(June 10, 2005) We humans seems happy to foul our own nest with utter disregard for the consequences and as the nest expands, so too the filth. Since 1957, more than 4000 space launches have led to the current population of approximately 13000 trackable objects (i.e. larger than 10 cm) in near-Earth space. This junk pile includes a lot of radioactive material.
(629.5699) WISE-Amsterdam - Of these 13000 trackable objects, only about 600-700 are operational spacecraft; the remainder is space debris, objects that no longer serve any useful purpose. About half of the trackable objects are fragments from explosions, or from the breakup of satellites or rocket bodies. There are a much greater number of objects in orbit that cannot be tracked because of their small size and additionally hundreds of thousands, perhaps millions, of pieces of space litter too small to be seen - ranging from nuts and bolts to paint chips. They may be small, but with closing speeds of up to 12 miles per second, they pack tremendous energy. In 1999, the space shuttle Discovery landed showing evidence of 64 impacts, at least 10 caused by manmade debris. So far, nothing bigger than 0.08 of an inch (2 millimeters) has struck a shuttle. But even such tiny particles can damage thermal tiles and windows.
According to a recent report to the Fourth European Conference on Space Debris, held in April in Darmstad (Germany), the junk pile includes about a ton of radioactive fuel from defunct reactors launched into orbit between 1967 and 1988.
The last satellite containing a nuclear power source and intended for Earth orbit was launched in 1988. However a renewed interest in radioisotopes power systems (RPSs) and nuclear propulsion could lead to new nuclear power sources in orbit around the Earth later on in this decade or the next. Today, at least eight radioisotope thermoelectric generators (which use the heat from decaying radioisotope to produce electricity), 13 nuclear reactor fuel cores and 32 nuclear reactors (one from the US and 31 from the former Soviet Union) are known to be still circling the Earth in orbits below 1700 km. So, in total about one ton of nuclear fuel is orbiting the Earth.
The United States has launched 22 missions with nuclear power sources. Three accidents have occurred, one resulting in release of radioactive materials. The U.S. launched one experimental space reactor, in 1965. It is now in a 3,000-year orbit.
The Soviet RORSAT program (a spacecraft equipped with a nuclear-powered radar) began sporadic operations in 1967. The program ceased flight operations in 1988 after five serious mishaps in 33 missions, including two nuclear reactors falling back to Earth from orbit and two launch failures. The nuclear reactor and high altitude storage system (needed to maneuver the reactor from its operational orbit of 250 km to a long-lived disposal orbit of 900-1,000 km) accounted for 1,250 kg and slightly more than half (5.8 m) the length of the spacecraft. The fuel assembly consisted of 37 cylindrical fuel elements with 31.1 kg (beginning of life) of 90% enriched uranium.
Following the re-entry of Kosmos 954 over Canada in 1978, the RORSAT reactor underwent several modifications, including the ability to eject the fuel assembly at the end of life, hopefully in the disposal orbit but prior to re-entry in the event of accident, as with Kosmos 1402 in 1983. Between 1980 and 1988, at least 14 RORSATs performed fuel assembly ejection in higher altitude storage orbits. However, not until 1994 did terrestrial-based space surveillance sensors detect what may be large numbers of very small particles of radioactive debris. There is evidence that 16 out of 31 RORSAT reactors lost radioactive reactor coolant, released when the fuel assembly was ejected.
To prevent radioactive material re-entering the Earth's atmosphere and endangering human health, most of the nuclear satellites were retired into orbits of between 700 and 1500 kilometers above the Earth, where they, in theory, will remain for hundreds of years as their radioactivity decays. But over this long period they will inevitably collide with other objects and produce further debris. Eventually these bits will fall into Earth atmosphere.
Today the U.S. uses plutonium-238 on board deep space missions for a power-generating source (RTG). But it also now plans to build nuclear reactors to power rocket engines. In August last year NASA and DOE signed a Memorandum of Understanding "that will lead to the development, design, delivery and operational support of civilian space nuclear reactors within NASA's Project Prometheus". The partnership is responsible for the development of the first NASA spacecraft: the Jupiter Icy Moons Orbiter (JIMO). However, according to an article in the Aviation Week & Space Technology, NASA may try to demonstrate a space-rated nuclear reactor on the Moon first, instead of a mission to the moons of Jupiter. DOE's naval reactor office, which will develop the space reactor, may choose for a lunar demonstration because that is a quicker way to 'prove the basic technology'. The budget allocated for the project Prometheus in fiscal year (FY) 2005 is $431.7 million, and in FY 2006, $319.6 million.
The Global Network Against Weapons and Nuclear Power in Space is again organizing the international Keep Space for Peace international week of protest against the militarization of space running from October 1-8.
Past nuclear space accidents
Sources: ESA's Announcement Fourth European Conference on Space Debris, April Darmstad;
FAS Space Policy Project web site; New Scientist, 23 April 2005; Baltimore Sun, 20 May 2005; The Aviation Week & Space Technology, 13 December 2004: Press release NASA, 7 August 2004; The Orbital Debris (NASA), April 2005