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Bob Bruninga bruninga at usna.edu
Sun Aug 14 21:52:52 UTC 2011


> As far as SATs go, what's presently flying or 
> near term planned for launch that will serve 
> as a message relay for nts type messages?

Since all of the packet digipeating satellties can also transparently carry email, it was interesting the other day when Nick Pugh K5QXJ suggested that not only can APRS satellites EMAIL their telemetry directly to their makers, the controllers can also send commands directly back to the satellites via conventional APRS mail as well!

For a satellite to email its telemetry directly to a callsign (for delivery by any worldwide email device) all it has to do is format its telemetry like any other APRS one-line email.  Here is the format:

PCSAT>APRS::EMAIL    :WB4APR at ARRL.NET I'm OK: V=12, I=140, T=30C

In this case PCSAT sends an email to WB4APR via his ARRL address with the words "I'm OK"... and then whatever other telemetry the satellite wants to include.  

This works this way because the global APRS system will take any packet anywhere that is addressed to "EMAIL" and then wrap it up into standard EMAIL and send it via the internet.

Since all IGates on the planet including the ones that are monitioring the satellites automatically do this, then the system is in place.  

For the satellite operator to send back a command to the satellite this too is aoutamitcally handled in all existing IGate software.  If an APRS message is seen anywhere on the planet addressed to any callsign, in this case, the callsign of a small satellite, then any IGate that is IN RANGE of the satellite at any instant (and has heard it) will attempt to transmit that packet onto the satellite uplink in real time.

No one has done this yet I dont think, because most Satellite IGates have mostly just been used for downlink, and no one has tried this uplink before.  The one thing that would have to change is the TIME-OUT time in the "has-been-heard" list of the IGates.  As it is, an IGate will try to return a message to another callsign if it has been heard in the last 30 minutes or so.  For satellites, we would want this to time out after only 10 minutes, since a LEO will be out of range by then.

But it is possible.  Might be fun.

Bob, Wb4APR



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