Andrew Yee[_1_]
February 7th 07, 02:24 PM
Union of Concerned Scientists
Cambridge, Massachusetts
Contact:
David Wright, Union of Concerned Scientists
617-301-8060
February 2, 2007
Debris from China's Kinetic Energy ASAT Test
Wang Ting and David Wright
On January 11, 2007 (U.S. time), China tested an anti-satellite (ASAT)
weapon against a defunct Chinese weather satellite. The test used a kinetic
energy ASAT weapon, which apparently destroyed the satellite by homing on it
and colliding with it at very high speed.
The satellite, called Feng Yun 1-C (FY-1C) had a mass of just under one ton
and was orbiting at roughly 850 km altitude when the collision occurred. The
collision took place at a speed greater than 8 km/s and would be expected to
completely break the satellite into fragments, the vast majority of which
would orbit the earth as space debris. Because this breakup took place at a
high altitude where the atmospheric density is very low, a large fraction of
this debris will remain in orbit for decades.
Debris from the Chinese Test
Because of their high speed, even small pieces of orbiting debris can
threaten satellites. Since high-altitude debris can stay in orbit for
decades or longer the amount of debris grows with time, and there is no
effective way to remove it. Controlling the production of debris is
therefore essential for preserving the long-term use of space.
Using a NASA model developed to describe satellite breakups at high speeds,
one can estimate the number of debris fragments with size greater than 1 mm
that resulted from the FY-1C breakup (see table below). This debris
represents a significant increase in the total estimated amount of debris of
this size at all altitudes up to 2,000 km, i.e., throughout low earth orbit
(LEO). By February 2, the U.S. Space Surveillance Network had already
cataloged more than 600 pieces of debris (presumably larger than 10 cm) from
the Chinese test.
Since the debris from this test is concentrated at altitudes near 850 km, it
would double the density of debris larger than 1 cm in that region for at
least five years. Moreover, 800 large pieces of debris is equal to the
debris that would be added to LEO in 30 to 40 years of space launches under
"business as usual," and 70 to 80 years of space activity if strict debris
mitigation measures of the kind being discussed internationally are put in
place.
Satellites cannot be shielded effectively against collisions at this speed
with debris larger than about 1 cm. Moreover, debris smaller than about 10
cm cannot be reliably tracked from the ground to give warning of a possible
collision.
Using the NASA model, debris and atmosphere data, and orbit calculations, we
can estimate how long the debris from this test will stay in orbit. Those
calculations (Figure 1) show that more than 50% of the debris with size
greater than 1 cm will remain in orbit for more than 20 years. The sections
of the curves that show sharp declines in debris are due to the periodic
maximums of solar activity, which cause the earth's atmosphere to expand
slightly, increasing the atmospheric drag on the debris.
Most of the debris from such a breakup will orbit at altitudes near the
altitude at which the collision took place. Over time the debris will spread
out in a shell around the earth, so that it places at risk all satellites
that pass through that altitude (Figures 2 to 5).
Debris from Larger Satellites
The breakup of satellites larger than FY-1C will produce significantly more
debris. Satellites that are considered likely targets of ASAT weapons, such
as spy satellites, have masses ten times that of the FY-1C satellite. The
breakup of a single large satellite with a mass of 10 tons would double the
amount of debris in low earth orbit with size larger than 1 cm, and could
increase the density of debris in altitudes near the breakup altitude by
several hundred percent. The debris estimates for this case are shown in the
table below.
[NOTE: Tables and images supporting this article are available at
http://www.ucsusa.org/global_security/space_weapons/debris-from-chinas-asat-test.html
]
Cambridge, Massachusetts
Contact:
David Wright, Union of Concerned Scientists
617-301-8060
February 2, 2007
Debris from China's Kinetic Energy ASAT Test
Wang Ting and David Wright
On January 11, 2007 (U.S. time), China tested an anti-satellite (ASAT)
weapon against a defunct Chinese weather satellite. The test used a kinetic
energy ASAT weapon, which apparently destroyed the satellite by homing on it
and colliding with it at very high speed.
The satellite, called Feng Yun 1-C (FY-1C) had a mass of just under one ton
and was orbiting at roughly 850 km altitude when the collision occurred. The
collision took place at a speed greater than 8 km/s and would be expected to
completely break the satellite into fragments, the vast majority of which
would orbit the earth as space debris. Because this breakup took place at a
high altitude where the atmospheric density is very low, a large fraction of
this debris will remain in orbit for decades.
Debris from the Chinese Test
Because of their high speed, even small pieces of orbiting debris can
threaten satellites. Since high-altitude debris can stay in orbit for
decades or longer the amount of debris grows with time, and there is no
effective way to remove it. Controlling the production of debris is
therefore essential for preserving the long-term use of space.
Using a NASA model developed to describe satellite breakups at high speeds,
one can estimate the number of debris fragments with size greater than 1 mm
that resulted from the FY-1C breakup (see table below). This debris
represents a significant increase in the total estimated amount of debris of
this size at all altitudes up to 2,000 km, i.e., throughout low earth orbit
(LEO). By February 2, the U.S. Space Surveillance Network had already
cataloged more than 600 pieces of debris (presumably larger than 10 cm) from
the Chinese test.
Since the debris from this test is concentrated at altitudes near 850 km, it
would double the density of debris larger than 1 cm in that region for at
least five years. Moreover, 800 large pieces of debris is equal to the
debris that would be added to LEO in 30 to 40 years of space launches under
"business as usual," and 70 to 80 years of space activity if strict debris
mitigation measures of the kind being discussed internationally are put in
place.
Satellites cannot be shielded effectively against collisions at this speed
with debris larger than about 1 cm. Moreover, debris smaller than about 10
cm cannot be reliably tracked from the ground to give warning of a possible
collision.
Using the NASA model, debris and atmosphere data, and orbit calculations, we
can estimate how long the debris from this test will stay in orbit. Those
calculations (Figure 1) show that more than 50% of the debris with size
greater than 1 cm will remain in orbit for more than 20 years. The sections
of the curves that show sharp declines in debris are due to the periodic
maximums of solar activity, which cause the earth's atmosphere to expand
slightly, increasing the atmospheric drag on the debris.
Most of the debris from such a breakup will orbit at altitudes near the
altitude at which the collision took place. Over time the debris will spread
out in a shell around the earth, so that it places at risk all satellites
that pass through that altitude (Figures 2 to 5).
Debris from Larger Satellites
The breakup of satellites larger than FY-1C will produce significantly more
debris. Satellites that are considered likely targets of ASAT weapons, such
as spy satellites, have masses ten times that of the FY-1C satellite. The
breakup of a single large satellite with a mass of 10 tons would double the
amount of debris in low earth orbit with size larger than 1 cm, and could
increase the density of debris in altitudes near the breakup altitude by
several hundred percent. The debris estimates for this case are shown in the
table below.
[NOTE: Tables and images supporting this article are available at
http://www.ucsusa.org/global_security/space_weapons/debris-from-chinas-asat-test.html
]