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Re: AO-40



Matt Donohoe wrote:
 
> Just curious as to why there is now a need to call on 'emergency'
> procedures to get the controllers back into the satellite....

Based on official word so far, we can only assume that something has
caused the satellite to stop listening to the command uplink channel,
or has caused it to stop hearing well on that channel.

Commands had been going to the omni antennas, which means that the
choices are bands V, U, and L.  Up until now, with telemetry coming
down on V, that left V and L for commands.

One possibility (speculation): perhaps they decided to test the UHF
transmitter to diagnose its problems (as mentioned in the 12/13/00
press release).  This would require them to stop using UHF for an
uplink channel.  Maybe a problem in the IF Matrix caused a failure
to switch the VHF receiver into place.  Maybe a stuck coaxial relay
had detached the receivers from their antennas.  Way too many other
possibilities to list.  Presumably, the IHU-1 software has some
sort of "watchdog timer" that tells it to go into a "safe mode" if
no commands have been received for a long time.  It assumes that there
is a problem with the command channel if it hears no activity there
for too much time.

> Which IHU is being used?

IHU-1 handles all mission-critical functions.  IHU-2 is considered
experimental and handles auxiliary functions.  Unfortunately, one
of the auxiliary functions that has been in use until recently is
to have IHU-2 "repeat" telemetry from IHU-1 on the VHF beacon.  So
a malfunction in IHU-2 could prevent (has prevented, for short
periods in the past) reception of telemetry.

> What has caused this situation.... From the post all that happened
> was the techs were working on the 400N Motor then no TLM...

Quoting directly from the post:

"These are programmed to start a spacecraft emergency routine called
"command-assist" which attempts to re-establish communications. This
offers the best chance of recovering evidence of the incident which
made the telemetry transmissions stop. When more information becomes
available, we will pass it along."

In other words, they CAN'T tell us because they don't yet have the
FACTS needed to know the answer!  So we HAVE to wait awhile.

> If indeed the controllers have to wait until Sunday Afternoon would
> they please supply more information, even if the details are a bit
> sketchy...

I would NOT assume that they are sitting on their thumbs until
Sunday.  They probably have a myriad of things to do that will
keep them PLENTY busy before the emergency routine kicks in.

Once again quoting from the 12/13/00 press release:

"James Miller had written a data collection program for IHU-2, thus
we have a very detailed account of all the events of this burn.  A
detailed analysis is under way, but we have already some first
indications of the nature of the problem and also possible ways to
cure it or at least to cope with it, provided that the motor was not
damaged by this event."

PLENTY of work to keep them busy.

We've GOT to be patient!

73 de KBØZEV
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