MIRNEWS.493    13 FEBRUARY 2001

Gradual descend:

The gradual descend of the MIR space station is still on-going. The word
'gradual' might give the impression that this is a smooth process, but these
days that is not the case. The solar activity is very high and also irregular.
This irregularity means that it is very difficult to be sure about determining
the day on which the last impulse for the re-entry has to be given. The fact
that thus far nobody knows the exact date, created a atmosphere of
uncertainty. People living between the latitudes 51.6 North and 51.6 South who
realize that if the re-entry operation goes wrong, dangerous situations can
emerge imaging things falling down in pieces, start to panic and ask
difficult questions. In this way the media gets involved thus generating the
stimulation of the whole process.

So it might be useful to put the facts together and in that way pour some oil
on the waters.

The MIR complex and the tanker Progress-M1-5 are fully under control of the
experts on TsUP (Mission Control Moscow), the Telemetry and Tele-command
systems are functioning flawlessly. The complex is moving in a slow spin around
the longitudinal axis, but can be controlled by the use of small steering
rockets enabling the complex to maintain or achieve the needed attitude for
the maximum efficiency of the solar batteries.

Daily the Russian ballistic computing centres issue accurate reports about the
orbit of MIR. These reports make it clear that the date for the final braking
impulse for re-entry has not yet been determined. If a possible date was
mentioned, for instance 6 or 8 March, a margin of +5 or -5 days had been given.

Today's report got the following prognostic addition:

The estimated time at which the station will pass the altitude of approx. 250
KM is on 8.03.2001 with a margin of +5 or -5 days.

It is necessary to observe a deviation of 15% when making prognoses about the
ultimate end of the station. This means with the average solar activity and if
no measures would be undertaken, the final decay would take place naturally on
26.03.2001 with a margin of +5 or -5 days.

These data were based on orbit number 85715. Period was 90.112 minutes and the
average altitude was 282.8 KM. During the last 24 hours the complex became 900
Meters lower. (At 1300UTC the Perigee was 272 KM, the Apogee 302 KM.)

If necessary the Progress-M1-5 can give 3 impulses to bring the complex
somewhat lower. The critical level at which the complex starts to loose her
status as an artificial earth satellite is approx. 250 KM, but experts hope to
administer the final braking impulse at approx. 225 KM and they also will be
pleased if at that moment the Perigee of MIR would be 150 KM over the target
area East of New Zealand. The duration of that particular impulse might be 15
or 20 minutes. The definite choices depend on the condition of the upper layers
of the atmosphere and the intensity of the solar activities in that period.
The exact moment of the commands given by the main Russian tracking stations
(Shcholkovo and/or Dzhusaliy) for that impulse, also depends upon those
circumstances.

After re-entry tracking stations situated more to the east can only follow the
decaying space station along her last trajectory. The use of some tracking
ships, for instance the Marshall Nedelin and/or if still operational the
Nikolay Pilyugin, might be useful for operational observations during the
decay and the issue of flash reports about deviations if something goes wrong.

AND:

Everybody may rest assured that the Russian ballistic experts will do all
what is necessary to execute the operation as safe as possible. Although they
never brought back such a huge and asymmetrical object like MIR, they have a
long successful practice in return operations of space objects (among which
space stations like the Almazy, almost all Salyuts and the overwhelming amount
of freighters of the Progress-series, all Descent Modules of Soyuzy, Kosmos
satellites, return capsules, etc.). And this certainly will help them now.

In Notams (Notices to Airmen) and Navigation Warnings for Ships, aircraft and
ships will be warned to avoid the possible areas in which surviving debris can
reach the earth’s surface.

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