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

ACE (Advanced Composition Explorer) ACE and its orbit
around the first Lagrangian point. NASA
acquisition
(1) The process of locating the orbit of a satellite or the
trajectory of a space probe so that tracking or telemetry
data can be gathered. (2) The process of pointing an
antenna or telescope so that it is properly oriented to
allow gathering of tracking or telemetry data from a satellite
or space probe.
ACRIMSAT (Active Cavity Radiometer Irradiance
Monitor Satellite)
Asatellite equipped to measure the amount of energy
givenoutbytheSun—thetotalsolarirradiance(TSI)—over
afive-year period. ACRIMSATcarries ACRIM-3 (Active
Cavity Radiometer Irradiance Monitor 3), the third in a
seriesoflong-termsolar-monitoringtoolsbuiltbyJPL(Jet
Propulsion Laboratory). This instrument extends the database
started by ACRIM-1, which was launched on SMM
(Solar Maximum Mission) in 1980 and continued by
ACRIM-2 on UARS (Upper Atmosphere Research Satellite)
in 1991. ACRIM-1 was the first experiment to show
clearlythattheTSIvaries.Thesolarvariabilityissoslight,
however, that its study calls for continuous state-of-theart
monitoring. Theory suggests that as much as 25% of
Earth’sglobalwarmingmaybeofsolarorigin.Italsoseems
thatevensmall(0.5%)changesintheTSIoveracenturyor
moremayhavesignificantclimaticeffects.ACRIMSATis
partofNASA’sEOS(EarthObservingSystem).
Launch
Date: December 21, 1999
Vehicle: Taurus
Site: Vandenberg Air Force Base
Orbit: 272 × 683 km × 98.3°
ACRV (Assured Crew Return Vehicle)
A space lifeboat attached to the International Space Station
(ISS) so that in an emergency, the crew could quickly
adapter skirt 7
evacuate the station and return safely to Earth. This role,
currently filled by the Russian Soyuz TMA spacecraft,
was to have been taken up by the X-38, a small winged
reentry ferry. However, budget cuts in 2001 forced NASA
to shelve further development of the X-38, leaving the
future of the ACRV in doubt. Among the possibilities are
that the present Soyuz could either be retained for the job
or be replaced by a special ACRV Soyuz that has been
under development for more than 30 years. Features that
distinguish the ACRV Soyuz from the standard model are
seats that can accommodate larger crew members and an
upgraded onboard computer that assures a more accurate
landing.
active satellite
A satellite that carries equipment, including onboard
power supplies, for collecting, transmitting, or relaying
data. It contrasts with a passive satellite.
ACTS (Advanced Communications
Technology Satellite)
An experimental NASA satellite that played a central role
in the development and flight-testing of technologies
now being used on the latest generation of commercial
communications satellites. The first all-digital communications
satellite, ACTS supported standard fiber-optic
data rates, operated in the K- and Ka-frequency bands,
pioneered dynamic hopping spot beams, and advanced
onboard traffic switching and processing. (A hopping
spot beam is an antenna beam on the spacecraft that
points at one location on the ground for a fraction of a
millisecond. It sends/receives voice or data information
and then electronically “hops” to a second location, then
a third, and so on. At the beginning of the second millisecond,
the beam again points at the first location.)
ACTS-type onboard processing and Ka-band communications
are now used operationally by, among others, the
Iridium and Teledesic systems. ACTS was developed,
managed, and operated by the Glenn Research Center. Its
mission ended in June 2000. 110
Shuttle deployment
Date: September 16, 1993
Mission: STS-51
Orbit: geostationary at 100°W
On-orbit mass: 2,767 kg
adapter skirt
A flange, or extension of a space vehicle stage or section,
that enables the attachment of some object, such as
another stage or section.