****  UoSAT-OSCAR-11    BULLETIN - 113  16 December 1987  ****

                   UoSAT MISSION CONTROL CENTRE,
         University of Surrey, Guildford, Surrey, England


** UoSAT SPACECRAFT OPERATIONS **

UoSAT-2 was returned to normal operations on Wednesday 161287
following problems experienced with the new FORTH DIARY On
Board Computer software loaded for the first time last month.
The FORTH DIARY has been developed to support more complex
attitude control algorithms on the spacecraft and to simplify
routine operations. The new software ran correctly when first
loaded into the UO-11 OBC but, when the spacecraft appeared on
the next orbit in range of UoS, the OBC had 'crashed' leaving
'null' (80H) characters being transmitted on the 145 MHz
downlink. Efforts at UoS were immediately directed towards
simulation and diagnosis of the problem using the identical
UO-11 spacecraft simulator on the ground (the new software had
been running on this simulator - the spacecraft engineering
model - for several weeks prior to loading into the OBC). It
proved impossible to recreate the problem on the ground and
thus it has been suggested that possibly the 32k byte memory
bank on UO-11 has a bad location(s) - this theory will be
tested by running diagnostics on the UO-11 OBC shortly.

Resumption of normal service took considerable time and effort
since control had to be effected through the less-amenable UHF
command uplink and very careful procedures had to be worked
out to minimise the risk to the spacecraft whilst at the same
time providing the maximum of diagnostic information on the
OBC software state.

We apologise for the interruption to the UO-11 service and
thank all those who sent their best wishes and offered help
during this period.