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

454 umbilical connections
for measurements to be made over the Sun’s poles. Originally
named the International Solar Polar Mission, the
spacecraft used a gravity-assist from Jupiter to leave the
ecliptic plane. It completed passes over the Sun’s southern
pole in November 1994 and northern pole in October
1995, at which point its primary mission was
completed. It then began an extended phase of observations.
umbilical connections
The electrical, hydraulic, and pneumatic connections
between the ground support equipment and a launch
vehicle.
umbilical cord
Often shortened to umbilical. (1) Any of the servicing
electrical or fluid lines between the ground and an
upright missile or space launch vehicle before launch. (2)
The cord that, in early manned missions, attached a
space-walking astronaut to his or her spacecraft.
umbilical swing arm
A metal arm that extends horizontally toward the space
vehicle from the umbilical. It supports the service lines
that link the space vehicle to the ground systems. The
swing arm is part of the umbilical tower swing arm system
and is supported by the tower and fastened to it by a
hinged joint that contains a rotary hydraulic actuator.
umbilical tower
The vertical structure that supports the electrical serving
and fluid lines running to a rocket in launch position.
Ume
See ISS (Ionospheric Sounding Satellite).
UNEX (University-class Explorer)
The lowest-cost type of Explorer satellite. The UNEX
Program is designed to provide frequent flight opportunities
for highly focused and relatively inexpensive science
missions whose total cost to NASA is limited to $13
million. The first two missions in the program were
CHIPS (Cosmic Hot Interstellar Plasma Spectrometer)
and IMEX (Inner Magnetosphere Explorer). The program
is managed by the Goddard Space Flight Center.
undershoot boundary
The lower side of a reentry corridor, marking the region
below which a spacecraft would suffer excessive heating
due to atmospheric friction.
United Space Alliance
A Boeing/Lockheed Martin joint venture, with headquarters
in Houston, to conduct the Space Flight Opera-
tions Contract for NASA. Since 1996, the United Space
Alliance has been responsible for the day-to-day operation
and management of the Space Shuttle fleet.
United States in space
See Apollo; Explorer; Galileo; Gemini; Robert Goddard;
guided missiles, postwar development; International
Space Station; JPL; Lunar Orbiter; Mariner;
Mercury, Project; NACA; NASA; Pioneer; Ranger;
Skylab; Space Race; Surveyor; Vanguard; Voyager;
White Sands Missile Range; and X planes.
United States launch vehicles
See Able, Aerobee, Agena, Athena, Atlas, Bumper
WAC, Centaur, Conestoga, Corporal, Delta, Juno,
Jupiter, Matador, Minotaur, Navaho, Pegasus (launch
vehicle), Redstone, Saturn, Scout, Sergeant, Space
Shuttle, Taurus, Thor, Titan, Viking (launch vehicle),
and WAC Corporal.
Unity
See International Space Station.
unrestricted burn
In solid-fuel rocket motors, a burn achieved by boring a
hole in the fuel along the motor’s longitudinal axis so
that the entire length of the fuel chamber burns simultaneously.
This method of burning produces a great
amount of thrust for a short time.
Uosat
Small satellites built by the University of Surrey, England,
for a variety of purposes including amateur radio and educational
experiments. They are launched as secondary payloads
when room is available. Uosat 1 was also known as
OSCAR 9 and was launched together with the SME (Solar
Mesosphere Explorer). Uosat 5, which weighed just 50 kg
and was launched on August 15, 1991, carried a CCD
(charge-coupled device) camera able to relay pictures of
the Earth to schools equipped with suitable receivers.
uplink
A signal sent to a spacecraft. See also downlink.
upper-air observation
A measurement of atmospheric conditions above the
effective range of a surface weather observation. Also
called sounding and upper-air sounding.
USA
Designation used by the United States since mid-1984
for military spacecraft. For example, Navstar 9 is also
known as USA 1 and LACE as USA 51.