Every spacecraft in space is exposed to a flux of microparticles. Collisions with these particles will typically take place with hypervelocity speed and may cause disturbances to the spacecraft.
Meteoroids are particles of natural origin. Nearly all meteoroids originate from asteroids or comets. The natural meteoroid flux represents, at any instant, a total of about 200 kg of mass within 2000 km of the Earth’s surface [RD 43]. Meteoroids that retain the orbit of their parent body can create periods of high flux and are called streams. Random fluxes with no apparent pattern are called sporadic.
Space debris is a population of man-made microparticles which reside orbiting Earth. The mission will only be exposed to this environment during launch and early transfer phases. Therefore, the impact of space debris on the mission will be neglected. More than 90% of these objects are space debris, i.e., man-made objects that do not serve any useful purpose. The number of space debris objects larger than 1 cm is estimated to be of the order of 500000 to 700000 (2007). Smaller particles are far more abundant still. Space debris is mainly concentrated in LEO (below 2000km) and in GEO.
The damage caused by collisions with meteoroids will depend on the size, density, speed and direction of the impacting particle and on the shielding provided by the spacecraft to sensitive elements. Submillimeter sized particles can cause pitting and cratering of outer surfaces and lead to degradation of optical, electrical, thermal, sealing or other properties. Larger particles can puncture outer surfaces and may cause damage to structure or equipment by penetration and spallation.
Flux models have been developed for both micrometeoroids and space debris. The resulting damage can be assessed through empirically derived design equations which give penetration capabilities, crater sizes, etc. as function of the particle parameters and target properties.