The meteoroid (or natural debris environment) has historically been a consideration for spacecraft design. Meteoroids are part of the interplanetary environment and sweep through near Earth orbital space at an average speed of 20 km/s. Observational data indicate that, at any given instant, a total of 200 kg of meteoroid mass is within 2000 km of the Earth's surface. Most of this mass is in meteoroids about 0.01 cm (100 micrometres) in diameter. This natural meteoroid flux is rather stable in the long term but sometimes there is high activity from a shower e.g. the Persied or Leonid populations. The meteoroid environment is well described by current models (Grün, Divine-Staubach).
Man-made space debris (or orbital debris) differs from natural meteoroids because it remains in earth orbit during its lifetime instead of passing through the space around the earth. The estimated mass of man-made orbiting objects within 2000 km of the earth's surface is about 3000000 kg. These objects are in mostly high inclination orbits and pass one another at an average relative velocity of 10 km/s. Most of this mass is contained in about 4000 spent rocket stages, inactive satellites and a comparatively few active satellite. A smaller amount of mass, about 60000 kg, is in the remaining 9000 objects currently being tracked by space surveillance sensors. Information about the current debris environment is obtained through several detecting devices, either located on the Earth's surface or space-borne sensors. Information about the current debris environment is limited by the inability to track and catalogue objects smaller than a few cm.
Space Debris Sources
|Source description||Size Range||Data Sources||Complications in Modeling||Source Database|
|Launched Objects||From nearly 4000 launches||several 10s of square metres and 1000 kg mass||UN catalog of launches, compendia of engineering data, catalog from US and Russian networks||Incomplete catalog (accurate mass, shape, EOL.) Prediction of future traffic||NASA reference database for historical space traffic|
|Fragmentation Events||Explosions, collisions, more than 150 events||Several sq metres to millimetres100 kg - mg||Observation of orbiting objects, ground tests||Validation of fragmentation models, shape information , total mass involved||Reference database for historical fragmentations provided by NASA and ESA|
|Degradation products||AO erosion, UV degradation Thermal cycling||1 cm - 5 µm||Retrieved hardware, simulation||Size distribution,yield rate of paint flakes from thermal cycling||DERA, ONERA, MASTER|
|West Ford needles||Released in 1963 by Midas 4 & 6 S/C||20 µm x 20 mm needles||US Catalog, X band Goldstone data||needles dispersion of particles||US Catalog, DISCOS database|
|Ejecta||Primary impacts on solar arrays and satellites or rockets||1 mm - 0.1 µm||Retrieved hardware, simulation||Velocity distribution||Ejecta models, ONERA, MASTER|
|Solid Rocket Motors||Aluminum oxide particles, by-product of combustion process||micron-sized particles and,by-products 100 µm to 5 cm||Motor manufacturer, few test-firings||Few experimental data, mainly for by-products, ej. velocity||NASA model|
|NaK Droplets||Leak from 16 RORSAT satellites, produced upon of release of coolant from nuclear reactors||0.1 to 10 mm||Analysis of Haystack radar data, Goldstone data||Core ejection procedure, temperature, evaporation process, min. size, ejection velocity||MASTER Model developed for ESA|
Some data pertinent to space debris are summarised in the Table 1.