Example Of Ground Control Of Satellite Payload

Andy came across this example of commanding small satellites on the amateur radio frequencies so he thought he'd share the example.


BACKGROUND


2 small satellites were built by US Midshipmen students at the US Naval Academy in Maine, and
launched in a recent shuttle mission. They are in a 51 degree inclination and small in size and power. One is called RAFT and the other ANDE-1: they are both described on the web by their "father" Bob Bruninga.

see for example that the RAFT mission is described at:

http://www.ew.usna.edu/~bruninga/craft/save-raft.html


COMMAND SEQUENCE FOR RAFT


On that webpage, Bruninga describes the command sequence to switch a particular device ON and he refers to it sending a sequence of numbers which the ground operator puts into a password generator and then uplinks the password:

RAFT-COMMANDS

I'm not describing the experiment here, just the command sequence to switch it on.


OBSERVATIONS


Both RAFT and ANDE (from the same stable) pass within range here at about 0200 - 0300 and so I monitor them automatically. RAFT is decaying fast and is low in elevation now, and weak, but I stumbled across one of the "big guns" in Germany (callsign DK3WN) commanding ANDE-1, using the same sequence - it's evident that it uses the same protocol as RAFT.

Here is my log of the downlink from ANDE-1 responding to DK3WN. Of course I can't hear his uplink from Germany but there are still a lot of interesting facts in the downlink.

The raw log is attached - note that first there is one beacon from 0500 the previous day.

Comments below are headed with
……….

Fm DK3WN To CQ Via ANDE-1* <UI pid=F0 Len=11

ping…# 2

Fm DK3WN To CQ Via ANDE-1* <UI pid=F0 Len=11

ping…# 3

……here DK3WN is trying to wake it up bys endin ga
small text "ping" as it only listens for 1 second
every minute

Fm ANDE-1 To BEACON <UI pid=F0 Len=39 >[02:00:36]
T#001,099,071,068,068,066,10000000,000

……..ANDE-1 wakes up and sends a telemetry beacon
(we can decode it later)
………DK3WN sends a "Connect" request to ANDE-1 (I don't know the callsign he uses, possibly DISC1) and ANDE-1 replies:

Fm DISC1 To DK3WN <UA F >[02:00:45]
……..in AX25, this is the reply to the connect request

Fm DISC1 To DK3WN <I R0 S0 pid=F0 Len=54 >[02:00:46]
31 16 4 64 28 43
51 55 61 64 28 14
40 20 6 3 35 18

…….here is ANDE-1 sending the code sequence like
in the GIF file attached

…….DK3WN runs his password generator and sends the
password: he is now in command of the satellite.
ANDE-1 invites him to send the command

Fm DISC1 To DK3WN <I R1 S1 pid=F0 Len=7 >[02:00:49]
prompt:

…….DK3WN is evidently resetting TELEMTRY and MXMIT settings and ANDE-1 responds:

Fm DISC1 To DK3WN <I R2 S2 pid=F0 Len=28 >[02:00:52]
TELEMTRY was 5 WAIT
prompt:

Fm DISC1 To DK3WN <I R3 S3 pid=F0 Len=21 >[02:00:54]
MXMIT was OFF
prompt:

Fm DISC1 To DK3WN <I R4 S4 pid=F0 Len=7 >[02:00:57]
prompt:

Fm DISC1 To DK3WN <I R5 S5 pid=F0 Len=7 >[02:00:58]
prompt:

Fm ANDE-1 To BEACON <UI pid=F0 Len=39 >[02:01:02]
T#002,130,050,053,050,214,11100001,660

Fm DISC1 To DK3WN <RR P/F R5 >[02:01:03]
Fm DISC1 To DK3WN <I R6 S6 pid=F0 Len=17 >[02:01:07]
$
EH?
prompt:

….EH? in AX25 means that the command sent was
unrecognized

….then I lose the satellite beacuse I am not tracking it in azimuth and elevation and it dopplers
low in frequency.

This sequence was done at 1200 bd AX25 AFSK on 145.825 simplex.

"Big guns"

There are probably only two or three big gun operators in europe who have the equipment and interest to monitor small satllites consistently. DK3WN is probably the biggest gun and that is why he's been entrusted with the european command role for Bob Bruninga. He was up at 3am doing it!!

I think I've given you his website address. It is far and away the best for results from cubesats.

All of us can receive the telemetry from ANDE-1. But without the password generator we can't command it.

So your CUBESAT can have a general beacon AND a password controlled switch.

Anyhow I just thought you would find it instructive to see how small satellites can be controlled easily.

best wishes

Andy Thomas

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