(word processor parameters LM=8, RM=78, TM=2, BM=2)
                      Taken from KeelyNet BBS (214) 324-3501
                           Sponsored by Vangard Sciences
                                    PO BOX 1031
                                Mesquite, TX 75150

                                  August 3, 1990

                       Courtesy of NASA BBS at 205 895-0028

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                                 POWER PROCESSING

           Power processors  for  primary-propulsion  thrusters  have  been
       under development for several years.   Early tests defined the power
       supply characteristics and control logic systems required to operate
       over large ranges of power and thrust.

           Processors capable of operating in vacuum have  been  developed.
       These processors, which  include  12  separate  power  supplies  and
       associated control logic, have electrical  efficiences  from  0.8 to
       0.92 over the thruster operating range.

           Although these efficiences are high, the large power requirement
       of the thruster (2.75 kW) implies that significant amounts of heat
       must be removed  from  each  power processor.  Meeting  the  thermal
       control requirements of the power processor challenges the designer,
       and a number   of  studies  have  been  made  to  formulate  systems
       approaches.

           One candidate  concept  uses  variable-conductance   heat  pipes
       similar to those  used  on  the Communications Technology  Satellite
       (CTS), launched in 1976.

           The power  processors  in  the  concept  are  buried  within the
       spacecraft body, and their waste heat  is  transported by heat pipes
       to radiators for injection to space (ref. 10).  This  concept, which
       among other features,  such  as  eliminating  the  need for thermal-
       control louvers, provides   excellent   isolation   of   the   power
       processors from the  environment.   And,  thus, the  impact  of  the
       multiple-mission capability requirement on spacecraft design
       is minimized.
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       If you have comments or other information relating to such topics as
       this paper covers,  please upload to KeelyNet or send to the Vangard
       Sciences address as listed on the  first  page.   Thank you for your
       consideration, interest and support.

           Jerry W. Decker.........Ron Barker...........Chuck Henderson
                             Vangard Sciences/KeelyNet

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