Space Security Index

of which fewer than 5 per cent are operational satellites. 2 ose objects that can be tracked
repeatedly and whose source has been identied are placed in the satellite catalog, currently
numbering more than 15,000 objects. 3 It is estimated that there are over 300,000 objects
with a diameter larger than 1 cm, and millions smaller. 4
Two key factors aecting the amount of space debris are the number of objects in orbit and
the number of debris-creating launches each year. Growth in the debris population increases
the probability of inter-debris collision, which may in turn create further debris. A study by
the U.S. National Aeronautics and Space Administration (NASA) has shown that, in LEO,
inter-debris collisions will become the dominant source of debris production within the next
50 years. As debris collides and multiplies, it will eventually create a “cascade of collisions”
that will spread debris to levels threatening sustainable space access. 5 Additional space debris
in LEO could be created by use of ground- and space-based midcourse missile defense
systems currently under development, or other weapons testing in space. 6
Between 1961 and 1996 an average of approximately 240 new pieces of debris were
cataloged each year; these new pieces were the result, in large part, of fragmentation and the
presence of new satellites. Between 8 October 1997 and 30 June 2004 only 603 new pieces
of debris were cataloged — a noteworthy decrease, particularly given the increased ability of
the system. is decline can be related in large part to international debris mitigation eorts,
which increased signicantly in the 1990s, combined with a lower number of launches per
year. In the 2007-2009 three-year period, an increase in the annual rate of debris production
was observed as a result of the aforementioned major debris-creating events occurring in each
of these years. Debris events in 2010 resulted in more than 800 cataloged pieces of debris
(i.e., 10 cm in diameter or larger), which constitutes a 5.1 per cent increase over 2009.
Collisions between such space assets as the International Space Station and very small pieces
of untracked debris are a frequent but manageable problem. 7 While collisions with larger
objects remain rare, in October 2010 the ISS had to maneuver to avoid a collision with a
large piece of debris, as described below. A U.S. National Research Council study found
that within the orbital altitude most congested with debris (900–1,000 km), the chance of
a typical spacecraft colliding with a large fragment was only about one in 1,000 over the
spacecraft’s 10-year functional lifetime. 8
However, the same study noted that, “although the current hazard to most space activities
from debris is low, growth in the amount of debris threatens to make some valuable orbital
regions increasingly inhospitable to space operations over the next few decades.” 9 Indeed,
some experts at NASA believe that collisions between space assets and larger pieces of debris
will remain rare only for the next decade, although there is ongoing discussion about this
assessment. 10 Incidents of varying severity are noted in Table 1.2 below.
Table 1.2: Unintentional collisions between space objects 11
Year Event
1991 Inactive Cosmos-1934 satellite hit by cataloged debris from Cosmos 296 satellite
1996 Active French Cerise satellite hit by cataloged debris from Ariane rocket stage
1997 Inactive NOAA-7 satellite hit by uncataloged debris large enough to change its orbit and create additional debris
2002 Inactive Cosmos-539 satellite hit by uncataloged debris large enough to change its orbit and create additional debris
2005 U.S. rocket body hit by cataloged debris from Chinese rocket stage
2007 Active Meteosat-8 satellite hit by uncataloged debris large enough to change its orbit
2007 Inactive NASA UARS satellite believed hit by uncataloged debris large enough to create additional debris
2009 Retired Russian communications satellite, Cosmos 2251, collides with U.S. satellite, Iridium 33, part of the Iridium
communications constellation.
The Space Environment
29