RORSAT
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Radar-equipped Ocean Reconnaissance SATellite or RORSAT is the western name given to the Soviet Upravlenniye Sputnik-Aktivny (US-A) satellites. These satellites were launched between 1967 and 1988 to monitor NATO and merchant vessels using active radar. RORSATs were launched under cover name of Cosmos satellites.
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. 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 incidents, some of which resulted in radioactive material re-entering the Earth's atmosphere.
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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 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 80km (50 miles) below its intended altitude.
[edit] Other concerns
Although a majority of the nuclear cores were successfully ejected into high orbits, these orbits still decay. If left untouched, the highly radioactive cores will return to the Earth's atmosphere after several hundred years.
RORSATs have also been identified as a major contributor to the space debris environment in the LEO region. During 16 reactor core ejections, approximately 128 kg of the NaK-78 (an eutectic alloy of 22 and 78 % w/w sodium and potassium respectively) from the primary coolant system of the BUK reactor have been released. While the smaller debris particles resulting from these events have already decayed, larger particles (up to 5.5 cm in diameter) are still in orbit. Since the metal coolant was irradiated with neutrons from the nuclear reactor it will contain quantities of the radioactive argon-39, which has a half-life of 269 years. However, this is a minor concern, as the droplets will burn up completely in the upper atmosphere once they reenter. The major concern is the risk of an impact into an operational satellite. At a typical impact velocity of 10 km/s, a 1 cm NaK droplet would have the destructive power of an exploding hand grenade.
[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. SBR would operate in conjunction with the Air Force's E-10 MC2A aircraft.
[edit] External links
[edit] Journal Articles
- 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.da:Atomreaktorer i rummet
