OVERVIEW

The Meteoroid and Orbital Debris Working Group studies meteoroids and orbiting spacecraft debris that poses a hazard to spacecraft, threatens to penetrate habitats and fuel tanks, and cause failure to solar cells and electrical wires.

What are meteoroids and orbital debris?

Meteoroids are natural particles in orbit about the sun. Their size is considerably smaller than an asteroid and considerably larger than an atom or molecule.
Orbital debris is man-made material induced by spacecraft that can be as large as spent rocket motors and as small as the dust particles ejected from the nozzles of maneuvering thrusters. Currently, over 7000 large objects (>10 cm) are being tracked as orbital debris.  The graphic shows the number of catalogued space objects in orbit as of 27 September 1991.

Meteroids and Orbital Debris Sources?

Meteoroids are natural particles that are not individually tracked and catalogued. The vast majority of meteoroids are cometary in nature but some have asteroidal origin as well. Orbiting spacecraft debris is the remains from space missions. The worst particulate pollution for orbital debris occurs when a rocket or spacecraft accidentally explodes at high altitudes. The graphic shows the sources of catalogued debris population.

Meteoroids

Meteoroids are usually too small to be observed in space prior to impact with spacecraft. As a consequence, meteoroid encounters with spacecraft must be treated statistically. Near the Earth, impact speeds of particles with respect to spacecraft, average 20km/s, twenty times the speed of a high powered rifle. In interplanetary space, meteoroids are the only penetration hazard to spacecraft and must not be overlooked in design.

Orbital Debris

Orbiting debris is a man-made hazard caused by previous space missions. Spent satellites, accidental explosions, and collisions between orbiting bodies are contributing towards a rapid increase in this hazard. A serious problem with orbital debris is that it can occur in a size range that is large enough to destroy a spacecraft but is too small to be tracked from the ground. The average impact speed of debris on a spacecraft is 10 km/s, only half that of meteoroids, but the population of debris in the typical earth orbits is much higher than that of meteoroids, making debris the greater hazard for most spacecraft. Since the beginning of human activity in space, there has been a growing amount of matter left in orbit, requiring a commitment to maintaining an up-to-date means of evaluating and reducing the orbital debris hazard.

Spacecraft Effects

Meteoroids and orbital debris pose a serious damage and decompression threat to space vehicles. Any spacecraft can suffer catastrophic damage or decompression if it receives a hypervelocity impact from an object larger than a few grams. Collisions with smaller objects cause serious surface erosion with subsequent effects on the surface thermal, electrical and optical properties. If a system cannot be shielded, operational constraints or procedures may be imposed to reduce the threat of critical damage to the spacecraft. The illustration shows the effects of a meteoroid/orbital debris penetration of the high gain antenna dish aboard the Hubble Space Telescope.

Mitigation Strategies

Mitigation strategies include tracking debris and maneuvering to avoid it, making shields capable of absorbing the energy of expected impacts, and locating sensitive components on spacecraft where impacts are least likely to occur. On several STS missions, the Shuttle has had to plan and execute a maneuver to avoid a close encounter with orbital debris. Designers often use multi-sheet construction, with voids between the sheets, to increase the penetration resistance of a spacecraft shield system as seen in the illustration.
 

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