Space Debris Dangers
The fact that a small paint chip can already be a problem is due to the enormous velocities: in low orbit, the speed is about 8 km/s, and the relative velocity on impact can be even greater. An artificial moon can be damaged by a collision with a small object. Space walks are also dangerous as a result. Solar panels of satellites are becoming larger and larger due to the increasing demand for energy, and the chance of such a panel being damaged by space debris is also increasing.
American Donald J. Kessler argued that an object can be smashed into pieces by a collision, further increasing the amount of space debris.
Most space debris is in low Earth orbit. There is still very little air resistance there, so all objects gradually lose speed and fall toward the earth. A small object usually burns up on re-entry into the atmosphere because of its speed and friction with the air. In the case of large satellites and space stations, a piece may still end up on Earth.
Clouds of very small particles are not as harmful, but can cause erosion, similar to sandblasting.
Space Debris Risks
The relative velocity between space debris and a near-Earth satellite with a high orbital inclination is, on the order of magnitude, ten kilometres per second. Due to the high velocity, a particle with a mass of 1 g has an energy of 50 kJ, which corresponds to the explosive force of about 12 g TNT, so that both the particle and the material directly hit explode.
The manned modules of the International Space Station (ISS) are equipped with double-walled meteoroid shields (Whipple shield) and can withstand impacts of space debris several centimetres in diameter due to the scattering effect created by the impact in the first wall.
Already now, on some orbits, the probability of failure of operational satellites caused by impacts of space debris is no longer negligible. Even impacts of smaller particles down to the submillimetre range can damage sensitive payloads or perforate space suits.
In 2007, the People's Republic of China deliberately launched its Fengyun-1C weather satellite from the ground to demonstrate its anti-satellite missile capability. However, this resulted in a cloud of at least 40,000 pieces of debris in space. The largest accidental collision in space to date was the satellite collision on 10 February 2009. A disabled Russian communications satellite and an Iridium satellite collided at an altitude of 789 km over northern Siberia. Both satellites were destroyed. The collision released a significant amount of further space debris.
The collision rate of objects of the order of 10 cm with one of the many satellites is estimated to be one event every 10 years.
The manned International Space Station, but also many of the satellites, are able to perform evasive manoeuvres to avoid a collision (probability p = 1/10,000) with one of the approximately 13,000 objects whose orbits are continuously tracked, which is considered not improbable. Already in 2004, the Earth observation satellite Envisat carried out two such manoeuvres. Space shuttles such as Discovery had to fly a total of six avoidance manoeuvres. By 2009, the ISS had successfully performed eight evasive manoeuvres.
The Kessler syndrome is the scenario in which the density of objects in low-Earth orbit is high enough that collisions between objects can cause a chain reaction in which each collision produces space debris that increases the likelihood of further collisions. The scenario was described in 1978 by NASA scientist Donald J. Kessler. He stated that space travel and the use of satellites in certain orbits would become more risky in the future.
The Kessler syndrome, or Kessler effect, is the cascading increase in the number of small space debris objects due to random collisions. This scenario is named after Donald J. Kessler. As an astronomer, he had statistically modelled fragmentation processes in the asteroid belt and, as a NASA employee, transferred this to objects near Earth. In 1978, he warned that space travel would become more risky for future generations.
Collisions between small objects are very unlikely because they usually miss each other. Collisions between the comparatively few large objects are also unlikely (and avoidable, but see the satellite collision on 10 February 2009). The number of small objects thus increases mainly due to collisions with large objects. Here, the explosive force from the kinetic energy of the impactor can fragment the larger object.
Kessler recommended moving away as soon as possible from the then common practice of leaving large objects such as payload fairings, burnt-out upper stages and retired satellites in orbit. This would slow down the dangerous development, but not prevent it.
Kessler Syndrome In Fiction
The Kessler Syndrome plays a role in Ken MacLeod's novel The Sky Road, Peter F. Hamilton's novel Fallen Dragon, the film Gravity and the anime Planetes. It is a negative anomaly on colonisable planets in the 4X strategy game Endless Space.
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