The TDRS spacecraft is shipped to Kennedy
Space Center, Fla., where it undergoes checkout and mating with the two-
stage Inertial Upper Stage (IUS) which will boost it into geosynchronous
orbit. Tests are conducted using the Cargo Integrated Test Equipment
(CITE) to make sure the two elements are correctly mated and that they
will function as an integrated unit following deployment from the Shuttle.
The Merritt Island Launch Area (MILA)
tracking station has a TDRS ground terminal. It can relay test data
between user spacecraft being checked out on the ground at KSC and project
control centers at other locations, via the TDRS network, to the ground
station at White Sands, N.M.
The TDRS spacecraft with its attached upper
stage is launched aboard the Shuttle and deployed from the orbiter payload
bay, nominally about six hours into the mission. To boost the TDRS into
geosynchronous orbit, the IUS upper stage fires twice. The booster's first
stage motor fires about an hour after deployment, placing the TDRS into an
elliptical geotransfer orbit. The first stage then separates. The IUS
second stage motor fires about 12 1/2 hours into the mission,
circularizing the orbit and shifting the flight path so that the satellite
is moving above the equator. The IUS second stage and TDRS will separate
at about 13 hours after launch.
With the TDRS now in geosynchronous orbit,
its appendages-including the vital solar panels and parabolic antennas-are
then deployed, and the satellite will be ready for controllers to begin
checking out about 24 hours after launch. The spacecraft is initially
positioned at an intermediate location for checkout and testing, and then
moved to its final station.
The first TDRS was launched from Kennedy
Space Center on April 4, 1983. Initially placed in an incorrect orbit by
the upper stage, TDRS-A was eventually raised to the proper geosynchronous
orbit and has been supporting users since the 1983 STS-9
Spacelab mission. Known by its on-orbit designation of TDRS-1, the
spacecraft was first located above the equator over the northeast coast of
Brazil, at 41 degrees west longitude. This position also is referred to as
TDRS-1 was later moved to serve as an
on-orbit backup, located at 62 degrees west longitude above Quito,
Ecuador. It was then moved again, this time to its present position as an
on-orbit backup at 171 degrees west longitude, over the Pacific Ocean
southwest of the Hawaiian islands.
The second TDRS launched, TDRS-B, was lost
in the 1986 Challenger accident.
The third TDRS spacecraft, TDRS-C, was
successfully deployed during the STS-26
mission in September 1988. Currently located at 62 degrees west longitude
as an on- orbit backup, it was redesignated as TDRS-3 once on station.
TDRS-1 and TDRS-3 have impaired S-band/Ku-band single-access service
A fourth TDRS, TDRS-D, was launched in
March 1989 during the STS-29
mission and is currently located at 41 degrees west longitude in the TDRS-East
slot. This spacecraft was redesignated as TDRS-4 once on orbit.
The fifth TDRS, TDRS-E, was launched aboard
in August 1991 and redesignated as TDRS-5 on-orbit. The spacecraft was
inserted into a 178 degrees west longitude location, moved to 150 degrees
west longitude for checkout, and then moved to 174 degrees west longitude.
After the sixth TDRS, TDRS-F, is deployed
during Space Shuttle Mission STS-54,
it initially will be located at 150 degrees west longitude for activation,
calibration and testing. Once the approximately 90-day on-orbit test
program is completed, TDRS-F is expected to be moved to a final position
of 62 degrees west longitude. Its designation will be TDRS-6.
Concurrently, TDRS-3 will be moved from the
62 degrees west longitude position to 171 degrees west longitude, and
TDRS-1 from the latter location to 85 degrees east longitude. Neither
TDRS-4 (TDRS-East) nor TDRS-5 (TDRS-West) will change locations. Once the
reconfiguration is complete, TDRS-3 and TDRS-6 will function as on-orbit
backups to insure a fully operational network. TDRS-1 will be devoted to
supporting the Compton Gamma Ray Observatory (GRO) via a tracking station
in Tidbinbilla, Australia. GRO data and the White Sands control of TDRS-1
will be relayed via an INTELSAT satellite. This will mark the first
attempt to control an out-of-view TDRS from White Sands.
A seventh TDRS, TDRS-G, is scheduled to be
available for launch
in the mid-1990s. TDRS-G is the replacement for the TDRS-B lost in the