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PCsat GPS SUCCESS!



PCsat GPS Success!

Background:  PCsat is in a phase of worst case eclipses (35 mins)
(you can see it plotted on a link on http://www.ew.usna.edu/pcsat)
so we cannot turn on the GPS for more than a 10 minute pass at a time.
And we also have the 9600 baud UHF receivers off also to save power.

On with the story:
On today's GPS test pass, we got a late start and since the process in
lower-power ops these days requires a four separate logon/logoff
sequence to enable UHF receivers, then enable GPS, then Command GPS,
then UHF and GPS off, we were only able to have the GPS on for about 3
minutes or  less.  We had difficulty getting logged on for the final step
to make sure the GPS and UHF receivers were both off...

But in the last second, we did get the GPS-OFF command transmitted
(though not confirmed).  The data file we captured was small, but we
edited it up and sent it to the GPS engineers anyway..  The objective for
the next and final pass of the day was to make certain UHF and GPS was
off. (We now only get the later 3 passes during working hours.  The other
three are between midnight and 4 AM).

Good news, PCsat came over the horizon with both off, so we had been
successful in getting everything off in time.  And as we sat there, the
phone rang.  It was Sunny Leung from DLR in Germany.  He was excited,
because the data we had sent him only an hour earlier confirmed that PCsat
had AQUIRED 11 satellites and had a GPS FIX and good signal strengths up
to 16 (the best we had on the ground after the goop disaster).

In the three 1-per-30 second data packets we sent them, the first showed
no lock, but the second showed 11 satellites and the final one showed
all 12 channels in lock!

Can't wait to tomorrow.

We have developed an improvd procedure for the next GPS test orbit cycle:
1) The pass before, we will turn on the UHF 9600 baud receiver.
2) DUring the GPS pass, we only have to command on, then off the GPS
3) During the final pass we will turn off the UHF receiver.

This reduces the logon process to only one process per pass, maybe 2,
instead of 4.  THus greatly extending the time we can let the GPS be on
and still have a margin of safety at the end.

Here is the position data we received in XYZ coordinates:
PCsat header & GPS time:     PCSAT-12>APRS,SGATE:F401138313275.0000013
XYZ Coordinates:             +2873638.13 -5441977.29 +3687550.30
XYZ Velocity:                +4193.65050 -1649.51147 -5694.28574
GPS Mode (3D)                2
Sats in Lock:                11
PDOP:                        1.2
Checksum:                    64

WHile the GPS is on, you may hear some $GPGGA sentences from W3ADO-1 on
the 145.825 while over Annapolis (one pass a day).  The reason this GPS
commanding is not easy is because all of its engienering data comes down
at 9600 baud on 144.39 over the command station and we have as much of a
hard time hearing the data as anyone else listening to all the local QRM
on 144.39...

When we get back to full sun for 2 weeks in January, we may be able to
leave the GPS on for full orbits at least twice a day...

But anyway, this is the first lock we have gotten from the GPS, and mostly
because this is only the second orbit when we have tried in a month since
launch to upload a new set of keps to the GPS engine...

Bob



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