Aeronautics and Space Report of the President FY 1995 Activities



Pathfinder A program that focuses on the processing, reprocessing, maintenance, archiving, and distribution of existing Earth science data sets to make them more useful to researchers; NASA, NOAA, and USGS are involved in specific Pathfinder efforts

PBW Power-by-wire (avionics system)

PCA Propulsion Controlled Aircraft

PEACESAT Pan-Pacific Education and Communication Experiments by Satellite

petrology The science that deals with the origin, history, occurrence, structure, and chemical classification of rocks

photogrammetry The process of surveying, as in map making, by taking aerial photographs

piezoelectricity The property exhibited by some asymmetrical crystalline materials that, when subjected to strain in suitable directions, develop polarization proportional to the strain

pixels Short for "picture elements," which provide image resolution in vidicon-type detectors plage; bright, granular areas in the chromosphere of the Sun

plasma A gas formed when one or more negatively charged electrons escape from an atom's positively charged nucleus, creating an electrically neutral gas composed of positive and negative particles; because it is ionized, plasma interacts with electric and magnetic fields; approximately 99 percent of matter in the universe is thought to be in the plasma state

plasma sheet An extensive area of low-energy, ionized gases in the tail region of the magnetosphere that undergoes considerable change during magnetospheric storms

POAM Polar Ozone and Aerosol Measurement (experiment)

POES Polar-orbiting Operational Environmental Satellite (program)

polar orbit The path of an Earth satellite that passes near or over the North and South Poles

power-by-wire The use of electrical power, in place of hydraulics, to move the control surfaces of an aircraft via electromechanical actuators

PPS Precise Positioning Service

Pu-238 A specific plutonium isotope

pulsar A pulsating radio star, which is thought to be a rapidly spinning neutron star; the latter is formed when the core of a violently exploding star called a supernova collapses inward and becomes compressed together; pulsars emit extremely regular pulses of radio waves

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Curator: Lillian Gipson
Last Updated: September 5, 1996
For more information contact Steve Garber, NASA History Office,