[sci.astro] Magellan Update - 02/07/91

baalke@mars.jpl.nasa.gov (Ron Baalke) (02/08/91)

                          MAGELLAN STATUS REPORT
                            February 7, 1991
 
     The Magellan spacecraft is performing as expected.  All STARCALS (star
calibrations) and DESATS (desaturations) of the past 24 hours were successful.
The spacecraft is now in its 958th mapping orbit and the radar system
performance is nominal.
 
     Temperatures of spacecraft subsystems continue to be the focus of mission
controllers.  The geometry of Magellan's orbit about Venus and its position
relative to the sun during mapping and playback were expected to produce
higher temperatures during the this part of the prime mission and extending
into the extended mission cycle.  Anticipating these higher temperatures, two
strategies were developed.
 
     One strategy, called "Flip Flop," controls the temperatures by turning the
opposite side of the spacecraft to the sun during the second playback period.
The timing of the mapping pass and playback periods would be unchanged.  The
disadvantage of this approach is that spacecraft parts would be subjected to
more thermal cycles.  If used, the Flip Flop strategy would be implemented
starting with the April 9 command load, and continuing until April 30, then
switching to the second strategy.
 
     The second strategy, called "Two Hide," controls spacecraft temperatures
by including two periods in each orbit when the equipment bays would "hide" in
the shade of the High Gain Antenna.  This strategy would require a shortening
of the mapping pass and playback periods similar to the strategy during
occulted mapping.  This strategy would be used from the April 30 command load
until the July 23 load.
 
     Using both strategies is a severe challenge to the sequence planners
since command sequences are started at least six weeks before the date of the
command upload.  At the Spacecraft Technical Interchange Meeting in Denver
last week, predicted spacecraft temperatures for this transition period were
presented, and the pros and cons of the two strategies discussed.  Based on
this discussion, the Mission Director, Jim Scott, decided to stay with the
nominal mapping sequence thru April 16, then go directly to the "Two Hide"
strategy for the mapping loads for the next 14 weeks.
      ___    _____     ___
     /_ /|  /____/ \  /_ /|      Ron Baalke         | baalke@mars.jpl.nasa.gov
     | | | |  __ \ /| | | |      Jet Propulsion Lab | 
  ___| | | | |__) |/  | | |___   M/S 301-355        | It's 10PM, do you know
 /___| | | |  ___/    | |/__ /|  Pasadena, CA 91109 | where your spacecraft is?
 |_____|/  |_|/       |_____|/                      | We do!