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Mir Crash
Concerning the matter of safety of the Mir station de-orbitation
Senior Engineer, Mr. Ilyin Alexei Leonidovich
Central Aerodynamic Institute Russia CAGI,
tel: +7 (095) 556-36-65
DRAFT TRANSLATION - Russian Original
In connection with the forthcoming deorbitation of the Mir station there is a question of the safety of such operation. So far this matter have been unreasonable remained in a shadow. Meanwhile it is possible to assert that it is impossible to submerge a 130 t-weight station having in disposal one Progress ship for its braking and to ensure in the mean time the acceptable value of dispersedness of splinters. This fact should have been considered already at the stage of making the decision of the submerging. The matter of the possibilities available to de-orbitation-safety is also in close relation with the matter of the possibilities of the station's ascent, which will be shown below.
There are two ways of arbitrary object de-orbitation into the atmosphere. Firstly, it is possible to wait, while as a result of natural descent satellite will reach the conventional boundary of an atmosphere (100 km). After that the atmosphere contact coil (within the limits of several pieces) and the point of enter on the appointed coil can be chosen using series of braking or racing impulses. For want of it satellite enters the atmosphere practically on a tangent and it is difficult to suppose that the dispersedness of the place of falling on a the Earth surface will earth make in this case less then a quarter of the coil, i.e. 10000 km. For an more accurate preliminary determination of the fall-place in this case an accurate aerodynamic calculation is necessary, that is hardly possible because of the low accuracy of appropriate calculation methodic as well as:
Dependence of resistance factor ?? of the spacecraft from a range of speed, current orientation, occurring, chemical and physical reactions in a stream of surrounding gas, strong influence of all the atmosphere layers on the fall-place.
The second way traditionally used is concluded in entering the atmosphere
The alternate path, used traditionally, consists in the entry into the atmosphere from elliptic orbit through a half-coil after giving a brake impulse. In the role of the determining parameter, describing a heating level, originating loads and dispersedness of the place of landing in this case is so called entry angle, at which the trajectory of the spacecraft intersects the boundary of the conventional atmosphere. The larger is the angle, the higher is the construction's heat, originating overload and the less is the dispersedness of the place of landing. Moreover, has the angle less then critical value, there is no rounding up the descending spacecraft by the atmosphere and it return back to the space along a new elliptic orbit with a smaller value of main half-axes. This effect is sometimes used for smooth braking by several coils of the descending spacecraft flying up to an other planet on high speed to reduce loads and heating on the entry into the atmosphere after the last coil. For each spacecraft For each apparatus, depending on accepted overloads, heating and speed of flight by the entry into the atmosphere of each planet exists so called "entry corridor", i.e. a range of allowable values of the entry-angle. It is obvious that by the submerging of the Mir station with the purpose of the most complete combustion in an atmosphere and minimization of dispersedness of splinters fall it is necessary to provide the possibly largest value of the entry angle.
General estimations of possibilities on safety in such case can be evaluated without detailed information about technical possibilities available and concrete submerging-plan. There is ???? 25645,301-83 " Calculations ballistic of artificial satellites of the Earth. The methods of calculation of fuel expenditure for shunting ", containing the methods of determination of the entry angle (p.6) and the tables with the ready results calculated according to this methods (table 9 on p.37 - table 47 on p.75, 76). The tables are created for fixed values of the entry-angle and include the dependence of given impulse-value (value of slowing down of satellite, m/sec.), necessary for attaining an "entry-angle of the whole table", from initial height of flight on a circle orbit. An angle of impulse-generation relatively a tangent to an initial trajectory is also set on heights that are close to the conventional boundary of atmosphere. For heights over 140 km and entry-angles less than 1,1° the braking impulse is set on a tangent. The common legitimacy is traced. As initial height decreases with a fixed entry-angle, necessary impulse at first decreases and then increases again. The initial decrease is explained by decrease of distance up to the atmosphere, that has to be overcome as a result of transition to an other trajectory after generation of braking impulse, and the consequent increase is explained by necessity of a of a trajectory-turn of satellite, flying on high speed close to the atmosphere-bounder (for such satellite the entry along an elliptic trajectory by a half-coil on a determined angle is impossible). So for each value of entry-angle exists a minimal impulse necessary for its achievement and an optimal height of generation. It is also possible to solve a reverse task, in particular to determine extreme accessible entry-angle and optimal height of generation using the value of impulse.
These are the figures, describing the de-orbitation-situation.
During submerging the last Progress the 78 m/sec. impulse was generated on the height 280 km approximately which corresponds with the entry-angle between 1° and 1,1° (tables 17, 18 p.45, 46). It was possible to safe 5 to 10 m/sec. by waiting for the optimal height 210 km, which was not done, perhaps, due to limitation of term of standalone flight. For the station 50 kg of fuel are used for 1 m/sec. of impulse (the appropriate value of losses 16 %), delivered by Progress stock 2 t, summary impulse 40 m/sec. According to the table 13, p. 41 the entry-angle is 0,6° with the generation height 170 km. So the provided angle is smaller than for Progress despite of 20 times heavier weight of Mir and the fact that the tank of one of Progress-compartments is made of Magnesium-alloy.
Therefore the safe de-orbitation of the heavy station by the Progress alone is impossible. Specialists state that the situation with the station-de-orbitation will be more difficult because its final weight will exceed the Mir weight three times. For a safe submerging of heavy orbital stations it is necessary to provide manufacturing of a large racing block at the end of exploitation. However, practically the same block is able to provide a burial of the station on a high orbit.
In connection with the said above there are serious questions concerning some statements of responsible persons maid lately. For example, it is contended that in case the connected to Mir Progress is used for not submerging but lifting of the station, the height of circle orbit can be raised only 30 - 40 km but not 70 km higher. The following conclusions can be done concerning this fact.
First, let us explain occurrence of the figure 70 km itself. There is a proportion between increase of speed by generation of racing-impulse and increase of a circle orbit-height. In fact, the speed decreases during the ascent and transition from one circle orbit on an other at one dispersal is impossible. However, the relation between the value of instant dispersal and orbit height-increase exists and can be described in a formula where r = h + 6371 km (6371 km - average radius of the Earth under orbit with inclination 51°), µ - 3,986x105 ........ - the product of the Earth-weight into its gravitational constant . For heights 250,300,350 km there is a value .................................... accordingly. With 2 t of a fuel stock on Progress and 40 m/sec. impulse, the ascent of Progress is 70 km.
If as a result of any reasons a half of ascent-height is "lost", it means a "loss" of half of the generated impulse. Then for a 20 m/sec.-impulse, as per the table 10 p. ???? 25645,301-83, the entry-angle will make 0,3° with the generation-height 130 km, i.e. 3 times less than for Progress. The question is possible, if the station will be kept in the atmosphere with such value of the entry-angle. On the "second circle" the station will go on separate units. Each of them will go on its individual trajectory, have each of them will go along the individual trajectory, have complex aerodynamics due to burns-out. Solar batteries and so on will be blown off by a stream, fuel tanks most likely already will blow up. All the blocks will enter the atmosphere at the next coil absolutely unguided. If the station will be kept in the atmosphere, the dispersedness of splinters' fall along the trajectory will be very wide. Concerning the said, there is an interest, to which value of the entry-angle is related the value of dispersedness of 5000 km, stated by Yu.N.Koptiev in his tele-interview.
The question appearing is, why nothing is said about such danger in any official reports? For myself I am answering as follows: because there is no such danger. The figure 5000km - is reality, it is related to the entry-angle 0,6°, the Progress generates the necessary 40 m/sec. of the impulse. The reports on the decrease of the ascent-height are intentional de-information in order to hide the fact of remaining possibility to ascent the station from the public. For the benefit of this reason the following argument can be adduced. The statements are distributed that the increase of the fuel-usage (from 16% up to 60%) was resulted by a failure of girodines. Firstly, girodines are serviceable but switched off. Secondly, girodines could never counteract the moment occurring by racing of an unbalanced station. Thirdly, girodin is not non-basis propulsive device, it can collect the moment of impulse, but then it needs to be reset by spending the fuel saved previously.
It turns out, that in the situation of the station the public repeatedly collided with deliberate de-information. The following three statements are all INCORRECT: 1) that Mir is in a bad condition; 2) That Mir cannot be elevated safely 3) that de-orbiting is safe. All this provokes this it directs on sad thoughts about the future of the branch and the destiny of the station. No one analyzes the situation and looks for ways of its saving. For the benefit of such opinion is also the fact that the braking impulse is generating earlier then the moment when the station reaches the optimal height of its generation. Induces on suspicions the close character of the information about the condition of the station, the nature of the additionally appeared losses and the notorious plan of three-impulse-de-orbitation. The author, employee of CAGI, despite of his insisting requests, did not succeed to get access to this information.
Ilyin Alexei Leonidovich, engineer with CAGI, tel: (095) 556-36-65 Central Aerodynamic Institute Russia