PCsat2 COMMAND AND CONTROL SYSTEM                            WB4APR
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                                                        29 Jan 2003

The simple Naval Academy telemetry and command system design has
been flight proven on PCsat launched on 30 Sept 2001.  It can 
provide the following capabilities on orbit with the minimum power 
requirements suitable for this mission:

1) Routine Telemetry of 5 to 20 analog parameters (0-5 volts) per min
2) Bi-directional serial telemetry periodically, or on command..
3) Eight on/off command channels (maybe 10)
4) AX.25 1200 baud compatibilitiy with all existing packet systems 
   and the worldwide internet linked APRS gnd stations on 145.825.
5) PCsat style USER communications worldwide at low duty cycle
6) Reception by student stations with only a whip antenna.
6) Average power requirement of about 5 watts

The power budget has been derived from the assumptions that the 
Satellite is in view of each command station on 4 passes a day.  
There are about 6 full time commmand station areas, East USA, West USA,
East Europe, West Europe, east Australia and Japan.  The satellite may 
be used in other locations, but the duty cycle will be insignificant 
to these six.

Each such pass is assumed to last 10 minutes.  Thus the total access
times average to about 5 hours a day for an estimated 20% user
access dutycycle.  While in use, the half-duplex link is only in 
transmit about 20% of the time.  All the rest of the time, only the 
load of the TNC/Receiver and occassional 1 minute telemetry are involved.

  Receivers    -  100ma @ 12 volts @ 100%        = 1.2 W
  TNCs         -   60ma @ 12 volts @ 100%        =  .8 W
  DTMF Decoders-   20ma @ 12 volts @ 100%        =  .3 W
  XMTRs (pkt)  -  600ma @ 12 volts @  30% of 20% =  .4 W
  XMTRS Comms  -  600ma @ 12 volts @  20%        = 1.5 W
 
  Total AVERAGE Power               packet only = 2.8 W
                                    and PSK-31  = 4.3 W
                                    and Voice   = 5.8 W

PSK-31 and Voice modes will only be activated when the power budget
permits.

Present expectations of the location of PECsat on ISS are above the
aplha joint so that the solar panel is facing the sun whenever the ISS
is in the sun. 

de WB4APR, Bob Bruninga