Glossary — P
23 terms
Propellant
The chemical mass a rocket expels to generate thrust, comprising fuel and oxidizer.
Example: Cryogenic propellant must be loaded just before launch to limit boil-off.
Payload
The cargo a launch vehicle carries, or the mission-specific equipment of a spacecraft.
Example: The fairing protected the payload until it reached space.
Pitchover
The initial tipping of a rocket from vertical toward horizontal.
Example: Pitchover introduced a slight tilt to build horizontal speed.
Polar orbit
An orbit with an inclination near 90 degrees, passing over or near both poles on each revolution.
Example: A polar orbit lets a satellite observe every latitude as Earth rotates beneath it.
Pitch
Rotation about the lateral axis, nose up or down.
Example: Pitch corrections kept the trajectory on profile.
Perigee
The point in an orbit closest to Earth.
Example: Atmospheric drag is strongest near perigee for low satellites.
Perihelion
The point in a solar orbit closest to the Sun.
Example: Earth passes perihelion in early January.
Periapsis
The closest point to the central body in any orbit.
Example: Aerobraking is planned near periapsis to shed energy gradually.
Pressure vessel
The sealed, stiffened structure holding a breathable atmosphere.
Example: The crew module is a pressure vessel designed for a safe cabin environment.
Plasma sheath
A layer of ionized gas surrounding a reentering vehicle.
Example: The plasma sheath blacked out radio signals briefly.
Propellant tank
The vessel storing propellant aboard a spacecraft.
Example: The propellant tank held enough fuel for years of station-keeping.
Powered descent
Using engine thrust to slow and control a landing.
Example: Powered descent brought the booster to a soft touchdown.
Parking orbit
A temporary orbit used to dwell before a further maneuver or injection burn.
Example: The upper stage coasted in a parking orbit before translunar injection.
Propellant loading
The process of filling a rocket with fuel and oxidizer.
Example: Propellant loading began about forty minutes before liftoff.
Parachute
A fabric canopy deployed to slow descent through air.
Example: The main parachute deployed to slow the capsule for splashdown.
Power system
The subsystem generating, storing, and distributing electrical energy.
Example: The power system switched to battery during the eclipse.
Planetary defense
A mission detecting or deflecting hazardous near-Earth objects.
Example: The planetary-defense test nudged an asteroid's orbit.
Pitch program
The commanded gradual pitchover that shapes the ascent trajectory.
Example: The pitch program steered the vehicle downrange toward orbit.
Pressurization
Using gas pressure to hold tank structure and feed propellant.
Example: Helium pressurization kept the tank walls rigid during ascent.
Plume
The visible exhaust gas jet expelled from a rocket.
Example: The engine plume expanded dramatically in the near-vacuum.
Pathfinder mission
A small mission sent ahead to investigate before a larger one.
Example: A pathfinder mission mapped landing hazards before the crew arrived.
Pointing accuracy
The precision with which a vehicle or instrument holds orientation.
Example: Pointing accuracy determined the image resolution.
Payload adapter
The hardware linking a payload to its launch vehicle.
Example: The payload adapter released the satellite at the commanded time.