Glossary of Space Exploration Terminology

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P
P & W
Pratt and Whitney (USA).
Parachute
An apparatus used to retard free fall, consisting of a light, usually hemispherical canopy attached by cords and stored folded until deployed in descent.
Parallel
Circle in parallel planes to that of the equator defining north-south measurements, also called line of latitude.
Parking orbit
Orbit in which a space vehicle awaits the next phase of its planned mission.
Parsec
Measure of distance, 1 parsec = approximately 3.26 light years.
Pascal
A unit of pressure equal to one newton per square meter.
Passive cooling
The use of painting, shading, reflectors and other techniques to cool a spacecraft.
Payload
Revenue-producing or useful cargo carried by a spacecraft; also, anything carried in a rocket or spacecraft that is not part of the structure, propellant, or guidance systems.
PBAN
Polybutadiene acrylic acid acrylonitrile. A polymetric fuel binder.
PDT
Pacific Daylight Time.
Pegasus
A rocket-vehicle concept for transportation of commercial high-priority freight or 172 passengers.
Periapsis
That point in an orbit which is nearest to the primary.
Perigee
That point in a terrestrial orbit which is nearest to the Earth.
Perihelion
That point in a solar orbit which is nearest to the Sun.
Perilune
That point in a lunar orbit which is nearest to the Moon.
Period of revolution
Time of one complete cycle in orbital motion - referred to as a year when applied to Earth.
Period of rotation
Time of one complete cycle - referred to as a day when applied to Earth.
Perturbation
Modifications to simple conic section orbits caused by such disturbances as air drag, non-uniformity of the Earth, and gravitational fields of more distant bodies such as the Moon.
Phase
Two meanings: (1) The particular appearance of a body's state of illumination, such as the full phase of the moon. (2) As applied to electromagnetic waves, phase is the relative measurement of the alignment of two waveforms of similar frequency.
Phase angle
The angle in which waves come to a body.
Photometer
An optical instrument that measures the intensity of light from a source.
Photometry
The measurement of light intensities.
Photon
A quantum of radiant energy.
Photon propulsion
The propulsion of a vehicle by the emission of photons, which possess momentum.
Photosphere
The visible surface of the Sun.
Photovoltaic cells
Crystalline wafers called solar cells which convert sunlight directly into electricity without moving parts.
Pitch
The rotation of a vehicle about its lateral (Y) axis, i.e. movement in elevation.
Planet
A nonluminous celestial body larger than an asteroid or a comet, illuminated by light from a star, such as the sun, around which it revolves. The only known planets are those of the Sun but others have been detected on physical (non-observational) grounds around some of the nearer stars.
Planetoid
An asteroid.
Plasma
A gaslike association of ionized particles that responds collectively to electric and magnetic fields.
Plasma detector
A device for measuring the density, composition, temperature, velocity and three-dimensional distribution of plasmas that exist in interplanetary regions and within planetary magnetospheres.
Plasma engine
A rocket engine in which thrust is obtained from the acceleration of a plasma with crossed electrical and magnetic fields.
Plasma wave
An oscillation or wave in a plasma that falls in the audio range of frequency.
Plasma wave detector
A device for measuring the electrostatic and electromagnetic components of local plasma waves in three dimensions.
Plasmasphere
The region of the atmosphere consisting of cold dense plasma originating in the ionosphere and trapped by the Earth's magnetic field.
PLSS
Portable Life Support System.
Plug nozzle
A doughnut-shaped combustion chamber which discharges engine gases against the surface of a short central cone (the plug). Adapted in the form of an LH2 cooled heat shield, it can be used as a combination rocket/ aerodynamic braking device.
Pluto
Ninth planet from the Sun, considered by many a minor planet.
Plutonium-238
A form of the radioactive element plutonium, characterized by high energy emissions.
PO
Polar Orbit.
Polar orbit
An orbit which passes over the poles.
Polarimeter
An optical instrument that measures the direction and extent of the polarization of light reflected from its targets.
Polymer
A compound used as a binder for solid rocket propellant systems; more generally, a compound consisting of repeating structural units.
Potential energy
The energy of a body due to its position in a field.
Pound
The U.S. customary unit of force defined as the weight of the standard pound at sea level and at the latitude of 45o.
ppm
Parts per million.
Precession
A change in the direction of the axis of spin of a rotating body.
Pressure suit
A suit, with helmet attached, which is inflated to provide body pressure and air, worn by the crew of certain spacecraft and aircraft which fly at great altitudes.
Pressurized
Containing air or other gas at a pressure higher than the pressure outside the chamber.
Primary
The body around which a satellite orbits.
Primitive
Used in a chemical sense, indicating an unmodified material representative of the original composition of the solar nebula.
Probe
An unmanned instrumented vehicle sent into space to gather information.
Prograde
Orbital motion in the same direction as the primary's rotation.
Propellant
A chemical or chemical mixture burned to create the thrust for a rocket or spacecraft.
Propulsion
The process of driving or propelling.
PST
Pacific Standard Time.
PTC
Passive Thermal Control.
Pulsar
Discovered in 1967. Pulsars emit radio signals the pulsations of which are extremely precise. The evidence suggests that pulsars are fast-spinning neutron stars.
Pyrotechnics
The use of electrically initiated explosive devices to operate valves, ignite solid rocket motors, and explode bolts to separate from or jettison hardware, or to deploy appendages.

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Rocketry & Space Technology

Glossary courtesy of Robert Braeunig's
Rocketry & Space Technology website.