Ensuring controlled descent of the Mir Orbital Station, Presentation to the UNO Science and Engineering Subcommittee
Mission Control Center
TsNIIMash [Central Scientific Research Machine Building Institute]
Rosaviakosmos [Russian Aviation and Space Agency]
Moscow, Russia
[http://www.mcc.rsa.ru/deorbit/www_eng/doklad/page_doklad.htm]
The material submitted to the UNO Science and Engineering Subcommittee 38
session on peaceful use of space (Vienna 12-13 Feb 2001) as an official
UNO document.
ENSURING CONTROLLED DESCENT OF THE MIR ORBITAL STATION
N.A. Anfimov
Director of TsNIIMash [Central Scientific Research Machine Building Institute]
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. Moreover,
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
operations.
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:
53°S, 175°W; 23°S, 175°W; 23°S, 132°W; 30°S, 127°W; 30°S, 90°W; 53°S, 90°W
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:
- 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. - Construction of the approximately 160 x 230 km descent orbit with a
perigee located above the sinking area using several burns of the
Progress M1 cargo vehicle engines. - 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 47°S, 140°W (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.
Conclusion
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
reliability.
