MIRNEWS.424    3 JUNE 1998

STS-91, Discovery. Start 2.06.1998 2206UTC.

Planned docking time at MIR: 4.06.1998 at 1659UTC.

(For Western Europe): During the final stage of the approach of Discovery to
MIR both objects will be in our range during MIR's orbit 70210, 1649-1657UTC.

Then radiotraffic might be possible on the following channels: 143.625 mc (MIR-
TsUP Moscow), 130.165 mc (MIR-Discovery) and 121.750 mc (not likely).

Traffic from MIR via Altair-2 with TV-images of the approaching Shuttle are
also possible during that orbit between 1613 and 1707UTC if this satellite will
be used for that purpose.

And there is a chance that images from the Shuttle of the MIR complex via a
TDRS and relayed by CNN reach us if the editors do not attach a higher priority
to other subjects.

Attitude control problems solved:

During the period in which the MIR crew was solving these problems the attitude
control was done by small thrusters of the MIR complex itself and Soyuz-TM27.
The replacement of the attitude control computer by a new or by an old spare
one did not help. TsUP transmitted to MIR the needed software. After loading
this into the computer the word 'error' appeared on the screen. After the
replacement of the Omega startracker in the Kristall module or switching over
to a reserve one the attitude control was activated again and worked well.

In the morning of 2.06.1998 the Russians successfully concluded the necessary
tests and they started to activate the 11 gyrodynes. In the course of 2.06.1998
all gyrodynes.

spinned at their maximum speed thus securing the accurate attitude control
badly needed for the approach and docking of Discovery on 4.06.1998. Moreover
Russian experts had stated that approach and docking also were possible when
the attitude control was done by thrusters, but thusfar this had not been
necessary during previous Shuttle operations and consequently this has never
been tried out.

During the period in which the crew was repairing and testing the attitude
control systems radiotraffic could be monitored far into the night. During
these communications Musabayev got commands from TsUP and loaded these into the
systems Svet and Simvol.

Altair-2:

A considerable time there were no communications via this
geostationary satellite. This is quite normal in periods in which the attitude
cannot be maintained by the gyrodynes.

Chris van den Berg, NL-9165/A-UK3202.