Space Debris

Complicating the use of near-Earth space is space debris. A half century has passed since Sputnik went up. Many nations now use space for civilian and military intelligence purposes. Not all material put into space comes down. For ISS, communications satellites, Earth-monitoring satellites, and space telescopes, space pollution is a present and growing danger. Space debris is associated with extremely high kinetic energies as it speeds around the planet. A collision with a piece of space debris only 1 cm in diameter can destroy a spacecraft in low-Earth orbit [26]. Even the smaller particulates can degrade spacecraft operations or seriously damage them. In geostationary orbit, the potential threat of debris is of a different nature as velocities among active spacecraft and debris tend to be lower, due to the relatively slow velocity of objects and the confined direction and orbital angle of working satellites, derelicts, and other forms of debris [27]. Nonetheless, the unique physical characteristics that make the geostationary orbit so desirable have resulted in high concentrations of satellites. Consequently, there is more debris located there and, thus, a greater chance of collision with valuable space satellites. Moreover, debris in low-Earth orbit, impacting the upper reaches of the atmosphere, may gradually disintegrate and disappear, but geosynchronous debris tends to remain a continual threat in the orbit area.

In 1989, ground trackers reported around 7500 spent rocket stages, dead satellites, screwdrivers and other man-made objects orbiting around the Earth [28]. Currently, The U.S. Satellite Catalog recorded that more than 9000 pieces of orbiting debris, larger than 10 cm in lower-Earth orbit and 1 m in geosynchronous orbit, are tracked by the U.S. Space Surveillance Network [29]. Moreover, the amount of debris keeps growing steadily larger, due both to increased space activities and the fact that each piece of debris involved in a collision can produce still more debris. Although NASA and other space agencies track debris large enough to be seen in telescopes, there is still much debris too small to track. A recent Science article warns that "[t]he current debris population in the [Low Earth Orbit] LEO region has reached the point where the environment is unstable" and "[a]n average of 18.2 collisions (10.8 catastrophic, 7.4 noncatas-trophic) would be expected in the next 200 years" [30].

In August 1996, a piece of suitcase-sized debris struck a French Ministry of Defense satellite, marking the first time that two objects previously catalogued by ground radar have collided [31]. In August 2000, two metal balls of fire, which were boosters from a Delta II rocket, fell over the western cape of South Africa [32]. Falling debris obviously presents different policy concerns from debris in orbit. Both are increasingly serious issues.

A variation of the debris issue pertains to "nuclear debris." For years, spacecraft sent to places in space, where solar or chemical propulsion have been inadequate, have used nuclear batteries called radioisotope thermoelectric generators (RTGs) for electricity needs. They use the power of radioactive decay from plutonium. There have been protests on the part of environmentalists and anti-nuclear groups about the launch of such spacecraft. A major protest took place in Florida when the Cassini Saturn probe was launched in 1997. More recently, the Pluto launch in 2006 was protested. Opponents worry that if the spacecraft exploded on launch or while near Earth, it would spread radioactive debris. No protest has yet stopped a launch. But there is well-justified wariness. U.S. launches require special precautions and international coordination in the event of a launch accident [33]. It was a matter of luck that when Columbia disintegrated in 2003, over East Texas and Louisiana, and rained debris, there were no human casualties on the ground.

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