Thermal Analysis of Inadvertant Activation of ANDE                20 Jan 2006
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                                                                 Bob Bruninga


QUESTION: Investigate the thermal effects of inadvertent activation of one of
the spheres due to rotation.

ANSWER: This situation has no significant impact other than early activation
of the spacecraft receiver system and minor shortening of mission life
due to the run time that would accrue prior to actual deployment.


ANALYSIS:   If ANDE MAA is activated within the CAPE here are the effects:

1) Receiver sleep/wake timer system begins and command receiver awakens
for 2 seconds out of every 16 seconds.  Sleep current is 0.005 amps per
side and wake current for both sides is 0.120 amps, total.  

2) At this fully activated sleep/wake dutycycle, the average current draw
is only 0.019 amps at 14 volts for a total dissipated power of 0.27 watts.  
This miniscule dissipation power would be undetectable in the 50kg thermal 
mass of the spacecraft and additional mass of the CAPE.

3) Transmitters do not come on unless command station sends commands.
Even then, transmitters only transmit 1 second data bursts in response
to commands and user accesses.  Even if ANDE MAA was activated and was
commanded and did see a full users load, while still in the CAPE, the
average dissipated power still only averages about 0.5W.  

4) Peak short term power could be as high as 6 Watts but this only
occurs at the 1 second brief transmissions and is protected from any
longer durations by multiple fail-safe circuits:

   a) Software only generates 1 second bursts at a time

   b) Highest possible TX duty cycle (of multiple 1 second bursts)
      is only about 40% since the channel is  half duplex and cannot
      have any data to transmit while the receiver is blocked.

   c) A Hardware watch-dog circuit prevents any transmission longer than
      20 seconds total.

   d) If both transmitters come on for longer than a minute or so, the
      total spacecraft current will exceed the long term trip point of 
      the PTC fuses and the fuses will open.

5)  The only additional potential for power dissipation is if the
lasers come on.  This would require 4 independent faults and is also
an insignificant heat rise.  Here are the protections against laser
turn on:
  
    a) Separation switch must be actvated
    b) Command ground station must be currently logged onto the 
       password protected operating system in the spacecraft.  This state 
       defaults back to off in there is inactivity for more than 
       45 seconds by hardware timer and more than 15 minutes by firmware.

    c) The command station must activate a battery switch to select an
       operating battery for the lasers.  Select A or B.  It used to be
       to select A2 or B1 or B2, but now is only an A or B selection 
       since B1 and B2 are connected in parallel.

    d) The laser command switch has to be activated.

If all four of these inhibits fail and turn on the lasers permanently,
the average power consumed is only 0.350 amps or about 4 Watts total
dissipated power.  Again, this dissipation is insignificant to the 
thermal mass of the ANDE sphere and CAPE system.

Bob Bruninga
US Naval Academy Satellite Lab
410-293-6417