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AO-27 Status



August 23, 2000
For Public Release

  AO-27 suffered a software reset on July 31 while in the southern
hemisphere several minutes before  entering the eclipse. This reset put the
onboard CPU back to the Bootloader software that places the satellite in
"safe mode."  While in safe mode, the transmitters are turned off and all
high level functions are suspended.

  This places the satellite in a condition that ground controllers need to
react to.  Normally this means uploading the high level software and
executing it.  It was decided that since the last reset was 6 1/2 years ago,
this reboot might be a single event upset or some other "random" reboot.
With that in mind, ground controllers downloaded only a small section of
memory and started to upload the high level code.

  This was not an easy task,  the primary control station used for uploading
code was not used for over 5 years and required days of work to get back
online.  Once the station was setup for uploading, the code was placed
onboard AO-27.  When the execute command was given, the satellite ran the
high level code for a few seconds, then rebooted.  This may show that the
reboot was not caused by a random act, but it is not conclusive.

  Several sections of memory were downloaded from AO-27 and no conclusive
data was found to explain the second reboot.  Ground controller are looking
into several leads.

  Jumping to conclusions as to cause are not productive during this process.
It will take controllers time to analyze and determine the cause for the
reboots.  It is unfortunate that during this process the analog repeater can
not be used, but the work done now may lead to a longer lifetime of AO-27.
There is no direct evidence at this time as to cause.  During the checkout
that has been performed so far, controllers have not found anything onboard
to be defective.  This is good news and gives us hope that a recovery is
possible.

Facts known about A0-27 as of August 23, 2000
---------------------------------------------
1) CPU rebooted on July 31, while in TEPR 6, southern hemisphere, in the Sun
   This means the batteries did not run down to cause the reboot.
2) TEPR times that were commanded on July 26 where intact and did not cause
   the reboot, i.e. the batteries where charged.
3) The last CPU telemetry frame was recovered and shows battery charge state
as OK.
4) The code was sampling telemetry at the time of the reboot.
5) Software Uptime was over 6 1/2 years, (February 1994)
6) The Amateur Transmitter works at exciter, low, and high power settings
7) The Amateur Receiver works
8) The analog repeater works
9) The Bootloader works
10) Software uploading/downloading and executing works
11) Battery voltages are nominal
12) The 1200 Baud AFSK modulator works
13) The 1200 Manchester demodulators work


  If you would like to follow AO-27, the exciter on 435.797 is turned on
full time and turned on to low power during uploads.  A good tracking beam
setup can hear the exciter if you place your receiver into USB and listen
for the doppler shifting tone.  The satellite is transmitting every pass so
you can hear it at night as well.

  Please keep in mind that all AO-27 ground controllers have full time jobs.
Several have already taken a week of personal vacation from work to spend
time on this problem.  Equipment used in the ground station has been
purchased by the controllers personal accounts.  This is an all voluntary
crew.  The best help the community can give is to not flood controllers with
e-mail about when is AO-27 going to be back on-line.  We are working as fast
as satellite passes allow, it takes 3 days of passes to upload code.  Once
high level code is running, we will need to spend a week of
on-orbit-checkout and gather whole-orbit-data to evaluate the health of
AO-27.  This is needed for continued longevity of this resource.  The
popularity and easy of use to Amateurs getting into satellites is very well
known to everyone involved in recovering AO-27.

  The ground controllers have only one request for amateurs,  please do not
transmit on the uplink during passes,  The analog repeater is turned off so
you will not be heard, and you will interfere with the software upload
process.  Thank you.

Michael Wyrick
N4USI
AO-27 Ground Controller

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