In the context of a great interest of the
world public to the final flight phase of the Mir space station
and particular actuality of questions put to B.I. Sotnikov, RSC
Energia Deputy General Designer, by the Moscow bureau of the German
information agency Springer we publish extracts from his interview. Boris Ivanovich Sotnikov is a Deputy
General Designer of the S.P.Korolev Rocket and Space Corporation
Energia, leader of the Research and Technical Center of the Corporation
engaged in design and calculation activities, Doctor of Sciences
(Engineering), 66 years old.
Question: Is there a precise calculation of
the Mir station de-orbiting trajectory to provide safe impact of
its fragments in the prescribed area of the Earth?
Answer: First, RSC Energia has
a great experience in providing controlled de-orbiting of Progress-type
transport cargo vehicles. All these vehicles are brought strictly
to a definite area of the Pacific Ocean.
Second, the Corporation possesses necessary programs and means to
support precise calculations of orbital flight trajectories in the
upper rarified atmosphere and de-orbiting of complex space objects
– controlled and uncontrolled space objects of different configurations,
space vehicle stages and Mir-type multi-module stations. Now, such
calculations for the station are performed regularly: its orbit
and descent trajectory are calculated, water landing area dimensions
are defined for those station fragments that will not burn in the
atmosphere and will reach the water surface. The calculations are
performed by specialists of RSC Energia and other specialized organizations,
the Mission Control Center (MCC) included.
Question: What area of the Earth
is the station descent planned to?
Answer: The station descent
is planned so as to bring it on de-orbiting to the assigned target
point. This point is located on the water surface of the Pacific
Ocean in the area far from existing aircraft and shipping routes,
populated islands. This area was already used before to submerge
expended rocket stages, satellites and space vehicles, including
Progress cargo vehicles, during controlled descent from near-earth
orbits.
Question: When is the station
descent from the near-earth orbit planned?
Answer: The date of descent depends on many
factors. Among them is: the Earth atmosphere condition, a station’s
changing attitude, implementation of the assigned program of controlled
lowering of its orbit under which the Progress M1-5 transport cargo
vehicle-tanker shall be launched. After the docking with the station
the vehicle will be in the dormant phase till the moment when the
station orbit altitude will reach 240-250 km. Then the vehicle will
begin active generation of a controlled descent trajectory of the
station. At present, the date of de-orbiting can be defined with
an accuracy of several days. This date will be clarified with time.
A more accurate forecast presents problems for objective available
errors in calculations of the Earth upper atmosphere density with
regard to its fluctuations because of solar activity changes. Permanent
tracking of these processes will be provided and a decision will
accordingly be made on the station de-orbit.
Question: Will the station be divided into
separate modules before de-orbiting? Is there a danger that before
de-orbiting it will divide spontaneously into modules and fragments
that will fall in another Earth’s area?
Answer: The Mir station will
de-orbit as an integral body without separation into modules and
separation of the Progress M1-5 vehicle from it. The cargo vehicle
propulsion system will impart several braking impulses in series
to the station to provide accurate generation of the trajectory
of bringing to the target point. No hazard exists that the station
will spontaneously divide into modules and fragments before de-orbiting.
Beginning from the altitude of about 120 km, when the station with
the cargo vehicle passes the upper atmosphere, as a result of increasing
aerodynamic drag followed by heating of structural elements to several
thousand degrees fragments will begin to separate as from an ordinary
meteor body entering the Earth atmosphere at a tremendous velocity.
These fragments will, in its turn, fall to smaller pieces.
Question: It is known that the Salyut-7 station
de-orbit was uncontrolled. Is there a danger of such de-orbit for
the Mir station?
Answer: The Salyut-7 station
is a passed stage in cosmonautics. Its control on de-orbiting was
not envisaged. This station was flying in a near-earth orbit loosing
height in the upper atmosphere under the action of natural aerodynamic
drag and was uncontrolled over a long period of time. The forecast
of the de-orbit date was made at regular intervals based on a more
strong "capture" by the Earth atmosphere. The station
de-orbited on February 7, 1991 as it was calculated during operational
short-term forecast. Its elements reached the Earth surface mainly
in the Atlantic Ocean water. A minor amount of them burnt over Argentina
and a still more minor amount fell on its territory. They did not
cause damages or fractures. According to official information from
Argentina, no damage was caused.
Question: How many people are engaged in solving
this problem? What will be the costs to implement the Mir station
controlled de-orbit procedure?
Answer: Many groups of experienced
highly skilled designers, testers, managers, developers of onboard
and ground systems are engaged in solving the problem. The work
is underway in different lines: ballistics, strength, thermal and
other design, analysis of telemetry data, provision of monitoring
and control of the station and vehicles, preparation of launch vehicles
and spacecraft for launch at the Baikonur cosmodrome and many other
operations. The best specialists at RSC Energia and tens of enterprises
included in the cooperation of developers under the Mir station
program are involved in the resolution of this problem. The Corporation
being the prime company of this program is in full control of the
situation.
As regards the costs, it depends on many factors as you have evidently
understood. The Progress M-43 cargo vehicle that docked to the station
in October 2000 and provided implementation of operations scheduled
under the program of safe completion of the station flight through
maintaining the automatic controlled flight and performing the Mir
station orbit correction, will be undocked from the station before
docking of a new cargo vehicle-tanker and brought, as it was made
before, to the above-assigned area of the Pacific Ocean. The costs
only for launch of these two cargo vehicles (Progress M-44 and Progress
M1-5) make up about 600 million roubles without regard for the costs
of other works, including the services of ground facilities and
personnel of space infrastructure.
Question: What and how many station’s pieces will
reach the Earth surface?
Answer: The mass of the station
with the Progress M1-5 cargo vehicle before de-orbiting will make
up about 130 t. On passage through the upper atmosphere this manmade
celestial body will break into many thousands of pieces the major
portion of which will burn over the Earth leawing flame-coloured,
quickly vanishing traces in the sky at altitudes of more than 10-20
km. No more than 1500 pieces will reach the Earth surface. The mass
of these small pieces will not exceed several kilograms. There will
not be very large pieces. As estimated, the largest fragment that
can reach the ocean surface can be no more than 300-400 kg in mass.
Question: What will the Mir station velocity be on entering
the upper atmosphere? What velocities will its fragments have when
they reach the Pacific Ocean surface?
Answer: The station will begin
to break into pieces beginning from the altitude of about 120 km.
At this altitude the, as well as the station, will move at a velocity
close to the first space velocity – about 8 km/s. Due to aerobraking
this velocity will be decreased and depending on the relationship
between the mass and effective cross-section area will be decreased
by a factor of tens, hundreds and thousands – and will not exceed
several meters per second for the majority of pieces. Heavy and
compact pieces will have the greatest velocity – up to 300-400 m/s.
They can reach the Pacific Ocean surface, however the number of
such pieces will be minor. Light pieces of structure burn in the
atmosphere as a rule.
Question: Should appropriate ground services, states,
air and sea companies be notified to prevent aircraft and ships
coming to the mentioned area of the Pacific Ocean at a period of
the station de-orbiting?
Answer: The scheme of the station
de-orbiting will of necessity be proclaimed and the area of its
debris full will be marked. All states, air and sea companies, world
public will be notified.
By decision of the Government of Russia of December 30, 2000, a
special interdepartmental commission, was formed of authoritative
managers and specialists that was assigned to control constantly
the station condition, its operability, to inform regularly the
public of this problem, including notification of the date of station
planned de-orbiting. It is assumed that the most detailed information
will be presented 10 days prior to the mentioned time moment.
Question: Are there radioactive sources aboard
the Mir station? Is there a danger of environment contamination?
Answer: There are no radioactive
sources, toxic substances aboard the station. It is a manned station
and shall provide safe conditions of crew life throughout long-duration
multi-month expeditions aboard the station without ill effects on
cosmonauts health and after return to the Earth.
Therefore, taking into account these factors, we can state: no hazard
for the Earth ecology exists. Burning of station’s pieces in the
Earth atmosphere and fall of its structure fragments in the ocean
water do not present a hazard for the ecology; in any case, it can
be compared with a catastrophy of one large air-liner, not to mention
sinking of a sea ship.
Question: Do You feel sorry for the station?
Answer: Undoubtedly, we feel
sorry. A lot of creative forces and energy of hundred thousands
of engineers, scientists, workers, employees of not only Russian
enterprises but also foreign companies and organizations was contributed
to this unique project of the end of the XX century. It was a part
of our life. Unfortunately, everything comes to an end in life.
And we have also got to this moment. The station has been functioning
in orbit for 15 years. It was our concern to implement its flight
programs we set and solve new tasks, thought of future projects
of stations of a new generation. The Mir station could continue
a controlled manned flight, unfortunately it was not supported with
necessary financial resources in due time. Many of us have got used
to the station. Nevertheless, without regard to our personal attitude
to the station the Government of Russia has made a decision to terminate
the station flight, and its implementation shall be provided.
Question: What will you feel when the station is
falling?
Answer: There will be no time
for sentimentality at that moment. The phase of de-orbiting and
atmospheric descent is a complex stage of operation of the Mir station
project technical management, interdepartmental commission, all
services of control, personnel of RSC Energia and other enterprises
participating in the project. We shall be at the Mission Control
Center, shall supervise the implementation of the station de-orbiting
procedure. It is a very intense operation. Its final stage takes
one-three days and is preceded by a mouth and a half of important
work.
Question: Will You be at the Mission Control Center
during this time?
Answer:
Yes, all this time period
we shall have to be at MCC. And upon completion of the station descent
the results can be summed up in the circle of work participants.
But it will not be funeral repast. Actually, the decisions tested
on the Mir station were used as the basis for the ISS project –
International Space Station. The stage of manned cosmonautics associated
with the Mir station comes to an end. A new stage – ISS – has already
begun. We always said: when the ISS will begin functioning in a
manned mode the problem on the Mir station fate may be considered.
Now it has happened – the Zvezda service module has been launched
and docked to the ISS, the crew of the first prime expedition has
proceeded to work.
Question:
Will the fall of station’s pieces to
the Earth look like a meter flow?
Answer:
There will be a firework,
of flame – coloured stripes in the sky. When Salyut-7 de-orbited,
a colourful sight was observed in Argentina. Magazines wrote that
it was very spectacular.
The area of falling of the Mir station pieces is for from islands
and routes, difficult of access. Therefore, it is unlikely that
some-body can observe the sight. It will not be observed at MCC
as well, as to support it, a specially equipped ship should be sent
to that area and operational transmission of video surveys through
telecommunication satellites should be provided; and it will result
in significant financial expenditures and risks.
Question:
Can we say to our readers that they should
not worry abort falling of Mir station pieces on the Germany territory?
Answer: We can say with confidence:
the probability that the station’s pieces will fall on the Germany
territory is essentially zero. The station flight routes are within
the latitude range from 51.6° S.L. to 51.6° N.L., i.e. pass only
over the southern part of the country, and the passage over this
region lasts no more than 2 minutes. Every day no more than two-three
station’s passages over the region can occur, and sometimes the
station route can be back from it. Thus, it is beyond reasons to
worry.
Question:
Is there a precise calculation of the Mir station de-orbiting trajectory to provide safe impact of its fragments
in the prescribed area of the Earth?
