RORSAT
Radar Ocean Reconnaissance SATellite or RORSAT is the western name given to the Soviet Upravlyaemyj Sputnik Aktivnyj (Управляемый Спутник Активный) (US-A) satellites, notorious for the use of nuclear reactors in orbital space. These satellites were launched between 1967 and 1988 to monitor NATO and merchant vessels using active radar. RORSATs were launched under the cover name of Cosmos (Kosmos) satellites.
Because a return signal from a target illuminated by a radar transmitter diminishes as the inverse of the fourth power of the distance, for the surveillance radar to work effectively, RORSATs 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 RORSATs 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 Soviet RORSAT program 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 6 months of operation.[1] The high orbiting TOPAZ-containing satellites were the major source of orbital contamination for satellites that sensed gamma-rays for astronomical and security purposes, as radiothermal generators (RTGs) do not generate significant gamma radiation as compared with unshielded satellite fission reactors, and all of the BES-5-containing RORSATs orbited too low to cause positron-pollution in the magnetosphere.[2] (The U.S. has launched only a single nuclear reactor into orbit-- the SNAP-10A mission in 1965).
The last RORSAT was launched 14 March, 1988. The many problems with the program as well as economic problems in the USSR, apparently caused it to be cancelled by Mikhail Gorbachev.
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[edit] Notable incidents
- RORSAT launch failure, April 25, 1973. Launch failed and the reactor fell into the Pacific Ocean north of Japan. Radiation was detected by U.S. air sampling airplanes.
- Cosmos 367 (04564 / 1970-079A), 3 October 1970, failed 110 hours after start, moved to higher orbit.
- Cosmos 954. The satellite failed to boost into a nuclear-safe storage orbit as planned. Nuclear materials re-entered the Earth's atmosphere on January 24, 1978 and left a trail of radioactive pollution over an estimated 124,000 km² of Canada's Northwest Territories.
- Cosmos 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 February 7, 1983.
- Cosmos 1900. The primary system failed to eject the reactor core into storage orbit, but the backup managed to push it into an orbit 80 km (50 mi) below its intended altitude.
[edit] Other concerns
Although most nuclear cores were successfully ejected into high orbits, their orbits will still decay after several hundred years.[citation needed]
RORSATs were a major source of space debris in low Earth orbit. During 16 reactor core ejections, approximately 128 kg of NaK-78 (a fusible alloy eutectic of 22 and 78 % w/w sodium and potassium respectively) escaped from the primary coolant systems of the BUK 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,[citation needed] with a half-life of 269 years. The risk of surface contamination is low, 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.
[edit] Non-Soviet equivalents
[edit] American radar satellites
The United States National Reconnaissance Office operates a series of terrain-mapping radar satellites known as Lacrosse. These do not have a maritime capability, but the U.S. Air Force and Space Command are developing a satellite constellation known as Space-Based Radar (or SBR). SBR will fulfill the maritime function of RORSATs, as well as have the ability to track aircraft and potentially ground-based vehicles.
[edit] German radar satellites
Germany currently is developing the SAR Lupe radar satellite program, which consists of five identical satellites. Three satellites were launched between December 2006 and November 2007. Others followed in 2008.
[edit] Israeli radar satellites
Israel launched TecSar, a synthetic aperture radar satellite, in 2008 using an Indian rocket. This is the first small and lightweight radar satellite in operation.
[edit] See also
- SNAP-10A, an experimental nuclear reactor launched into orbit by the United States
[edit] References
- Wiedemann, C., Oswald, M., Stabroth, S., Klinkrad, H., Vörsmann, P., Size distribution of NaK droplets released during RORSAT reactor core ejection, Advances in Space Research, Vol. 35, 2005, pp. 1290–1295.
- Wiedemann, C., Oswald, M., Stabroth, S., Klinkrad, H., Vörsmann, P., Modeling of RORSAT NaK Droplets for the MASTER 2005 Upgrade, Acta Astronautica, Vol. 57, 2005, pp. 478–489.
