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Orbital Debris Quarterly News
Volume 11, Issue 3 July 2007


Detection of Debris from Chinese ASAT Test
Increases; One Minor Fragmentation Event
in Second Quarter of 2007

The extent of the debris cloud created by the destruction of the
Fengyun-1C meteorological satellite on 11 January 2007 by a Chinese
ballistic interceptor is becoming more apparent as routine and special
radar observations of the fragments provide more data. By the end of
June 2007 the U.S. Space Surveillance Network (SSN) was tracking more
than 2200 objects with a size of at least 5 cm.

More than 1900 of these debris had been officially cataloged, making
the event by far the worst satellite fragmentation of the space age. The
Chinese anti-satellite (ASAT) test coupled with other satellite breakups
in the first quarter of the year has resulted in an increase of
fragmentation debris in Earth orbit of an estimated 75% (Figure 1).

The Fengyun-1C debris cloud extends from 200 km to 4000 km in altitude,
with the highest concentration near the breakup altitude of
approximately 850 km. The debris orbits are rapidly spreading (Figure 2)
and will essentially encircle the globe by the end of the year. Only a
few known debris had reentered more than five months after the test,
and the majority will remain in orbit for many decades.

The large number of debris from Fengyun-1C are posing greater collision
risks for spacecraft operating in low Earth orbit. The number of close
approaches has risen significantly. On 22 June, NASA's Terra spacecraft
had to execute a collision avoidance maneuver to evade a fragment from
Fengyun- 1C that was on a trajectory which would have passed within 19
meters of Terra.

After a flurry of satellite breakups in the first quarter of 2007, the
next three months witnessed only one minor fragmentation classified as
an anomalous event. An anomalous event is normally characterized by the
release of only one or a few debris with very small separation
velocities. The debris appear to "fall-off " their parent satellites,
probably due to environmental degradation or small particle impacts
(Johnson, 2004).

In April a new piece (U.S. Satellite Number 31408) from the derelict
U.S. Seasat spacecraft (International Designator 1978- 064A, U.S.
Satellite Number 10967) was detected. This was the 15th debris from
Seasat cataloged since 1983 and the fourth seen during the past four
years (Figure 3). These debris exhibit a variety of ballistic coeffi-
cients, but all decay relatively rapidly compared to Seasat itself,
which is in a stable, nearly circular orbit near 750 km. Additional
debris have been briefly detected from Seasat, but they have reentered
prior to being cataloged. The source of the debris could be either the
spacecraft or the Agena upper stage to which it is still attached.

Early in 2006 an anomalous event involving the 46-year-old Vanguard 3
was detected (Orbital Debris Quarterly News, 10-3, p. 2). A second piece
has now been cataloged (U.S. Satellite Number 31405), and it is likely
to have also separated from Vanguard 3 in 2006, possibly about the time
of the first piece. The newly discovered debris is decaying at a slower
pace than the debris seen last year, but both are falling back to Earth
much faster than Vanguard 3 from its orbit of 500 km by 3300 km.

1. Johnson, N.L., "Environmentally-Induced Debris Sources", Advances in
Space Research, Vol. 34, Issue 5, pp. 993-999, 2004.