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Accidental Collisions of Cataloged Satellites Identified (Forwarded)



 
 
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Old May 23rd 05, 01:17 AM
Andrew Yee
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Default Accidental Collisions of Cataloged Satellites Identified (Forwarded)

[From ORBITAL DEBRIS QUARTERLY NEWS, Volume 9 Issue 2, April 2005, NASA
Orbital Debris Program Office, Johnson Space Center]

Accidental Collisions of Cataloged Satellites Identified

Personnel of the U.S. Space Surveillance Network (SSN) have identified two
new cases of accidental collisions between cataloged objects from
different missions. One collision is recent, having occurred in January
2005, while the other is a much older event which occurred in late 1991
but has just now been recognized.

The subjects of the recent collision were a 31-year-old U.S. rocket body
(1974-015B, U.S. Satellite Number 07219) and a fragment (1999-057CV, U.S.
Satellite Number 26207) from the third stage of a Chinese CZ-4 launch
vehicle, which exploded in March 2000. The event occurred on 17 January
2005 at an altitude of 885 km above the south polar region, a regime in
low Earth orbit (LEO) with an above-average satellite population density.
Both objects were in similar retrograde orbits at the time of the
collision.

Analysis indicates that the orbits of both objects were slightly perturbed
at the same time that three debris (subsequently cataloged as U.S.
Satellite Numbers 28591-28593) were released from the U.S. rocket body.
The rocket body was the relatively small (1 m2) upper portion of a Thor
Burner 2A final stage. The fragment of the Chinese rocket body possessed a
radar cross-section of only 0.06 m2.

The recently recognized collision of late December 1991 involved a Russian
non-functional navigation satellite, Cosmos 1934 (1988-023A, U.S.
Satellite Number 18985) and a piece of debris from a sister spacecraft,
Cosmos 926. Both objects were in similar orbits with a mean altitude of
980 km and an inclination of 83 deg. Two pieces of debris (1988-023C, U.S.
Satellite Number 21912 and 1988-023D, U.S. Satellite Number 22919) from
Cosmos 1934 were discovered by the SSN within a few weeks of the event,
although they were not cataloged until later.

In this case the smaller impacting object apparently broke up into much
smaller debris and was no longer trackable by the SSN, i.e., it could not
be found after the collision. The event was only recognized recently when
SSN specialists were examining historical tracking data.

The first recognized collision between cataloged objects from different
missions involved an operational spacecraft and a fragment from a launch
vehicle upper stage which had suffered a postmission breakup. In that
event, which occurred on 24 July 1996, the French CERISE spacecraft
(1995-033B, U.S. Satellite Number 23606) collided with a fragment
(1986-019RF, U.S. Satellite Number 18208) from the third stage of an
Ariane 1 launch vehicle, which had exploded ten years earlier.

As the number of objects in Earth orbit increases, the likelihood of
accidental collisions will also increase. Currently, hundreds of close
approaches (i.e., passes within less than one kilometer) between cataloged
objects occur on a daily basis. If future spacecraft and rocket bodies are
not removed from LEO within a moderate amount of time after the end of
mission, e.g., within 25 years, the rate of accidental collisions will
increase markedly later in this century.

 




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