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