Natural objects and man-made junk

More than 500,000 pieces of debris, or “space junk,” are tracked as they orbit the Earth. They all travel at speeds up to 17,500 mph, fast enough for a relatively small piece of orbital debris to damage a satellite or a spacecraft.

The rising population of space debris increases the potential danger to all space vehicles, but especially to the International Space Station, space shuttles and other spacecraft with humans aboard.

NASA takes the threat of collisions with space debris seriously and has a long-standing set of guidelines on how to deal with each potential collision threat. These guidelines, part of a larger body of decision-making aids known as flight rules, specify when the expected proximity of a piece of debris increases the probability of a collision enough that evasive action or other precautions to ensure the safety of the crew are needed.

Orbital Debris:

Space debris encompasses both natural (meteoroid) and artificial (man-made) particles. Meteoroids are in orbit about the sun, while most artificial debris is in orbit about the Earth. Hence, the latter is more commonly referred to as orbital debris.

Orbital debris is any man-made object in orbit about the Earth which no longer serves a useful function. Such debris includes nonfunctional spacecraft, abandoned launch vehicle stages, mission-related debris and fragmentation debris. There are more than 20,000 pieces of debris larger than a softball orbiting the Earth. They travel at speeds up to 17,500 mph, fast enough for a relatively small piece of orbital debris to damage a satellite or a spacecraft. There are 500,000 pieces of debris the size of a marble or larger. There are many millions of pieces of debris that are so small they can’t be tracked.

Even tiny paint flecks can damage a spacecraft when traveling at these velocities. In fact a number of space shuttle windows have been replaced because of damage caused by material that was analyzed and shown to be paint flecks.

Tracking Debris:

The Department of Defense maintains a highly accurate satellite catalogue on objects in Earth orbit that are larger than a softball. NASA and the DoD cooperate and share responsibilities for characterizing the satellite (including orbital debris) environment. DoD’s Space Surveillance Network tracks discrete objects as small as 2 inches (5 centimetres) in diameter in low Earth orbit and about 1 yard (1 meter) in geosynchronous orbit. Currently, about 15,000 officially catalogued objects are still in orbit. The total number of tracked objects exceeds 21,000. Using special ground-based sensors and inspections of returned satellite surfaces, NASA statistically determines the extent of the population for objects less than 4 inches (10 centimetres) in diameter.

Collision risks are divided into three categories depending upon size of threat. For objects 4 inches (10 centimetres) and larger, conjunction assessments and collision avoidance manoeuvres are effective in countering objects which can be tracked by the Space Surveillance Network. Objects smaller than this usually are too small to track and too large to shield against. Debris shields can be effective in withstanding impacts of particles smaller than half an inch (1 centimetre).

Facts about Debris:

  • More than 35,000 orbital debris larger than 10 cm (4 inches) are known to exist in our orbit. The rough number of space debris that float around the Earth is estimated at 500,000 elements that range between 1 and 10 cm in diameter, and over 100 million other debris less than 1cm. Pretty crowded!
  • Large debris over 10cm are monitored by the U.S. Space Surveillance Network, whilst the smaller particles can be detected by ground-based radars. Other space debris that are smaller than 1cm are calculated by examining impact features on the surfaces of returned spacecraft.
  • According to the European Space Agency (ESA) the number of collision alerts (satellites vs debris) has doubled in the past decade to 1,200 per year. The study suggests that this number will quadruple over the next 5 years – if we don’t find a solution.
  • Fengyun-FY-1C is a Chinese weather satellite launched into our orbit in 2007 that was later destroyed deliberately to test the anti-satellite weapon. It contributed to over 2,000 pieces of junk bigger than 10cm, and around 35,000 of particles more than 1cm across.
  • Most space junk can be found within 2,000 km (1200 miles) of the Earth’s surface, but the highest concentration of waste is found 750 to 800 km above our heads. The vast majority of space debris travel at the speed of 7 to 10 km per second (4 to 10 miles per second).
  • The International Space Station (ISS) is required between 1 to 3 times per year on average to manoeuvre away from a collision course with debris – or if the chance of a possible impact exceeds 1 in 10,000. The U.S. Space Surveillance Network spends nearly $400,000 per year on tracking debris that could harm ISS despite the fact that the Station is the most heavily shielded spacecraft ever flown.
  • The junk left in orbits below 600 km (370 miles) will normally fall back to Earth within several years, however debris above 1,000 km (600 miles) will continue to orbit us for centuries.
  • Tsinghua University scientists in Beijing, China are working on a spacecraft that will turn orbital waste into fuel, just like we have witnessed DeLorean DMC-12 in the “Back To The Future” series. The plan is to turn debris into a plasma of positive ions and electrons by heating it to high temperatures
  • The biggest orbital piece of junk made by humans is the American Vanguard I that was launched into Earth’s orbit in 1958. It’s also the oldest surviving man-made space debris still in orbit.
  • There are almost 10,000 operational satellites in the orbit, 19,000 shuttle-like known large objects (in terms of size), and more than 30,000 spacecraft launched by humans.

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