[Author's Note: This posts documents three cases of nuclear power supplies on spacecraft whose orbit decayed. At this time I don't have any hard information about the size of the nuclear power supplies, radioactivity levels or expert opinion on any environmental damage. --PB--]
Sometimes nuclear power is the only source of long-term power stable enough to drive spacecraft and/or their onboard experiments. That may seem to be funny thing to put at the top of a post about nuclear mishaps but the point I'm trying to make is that nuclear power supplies will likely be a growing reality in space. Space debris isn't an issue only spacers need to worry about. It has and can continue to have an impact down here on the surface.
On December 12, 1959, quickly following the 1957 launch of Sputnik, the United Nations (UN) General Assembly adopted Resolution 1472 (XVI) - International Co-operation in the Peaceful Uses of Outer Space beginning with the following laudable sentiments;
"The General Assembly,
Recognizing the common interest of mankind as a whole in furthering the peaceful use of outer space,
Believing that the exploration and use of outer space should be only for the betterment of mankind and to the benefit of States irrespective of the stage of their economic or scientific development,
Desiring to avoid the extension of present national rivalries into this new field,
Recognizing the great importance of international cooperation in the exploration and exploitation of outer space for peaceful purposes,
Noting the continuing programmes of scientific cooperation in the exploration of outer space being undertaken by the international scientific community,
Believing also that the United Nations should promote international co-operation in the peaceful uses of outer space,"This resolution calls for reports from the Committee for Peaceful Uses of Outer Space which is overseen by the United Nations Office for Outer Space Affairs (UNOOSA) which, along with other programs, maintains the Register of Objects Launched into Outer Space.
The register has a searchable index. Setting the search form to 'Uses Nuclear Power Source: Yes' and clicking the search button shows a list of the 62 objects shot into space with nuclear power sources aboard.
Adding 'Presently in Space: No' reduces the results to 11 objects, two of which are on Mars and six are listed as recovered . The remaining three suffered orbital decay, one of which burned up completely in Earth's atmosphere another burned partially spewing 'fragments' into the Pacific Ocean and a third sprayed radioactive debris across thousands of square miles of Canada.
The registration report dated May 23, 1997, describes, in dry, technocratic tones, the demise of Mars-96. The spacecraft, launched November 16, 1996 from the Baikonur launch site by a Proton carrier rocket on a mission to do a global study of the surface of the planet Mars and its internal structure and surrounding plasma, carried a Pu-238 RTG power supply.
"Transfer of the unmanned interplanetary station Mars-96 from artificial Earth satellite orbit to flight path to the planet Mars did not take place The Mars-96 station entered the dense layers of the atmosphere and broke up, with individual fragments falling into the water areas of the Pacific Ocean" [emphasis added]
"Potential radiation impacts from launch of the Ulysses solar exploration experiment were evaluated using eight postulated accident scenarios. Lifetime individual dose estimates rarely exceeded 1 mrem. Most of the potential health effects would come from inhalation exposures immediately after an accident, rather than from ingestion of contaminated food or water, or from inhalation of resuspended plutonium from contaminated ground. For local Florida accidents (that is, during the first minute after launch), an average source term accident was estimated to cause a total added cancer risk of up to 0.2 deaths. For accidents at later times after launch, a worldwide cancer risk of up to three cases was calculated (with a four in a million probability). Upper bound estimates were calculated to be about 10 times higher."
Cosmos 1402, another nuclear accident in the sky carrying a BOUK, described by the State Research Center of Russian Federation Institute of Physics and Power Engineering (IPPE) as "a small fast neutron reactor and remote thermoelectric generator based on semiconductors", launched Aug. 30, 1982. While the IPPE site says "more than 30 BOUK units were in operation on the board of the Cosmos spacecraft for a number of years" and there's nothing pointing to the reactor as the source of failure, Cosmos 1402 only lasted little more than 5 months.
Cosmos 954, launched Sept. 18, 1977 and also carrying a BOUK, crashed to the ground on Jan. 24, 1978 in northern Canada spreading radioactive debris over a wide swath of remote territory south and east of Great Slave Lake in Canada's Northwest Territories (Google map of approximate location).
In his report of December 22, 1978, the Permanent Representative of Canada notified UNOOSA that the search for the scattered remains of Cosmos 954 had ended. The details of the recovery of a number of parts emitting "man-made radiation" included;
- 6 beryllium cylinders approximately 10 cm. diameter x 25 cm. long
- 41 beryllium rods approximately 10 cm. long x 2.5 cm. [diameter]
- 1 piece of "sheath-like material"
- 18 small flakes, slivers and chunks
- 1 metallic cylinder approximately 51 cm. max length x 36 cm. diameter with a 2.5 mm. thick wall