By the third millennium, mankind is actively studying and exploring space. The number of space flights is increasing and they are constantly running into a number of problems. One of these is a question of the increasing contamination of space with objects from our explorations. These objects are better known as space debris or simply said – space junk.
Space debris is man-made objects in Earth’s orbit or objects that reenter the atmosphere, including parts that have finished their active existence and are no longer useful. This widely accepted official definition was adopted by the Inter-Agency Space Debris Coordination Committee (IADC), an international governmental forum for the worldwide coordination of activities related to the issues of man-made and natural debris in space (Rossi, 2011).
According to A. Rossi (2011), since October 4, 1957, when the first satellite Sputnik-1 was launched by USSR, there have been more than 5000 launches with nearly 7000 payloads placed in orbit. Most of these spacecraft eventually reentered Earth’s atmosphere. Currently there are about 3500 satellites and probes orbiting the Earth together with about 1800 upper stages, i.e. parts of the rockets used to bring them to space. Of all these spacecraft only about 900 are operational and all of the rest are space debris. This population of satellites and rocket bodies’ account for about 99% of the debris orbiting the Earth are estimated to be around 5000 metric tons.
There are more than 20,000 pieces of debris larger than a softball orbiting the Earth. This debris can travel at speeds up to 17,500 mph. Even a relatively small piece of space debris can damage a satellite or a spacecraft at these speeds. Additionally, there are more than 500,000 pieces of debris the size of a marble or larger and many millions of pieces of debris that are so small they can’t be tracked (NASA, September 2013).
Spacecraft have to maneuver or change their position to prevent impacts with space debris. It is bringing the additional fuel consumption, and a number of other difficulties. According to the calculations the International Space Station (ISS) “MIR” will have to maneuver twice a year, avoiding the dangerous objects. For the first dozen years of its existence, the ISS averaged only one collision avoidance maneuver per year. However, in the past 12 months (April 2011 to April 2012), the ISS was forced to execute four collision avoidance maneuvers and would have conducted two additional maneuvers if the warnings had come sooner (NASA, 2012). The threat level at which an ISS collision maneuver is required when risk is greater than 1 in 10,000 (NASA, 2012).
Space debris contamination level of outer space is determined by four factors:
1. Time debris spent in orbit
2. Areas of its concentration
3. Orbital altitude
4. Orbital trajectory
Scientists have developed space debris mitigation mathematical models to give them a rough idea about the concentrations of space debris. These...