With all the hubbub going around about the latest belly up satellite doing a re-entry into places unknown, a small piece of space junk esoterica for your entertainment.
The low Earth orbit, located 2,000 km above the Earth's surface, has the highest concentration of space debris.Quote:
A decommissioned satellite the size of a bus re-entered the Earth’s atmosphere over the Pacific Ocean on Sept. 23-24, NASA announced.
While most of the Upper Atmosphere Research Satellite (UARS) likely burned up upon re-entry, NASA was concerned that 26 potentially hazardous sections — including four titanium fuel tanks and a heavy aluminium structure — could strike Earth at speeds of between 90 and 385 kilometres an hour.
The satellite is one of the more prominent examples of space junk, the common term for human debris that orbits the Earth and can mean anything from the remains of old booster rockets to the tool bag that drifted free from an astronaut outside the International Space Station (ISS) in November 2008.
Most orbital debris is located within 2,000 kilometres of the Earth's surface and while they range from very small to very large, they can also travel at very high speeds — up to 28,800 km/h — where even the smallest objects can pose a threat to satellites and manned craft.
According to the NASA Orbital Debris Program Office, the ISS had to execute a "collision avoidance manoeuvre" in April 2011 to avoid a piece of orbital debris — the fifth time it’s had to do so in two and a half years.
Space junk emphasizes one of the truisms of life on Earth, as well as in space: what goes up must inevitably come down.
Because satellites and supply craft are not built to withstand the intense heat of re-entry into the Earth's atmosphere, these craft are typically sacrificed as space junk once they've outlived their usefulness.
In order to dispose of them, engineers manipulate their propulsion systems to push them through the atmosphere, where much of the structure is burned, and to steer them into unpopulated areas like deserts or oceans.
The Russian space station Mir, which was launched into orbit in 1986, was decommissioned in 2001. After a three-stage de-orbiting process that incinerated much of the structure upon re-entry, the remains of Mir crashed into the South Pacific Ocean on March 23, 2001.
The International Space Station is headed for a similar fate. Launched in 1998, it is scheduled to be de-orbited in 2020.
The 417,000-kilogram spacecraft loses approximately 100 feet in altitude every day, which is why several times a year it requires a boost back up above 350 kilometres. This is accomplished using an unmanned resupply craft and about 1,400 kilograms of propellant.
Here's a by-the-numbers look at the whirring, perilous state of space junk circling our planet.
500,000 — the number of debris objects measuring between one and 10 centimetres, according to NASA's Orbital Debris Program Office.
19,000 — the number of debris objects larger than 10 cm.
27,000 km/h — the average speed of most orbital debris in low Earth orbit (below 2,000 km).
36,000 km/h — the average impact speed of orbital debris with another space object, according to NASA.
900 — the number of pieces of debris created when China destroyed its Fengyun 1-C satellite in January 2007.
600 — the number of pieces of debris estimated to have been released into space in the collision between the American Iridium 33 satellite and a Russian Kosmos 2251 military satellite in February 2009.
42,120 km/h — the speed at which Iridium 33 and Kosmos 2251 collided. (A pea-sized piece of debris measuring one-centimetre and travelling at 10 km/second has the same kinetic energy as a 250-kilogram dumpster whirring along at 100 km/hour, according to NASA.)
250 kilograms — size of a propellant tank from a launch vehicle that landed near Georgetown, Tx, in 1997.
100 years — the approximate amount of time that space debris that is more than 1,000 kilometres above the Earth's surface will continue to orbit the Earth before re-entering the atmosphere. Debris travelling in orbits below 600 kilometres falls to Earth after several years. At altitudes below 400 kilometres, the debris is likely to fall to Earth before it has even been detected or identified.
36,000 kilometres — the altitude at which most telecommunications and meteorological spacecraft rest.
30 km/h — the estimated impact velocity of a light piece of debris falling to Earth. The velocity for larger objects is 300 km/hr, according to the Center for Orbital and Re-entry Debris Studies.
$100,000 — the value of a tool bag lost during a spacewalk in November 2008 by U.S. astronaut Heidemarie Stefanyshyn-Piper as she attempted to mop up grease that spilled out of a grease gun.
One piece a day — the average rate at which orbital debris has fallen to Earth during the past 40 years.
One in one trillion — the odds that a person will be struck and injured by a piece of space debris, according to the Center for Orbital and Re-entry Debris Studies.
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