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RE: Pacsat's clock



All satellites under my command (which for amateur satellites are UO-22 and
TO-31) are time synchronised to GPS at least once per day (under normal
operations).

UO-22 normally only drifts by about 100ms per day, so even if time sync was
not carried out for a few days, it is still a good and accurate source of
time.

TO-31 drifts by about 2 seconds per day however normally this satellite is
time synced every pass so it doesn't normally get out by more than 1 second.

The time on the downlink is not 100% accurate since it is read from the
on-board clocks, and then takes time to get sent and processed - so it will
be delayed by maybe 1 second.  However, these are good sources of reasonably
accurate time and if nothing else they ensure that your clock doesn't drift
too far.

The attitude control software employed on the above satellites requires
accurate time and failure for us to employ this has far greater consequences
than just the time on telemetry etc being wrong.

As a side note, KO-23/KO-25 are not automatically synced.  We developped
this software after these satellites were launched and it has not been
updated.

Regards
Chris G7UPN / ZL2TPO


Chris Jackson
Groundstation and Operations Manager
Surrey Satellite Technology Ltd
University of Surrey
Guildford, Surrey GU2 5HX,  UK
Ph: +44 1483 259-141
Fax: +44 1483 259-503
http://www.ee.surrey.ac.uk/EE/CSER/UOSAT/



-----Original Message-----
From: Francisco Costa [mailto:nop06152@mail.telepac.pt]
Sent: 18 February 1999 20:49
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] Pacsat's clock


Hi

Because every pacsat session the PC DOS clock is updated
it's obvious the actual pacsat's (UO22, KO23,25 and TO31) aren't
in sync. Neither are (or pretend to be) atomic clock's.
So my question is: who is the most accurate??? (The last one?)

Thanks in advance for your reply.

73 F.Costa, CT1EAT

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