Mir Deorbit Info

From: Igor Lissov (i-cosmos@mtu-net.ru)
Date: Thu Mar 01 2001 - 03:45:05 PST

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    According to the Russian Mission Control Site (see url below), this material
    was submitted
    to the UN Science and Engineering Subcommittee 38 session on peaceful use of
    (Vienna 12-13 Feb 2001) as an oficial UN document.
    Igor Lissov
    Ensuring Controlled Descent of the Mir Orbital Station
    N.A. Anfimov
    Director of TsNIIMash, RUSSIA
    The history of the world cosmonautics is on the eve of witnessing a very
    remarkable event. Fifteen years ago, on February 20, 1986 the launching of
    the Core Block marked the beginning of the Mir Orbital Station construction.
    Currently the Mir Station consists of 6 modules. They are the Core Block,
    Kvant, Kvant-2, Kristall, Spectr and Priroda as well as the Docking
    Compartment (for docking with US Space Shuttle orbiters) and two transport
    vehicles known as Progress and Soyuz.
    The Mir Orbital Station is undoubtedly one of the most important engineering
    achievements of cosmonautics in the XX century. The Mir Station total mass
    is near 130 tons. Through 15 years of its orbital life the Mir Station was
    inhabited for 12 years and 7 months. The station housed 104 cosmonauts and
    astronauts including 62 foreign citizens from 11 countries to stay and work
    there at that period. US astronauts constantly stayed and worked at the Mir
    Station from March 24, 1996 till June 08, 1998. The Mir Station accommodated
    28 long-term basic expeditions accompanied by 16 visiting expeditions
    lasting from a week to a month. Of them 15 expeditions were international
    ones. More over, 9 visiting expeditions were conducted with Space Shuttle
    orbiters ferrying 37 US astronauts, 1 Canadian astronaut, 1 ESA astronaut, 1
    French astronaut and 4 Russian cosmonauts. The Mir Station became
    essentially the first international space station.
    23 research experiments and studies to Russian and international programs
    have been conducted for the Mir Station lifetime. Many of those experiments
    and studies were unique in the world.
    The Mir Station has become essentially a flying testbed for actual testing
    of many technological solutions and processing techniques to be used at the
    International Space Station.
    Currently the Mir Station mission program has been completed and the Russian
    Federation government agreed with a proposal by the Russian Aviation and
    Space Agency (Rosaviakosmos) to terminate the Mir Station operation program
    in February-March 2001 providing its controlled safe deorbiting and sinking
    in the World Ocean waters. A special Interagency Commission was established
    to ensure the Mir Station final stage of flight and controlled descent. The
    Commission is headed by Ju.N. Koptev,General Director of Rosaviakosmos.
    Preparations for the final operations are under way.
    It is worth to mention that the world community expresses a great interest
    and, in some sense, concern about forthcoming deorbiting of that huge space
    object. Therefore it seems appropriate to advise this high-level forum of
    the procedures for conducting the forthcoming unique and previously
    unparalleled operation to deorbit the Mir Station. Also, it is to the point
    to discuss some aspects defining available capabilities and limitations for
    the Mir Station descent realization.
    The information on the final stage of the Mir Station flight is constantly
    updated at the TsUP TsNIIMash web-site (http://www.mcc.rsa.ru) and
    Rosaviakosmos web-site (http://www.rosaviakosmos.ru).
    Two aspects are the most principle in relation to implementation of the
    forseen strategy for the Mir Station deorbiting and sinking in a specified
    zone of the Pacific Ocean. They are:
    -         the Mir Station technical status, that ensures implementation
    feasibility for the defined program and
    -         ballistic & navigation support of defined dynamic operations.
    The Mir Station technical status is constantly monitored by the Energia RSC
    as a primary designer as well as by TsNIIMash and associated entities. At
    the moment the Mir Station current technical status is estimated as
    satisfactory one without precluding from implementation of the specified
    The TsNIIMash Mission Control Center (TsUP) undertakes a ballistic &
    navigation support for the Mir Station flight control. However surveillance
    from Russian territory could be conducted only for a half of daily orbits.
    The other half (so called "dark orbits") cannot be tracked from the Russian
    territory. That is why it is impossible in TsUP normally to update the
    Station motion parameters from those orbits. Since the requirements for
    constant control of the Mir Station flight is of a primary importance for
    the whole period of final station deorbiting preparation the Interagency
    Commission has made up and implemented an extensive set of technical and
    administrative arrangements to provide the final Mir Station operation
    stage. Specifically, all Russian satellite orbit monitoring facilities were
    involved. Moreover agreements were reached with NASA and ESA to attract
    their appropriate technical facilities for Mir Station orbit tracking.
    Discrepancies in ballistic estimates are referred to uncertainty of the
    Earth upper atmosphere density and significant inaccuracies in its
    forecasting. To update forecasts of solar activity and geomagnetic
    perturbations decisively affecting the upper atmosphere density Russian
    primary associated institutes are attracted to the mission. Also data from
    ESA and NASA are in use. Cooperation of all participating organizations and
    services is arranged under TsUP control.
    For sinking unburned Mir Station fragments after reentering atmosphere a
    Southern Pacific Ocean area limited by the following point coordinates:
    53S, 175W; 23S, 175W; 23S, 132W; 30S, 127W; 30S, 90W; 53S, 90W
    is choosen. That area located between Australia and South America is free
    from shipping routes and is usually used for sinking debris of launch
    vehicles and spacecraft by Russia and other countries.
    The forseen controlled deorbit of the Mir Station would cover three stages.
    They are:
    1.     Passive waiting the date when the orbital altitude decreases to
    250-240 km (so called pre-descent orbit). This stage started after docking
    the Progress M1 cargo vehicle on January 27, 2000.
    2.     Construction of the approximately 160  230 km descent orbit with a
    perigee located above the sinking area using several burns of the Progress
    M1 cargo vehicle engines.
    3.     Progress M1 executes the final deorbit impulse and Mir Orbital
    Station passes to the reentry trajectory.
    Undestroyed station fragments could impact the outlined Pacific area from
    three diurnal orbits. According the basic estimated case the final deorbit
    impulse would be executed at the orbit arc from the Gulf of Guinea to the
    Caucasus. The coordinates of the aiming point for the Mir Station deorbit
    are 47S, 140W (can be updated depending on a specific deorbit date and
    selection of a basic orbit for reentry).
    During Mir Station descending along the last reentering orbit the station
    main body and its external elements would sustain progressively increasing
    stress and thermal loads due to atmosphere density increase. Outer antennas
    and solar panels will burn first at altitudes of 110-100 km. The main body
    structural elements destruction and hence the primary fragmentation of the
    whole object can take place at altitudes 90-80 km. The formed separate
    fragments continue their descent in the atmosphere independently. They can
    further split into parts, and the fragmentation process terminates at
    altitudes of 50-40 km. The majority of fragments melts and completely burns
    down, but the most heavy and high-melting ones can reach the Earth surface.
    Aerodynamic characteristics of separate fragments can differ essentially and
    hence their descent downrange is also different, that forms the fragments
    dispersion area. Moreover, the descent downrange of fragments depends on an
    altitude where they are formed. The dispersion area width is determined by
    the lateral force coefficient of each fragment during its motion in the
    atmosphere. The development of the destruction model for a complex
    artificial space object is a non-deterministic problem that can not be
    solved precisely, at least at the present time. The main reasons of this
    situation are the following:
    -       A sequence of the fragments separation and their shapes are
    determined by an initial object orientation, uncontrolled object motion
    relative to the center of mass under the action of aerodynamic moments that
    is impossible to analyze precisely.
    -       Precise determination of aerodynamic characteristics of separate
    fragments along the descent trajectory is not possible due to the
    uncertainty of their shape and also fragments rotation around their centers
    of mass.
    Therefore it is practically impossible to determine a complete set of
    fragments formed during the object reentry into the atmosphere, and also
    longitudinal and lateral dispersion of the fragment impact points basing on
    precise solution of the space object fragmentation problem and fragment
    motion in the atmosphere problem. Therefore, the problem of successive
    disintegration of the Mir Station into fragments and that of their final set
    was solved in a approximate way.
    A total estimated mass of unburned fragments would be 20 - 25 tons with a
    total expected number of fragments equal to about 1500 pieces. Length of the
    fragment impact area along the reentry path is estimated to be 6 thousand km
    with about 200 km in width.
    The nominal implementation of the developed Mir deorbit and sinking plan
    practically entirely excludes any damage infliction. Nevertheless it is not
    possible to exclude entirely an occurrence of contingencies onboard the
    station or in the flight control loop. All such possible situations have
    been analyzed and methods to control them have been developed, including a
    launch of the Soyuz transport vehicle with the crew to dock the station and
    to perform repair woks there. Of course there is a small probability that
    the planned three stages program of the Mir deorbit could not be
    implemented. But even in this case an option remains to correct the station
    trajectory using engines or changing an orientation of the station or its
    separate solar panels in order to avoid hitting the land. Thus a risk of the
    Mir deorbit in a completely uncontrolled mode and fragments falling on the
    land are inessential.
    The set of implemented preparatory efforts and the developed program of
    controlled MIR Station deorbit should provide a safe sinking of unburned
    fragments in pre-determined area of the Pacific Ocean at high enough
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