two or more inputs and whose output is a representation of the product of the quantities represented by the input signals.
2. = multiplier phototube.
multiplier phototube
(NASA SP-7, 1965)
A phototube with one or more dynodes between its photocathode and the output electrode.
multipliers
(NASA Thesaurus)
Devices which have two or more inputs and whose output is a representation of the product of the quantities represented by the input signals.
multipropellant
(NASA SP-7, 1965)
A rocket propellant consisting of two or more substances fed separately to the combustion chamber. See bipropellant.
multisensor fusion
(NASA Thesaurus)
A combination of data or images from more than one sensor source (or from multispectral sensors) for display as a single image.
multispectral
(Global Land Information System Glossary - USGS)
The use of one or more sensors to obtain imagery from different portions of the electromagnetic spectrum.
multispectral linear arrays
(NASA Thesaurus)
Large number of interconnected solid state detectors in a pushbroom mode wherein the forward motion of the vehicle (spacecraft) sweeps the assembly of detectors which are oriented perpendicular to the ground track. Used for MLA.
Multispectral Resource Sampler
(NASA Thesaurus)
An experimental remote sensing instrument for satellites to measure both intensity and polarization at several wavelengths. The first one was launched in the late 1980s.
multistage compressor
(NASA SP-7, 1965)
An axial flow compressor having two or more, usually more than two, stages of rotor and stator blades; a radial-flow compressor having two or more impeller wheels. Also called a multiple-stage compressor.
multistage rocket
(NASA SP-7, 1965)
A vehicle having two or more rocket units, each unit firing after the one in back of it has exhausted its propellant. Normally, each unit, or stage, is jettisoned after completing its firing. Also called a multiple-stage rocket or, infrequently, a step rocket.
multistage rocket vehicles
(NASA Thesaurus)
Vehicles having two or more rocket units, each unit firing after the one in back of it has exhausted its propellant. Normally, each unit, or stage, is jettisoned after completing its firing.
(NASA Thesaurus)
System in which successive lobes of the antenna are sequentially engaged to provide a tracking capability without physical movement of the antenna. Used for bistatic radar.
multivibrator
(NASA Thesaurus / NASA SP-7, 1965)
A two-stage regenerative circuit with two possible states and an abrupt transition characteristic. See bistable multivibrator.
Multivibrators are used in digital computer for computation in binary notation.
muon
(NASA SP-7, 1965)
= mu meson.
See meson.
muon spin rotation
(NASA Thesaurus)
Particle spin depolarization caused by sensitivity of muon spin to the presence of defects in certain metals.
Mus, Musc
(NASA SP-7, 1965)
International Astronomical Union abbreviations for Musca. See constellation.
musa antenna
(NASA SP-7, 1965)
A multiple-unit steerable antenna consisting of a number of stationary antennas, the composite major lobe of which can be aimed electrically.
Musca
(NASA SP-7, 1965)
(abbr Mus, Musc)
See constellation.
muscovite
(NASA Thesaurus)
An important mineral of the mica group.
mushy zones
(NASA Thesaurus)
Regions of liquid plus solid phases in alloys that solidify over a range of temperatures. Used for liquid plus solid zones.
mutagens
(NASA Thesaurus)
Agents that raise the frequency of mutations above the spontaneous rate.
MX missile
(NASA Thesaurus)
United States strategic intercontinental ballistic missile.
myria
(NASA SP-7, 1965)
A prefix meaning multiplied by 104.
myriameter
(NASA SP-7, 1965)
= ten-thousand meters.
myriametric wave
(NASA SP-7, 1965)
See frequency band.
Mystere 50 aircraft
(NASA Thesaurus)
A tri-engine business jet aircraft (Dassault). Used for Dassault Mystere 50 aircraft.
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