ARRL

ARRL Satellite Bulletin ARLS026 (2000)

SB SPACE @ ARL $ARLS026
ARLS026 AO-40 still silent

ZCZC AS26  
QST de W1AW  
Space Bulletin 026  ARLS026
From ARRL Headquarters  
Newington, CT  December 19, 2000
To all radio amateurs

SB SPACE ARL ARLS026
ARLS026 AO-40 still silent

AMSAT OSCAR-40 remains silent, and command stations on the ground
still have been unable to reestablish contact with the Amateur Radio
satellite. It had been hoped that an onboard computer timeout
expected on or about December 16 would restart the beacon telemetry
and give the ground crew some clues as to why AO-40 suddenly stopped
transmitting on December 13.

AMSAT-Germany's Peter Guelzow, DB2OS, of the AO-40 team, said
nothing was heard over the weekend, and command stations tried to
re-establish communication by sending blind commands. If the reset
had occurred, the satellite would have been restored to its
post-launch configuration and attempt to transmit on 70 cm. However,
the 70-cm transmitter has been problematic, and the satellite likely
still would need to be reconfigured for 2-meter transmission at that
point to be heard on Earth.

The AO-40 team is continuing to investigate reports of weak signals
on the 2-meter downlink frequency of 145.898 MHz that seem to be
coming from AO-40, but it has discounted reports of telemetry heard
there as a hoax. Other reports persist of a weak, unmodulated
carrier, however.

Guelzow said today that the AO-40 team is encouraged by a report
from the North American Air Defense Command--NORAD. The report
indicates that AO-40 was found to be in one piece, that the orbit
was exactly were it should be, that the radar cross-section was as
expected, and that no other pieces were found. Guelzow said the
NORAD data counter rumors ''which no one on the inner team
believed'' that AO-40 might have exploded.

AMSAT-NA President Robin Haighton said ground controllers were
exploring several options.

When and whether the satellite will be heard from again depends, in
part, on whether AO-40 has picked up any of the ''blind commands''
sent by ground controllers. Guelzow says that if no commands were
accepted by the IHU-1 onboard computer since contact was lost
December 13, then a ''command-assist'' watchdog routine on December
21 will cycle the satellite through various receive, transmit,
high-gain and low-gain antenna modes. If AO-40 did pick up some
commands, Guelzow said, the command-assist watchdog will be reset
for another 10 orbits. That could extend the wait until sometime
after Christmas.

Guelzow says the ''watchdogs'' are software resets. Ground
controllers want to avoid doing a hard re-boot of the main computer,
which is considered a last resort. ''There is no need to hurry, and
the command team doesn't want to miss any option,'' he said.  
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/EX