Aerospace Science and Technonlogy Dictionary E Section

E glass: A low alkali lime borosilicate glass made into glass fiber filaments used in composite materials.
E layer: A division of the ionosphere, usually found at an altitude between 100 and 120 kilometers in the E region. It exhibits one or more distinct maximums and sharp gradients of free electron density. It is most pronounced in the daytime but does not entirely disappear at night. Also called E₁ - layer, Kennelly-Heaviside layer, Heaviside layer. See sporadic E layer (under ionosphere), atmospheric shell, ionosphere.
There is some evidence to indicate a second layer above the normal E layer located at about 150 kilometers, and called the E₂-layer.
E region: A portion of the ionosphere extending from about 90 to 150 km. In daylight, the electron density has one maximum at about 105 km and is dependent upon solar activity and the solar zenith angle. At night the E region nearly disappears except at high latitudes where particle precipitation can produce ionization at altitutes greater than those experienced under sunlight conditions.
E region: The region of the ionosphere in which the E layer tends to form. See atmospheric shell.
The E layer has been observed to be subdivided into two or more layers, and these are then assigned the designation, E₁, E₂, etc. Patchy and intermittent clouds of fairly high ionization, known as sporadic E layers, also form in the same general region.
E-display: In radar, a rectangular display in which targets appear as blips with distance indicated by the horizontal coordinate and elevation by the vertical coordinate. Also called E-scan and E-scope.
E-scan: = E-display.
E-scope: = E-display.
E.T. (abbr): = ephemeris time.
E₁ layer: See E layer.
E₂ layer: See E layer note.
earphone: An electroacoustic transducer operating from an electrical system to an acoustical system and intended to be closely coupled acoustically to the ear.
Earth (planet): That planet of the solar system which is fifth in size of the 9 major planets, and third (between Venus and Mars) in order of distance from the sun (about 93 million miles). Major data for the Earth: equatorial radius: 6,378 kilometers (3,963.5 miles); polar radius: 6,357 kilometers (3,941 miles); equatorial circumference: 40,075 kilometers (24,902 miles).
Earth (planet): See planet, table.
Earth albedo: The fraction of the solar incident radiation that is reflected off the Earth and back into space.
Earth axis: Any one of a set of mutually perpendicular reference axes established with the upright axis (the Z-axis) pointing to the center of the earth, used in describing the position or performance of an aircraft or other body in flight.
The earth axes may remain fixed or may move with the aircraft or other object.
Earth cryosphere: The part of the Earths surface that is perennially frozen - the zone of the Earth where ice and frozen ground are formed.
earth current: A large-scale surge of electric charge within the earth's crust, associated with a disturbance of the ionosphere.
Current patterns of quasi-circular form and extending over areas the size of whole continents have been identified and are known to be closely related to solar-induced variations in the extreme upper atmosphere.
Earth Data Analysis Center: Earth Data Analysis Center (EDAC), also known as the Technology Applications Center (TAC), has served as a NASA center since 1964. EDAC operates under the objective of transferring Earth-observing technologies to the user community. It supports and works directly with industries developing technologies related to space science and collaborating with them to enhance and encourage the user community to adopt the new technologies. EDAC also supports and works with public agencies, private citizens, educational organizations, and volunteer groups to ensure ready accessibility to NASA generated space imagery.
Earth hydrosphere: That part of the Earth that consists of the oceans, seas, lakes, and rivers. Used for hydrosphere (Earth).
Earth mantle: The zone of the Earth below the crust and above the core (to a depth of 3480 km), which is divided into the upper mantle and the lower mantle, with a transition zone between. Used for mantle (Earth structure).
Earth observations (from space): The acquisition of Earth surface data from aircraft or spacecraft.
Earth Observing System (EOS): NASA's orbital multisensor observatory system for the long term acquisition of Earth sciences data to be operated in conjunction with an integrated ground-based science information system. This international system will become operational in 1995 when the first of four polar platforms will be launched. The first and third will be launched under U.S. auspices. The second under ESA auspices and the last under Japanese auspices.
earth point: The point where the forward straight-line projection of a meteor trajectory intersects the surface of the earth.
earth radiation: = terrestrial radiation.
Earth radiation budget experiment: Radiation measurements to determine the spatial and temporal variations of the Earth's radiance. The measurements have continued for the past two decades beginning with Explorer 7 in 1959 and through Nimbus 6 and 7. Used for ERBE.
Earth resources: Power sources and renewable or nonrenewable materials occurring naturally on Earth.
Earth Resources Observation Systems: The Earth Resources Observation Systems (EROS) program was established in the early 1970s, under the Department of the Interior's U.S. Geological Survey, to receive, process, and distribute data from United States Landsat satellite sensors and from airborne mapping cameras. See also Earth Resources Observation Systems Data Center (EDC).
Earth Resources Observation Systems Data Center: Earth Resources Observation Systems Data Center (EDC) is a national archive, production, distribution, and research facility for remotely sensed data and other geographic information. See also Earth Resources Observation Systems (EROS).
earth satellite: A body that orbits about the earth; specifically, an artificial satellite placed in orbit by man.
earth shine: = earthlight.
Earth terminal measurement system: NBS system for measuring electromagnetic parameters of communication satellites and ground stations relative to antenna gain, ratio of carrier power to operating noise temperature, and satellite effective isotropic power.
Earth terminals: Portable or stationary ground-based equipment used to transmit and receive signals and other data via satellites in communications networks.
earth tide: A periodic movement of the earth's crust caused by the tide-producing forces of the moon and sun.
earth's rate correction: A command rate applied to a gyro to compensate for the apparent precession of the gyro spin axis with respect to its base caused by the rotation of the earth.
Earth-ionosphere waveguide: A natural waveguide consisting of the atmospheric duct formed by the ionospheric D region and the surface of the Earth making possible long-range communications in the 10KHz frequency range.
earth-rate unit: (abbr eru)
A unit of angular drift, as of a gyro, equal to the rate of angular movement of the earth with respect to the stars, 15° per hour.
earthlight: The illumination of the dark part of the moon's disk produced by sunlight reflected onto the moon from the earth's surface and atmosphere. Also called earthshine.
Spectroscopic observations reveal that earthlight is relatively richer in blue light than is direct sunlight; this condition results from the fact that an appreciable part of the total earth reflection is backward-scattered light which, in accordance with Rayleigh law, is relatively rich in the blue and poor in the red.
earthquake resistance: Structural strength of natural geological formations reacting to seismic forces.
earthquake resistant structures: Buildings and other structures designed for maximum safety and protection from the effects of earthquakes.
earthquakes: Sudden motions or tremblings in the Earth caused by the abrupt release of slowly accumulated strain.
EBCDIC: Extended Binary Coded Decimal Interchange Code, an 8-bit character encoding scheme used primarily on IBM machines.
Ebert ion counter: An ion counter of the aspiration condenser type, used for the measurement of the concentration and mobility of small ions in the atmosphere.
ebullism: The formation of bubbles, with particular reference to water vapor bubbles in biological fluids caused by reduced ambient pressure; the boiling of body fluids.
eccentric: Non-circular; elliptical (applied to an orbit).
eccentric: Not having the same center; varying from a circle.
eccentric anomaly: (symbol E)
See anomaly.
eccentricity: The distance between the foci of an ellipse divided by the major axis.
eccentricity: (symbol e)
1. Of any conic, the ratio of the length of the radius vector through a point on the conic to the distance of the point from the directrix.
2. Of an ellipse, the ratio of the distance between the center and focus of an ellipse to its semimajor axis. Also called numerical eccentricity.
The eccentricity e of an ellipse can be computed by the formula where a is the semimajor axis and b is the semiminor axis.
3. Of an ellipse, the distance between the center and the focus. Also called linear eccentricity.
echo: 1. A wave that has been reflected or otherwise returned with sufficient magnitude and delay to be detected as a wave distinct from that directly transmitted.
2. In radar, a pulse of reflected radio frequency energy; the appearance on a radar indicator of the energy returned from a target. Also called blip.
echo intensity: The brightness or brilliance of a radar echo as displayed on an intensity modulated indicator. Echo intensity is, within certain limits, proportional to the voltage of the target signal or to the square root of its power. Compare echo power.
echo power: The electrical strength, or power, of a radar target signal. Echo power is normally measured in watts or dbm (decibels referred to a milliwatt).
echo pulse: A pulse of radio energy received at the radar after reflection from a target; that is, the target signal of a pulse radar.
echo signal: = target signal.
echoencephalography: A diagnostic technique in which pulses of ultrasonic waves are beamed through the head from both sides, and echoes from the midstructures of the brain are recorded as graphic tracings.
eclipse: 1. The reduction in visibility or disappearance of a nonluminous body by passing into the shadow cast by another nonluminous body.
2. The apparent cutting off, wholly or partially, of the light from a luminous body by a dark body coming between it and the observer.
1. The first type of eclipse is exemplified by a lunar eclipse, the moon passing through the shadow cast by the earth; or by the passage of a satellite into the shadow cast by its planet; but when the satellite actually passes directly behind its planet, it may properly be termed an occultation.
2. The second type of eclipse is exemplified by a solar eclipse, caused by the moon passing between the sun and the earth. If the relative positions and distances are such that at a point on the earth the sun is completely obscured, the eclipse is total; if the distances are such that, when in line with the sun, the moon is surrounded by a ring of light, the eclipse is annular; and when the moon passes to one side of a straight line from sun to observer and shows a crescent of light, it is a partial eclipse.
eclipse year: The interval between two successive conjunctions of the sun with the same node of the moon's orbit, averaging 346 days 14 hours 52 minutes 52.42 seconds in 1962, and increasing at the rate of 0.0276 second annually. See year.
ecliptic: The apparent annual path of the sun among the stars; the intersection of the plane of the earth's orbit with the celestial sphere.
The ecliptic is a great circle of the celestial sphere inclined at an angle of about 23° 27' to the celestial equator.
ecliptic longitude: = celestial longitude.
ecliptic pole: On the celestial sphere, either of the two points 90° from the ecliptic.
ecliptic system of coordinates: A set of celestial coordinates based on the ecliptic as the primary great circle. See coordinate, table.
The points 90° from the ecliptic are the north and south ecliptic poles. Angular distance north or south of the ecliptic, analogous to latitude, is celestial latitude. Celestial longitude is measured eastward along the ecliptic from the vernal equinox through 360°.
ecological system: A habitable environment, either created artificially, as in a manned space vehicle, or occurring naturally, such as the environment on the surface of the earth, in which man, animals, or other organisms can live in mutual relationship with one another and the environment.
Ideally the environment furnishes the sustenance for life, and the resulting waste products revert or cycle back into the environment to be used again for the continuous support of life.
ecology: The study of the environmental relations of organisms. See environment.
econometrics: The application of mathematics and statistical techniques to the testing and quantifying of economic theories and the solution of economic problems.
economic impact: The impact on the economy from whatever cause.
economics: Study of the production, distribution, and consumption of goods and services.
economizer: A reservoir in a continuous-flow oxygen system in which oxygen exhaled by the user is collected for recirculation in the system.
ecosphere: 1. = biosphere.
2. A volume of space surrounding the Sun, extending from the orbit of Venus past the orbit of Mars, in which some biologists believe conditions are favorable for the development and maintenance of life.
ecosystems: Ecologic systems composed of interacting organisms and their environments. The result of interaction between biological, geochemical and geophysical systems.
Eddington limit: The theoretical limit at which the photon pressure would exceed the gravitational attraction of a light-emitting body. That is, a body emitting radiation at greater than the Eddington limit would break up from its own photon pressure.
eddy: In a fluid, any circulation drawing its energy from a flow of much larger scale and brought about by pressure irregularities.
eddy coefficient: = exchange coefficients.
eddy currents: Electric currents caused to flow in a conductor by the time or space variation, or both, of an applied magnetic field.
eddy stresses: = Reynolds stresses.
eddy velocity: The difference between the mean velocity of fluid flow and the instantaneous velocity at a point. For example u' = u - , where u' is the eddy velocity; u is the instantaneous velocity; and is mean velocity. Also called fluctuation velocity.
Over the same interval which defines the mean velocity, the average value of the eddy velocity is necessarily zero.
eddy viscosity: The turbulent transfer of momentum by eddies giving rise to an internal fluid friction, in a manner analogous to the action of molecular viscosity in laminar flow, but taking place on a much larger scale.
The value of the coefficient of eddy viscosity (an exchange coefficient) is of the order of 10⁴ square centimeters per second, or 100,000 times the molecular kinematic viscosity.
edge effect: See diffraction, note.
Edison effect: the flow of an electric current through a laboratory vacuum, between two metal wires, one of which is heated. The current flows only when the heated wire is more negative, because it is due to free electrons released from the wire by heat. The Edison effect made possible "vacuum tubes" used in radio and television equipment before the invention of the transistor.
edit: In computer terminology, to arrange, delete, select, or add to information.
EDP (abbr): = electronic data processing.
EDR: Experiment Data Record.
education: Of a computer, stored subroutines and subprograms which are available for use in automatic programming.
effective aperture: = effective area.
effective area: 1. In antenna design, the ratio of the received power available at the terminals of an antenna to the power per unit area in the incident wave. For all antennas, effective area A is related to gain G at a given wavelength by the equation: A / G = ² / 4 Also called effective aperture. See aperture.
The effective area of an ideal antenna is equal to its physical area S. In practice, A/S for microwave antennas is always less than one, a representative value for paraboloids being 0.6.
2. Same as scattering cross section.
effective atmosphere: 1. That part of the atmosphere which effectively influences a particular process or motion, its outer limits varying according to the terms of the process or motion considered.
For example, an earth satellite orbiting at 250 miles altitude remains within the ionosphere, but because the air particles are so sparse at this altitude as to cause no appreciable friction of deflection, the satellite may be considered to be outside the effective atmosphere. For movement of air vehicles the effective atmosphere ends at the aeropause (which see).
2. = optically effective atmosphere.
effective earth radius: See effective radius of the earth.
effective exhaust velocity: (symbol c_e)
A fictitious exhaust velocity that would theoretically produce the observed value of jet thrust.
The effective exhaust velocity c_e is determined by the equation c_e = V + [A(p₁ - p₂) g / w] where V is the velocity of the exhaust gases; A is the nozzle exit area; p₁ is static pressure at the nozzle exit; p₂ is ambient pressure; g is the acceleration of gravity; and w is the weight flow rate of exhaust gases.
effective half-life: Time required for a radioactive substance contained in a biological system (such as a person or an animal) to reduce its radioactivity by half, as a combination result of radioactive decay and biological elimination from the system.
effective multiplication factor: (symbol k_e)
The ratio of the neutron flux in a nuclear reactor to that supplied by a neutron source.
effective neutron cycle time: The lifetime of an average neutron within a reactor from the time it is produced to the time it is fission captured.
This average takes into account delayed as well as prompt neutrons.
effective propagation velocity: The velocity of an electromagnetic signal which, when multiplied by the transit time for a ray path, gives a value for actual path length.
effective radiation: = effective terrestrial radiation.
effective radius of the earth: A fictitious value for the radius of the earth, used in place of the geometrical radius to correct for atmospheric refraction when the index of refraction in the atmosphere changes linearly with height. See modified index of refraction.
Under conditions of standard refraction the effective radius of the earth is 8.5 * 10⁶ meters, or four-thirds the geometrical radius. If the effective radius is used in ray tracing diagrams, the rays may be drawn as though they were traveling in straight lines.
effective Reynolds number: A fictitious Reynolds number applied to the flow of air about a body in a wind tunnel, equal to the free-air Reynolds number at which the effect obtained is the same as the effect obtained in the wind tunnel.
effective sound pressure: The root-mean-square value of the instantaneous pressure of sound waves, taken over a complete cycle or a period long compared with a cycle, at that point. The unit is the microbar (dynes per square centimeter).
effective temperature: 1. In astrophysics, a measure of the temperature of a star deduced by means of the Stefan-Boltzmann law, from the total energy emitted per unit area. Compare brightness temperature, color temperature.
Effective temperature is always less than actual temperature.
2. In physiology, the temperature at which motionless, saturated air would induce, in a sedentary worker wearing ordinary indoor clothing, the same sensation of comfort as that induced by the actual conditions of temperature, humidity, and air movement. Compare sensible temperature, standard operative temperature, operative temperature.
Effective temperature is used as a guide in air-conditioning practice, and, on the comfort chart (American Society of Heating and Air Conditioning Engineers) it appears as a family of curves which serves as one coordinate in defining comfort zones.
effective terrestrial radiation: The amount by which outgoing infrared terrestrial radiation of the earth's surface exceeds downcoming infrared counter-radiation from the atmosphere. Also called nocturnal radiation, effective radiation. See actinometer.
It is to be emphasized that this amount is a positive quantity, of the order of several tenths of a langley per minute, at all times of day (except under conditions of low overcast clouds). It typically attains its diurnal maximum during the midday hours when high soil temperatures create high rates of outgoing terrestrial radiation. (For this reason the synonym nocturnal radiation is apt to lead to slight confusion.) However, in daylight hours the effective terrestrial radiation is generally much smaller than the insolation, while at night it typically dominates the energy budget of the earth's surface.
effective wavelength: The wavelength corresponding to the effective propagation velocity.
effector: Any device used to maneuver a rocket in flight, such as an aerodynamic surface, a gimbaled motor, or a jet.
efficiency: (symbol )
Of a device with respect to a physical quantity which may be stored, transferred, or transformed by the device, the ratio of the useful output of the quantity to its total input.
Unless specifically stated otherwise, the term efficiency means efficiency with respect to power.
effusive eruption: An eruption dominated by the outpouring of lava onto the ground is often referred to as an effusive eruption (as opposed to the violent An eruption dominated by the outpouring of lava onto the ground is often referred to as an effusive eruption (as opposed to the violent fragmentation of magma by explosive eruptions). Lava flows generated by effusive eruptions vary in shape, thickness, length, and width depending on the type of lava erupted, discharge, slope of the ground over which the lava travels, and duration of eruption.
egads (abbr): = electronic ground automatic destruct sequencer.
egads button: A button used by the range safety officer to initiate destruction of a rocket vehicle in flight if its course, as plotted during flight, is predicted to go beyond the destruct line. See egads, impact predictor system.
egress: The action, right, place or means of going or coming out; exiting.
EHF (abbr): = Extremely High Frequency. See frequency band.
EHz: ExaHertz (10FM¹⁸ Hz)
eigenmode: = normal mode of vibration.
eigenvalue: See characteristic value problem.
eight ball: Common name given to a flight attitude indicator.
eikonal equation: An equation for propagation of electromagnetic or acoustic waves in an inhomogenous medium; valid only when the scale length for variation in the properties of the medium is small compared to a wavelength.
EISCAT radar system (Europe): The European Incoherent Scatter Radar system. Used for European Incoherent Scatter Radar.
ejecta: Matter ejected during impact cratering processes, usually meteoritic.
ejection capsule: 1. In an aircraft or manned spacecraft, a detachable compartment serving as a cockpit or cabin, which may be ejected as a unit and parachuted to the ground.
2. A satellite, probe, or unmanned spacecraft, a boxlike unit, usually containing recording instruments or records of observed data, which may be ejected and returned to earth by a parachute or other deceleration device.
ejection seats: An emergency escape seat or device for propelling an occupant out and away from a high speed vehicle.
ejector: A device consisting of a nozzle, mixing tube, and diffuser utilizing the kinetic energy of a fluid stream to pump another fluid from a low pressure region by direct mixing and ejecting both streams.
Ekman layer: The layer of transition between the surface boundary layer, where shearing stress is constant, and the free atmosphere, where the atmosphere is treated as an ideal fluid in approximate geostrophic equilibrium. Also called spiral layer.
In Ekman's analysis (see Ekman spiral), the coefficient of eddy viscosity is assumed constant within this layer; subsequent calculations have relaxed this assumption.
Ekman spiral: As used in meteorology, an idealized mathematical description of the wind distribution in the planetary boundary layer of the atmosphere, within which the earth's surface has an appreciable effect on the air motion. The model is simplified by assuming that within this layer eddy viscosity and density are constant, the motion is horizontal and steady, the isobars are straight and parallel, and the geostrophic wind is constant with height.
EL: Elevation
el Nino: A warming of the surface waters of the eastern equatorial Pacific Ocean that cccurs at irregular intervals of 1-2 years, usually lasting 1-2 years.
Elara: A natural satellite of Jupiter, orbiting at a mean distance of 11,737,000 kilometers.
elastic buckling: The collapse of a structural member under a load which compresses it within its elastic range.
elastic collision: A collision between two particles in which no change occurs in the internal energy of the particles, or in the sum of their kinetic energies. Commonly referred to as a billiard-ball collision.
elastic properties: Properties of materials by virtue of which they tend to recover their original size and shape immediately after removal of the forces causing deformation. Used for elastic constants and elasticity.
elastic wave: See sound.
elasticity: The ability of a body which has been deformed by an applied force to return to its original shape when the force is removed.
elasticizer: An elastic substance or fuel used in a solid rocket propellant to prevent cracking of the propellant grain and to bind it to the combustion-chamber case.
elastodynamics: The field of mechanical dynamics that deals with the transmission and properties of elastic waves.
elastomers: Macromolecular materials which, at room temperature, are capable of recovering substantially in size and shape after removal of a deforming force.
elastomers: Rubber-like compounds.
Elastomers are used as pliable components, as in tires, seals, or gaskets.
elastoplasticity: The condition shown by a material that has deformed in both its elastic and plastic properties.
Elber equation: In fatigue crack propagation studies, the effective stress range ratio U = 0.5 + 0.4R, where R is the stress ratio.
electric arcs: (1) a luminous discharge of electricity through a gas. (2) A prolonged electrical discharge or series of prolonged discharges between two electrodes with no physical contact between them.
electric connectors: Connecting devices, ordinarialy designed for use in a fixed location to which a wire or wies of a circuit may be attached and that are arranged for the insertion of a plug. Used fojacks (electrical).
electric corona: A luminous, and often audible, electric discharge that is intermediate in nature between a spark discharge (with, usually, its single discharge channel) and a non point discharge (with its diffuse, quiescent, nonluminous character). Used for corona discharges.
electric current: A continuous flow of electrons and/or ions, through a material with conducts electricity. A currents usually flows in a closed circuit, without beginning or end. In daily life currents are generally driven through wires by voltages produced by batteries or generators. In space plasmas, some currents may be produced this way, but many are inherent to the way ions and electrons move through magnetic fields, e.g. their drifts. >
electric dipole: A pair of equal and opposite charges an infinitesimal distance apart.
In electromagnetics, the term dipole is often applied to two equal and opposite oscillating charges an infinitesimal distance apart; in this sense, it is synonymous with an electric-current element.
electric discharge: The flow of electricity through a gas, resulting in the emission of radiation that is characteristic of the gas and of the intensity of the current. Also called discharge, gaseous electric discharge, gaseous discharge. See corona discharge, point discharge, spark discharge, lightning discharge.
electric field: 1. A region in which a charged particle would experience an electrical force; the geometric array of the imaginary electric lines of force that exist in relation to points of opposite charge.
An electric field is a vector field in which magnitude of the vector is the electric-field strength and the vector is parallel to the lines of force.
2. = electric-field strength. See atmospheric electric field.
electric fields: Regions in which electric forces can be observed, e.g. near an electric charge. As fields, they may also be viewed as a region of space modified by the presence of electric charges.
electric furnaces: Furnaces whose heat is derived from electrical energy, generally achieved through resistance heating. Materials research and space processing are research uses.
electric hybrid vehicles: Surface vehicles which utilize propulsion systems of both electric motors and conventional internal combustion engines.
electric intensity: = electric-field strength.
electric lines of force: Imaginary lines defined by the paths traced by unit charges placed in an electric field. Lines of force are everywhere parallel to the electric-field strength vector. Their principal use is as a convenient means of picturing the geometry of an electric field. See magnetic lines of force.
electric potential: In electrostatics, the work done in moving unit positive charge from infinity to the point whose potential is being specified. Sometimes shortened to potential.
electric potential gradient: = electric-field strength.
electric power level: = level.
electric propulsion: A general term encompassing all the various types of propulsion in which the propellant consists of charged electrical particles which are accelerated by electrical or magnetic fields, or both; for example, electrostatic propulsion, electromagnetic propulsion, electrothermal propulsion.
electric-current element: = electric dipole.
electric-field intensity: = electric-field strength.
electric-field strength: The electrical force exerted on a unit positive charge at a given point in space. Electric-field strength is expressed, in the practical system of electrical units, in terms of volts/centimeter. It is a vector quantity, being the magnitude of the electric-field vector. Also called electric field, electric intensity, electric field intensity, electric potential gradient, field strength.
The electric-field strength of the atmosphere is commonly referred to as the atmospheric electric field.
electrical: Involving the flow of electricity in a conductor. Compare electronic.
electrical conductivity: Degree to which a substance conducts electric current. Can be defined by: (current density) = (conductivity) * (applied electric field) Electrons and ions both contribute to current in proportion to their mobility in the system. In a plasma with a magnetic field, there is no longer a one-to-one correspondence between current and electric field. Instead, the current in each direction can be due to combinations of the electric fields in all the other directions. In this case, the current density and the electric field are vectors, and the conductivity becomes a tensor (matrix) which relates them.
electrical distance: The distance between two points expressed in terms of the duration of travel of an electromagnetic wave in free space between the two points.
A convenient unit of electrical distance is the light microsecond or approximately 983 feet (300 meters). In the use of this unit, electrical distance is numerically equal to transmission time in microseconds.
electrical element: See element, sense 2.
electrical engine: A rocket engine in which the propellant is accelerated by some electrical device. Also called electric propulsion system, electric rocket.
Electrical engines can be classified as electrothermal, electrostatic, or electromagnetic, depending on the nature of the accelerating device.
electrical engineering: Branch of engineering related to the design, development, and operation of electrical devices and systems.
electrical insulation: A material of relatively low electrical conductivity and high dielectric strength, usually used to support or provide electrical separation for conductors, in which a voltage applied between two points on or within the material produces a small and sometimesnegligible current.
electrical resistivity: A factor such that the conduction-current density is equal to the electric field in the material divided by resistivity.
electroacoustic transducer: A transducer for receiving waves from an electric system and delivering waves to an acoustic system, or vice versa.
Microphones and earphones are electroacoustic transducer.
electroacoustic transducers: Transducers for receiving waves from an electric system and delivering waves to an acoustic system, or vice versa. Microphones and earphones are electroacoustic transducers.
electrochemical: See chemical energy.
electrochemical cells: Electrochemical systems consisting of an anode and a cathode in metallic contact and immersed in an electrolyte. (The anode and cathode may be different metals or dissimilar areas on the same metal surface).
electrochemical synthesis: A chemical synthesis reaction that is induced by an electric current.
electrochemical transducer: A transducer which uses a chemical change to indicate the input parameter.
electrochemistry: The branch of science and technology which deals with transformations between chemical and electrical energy.
electrochromism: A phenomenon whereby a select number of solid materials will change color when an electric field is applied.
electrode: 1. A terminal at which electricity passes from one medium into another. The positive electrode is called anode; the negative electrode is called cathode.
2. In a semiconductor device, an element that performs one or more of the functions of emitting or collecting electrons or holes, or of controlling their movements by an electric field.
3. In electron tubes, a conducting element that performs one or more of the functions of emitting, collecting or controlling, by an electromagnetic field, the movements of electrons or ions. See anode (electron tubes) and cathode.
electrodynamics: The science dealing with the forces and energy transformations of electric currents, and the magnetic fields associated with them.
electroepitaxy: Crystal growth process achieved by passing an electric current through the substrate solution.
electrojet: A laterally limited relatively intense electric current located in the ionosphere.
electrokinetic transducer: A transducer that depends for its operation on the dielectric polarization in certain liquids resulting from viscous shearing stress that accompanies flow through porous materials.
electroless deposition: Controlled autocatalytic reduction method of depositing coatings.
electroluminescence: Emission of light caused by an application of electric fields to solids or gases.
In gas electroluminescence, light is emitted when the kinetic energy of electron or ions accelerated in an electric field is transferred to the atoms or molecules of the gas in which the discharge takes place.
electrolysis: The production of chemical changes by the passage of current through an electrolyte.
electrolytic cells: Unit apparatus in which electrochemical reactions are produced by applying electrical energy, or which supply electrical energy as a result of chemical reactions and which include two or more electrodes and one or more electrolytes contained in a suitable vessel. Used for galvanic cells.
electromagnetic: Of or pertaining to magnetism produced by or associated with electricity.
Magnetoelectric pertains to electricity produced by or associated with magnetism.
electromagnetic acceleration: The use of perpendicular components of electric and magnetic fields to accelerate a current carrier.
electromagnetic coupling: A means of extracting energy from a magnetically confined plasma, where the plasma expands and pushes on the confining magnetic field, causing electrical energy to be generated in the external field-generating circuits.
electromagnetic energy: = electromagnetic radiation.
electromagnetic environment experiment: Shuttleborne radio frequency experiment.
electromagnetic field: An electromagnetic field consists of energy oscillations associated with electric and magnetic fields initially caused by the motions of electric charges. The resulting waves propagate through space at the speed of light.
electromagnetic fields: The regions of space near electric currents, magnets, broadcasting antennas etc., regions in which electric and magnetic forces may act. Generally the electromagnetic field is regarded as a modification of space itself, enabling it to store and transmit energy.
electromagnetic force: One of the fundamental forces of interaction which influences charged entities. In quantum field theory, the EM force is mediated by particles of exchange called (virtual) photons. Photons are massless and travel at the speed of light c.
electromagnetic radiation: Energy propagated through space or through material media in the form of an advancing disturbance in electric and magnetic fields existing in space or in the media. The term radiation , alone, is used commonly for this type of energy, although it actually has a broader meaning. Also called electromagnetic energy or simply radiation. See electromagnetic spectrum.
electromagnetic rockets: = plasma rockets. See electric propulsion.
electromagnetic spectra: Spectra of known electromagnetic radiations, extending from the shortest cosmic rays, through gamma rays, x rays, ultraviolet radiation, visible radiation, and including microwave and all other wavelengths of radio energy.
electromagnetic spectrum: Electromagnetic radiation is energy propagated through space between electric and magnetic fields. The electromagnetic spectrum is the extent of that energy ranging from cosmic rays, gamma rays, X-rays to ultraviolet, visible and infrared radiation including microwave energy.
electromagnetic spectrum: The ordered array of known electromagnetic radiation, extending from the shortest cosmic rays, through gamma rays, X-rays, ultraviolet radiation, visible radiation, infrared radiation, and including microwave and all other wavelengths of radio energy. See absorption spectrum.
The division of this continuum of wavelengths (or frequencies) into a number of named subportions is rather arbitrary and, with one or two exceptions, the boundaries of the several subportions are only vaguely defined. Nevertheless, to each of the commonly identified subportions there correspond characteristic types of physical systems capable of emitting radiation of those wavelengths. Thus, gamma rays are emitted from the nuclei of atoms as they undergo any of several types of nuclear rearrangements; visible light is emitted, for the most part, by atoms whose planetary electrons are undergoing transitions to lower energy states; infrared radiations are associated with characteristic molecular vibrations and rotations; and radio waves, broadly speaking, are emitted by virtue of the accelerations of free electrons as, for example, the moving electrons in a radio antenna wire.
electromagnetic theory: See electromagnetic radiation.
electromagnetic wave: A combination of oscillating magnetic and electric fields, spreading in wavelike fashion through space at a speed of about 300 000 km.sec. Such waves include all forms of light, as well as infra-red and ultra-violet, radio waves, microwaves, x-rays and gamma rays.
electromagnetic wave: A wave produced by oscillation of an electric charge. See electromagnetic radiation.
electromagnetism: 1. Magnetism produced by an electric current.
2. The science dealing with the physical relations between electricity and magnetism.
electromagnets: Magnets powered by an electric current. Usually the current flows in a coil, which may or may not contain a core of iron or of some other magnetic material
electromechanical transducer: A transducer for receiving waves from an electric system and delivery waves to a mechanical system, or vice versa.
electrometeor: A visible or audible manifestation of atmospheric electricity. This includes, therefore, not only visible electric discharges (igneous meteors) but also the sounds produced by them, principally thunder.
electrometer: An instrument for measuring differences of electric potential.
electromotive forces: Forces capable of maintaining a potential difference, and thus a current, within a circuit. They can be established by chemical action or by mechanical work.
electromyogram: A record of the response of a muscle to an electric stimulation.
electromyography: The study of the response of a muscle to an electric stimulation.
electron: A negatively charged elementary particle that normally resides outside (but is bound to) the nucleus of an atom.
electron: The subatomic particle that possesses the smallest possible negative electric charge (4.80298 * 10^-10 electrostatic units). See physical constants, table.
The mass of the electron is approximately equal to 1/1836 that of a hydrogen atom; its theoretical rest mass (symbol m_e) is equal to 9.109 3897(54) * 10^-31 kg and its rest energy is equal to 0.510 999 06(15) million electron-volt. The charge-to-mass ratio for the electron (symbol e/m_e) is 1.758796 cc^½ / g^½.
The term electron is usually reserved for the orbital or extranuclear particle, whereas the term beta particle refers to a nuclear electron.
*The numbers in bold type were taken from the 1987 publication of Fundamental Physical Constants: 1986 CODATA (Committee on Data for Science and Technology of the International Council of Scientific Unions) Recommended Values issued by the U. S. Department of Commerce, National Bureau of Standards.
"Digits in parentheses represent one standard deviation uncertainty in the final digits of the given value, based on a least-squares analysis with five variables and 17 degrees of freedom."
electron acceleration: The acceleration of electrons by action of solar cosmic rays.
electron avalanche: The process in which a relatively small number of free electrons in a gas that is subjected to a strong electric field accelerate, ionize gas atoms by collision, and thus form new free electrons to undergo the same process in cumulative fashion.
An avalanche cannot begin until the local electric field strength is high enough to accelerate a free electron to the minimum ionizing speed in the space and time interval corresponding to one mean free path of the electron, for upon collision, the electron usually loses its forward motion in the direction of the field.
electron beam: Specifically, a focused stream of electrons used for neutralization of the positively charged ion beam in an ion engine. Also used to melt or weld materials with externally high melting points.
electron cyclotron heating: A type of radio frequency plasma heating in which high-power microwave energy is introduced into the plasma region.
electron density: Number of electrons in a unit volume.
electron device: A device in which electricity is conducted principally by electrons moving through a vacuum, gas, or semiconductor.
electron diffraction: The phenomenon, or the technique of producing diffraction patterns through the incidence of electrons as a function of kinetic energy.
electron gun: An electrode structure which produces and may control, focus, deflect, and converge one or more electron beams.
electron microscopy: The interpretive application of an electron microscope for the magnification of materials that cannot be properly seen with an optical microscope.
electron optics: The science that deals with the propagation of electrons, as light optics deals with light and its phenomena.
electron probes: Narrow beams of electrons used to scan or illuminate an object or screen.
electron runaway (plasma physics): High acceleration of electrons in a collisional plasma caused by a suddenly applied electric field (which greatly reduces the collision cross section of the electrons).
electron spectroscopy: The study and interpretation of atomic, molecular, and solid state structure based on x ray induced electron emission from substances.
electron trajectories: The paths of electrons. Used for electron paths.
electron tube: A device in which conduction by electrons takes place through a vacuum or gaseous medium within a gastight envelope.
electron volt: The change of potential energy experienced by an electron moving from a place where the potential has a value of V to a place where it has a value of (V+1 volt). This is a convenient energy unit when dealing with the motions of electrons and ions in electric fields; the unit is also the one used to describe the energy of X-rays and gamma-rays.
electron volt: A measure of the energy of subatomic particles.
electron volt: (abbr eV)
A unit of energy equal to the energy required to move an electron through a potential difference of 1 volt. Often shortened to volt.
One electron volt equals 1.6020 * 10^-9 joule.
electron-hole drops: Exciton condensations exhibiting the properties of electrically conducting plasmas which form in germanium and silicon crystals at sufficiently low cryogenic temperatures.
electronic: 1. Involving the flow of electrons in a vacuum or through semiconductors.
2. Of or pertaining to electronics, i.e., to that branch of physics that treats of the emission, transmission, behavior, and effects of electrons, especially as applied by means of vacuum tubes, cathode-ray tubes, photoelectric cells, and the like, together with the associated electrical devices.
electronic aircraft: Designation for tactical electronic warfare aircraft.
electronic Bohr magneton: = Bohr magneton.
electronic data processing: The use of electronic devices and systems in the processing of data so as to interpret the data and put them into usable form.
electronic equipment: Equipment in which electricity is conducted principally by electrons moving through a vacuum, gas, or semiconductor.
electronic missile acquisition: (abbr EMA)
A crossed baseline interferometer system giving azimuth and elevation angles.
This system was designed as an acquisition aid for theodolites. The EMA equipment operates on the Dovap transponder frequency.
electronic sky screen equipment: See elsse.
electronic transducer: A unilateral transducer that depends for its operation on the generation of a voltage by the relative motion of the electrodes in a vacuum tube.
electronic warfare: Military action involving the use of electromagnetic energy to determine, exploit, reduce, or prevent hostile use of the electromagnetic spectrum, and action which retains friendly use of the electromagnetic spectrum.
electronic work function: = Helmholtz function.
electronics: Study and application of the motions of electrons through vacuum and gaseous, conducting, or semiconducting media.
electronics: That branch of physics that treats of the emission, transmission, behavior, and effects of electrons. See electronic.
electrons: Particles of very small mass, carrying a unit negative or positive charge. Negative electrons, surrounding the nucleus (i.e., orbital electrons) are prewent in all atoms. Their number is equal to the number of positive charges (or protons) in the particular nucleus. The term electron, when used alone, commmonly refers to a negative electron. A positive electron is usually called a positron, and a negative electron is sometimes called a negatron.
electrophoresis: The movement of colloidal particles produced by the application of an electric potential. Used for continuous flow electrophoresis.
electropolishing: The improvement in surface finish of a metal effected by making it anodic in an appropriate solution. Used for electrolytic polishing.
electroscope: A simple instrument, indicating the presence of electric charge by the spreading-apart of two leaves of metal foil, hanging next to each other inside a glass jar. The rate at which an electroscope in dry air loses its charge is a rough indicator of the prevailing level of ionizing radiation.
electrostatic bonding: Use of the particle-attracting property of electrostatic charges to bond particles of one charge to those of the opposite charge.
electrostatic confinement: An approach to fusion based on confining charged particles by means of electric fields, rather than the magnetic fields used in magnetic confinement.
electrostatic engines: The electric system or engine that obtains the highest degree of conversion of electric power into thrust, high exhaust velocity, and a longest operational lifetime working on the principle of ionization of propellant gas through the use of direct electron bombardment or radio frequency fields to increase the temperature of the gas and cause the desired thrust; also called the ion engine.
electrostatic memory: The ability of a substance or device to retain an electrostatic charge after the charging force is removed.
electrostatic rocket: = ion rocket. See electric propulsion, ion engine.
electrostatic storage: In a computer, storage of information in the form of electrostatic charges.
electrostatic waves: Longitudinal oscillations appearing in a plasma due to a perturbation of electric neutrality. For a cold unmagnetized plasma, or at large wavelengths, the frequency of these waves is by definition the plasma frequency.
electrostatic-storage tube: A cathode-ray tube in which information is stored as positive or negative charges on a dielectric surface.
electrostriction: The phenomenon wherein some dielectric materials experience an elastic strain when subjected to an electric field, this strain being independent of polarity of the field.
electrosynthesis: See electrochemical synthesis
electrothermal rocket: = electric thermal rocket. See electric propulsion.
electrowinning: The production of metals by electrolysis with insoluble anodes in solutions derived from ores or other materials.
element: 1. One of the simple parts of which a complex entity is composed.
2. In chemistry, a substance which cannot be broken down by ordinary chemical means into simpler components.
3. In an electron tube, a constituent part of the tube that contributes directly to the electrical operation of the tube.
4. In a circuit, any electrical device (such an inductor, resistor, capacitor, generator, line, electron tube) with terminals at which it may be directly connected to other electrical devices.
5. In a semiconductor device, any integral part of the semiconductor device, any integral part of the semiconductor device that contributes to its operation.
6. = orbital element.
elements: One of the fundamental chemical substances which cannot be divided into simpler substances by chemical means. Atoms with the same atomic number (# of protons) all belong to the same element.
elevated pole: The celestial pole above the horizon.
The celestial pole below the horizon is called depressed pole.
elevation: Direction or bearing above the horizontal plane.
elevation: = angle of elevation.
elevation angle: = angle of elevation.
ELF (abbr): = extremely low frequency. See frequency band.
ellipse: A plane curve constituting the locus of all points the sum of whose distances from two fixed points called focuses or foci is constant; an elongated circle. See conic section.
The orbits of planets, satellites, planetoids, and comets are ellipses, the primary being at one focus.
ellipsoid: A surface whose plane sections (cross sections) are all ellipses or circles, or the solid enclosed by such a surface. Also called ellipsoid of revolution, spheroid.
ellipsoid of revolution: = ellipsoid.
It is so named from the fact that it can be formed by revolving an ellipse about one of its axes.
ellipsometers: Instruments for determining the ellipticity of polarized light. Used to measure the thickness of very thin transparent films.
elliptic: Pertaining to an ellipse, or in the form of an ellipse.
elliptical plasmas: Confined non-circular plasmas.
elliptical polarization: The polarization of a wave radiated by an electric vector rotating in a plane and simultaneously varying in amplitude so as to describe an ellipse.
elliptical system: A tracking or navigation system where ellipsoids of position are determined from time or phase summation relative to two or more fixed stations which are the focuses for the ellipsoids.
elliptically polarized sound wave: A transverse wave in an elastic medium in which the displacement vector at any point rotates about the point and has a magnitude which varies as the radius vector of an ellipse.
An elliptically polarized wave is equivalent to two superposed plane polarized waves of simple sinusoidal form in which the displacements lie in perpendicular planes and are 90° apart in phase.
ellipticity: (symbol e)
The amount by which a spheroid differs from a sphere or an ellipse differs from a circle, calculated by dividing the difference in the length of the axes by the length of the major axis. Also called compression. See flattening.
ellipticity ratio: 1. The ratio of the major axis to the minor axis of an ellipse.
2. As a measure of elliptical polarization, the power ratio of the maximum to the minimum electric vectors of an elliptically polarized antenna.
elongation: The state of being elongated or lengthened; the process of growing or increasing in length; the percentage of extension produced in a tensile test; the angular distance of a celestial body from another around which it revolves or from a particular point in the sky.
elongation: The angular distance of a body of the solar system from the sun; the angle at the earth between lines to the sun and another celestial body of the solar system. The term is usually used only in connection with inferior planets.
The greatest elongation of such a body is its maximum angular distance from the sun before it starts back toward conjunction. The direction of the body east or west of the sun is usually specified, as greatest elongation east.
elsse: = Electronic sky screen equipment.
An electronic device which indicates the departure of a rocket from a predetermined trajectory.
ELV: Expendable launch vehicle
elves: Transient air glow events observed near 90 km, nearly simultaneously with a strong cloud-to-ground lightning stroke. They often precede sprites, which may occur at lower altitudes a few milliseconds later. It is believed that elves are the result of wave heating by very low frequency (VLF) radio pulses emitted by the lightning discharge current.
EMA: = electronic missile acquisition.
embedded atom method: A semiempirical calculation method developed by Daw and Baskes for determining the energetics of atoms in a bulk environment. The original form of the method was based on density functional theory and was intended primarily for tight-packed transition metals. More recent modifications have extended the applicability of the method to a large number of elements in the periodic table.
embedded computer systems: Computer systems physically incorporated into larger systems whose primary function is not data processing.
embolism: Large amounts of air in the blood stream which, reaching the heart, cause it to fail; small amounts are resorbed and cause no symptoms.
embossing: Raising in relief on a surface.
embrittlement: The severe loss of ductility or toughness or both, of a material, usually a metal or alloy.
emergency locator transmitters: Aircraft distress signal equipment with a radio beacon on a specific emergency frequency and used for locating downed aircraft. The set is activated by the impact of the crash.
emissance: = emittance, sense 2.
emission: The act or instance of emitting; something sent forth by emitting as by radiation or being discharged; release of electrons from parent atoms on absorption of energy in excess of normal average.
emission: 1. With respect to electromagnetic radiation, the process by which a body emits electromagnetic radiation as a consequence of its temperature only. Compare reflection, transmission. See emittance, emissivity.
2. With respect to electric propulsion and energy conversion, the sending out of charged particles from a surface causing the generation of these particles; e.g., emission of ions from an ionizing surface in ion engines.
emission line: A minute range of wavelength (or frequency) in the electromagnetic spectrum within which radiant energy is being emitted by a radiating substance. See spectral line, emission spectrum.
emission spectrography: This destructive analytical technique is used to determine concentrations of specific chemical elements based on their emission or absorption of specific wavelengths of electromagnetic radiation.
emission spectrum: The array of wavelengths and relative intensities of electromagnetic radiation emitted by a given radiator.
Each radiating substance has a unique, characteristic emission spectrum, just as every medium of transmission has its individual absorption spectrum.
emissive power: The rate of thermal emission of radiant energy per unit area of emitting surface. Usually called thermal emissive power.
emissivity: (symbol )
A property of a material, measured as the emittance of a specimen of the material that is thick enough to be completely opaque and has an optically smooth surface.
emittance: (symbol E, )
1. The radiant flux per unit area emitted by a body.
2. The ratio of the emitted radiant flux per unit area of a sample to that of a blackbody radiator at the same temperature and under the same conditions.
Spectral emittance refers to emittance measured at a specified wavelength.
Because of the two common meanings of emittance, it should be defined when used unless the context allows no misinterpretation.
emulsion: In photography, a light-sensitive coating on a film, plate, or paper. See nuclear emulsion.
emulsion plate: A plate with a photographic emulsion specially designed to permit observation of the individual tracks of ionizing particles.
emulsions: Suspensions of fine particle or globules of one or more liquids in another liquid.
enamel: A thin ceramic coating, usually of high glass content, applied to a substrate, generally a metal.
enamels: Thin ceramic coatings, usually of high glass content, applied to a substrate, generally a metal.
enantiomers: Isomeric pairs whose crystalline forms or molecular structures are non-superimposable mirror images.
encapsulated microcircuits: Microelectronic circuits enclosed in plastic.
Enceladus: A satellite of Saturn orbiting at a mean distance of 238,000 kilometers.
Encke comet: A very faint comet with a periodicity of 3.3 years which is the shortest of any known comet.
encoder: = analog to digital converter.
end-fire array: A linear antenna array whose direction of maximum radiation is along the axis of the array.
end-to-end data systems: Comprehensive data systems which demonstrate the processing of sensor data to the user thus reducing data fragmentation.
endangered species: Living organisms (except plants) whose populations have diminished to such low levels that survival may require extraordinary conservation procedures. Changes in size and quality of the ecology are considered the cause of the possible extinction of some species.
endothermic fuels: Any material used to provide power which requires heat in order to proceed.
Energetic and Relativistic Nuclei and Electron experiment: Instrument aboard SOHO which analyzes high energy nuclei and electrons in the solar wind.
energetic particles: Charged particles having energies equaling or exceeding a hundred MeV
energy: Typically defined as "the ability to do work". Power is the rate at which work is done, or the rate at which energy is changed. "Work" characterizes the degree to which the properties of a substance are transformed. Energy exists in many forms, which can be converted from one to another in various ways. Examples include: gravitational energy, electrical energy, magnetic and electric field energy, atomic binding energy (a form of electrical energy really), nuclear binding energy, chemical energy (another form of electrical energy); in addition to these forms of potential energy there are also kinetic energy (energy due to motion), and thermal energy ("heat"; a form of kinetic energy where the motion is due to thermal vibrations/motions), and so on.
energy: Any quantity with dimensions mass x length squared divided by time squared. Compare entropy.
energy budgets: Quantitative descriptions of the total energy exchange into and out of a given physical or ecological system; may include radiation heat, kinetic, and biological process.
energy confinement time: Characteristic time in which 1/e (or sometimes 1/2) of a system's energy is lost to its surroundings. In a plasma device, the energy loss time (or the energy confinement time) is one of three critical parameters determining whether enough fusion will occur to sustain a reaction. (See Lawson criterion)
energy conversion: The change of a working substance or natural power into a more useable form of energy such as electricity or mechanical motion.
energy conversion efficiency: The efficiency with which a nozzle converts the energy of the working substance into kinetic energy, expressed as the ratio of the kinetic energy of the jet leaving the nozzle to the kinetic energy of a hypothetical ideal jet leaving an ideal nozzle using the same working substance at the same initial state and under the same conditions of velocity and expansion.
energy density: The sound energy per unit volume in a sound wave. The unit is the erg per cubic centimeter.
energy density spectrum: The square of the amplitude of the (complex) Fourier transform of an aperiodic function. Sometimes called energy spectrum. See power spectrum.
energy diagram: A graphical depiction of the stored capacity of a body or system to do work versus the position of a particle, or versus one generalized coordinate of a system.
energy dissipation: The difference between energy input and output as a result of transfer of energy between two points. Used for energy loss.
energy equation: See thermodynamic energy equation, mechanical energy equation, total energy equation.
energy flux: The rate of flow of electrons through a reference surface. In cgs units, measured in electrons s^-1, or simply s^-1.
energy gaps (solid state): A range of forbidden energies in the band theory of solids. Used for bandgap.
energy level: Any one of different values of energy which a particle, atom, or molecule may adopt under conditions where the possible values are restricted by quantizing conditions.
During transitions from one energy level to another, quanta of radiant energy are emitted or absorbed, their frequency depending on the difference between the energy levels.
energy management: In rocketry the monitoring of the expenditure of fuel for flight control and navigation.
energy principle: In magnetohydrodynamic theory, this principle states that a perturbation is unstable if it reduces the stored potential energy of the system (and thus allows the conversion of potential energy to kinetic energy of the instability).
energy spectrum: = energy density spectrum.
engine: A machine or apparatus that converts energy, especially heat energy, into work. Also called motor.
engine airframe integration: Physics of the interface between the engine and the airframe.
engine control: Any control for regulating the power and speed of an engine, such as the throttle, mixture control, manifold-pressure regulator, fuel-pressure control, supercharger control, etc.
engine coolants: Liquids used in an engine cooling system to transfer heat from the engine to the radiator.
engine mount: A structure used for attaching an engine to a vehicle.
engine spray: That part of a pad deluge that is directed at cooling a rocket's engine or engines during launch.
engine-exhaust trail: = exhaust trail.
engineering: The useful application of scientific or other systematic knowledge of the properties of matter and the sources of energy in nature.
English candle: = international candle.
enhanced radiation: Increased radio wave or thermal radiation from the sun, of several hours or days duration.
Enhanced radiation is usually accompanied by many bursts.
enthalpy: A mathematically defined thermodynamic function of state h = u + pv where h is specific enthalpy; u is specific internal energy; p is pressure; and v is specific volume. Also called heat function.
The change in enthalpy measures the heat imparted to a system during a reversible isobaric process: dh = dq where dq is the heat increment per unit mass. For a perfect gas, dh = c_pdT where c_p is the specific heat at constant pressure and dT is the temperature increment.
entropy: 1. A measure of the extent to which the energy of a system is unavailable. A mathematically defined thermodynamic function of state, the increase in which gives a measure of the energy of a system which has ceased to be available for work during a certain process: ds = (du + pdv)/T >= dq/T where s is specific entropy; u is specific internal energy; p is pressure; v is specific volume; T is Kelvin temperature; and q is heat per unit mass. For reversible processes, ds = dq/T In terms of potential temperature , ds = c_p (d/) where c_p is the specific heat at constant pressure. See third law of thermodynamics.
In an adiabatic process, the entropy increases if the process is irreversible and remains unchanged if the process is reversible. Thus, since all natural processes are irreversible, it is said that in an isolated system the entropy is always increasing as the system tends toward equilibrium, a statement which may be considered a form of the second law of thermodynamics.
2. In communication theory, average information content.
entropy (statistics): A factor or quantity that is a function of a mechanical system and is equal to the logarithm of the probability of the particular arrangement in that state.
entry corridor: Depth of the region between two trajectories which define the design limits of a vehicle which will enter a planetary atmosphere.
entry guidance (STS): The precise steering commands for trajectory from initial penetration of the Earth's atmosphere until the terminal area guidance is activated at an Earth-relative speed (about 2500 fps).
envelope: 1. Of a variable, a curve which bounds the values which the variable can assume, but does not consider possible simultaneous occurrences or correlations between different values.
2. The bounds within which a certain system can operate as a flight envelope, especially a graphic representation of these bounds showing interrelationships of operational parameters.
environment: An external condition or the sum of such conditions, in which a piece of equipment, a living organism, or a system operates as in temperature environment, vibration environment,or space environment.
Environments are usually specified by a range of values, and may be either natural or artificial.
environment pollution: Alterations of the natural environment that are harmful to life; normally as produced by human activities.
environmental chamber: A chamber in which humidity, temperature, pressure, fluid contents, noise, and movement may be controlled so as to simulate different environments.
environmental chemistry: Collective term comprising the complex chemical relationships involving the atmosphere, climatology, air and water pollution, fuels, pesticides, energy, biochemistry, geochemistry, etc.
environmental lapse rate: The rate of decrease of temperature T with elevation z in the atmosphere, - T / z or occasionally T / p, where p is pressure. See autoconvective lapse rate, superadiabatic lapse rate.
The concept may be applied to other atmospheric variables (e.g., lapse rate of density) if these are specified. The environmental lapse rate is determined by the distribution of temperature in the vertical at a given time and place and should be carefully distinguished from the process lapse rate, which applies to an individual air parcel.
environments: External conditions or the sum of such conditions, in which pieces of equipment, living organisms, or systems operate as in temperature environment, vibration environment, or space environment. Environments are usually specified by a range of values, and may be either natural or artificial.
EOS data and information system: A system to manage data resulting from NASA's Earth Observing Systems's science research satellites and field measurement programs, and other data essential for interpreting these measurements.
eosinophils: A type of white blood cell or leukocyte which stains a red color with eosin stain; normally about 2 to 3 percent of white cells in the blood but tending to decrease during stressful situations and thus usable as an index for stress.
EOT: End Of Track, used in DSN operations
EPA--Environmental Protection Agency: Established on December 2, 1970, the EPA is charged with protecting and enhancing the environment for present and future generations to the fullest extent possible under Congressional law with responsibilities including the control of solid waste, pesticides, radiation, and toxic substances, and the abatement of air and water pollution. The EPA coordinates research and antipollution activities with State and local governments, educational institutions, private and public groups, and individuals.
ephemeris: A table of predicted satellite orbital locations for specific time intervals. The ephemeris data help to characterize the conditions under which remotely sensed data are collected and are commonly used to correct the sensor data prior to analysis.A table of predicted satellite orbital locations for specific time intervals. The ephemeris data help to charac