STS-75 press kit

Edited by Richard W. Orloff, 01/2001/Page 19
TETHERED SATELLITE FLIGHT OPERATIONS
The Tethered Satellite's primary scientific data will be taken during a planned 22-hour period when the
satellite is extended to the maximum distance from the Shuttle and throughout the 7- to 10-hour period
after the satellite has been reeled back to within approximately 1.2 miles (3.2 kilometers) of the Shuttle.
Secondary science measurements will be taken before and during the 5.5-hour deployment and retrieval
operations, and throughout the period when the satellite is within approximately 1.5 miles of the Shuttle.
Most activities not carried out by the crew will be controlled by command sequences stored in an onboard
computer. To make the mission more flexible, however, modifications to these sequences may be uplinked,
or commands may be sent in real-time to the instruments aboard the Shuttle. During the mission, teams of
scientists will be stationed in the Science Operations Area at Marshall's Spacelab Mission Operations
Control Center.
The responsibility for flying the Tethered Satellite, controlling the stability of the satellite, tether and
Columbia, lies with the flight controllers in Mission Control at the Johnson Space Center in Houston. The
primary flight control positions that will contribute to the flight of the Tethered Satellite System are the
Rendezvous Guidance and Procedures (RGPO, commonly called Rendezvous) area and the Payloads area.
Rendezvous officers will oversee the dynamic phases of the deployment and retrieval of the satellite and
are responsible for determining the correct course of action to manage any tether dynamics. To compute
corrective actions, the Rendezvous officers will combine data from their workstations with inputs from
several investigative teams. The Payloads area will oversee control of the satellite systems, the operation of
the tether deployer and all other TSS systems. Payloads also serves as the liaison between Mission Control
and the science investigators at Marshall, where all real-time commands for science operations will
originate. Columbia's crew will control the deployer reel and the satellite thrusters from onboard the
Shuttle.
Deploy Operations
The satellite will be deployed from Columbia when the cargo bay is facing away from Earth, with the tail
slanted upward and nose pitched down. A 39-foot long boom, with the satellite at its end, is raised out of
the cargo bay to provide clearance between the satellite and Shuttle during the deploy and retrieval
operations. The orbital dynamics will result in the Tethered Satellite initially being deployed upward but at
an angle of about 40 degrees behind Columbia's path.
As an electric motor at the end of the boom pulls tether off of the reel and a nitrogen gas thruster on the
satellite pushes the satellite away from Columbia, the satellite will begin its journey. The deploy will begin
very slowly, with the satellite eventually moving away from Columbia at about one-half mile per hour.
The initial movement of the satellite away from the boom will be at less than two-hundredths of one mile
per hour. The speed of deploy will continue to increase, peaking after one and a half hours from the initial
movement to about one mile per hour. At this point, when the satellite is slightly less than one mile from
Columbia, the rate of deployment will be slowed briefly, a maneuver that will reduce the 40-degree angle
of the satellite to the Shuttle to five degrees and will put the satellite almost directly overhead of Columbia,
by the time about three miles of tether has been unwound.
When the satellite is almost 2,000 feet, or 600 meters, from Columbia, it will be allowed to begin a very
slow rotation. Once the satellite reaches about 3.7 miles from the Shuttle, about two and a half hours after
the start of deployment, the rotation rate will be increased by the satellite's attitude control system thrusters
to a one- quarter-of-a-revolution-per-minute spin. The slight spin is needed for science operations with the
satellite. After this, the speed of deployment will again be increased gradually, climbing to a peak
separation from Columbia of almost 5 mph about four hours into the deployment, when the satellite is