Posted: Thursday, January 4, 2001
Within a few weeks we can expect the decay of the MIR-space station. The operation to dispatch the huge asymmetrical complex is not easy. In fact thus far this has never been done. The Russian experts who are responsible for the safe return of MIR in the atmosphere, are not so sure as they were a year ago. Russia cannot afford a third disaster after the events with the submarine Kursk and the TV tower Ostankino.
In August 1998 we expected that MIR would be brought back in the atmosphere within a year and in my MIR-report nr. 432 I tried to give my opinion about such a difficult process. I did not get a lot of reactions on my story, in fact nobody shared my concern about this almost 'mission impossible'. I had the impression that even official circles in Russia were sure that nothing serious could happen.
Towards the end of 1999 and in the beginning of 2000 there emerged plans to continue for some years the exploration of the MIR-space station on a commercial basis. So, nobody any longer bothered about the final operation to bring the station back into the atmosphere.
But after the unsuccessful commercial adventure of MIRcorp it was obvious that the end of MIR's life was imminent and the Russian government, represented by Rosaviakosmos, became fully aware of her duty to bring MIR back into the atmosphere in such a way that only a few pieces would fall down in a designated area in the Pacific Ocean, East of New Zealand.
Many of the original scientists and constructors who worked on the MIR project in the beginning, are no longer among us or have retired. In that time their life was so dominated by building and exploring space stations that they did not anticipate the inevitable decay problem of their objects in the future. If so, they would have inserted the possibility to separate every module from the complex and to enable them to make a safe reentry, for instance by using their own engines and attitude control systems. Now this option, so bringing back into the atmosphere of the components of the station in a safe way, no longer exists for the most of the modules and for the base block itself. Theoretically the Kvant-2 and the Priroda might be able to this, but only when it will be sure that the engines and steering rockets still have fuel, can be refueled and still are in good shape. During their flight to MIR the modules had their own propulsion and orientation means, but certainly the guarantee deadlines have been passed long ago and testing these systems while docked at MIR is not possible.
The Spektr, damaged after the collison in 1997, is unreliable. The astrophysical module Kvant-1 flew to MIR using an own tug, but pieces of that tug are lying in the bush-bush of Cameroun. The side of the engines on the Kristall module this module had been extended by the American Docking compartment. Some Americans were concerned about that thing, for formally Russia is responsible for damage caused by the MIR-station, but if somebody could prove that he suffered from pieces of that Docking compartment, the USA would have to pay for that compartment (approx. 3500 KG-s). It has been built by the Russians but is American property. The Base Block, so MIR's core module, with the spherical transition section, can only reenter by using a Progress ship.
Regularly the MIR crews (and even these days the crew of the ISS) had to check the so called úgli pasadki, the angles of attack under which their rescue vessel had to 'hit' the upper layers of the atmosphere in case of an emergency descent. Those angles vary between 139 to 144 degrees. The correct adjustment of these angles on the right time is a guarantee for the safe return. The slightest deviation could cause a catastrophe. Here we have to do with an apparatus constructed to survive the reentry in the atmosphere and it is quite clear that this is not so with the MIR-station.
The Russians have a lot of experience with the return flights of Progress freighters. After separation from the station these ships made some autonomous orbits around the earth after which they were put on a destruction course and before each ship reached the target area East of New Zealand, it had almost fully burnt up.
But the MIR-complex is another piece of cake:
Base block: 20.9 tons, dimensions 13.13 x 4.15 Meters, volume 90 Cubic Meters.
Kvant-1: 11.05 tons, 5.8 x 4.15 M, 40 Cubic Meters.
Kvant-2: 18.5 tons, 12.4 x 4.35 M, 61.3 Cubic Meters.
Kristall: 19.64 tons, 11.9 x 4.35 M, 60.8 Cubic Meters.
Spektr: 19.64 tons, 11.9 x 4.35 M, 61.9 Cubic Meters.
Priroda: 19.7 tons , 11.9 x 4.35 M, 66 Cubic Meters.
Docking compartment, attached at Kristall approx. 5 x 2.1 M, approx. 3.5 tons.
We also have to add the 7 tons weighing Progress-M, needed to give the complex the necessary engine impulses for reentry. So a total mass of approx. 120 tons. Estimated at 140 tons including cargo.
Figures like this do not say much. To help your imagination visit a railway museum where you can see the old huge steam locomotives, we call them Jumbo's, put 5 of them together and add some extra carriots: that is flying above us, descending gradually and has to come in the earth's atmosphere.
On the outer surface of the whole complex a lot of protruding things have been installed: the solar panels, 2 Strela girders, antennae, sensors, some huge masts in one of them the external thruster VDU, parts of the Kurs approach system, a great reflector for laser experiments on the Priroda, etc. You need to be a supernatural genius to calculate a reliable course with the use of aerodynamic laws.
These laws start to play a role when the MIR-complex ceases to be a space object and has to become an airplane during reentry. The Space Shuttle has been constructed to satisfy this condition. While slowing down in the upper layers of the atmosphere the Shuttle undergoes the metamorphosis from 'space object' to 'glider'.
The MIR-station has to come down and meets a increasing resistance of the gradually growing amount of air particles.. At about 150 KM-s above the earth's surface this is becoming critical. These particles start to slow down the complex, not with a favorable constant towards the center of gravity, but as a resultant of the forces, which will be administered on different components of the complex. It is not possible to predict this resultant and to determine which angle of attack is needed to achieve an optimal burning process. There will be a kind of friction, it is impossible to maintain the chosen angle of attack and then the SUD, the system for the control of movements will switch itself off and the same does the Tv.V.M., the main computer. The gyrodynes will stop immediately.
As soon as aerodynamic laws assert their influence, all attitude control systems on board MIR become worthless.
One of the possibilities under consideration in Moscow is the presence of a crew on board as long as possible for the maintenance and operation of the movement control systems. But when this crew leaves MIR, the station is still fully a space object and in that stage the movement control systems can continue to function. These systems are very vulnerable for external forces and as soon as the complex comes below 150 KM-s and meets more dense layers of the atmosphere the systems are without avail.
Then the cosmonauts are already in their Soyuz-TM ship for their return to earth.
Optimists expect that as soon as the station reaches the critical altitudes at which the burn up starts (the burn up of the Salyut-7/Cosmos-1686 began at approx. 100 KM-s and stopped at about 75 KM-s) the station spontaneously will break up in several pieces, not only by the burning up, but also by mechanical forces. For instance, modules would break off from the docking mechanisms. I do not believe this. Only extended parts like solar panels, antennae and other protruding things will be torn off, but the modules are firmly attached. The docking mechanisms consist of stone-hard alloys of duraluminium and steel. The complex will start to tumble and this will cause variations in the intensity of the burn-up. Whole pieces, and possibly even full modules, will not burn up. Parts of the complex will not burn for they will be shielded off by other parts.
The determination of the moment of the last impulse and the angle of attack at that moment will be crucial. This determines whether the complex will disintegrate exactly there where there will be no danger for populated areas on earth, but also if as much as possible pieces and particles will reach the desired target area. It can be expected that before the majority of these pieces will reach the target area, the complex will pass a trajectory of some thousands Kilometers (experts mentioned 8000-10000 KM-s) with a width of 200 KM-s where a rain of parts and particles will come down. These pieces might consist of strong steel containers, parts of the hulls of the MIR base block, the Kvant-1, Kristall, Kvant-2, Spektr and Priroda, but also of gyroscopes and rocket engines.
We can distinguish 3 flow regimes during the descent after passing the altitude of 200 KM-s:
1. the molecular flow:
Between 200 and 150 KM we find in fact still space, but there already are a lot of molecules. At about 200 KM-s the impulse for reentry has to begin and this impulse can continue until the altitude of 150 KM-s. It is possible, but not sure, that the vulnerable movement control systems will be able to withstand the minor slowing down by the scarce amount of molecules and so for a while can maintain the stability of the complex. That means in such a way that the complex will not yet start to tumble, but continues to dive in the attitude desired by the ballistic experts. In that stage the speed of the complex is still somewhat more than 8 KM/sec.
2. the transitional flow:
This is between 150 and roughly 75 KM-s. Between 150 and 100 KM-s the speed is still approx. 8 KM/sec, but the but the thin air is getting more dense and the slowing down begins to become manifest. A strong slowing down will be experienced. There is no longer any stability at all for the slowing down around the whole complex is not regular. Protruding parts and the modules will cause a very capricious spin and tumbling. Yet the speed at 75 KM-s will still be approx. 6 KM-s. The heating will be enormous and the air mass at that altitude will be coherent and getting more and more dense.
3. The more dense atmosphere:
Entering this zone takes place around 75 KM-s. While the speed is reducing until hypersonic speeds between 6 and 2 KM/sec, the irregular tumbling, spinning and still being surrounded by an enormous heath , the complex undergoes strong mechanical forces causing the breaking off of a number of parts. The smaller and lighter obstacles like antennae, solar panels, masts, sensors etc. had been broken off earlier and continue their destruction course independently. The ideal of the responsible ballistic experts will be that as many as possible big parts will burn up, but that will not be the case with a number of pieces. There will be parts, possibly full modules, which, during stages in which the temperatures reach its maximum, have been blocked off by other modules or parts and in that way do not have the possibility to burn up completely. Below the altitude of 50 KM-s the breaking off of pieces will be completed and there is no enormous heath any more. With speeds, varying for different pieces, of approx. 1 KM/sec the supersonic velocity will be reached and now the end of the trip of the majority of pieces has been achieved.
The target area: Mentioned has been an area at a distance of 1500 - 2000 KM-s from Australia. It is not clear if this is the normal area designated to receive for instance debris of returning Progress freighters east of New Zealand. To reach this area a trajectory has to be chosen that as much as possible passes the ocean. Presuming that the last command for the impulse of the Progress-M engines just before reentry in the atmosphere will be given when the complex is in range of a for that purpose suitable tracking station on Russian territory, this trajectory must go via the Arabian peninsular, the Indian Ocean, then South of Australia in the direction of that target area. When the, still with a speed of 8 KM/sec flying, complex reached the Indian Ocean it must at all costs avoid continental areas.
Most likely the tracking station via which the final commands to the Progress-M will be transmitted, will be the facility in Shcholkovo near Moscow; after Shcholkovo, the footprint of the complex comes in range of the facility Dzhuzaliy near Baykonur, making it possible to check the proceedings of the object.
Just before reaching Shcholkovo the footprint will sweep over Western-Europe giving us the possibility to say goodbye. If this takes place just after sunset we might be able to see the complex for the last time.
So in my opinion the trajectory at which the operation will be going on, will go from European Russia, the Black Sea, the Arabian peninsular, passing between the Horne of Africa and India and further on over the Indian Ocean. Then along a trajectory for a while reaching the latitude 51.6 South and slightly to the North East, south of Australia and New Zealand, to find MIR's seaman's grave over the Pacific Ocean.
Somewhere I read the option that the last engine impulses will be given approx. over Egypt and the descent will begin over Russian territory and to proceed in a southernly direction to the target area east of New Zealand. Personally I do not believe this, for the ground course would pass over too many areas belonging to foreign states.
Certainly we will soon get more information about the plans for this operation. This must be so, for it is a matter of international importance. There have also to be so called catastrophe scenario for instance if the attempts to put the complex on the correct destruction trajectory and adjusting will be no longer possible. And there is still the possibility that parts of the complex, broken off, will continue their life for a while as autonomously flying satellites.
Thus far there have been plans to execute this operation between 26 and 28.02.2001.
But meanwhile one of the Achilles' heels for the reentry operation announced herself: the telemetry communications (so the transponder for the reception of telemetric data as well as the transmission of tele commands.). In Septembeer 2000 a Television broadcast transmitter near Shcholkovo near Moscow made the reception of telemetry via the channel 638 mc/s fully impossible. The TV transmitter was used to fill up the gap in TV-networks which emerged after the fire in the Ostankino TV tower. Some political struggle was needed to cope with this problem.
Worse was the situation on 26.12.2000: during one day the telemetry transmitter of MIR was dead and flight control feared the worst. Communications were restored, but 2 days later a telecommand given for an attempt to tilt the station somewhat to get a better effect from the sun on some solar panels, did not come through. The experiences of the last months brought experts to the conclusion that the telemetry transponder of MIR was not stable and this emphasized the decision to prepare a service mission to MIR before daring to execute the reentry operation.
So the plan is to send a very skilled crew, of which the commander as well as the on board engineer have experience with manual docking maneuvers. If for instance during the final approach and docking attempt the complex will make unexpected movements, the Soyuz-TM has nevertheless to be docked manually. That is why the provisional choice fell upon the crews Padalka-Budarin and the stand ins Korzun-Vinogradov.
(Meanwhile -the 5th of January- the Russians decided to wait sending a crew to MIR, but will launch a Progress freighter on 16.01.01 which has to dock in the automatic mode on 18.01.01. If the attempt to dock automatically fails the above mentioned crew will go to MIR to guide the docking operation manually)
Chris van den Berg, NL-9165/A-UK3202
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