Designing for the Space Environment

Addressing the space debris/micro-meteoroid impact threat

Most human activities are at risk from unexpected impact damage. Tools and materials are dropped at construction sites and industrial plants. Cruise ships hit icebergs. Airplanes are hit by birds and hail. Cars hit deer trying to cross the road. Occasionally, these events result in injury or death. Man-made space debris and natural micro-meteoroids pose similar safety risks in space.

Man-made space debris is anything placed into orbit that is not operational. Dead satellites, expended rocket boosters, lost tools, broken equipment, waste products, or fragments of satellites and boosters comprise space debris. Micro-meteoroids are natural space debris comprised of small pieces of asteroids or comets. Micro-meteoroids are generally in orbit about the sun, not in orbit about the Earth.

The size of the debris/micro-meteoroids particles is an important consideration.  The probability of debris/micro-meteoroid impact increases as the particle size decreases.  When the probability of impact becomes significant, measures to mitigate the threat must be implemented.

Both debris and micro-meteoroids can impact with extremely high relative velocities. If the debris is orbiting in the opposite direction, then the relative velocity at impact may be as high as 50,000 feet per second. This is many times faster than high-powered rifle bullets. Even small sand grain-size particles have been known to cause local surface damage and penetrate thinner metal covers. To counter this threat, stand-off sacrificial bumpers are used. The high kinetic energy of the debris/micro-meteoroid causes it to vaporize when the bumper is hit and penetrated. This vaporization protects the primary structure from significant damage.

Larger size debris will penetrate both the bumper and the primary structure. Recognizing this danger, the U.S. Government surveys space to locate and catalog space debris larger than about 1 cm across so that impact avoidance measures can be undertaken. For example, if the projections of the orbital path of the debris will bring it within several miles of the Space Shuttle, International Space Station, or satellites, these will be moved to ensure that impact is avoided.

Most nations are now incorporating space debris prevention or mitigation methods.  Building an integrated spacefaring logistics infrastructure will enhance such reductions in debris by substantially less use of expendable components and by providing the means to remove dead satellites from orbit. While protection against micro-meteoroids will always remain an important design consideration, the natural atmospheric drag “cleansing” of lower Earth orbits of man-made debris, combined with a reduction in the creation of new debris, should substantially reduce the safety threat posed by space debris.

One issue that does remain is the threat posed by the intentional destruction of satellites producing debris or the release of damaging debris. In the Law of the Sea, such acts are considered to be hostile and warrant reactive and proactive countermeasures.

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