The possibility of a collision such as that shown in the
movie Gravity is real, although large objects are
usually tracked with sufficient precision to enable the
potential ‘target’ to take evasive action. The
Department of Defense (DoD) maintains a highly accurate
satellite catalog on objects in Earth orbit that are
larger than a softball. DoD’s Space
Surveillance Network tracks discrete objects as small as
2 inches (5 centimeters) in diameter in low Earth orbit
and about 1 yard (1 meter) in geosynchronous orbit.
A
large number of the world’s spacecraft operators are
members of the Space Data Association which was
specifically set up to reduce the risk of collisions
with space debris in earths orbit. At the present time
operators are protecting operational spacecraft using
avoidance maneuvers. NASA reports that it
takes the threat of collisions with space debris
seriously and has a long-standing set of guidelines on
how to deal with each potential collision threat. These
guidelines, part of a larger body of decision-making
aids known as flight rules, specify when the expected
proximity of a piece of debris increases the probability
of a collision enough that evasive action or other
precautions to ensure the safety of the crew are needed.
NASA has a set of long-standing guidelines that are used
to assess whether the threat of such a close pass is
sufficient to warrant evasive action or other
precautions to ensure the safety of the crew. These
guidelines essentially draw an imaginary box, known as
the “pizza box" because of its flat, rectangular shape,
around the space vehicle. This box is about a mile deep
by 30 miles across by 30 miles long (1.5 x 50 x 50
kilometers), with the vehicle in the center. When
predictions indicate that the debris will pass close
enough for concern and the quality of the tracking data
is deemed sufficiently accurate, Mission Control centers
in Houston and Moscow work together to develop a prudent
course of action.
The United Nations is promoting transparency and
confidence building measures to remove suspicion about
motives for tracking and removal of debris. Such
measures could include General Assembly Resolutions,
Treaties, Codes of Conduct and Forums to share
information. Lessons
learned from the evolution and deployment of the world’s
air traffic control systems could also be applied to the
creation of a space traffic control environment using
transponders on spacecraft and mandatory reporting of
maneuvers in orbit. In the longer term, concepts are
being developed to remove rocket bodies and defunct
spacecraft using devices such as harpoons, grappling
mechanisms, and nets.
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