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Upravlyaemy Sputnik Aktivnyy (russian: Управляемый Спутник Активный for Controlled Active Satellite), or US-A, also known in the west as Radar Ocean Reconnaissance Satellite or RORSAT ( GRAU index 17F16K), was a series of 33 Soviet
reconnaissance satellite A reconnaissance satellite or intelligence satellite (commonly, although unofficially, referred to as a spy satellite) is an Earth observation satellite or communications satellite deployed for military or intelligence applications. The ...
s. Launched between 1967 and 1988 to monitor NATO and merchant vessels using radar, the satellites were powered by nuclear reactors. Because a return signal from an ordinary target illuminated by a radar transmitter diminishes as the inverse of the fourth power of the distance, for the surveillance radar to work effectively, US-A satellites had to be placed in low Earth orbit. Had they used large solar panels for power, the orbit would have rapidly decayed due to drag through the upper atmosphere. Further, the satellite would have been useless in the shadow of Earth. Hence the majority of the satellites carried type BES-5 nuclear reactors fuelled by uranium-235. Normally the nuclear reactor cores were ejected into high orbit (a so-called "disposal orbit") at the end of the mission, but there were several failure incidents, some of which resulted in radioactive material re-entering the Earth's atmosphere. The US-A programme was responsible for orbiting a total of 33 nuclear reactors, 31 of them BES-5 types with a capacity of providing about two kilowatts of power for the radar unit. In addition, in 1987 the Soviets launched two larger TOPAZ nuclear reactors (six kilowatts) in Kosmos satellites ( Kosmos 1818 and Kosmos 1867) which were each capable of operating for six months. The higher-orbiting TOPAZ-containing satellites were the major source of orbital contamination for satellites that sensed gamma-rays for astronomical and security purposes, as radioisotope thermoelectric generators (RTGs) do not generate significant gamma radiation as compared with unshielded satellite fission reactors, and all of the BES-5-containing spacecraft orbited too low to cause positron pollution in the magnetosphere. The last US-A satellite was launched 14 March 1988.


Incidents

* Launch failure, 25 April 1973. Launch failed and the reactor fell into the Pacific Ocean north of Japan. Radiation was detected by US air sampling airplanes. *
Kosmos 367 The cosmos (, ) is another name for the Universe. Using the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos, and understandings of the reasons for its existence and significance, are studied in ...
(04564 / 1970-079A), 3 October 1970, failed 110 hours after launch, moved to higher orbit. *
Kosmos 954 Kosmos 954 (russian: Космос 954) was a reconnaissance satellite launched by the Soviet Union in 1977. A malfunction prevented safe separation of its onboard nuclear reactor; when the satellite reentered the Earth's atmosphere the follow ...
. The satellite failed to boost into a nuclear-safe storage orbit as planned. Nuclear materials re-entered the Earth's atmosphere on 24 January 1978 and left a trail of radioactive pollution over an estimated 124,000 square kilometres of Canada's
Northwest Territories The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...
. * Kosmos 1402. Failed to boost into storage orbit in late 1982. The reactor core was separated from the remainder of the spacecraft and was the last piece of the satellite to return to Earth, landing in the South Atlantic Ocean on 7 February 1983. *
Kosmos 1900 The cosmos (, ) is another name for the Universe. Using the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos, and understandings of the reasons for its existence and significance, are studied in ...
. The primary system failed to eject the reactor core into storage orbit, but the backup managed to push it into an orbit below its intended altitude.


Other concerns

Although most nuclear cores were successfully ejected into higher orbits, their orbits will still eventually decay. US-A satellites were a major source of
space debris Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict spacecr ...
in low Earth orbit. The debris is created two ways: *During 16 reactor core ejections, approximately 128 kg of
NaK In data networking, telecommunications, and computer buses, an acknowledgment (ACK) is a signal that is passed between communicating processes, computers, or devices to signify acknowledgment, or receipt of message, as part of a communicatio ...
-78 (a fusible alloy eutectic of 22% and 78% w/w sodium and potassium, respectively) escaped from the primary coolant systems of the BES-5 reactors. The smaller droplets have already decayed/reentered, but larger droplets (up to 5.5 cm in diameter) are still in orbit. Since the metal coolant was exposed to neutron radiation, it contains some radioactive argon-39, with a half-life of 269 years. There is no risk of surface contamination, as the droplets will burn up completely in the upper atmosphere on re-entry and the argon, a chemically inert gas, will dissipate. The major risk is impact with operational satellites. *An additional mechanism is through the impact of space debris hitting intact contained coolant loops. A number of these
old Old or OLD may refer to: Places *Old, Baranya, Hungary *Old, Northamptonshire, England *Old Street station, a railway and tube station in London (station code OLD) *OLD, IATA code for Old Town Municipal Airport and Seaplane Base, Old Town, Mai ...
satellites are punctured by orbiting space debris—calculated to be 8 percent over any 50-year period—and release their remaining NaK coolant into space. The coolant self-forms into frozen droplets of solid sodium-potassium of up to around several centimeters in size,C. Wiedemann et al, "Size distribution of NaK droplets for MASTER-2009", ''Proceedings of the 5th European Conference on Space Debris'', 30 March-2 April 2009, (ESA SP-672, July 2009). and these solid objects then become a significant source of space debris themselves.A. Rossi et al
"Effects of the RORSAT NaK Drops on the Long Term Evolution of the Space Debris Population"
University of Pisa, 1997.


See also

* SNAP-10A, an experimental nuclear reactor launched into orbit by the United States * Space-based radar *
List of Kosmos satellites This is a list of Kosmos (satellite), Kosmos satellites. Due to its size, the list has been split into groups of 250 satellites: * List of Kosmos satellites (1–250) * List of Kosmos satellites (251–500) * List of Kosmos satellites (501–750) ...


References

*


External links


Encyclopedia Astronautica article on the US-A RORSAT programme.


* * {{Cite news , url=http://www.space.com/6322-nuclear-powered-soviet-satellite-acts.html , title=Old Nuclear-Powered Soviet Satellite Acts Up , author=Leonard David , work=Space.com , date=15 January 2009 Reconnaissance satellites of the Soviet Union Space radars Nuclear power in space Nuclear technology in the Soviet Union