Glossary of Space Exploration Terminology

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U
UDMH
Unsymmetrical Dimethyl Hydrazine. A liquid hypergolic fuel.
UHF
Ultrahigh Frequency.
Ullage
The amount by which a container, such as a tank, falls short of being full.
Ullage Maneuver
To supply positive acceleration to seat propellant in the bottom of its tanks.
Ultrahigh frequency
Short radio waves used for communicating with spacecraft.
Ultraviolet
A band of electromagnetic radiation with a higher frequency and shorter wavelength than visible blue light. Ultraviolet astronomy is generally performed in space, since Earth's atmosphere absorbs most ultraviolet radiation.
Umbilical
A cable conveying power to a rocket or spacecraft before liftoff. Also a tethering or supply line for an astronaut outside a spacecraft.
Universal time
The mean solar time of the meridian of Greenwich, England. Formerly called Greenwich mean time.
Universal time coordinated
The world-wide scientific standard of timekeeping; based upon carefully maintained atomic clocks and accurate to within microseconds. The addition or subtraction of leap seconds, as necessary, keeps it in step with Earth's rotation. Its reference point is Greenwich, England; when it is midnight there, it is midnight UTC.
Universe
All matter and energy, including Earth, the galaxies and all therein, and the contents of intergalactic space, regarded as a whole.
Uplink
The radio signal transmitted to a spacecraft from Earth.
Uranus
Seventh planet from the Sun, a gas giant or Jovian planet.
UT
Universal Time.
UTC
United Technologies Corporation; Chemical Systems Division (USA).
UTC
Universal Time Coordinated.
UV
Ultraviolet.

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Rocketry & Space Technology

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