Re: Observing TDRS maneuvers
Tue, 25 Jun 1996 14:44:20 -0400

     Viewing any geostationary satellite is a challenge but I don't think 
     that the operation of the thrusters will result in any signature that 
     would help to see that TDRS satellite move.  Hydrazine is a 
     monopropellant that provides hot gas propulsion.  The gas is clear.  
     There is no orange flame.  Unless you have an IR telescope, the 
     satellite looks the same whether the thrusters are firing or not.
     I got the following info from
     Jeff Barker
     TDRS Propulsion and attitude control
     The TDRS propulsion subsystem is a monopropellant hydrazine system 
     which provides impulse for attitude control, unloading
     momentum wheels, and velocity corrections for positioning and 
     stationkeeping. The propulsion subsystem propellant maximum
     capacity is 1300 lb. 
     The system provides for a 10-year operational life and a 7-year 
     maximum storage life. The combines storage and operational
     life is 11 years. The propellant budget is predicated on several use 
     and efficiency factors, including orbit insertion error
     correction and lifetime attitude control and stationkeeping. 
     The propulsion subsystem consists of the following components: 
          2 propellant tanks 
          2 redundant groups of 12 thrusters 
          6 latching isolation valves 
          3 fill and drain valves 
          2 filters 
          pressure and temperature instrumentation 
          thermal management 
          mounting brackets 
     To prevent firing of the TDRS thrusters in the orbiter payload bay, 
     the propulsion system is equipped with arm/disarm functions
     in the ordnance arming unit.