The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

perigee kick motor
A rocket motor fired at the perigee (low point) of an
orbit to establish a more elliptical one. The new orbit will
have the same perigee as the old, but a higher apogee.
Compare with apogee kick motor.
perihelion
For an object in an elliptical solar orbit, the point on the
orbit that is nearest to the Sun. Compare with aphelion
and perigee.
perilune
The point on an elliptical lunar orbit that is nearest to the
Moon.
perturbation
A disturbance to a planned trajectory or orbit, caused by
atmospheric drag, gravitation, radiation pressure, or
some other external influence.
Petrov, Boris N. (1913–1980)
A leading Soviet scientist whose later years were devoted
to space exploration. Petrov was a senior academician in
the Soviet Academy of Science and chair of the Inter-
Cosmos Council, which promoted cooperation in space
among eastern European nations during the height of the
Cold War from 1966 to 1980.
PFS (Particles and Fields Subsatellite)
Subsatellites released from Apollo 15 and 16 into lunar
orbit to collect data on particles and fields in the Moon’s
vicinity. (See table, “PFS Deployments.”)
PFS Deployments
Spacecraft Release Date Mass (kg)
PFS, Apollo 15 Aug. 4, 1971 36
PFS, Apollo 16 Apr. 24, 1972 36
Phillips, Samuel C. (1921–1990)
A senior U.S. Air Force officer who led the Apollo program.
Phillips trained as an electrical engineer at the University
of Wyoming and also participated in the Civilian
Pilot Training Program during World War II. Following
his graduation in 1942, he entered the Army infantry but
soon transferred to the air component. As a young pilot
he served with distinction in the Eighth Air Force in England,
earning two distinguished flying crosses, eight air
medals, and the French croix de guerre. His growing
interest in aeronautical research and development led
him to become involved in the development of the B-52
bomber in the early 1950s and then to head the Minute-
PICASSO-CENA 319
man intercontinental ballistic missile program in the latter
part of the decade. In 1964, Phillips, by this time an
Air Force general, was seconded to NASA to head the
Apollo Moon landing program. He returned to the Air
Force in the 1970s and commanded Air Force Systems
Command up to his retirement in 1975. 295
Phobos
See Fobos.
photometer
An instrument that measures the intensity of light from a
source.
photon
A particle of light or, more precisely, a quantum of the
electromagnetic field. It has zero rest mass and a spin of
1. Apart from its obvious role as the carrier of virtually all
the information that we have so far been able to gain
about phenomena beyond the Solar System (with the
exception of cosmic rays and, possibly, gravitational
waves), the photon is also the exchange particle of the
electromagnetic force acting between any two charged
particles. See electromagnetic radiation.
photon propulsion
A form of rocket propulsion, yet to be developed, in
which the reaction is produced by electromagnetic radiation.
Two specific forms of photon propulsion are the
solar sail and laser propulsion.
photosynthetic gas exchanger
A device that utilizes plants and light energy to convert
back into oxygen the carbon dioxide generated by man
or animals through breathing oxygen.
photovoltaic cell
See solar cell.
physiological acceleration
The acceleration experienced by a human or animal test
subject in an accelerating vehicle.
physiological factors
Factors that affect a crew’s health and ability to function.
PICASSO-CENA (Pathfinder for Instruments for
Cloud and Aerospace Spaceborne Observations—
Climatologie Etendue des Nuages et des Aerosols)
An earlier name for the satellite now called CALIPSO.