# US-A

Upravlyaemy Sputnik Aktivnyy (Russian: Управляемый Спутник Активный for Controlled Active Satellite), or US-A, also known in the Western world as Radar Ocean Reconnaissance Satellite or RORSAT (GRAU index 17F16K), was a series of 33 Soviet reconnaissance satellites. 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 (04564 / 1970-079A), 3 October 1970, failed 110 hours after launch, moved to higher orbit.$^{:10}$
* Kosmos 954. 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.
* 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 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.$^{:56,58}$

## 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 in low Earth orbit. The debris is created two ways:
* 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 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 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, and these solid objects then become a significant source of space debris themselves.

## List of US-A satellites

There were 38 Rorsat satellite launches from Baikonur, all with reported mass of 3,800 kg.
Rorsat satellite launches :
| Launch Date | Satellite Name | Launch Vehicle | Perigee (km) | Apogee (km) | Inclination (deg) | Period (min) |
| 1968 March 22 | Cosmos 209 | Tsyklon | 876 | 927 | 65.30 | 103.00 |
| 1969 January 25 | US-A Mass Model | Tsyklon | - | 100 | - | - |
| 1970 October 3 | Cosmos 367 | Tsyklon 2 | 915 | 1,022 | 65.30 | 104.50 |
| 1971 April 1 | Cosmos 402 | Tsyklon 2 | 965 | 1,011 | 65.00 | 104.90 |
| 1971 December 25 | Cosmos 469 | Tsyklon 2 | 948 | 1,006 | 64.50 | 104.60 |
| 1972 August 21 | Cosmos 516 | Tsyklon 2 | 906 | 1,038 | 64.80 | 104.50 |
| 1973 April 25 | failure | Tsyklon 2 | - | - | - | - |
| 1973 December 27 | Cosmos 626 | Tsyklon 2 | 907 | 982 | 65.40 | 103.90 |
| 1974 May 15 | Cosmos 651 | Tsyklon 2 | 890 | 946 | 65.00 | 103.40 |
| 1974 May 17 | Cosmos 654 | Tsyklon 2 | 924 | 1,006 | 64.90 | 104.40 |
| 1975 April 2 | Cosmos 723 | Tsyklon 2 | 899 | 961 | 64.70 | 103.60 |
| 1975 April 7 | Cosmos 724 | Tsyklon 2 | 852 | 943 | 65.60 | 102.90 |
| 1975 December 12 | Cosmos 785 | Tsyklon 2 | 907 | 1,004 | 65.10 | 104.20 |
| 1976 October 17 | Cosmos 860 | Tsyklon 2 | 923 | 995 | 64.70 | 104.30 |
| 1976 October 21 | Cosmos 861 | Tsyklon 2 | 928 | 987 | 64.90 | 104.20 |
| 1977 September 16 | Cosmos 952 | Tsyklon 2 | 911 | 990 | 64.90 | 104.10 |
| 1977 September 18 | Cosmos 954 | Tsyklon 2 | 251 | 265 | 65.00 | 89.70 |
| 1980 April 29 | Cosmos 1176 | Tsyklon 2 | 873 | 962 | 64.80 | 103.40 |
| 1981 April 21 | Cosmos 1266 | Tsyklon 2 | 911 | 941 | 64.80 | 103.60 |
| 1981 August 24 | Cosmos 1299 | Tsyklon 2 | 926 | 962 | 65.10 | 103.90 |
| 1981 March 5 | Cosmos 1249 | Tsyklon 2 | 904 | 976 | 65.00 | 103.90 |
| 1982 August 30 | Cosmos 1402 | Tsyklon 2 | 250 | 266 | 65.00 | 89.60 |
| 1982 June 1 | Cosmos 1372 | Tsyklon 2 | 919 | 966 | 64.90 | 103.90 |
| 1982 May 14 | Cosmos 1365 | Tsyklon 2 | 881 | 979 | 65.10 | 103.60 |
| 1982 October 2 | Cosmos 1412 | Tsyklon 2 | 886 | 998 | 64.80 | 103.90 |
| 1984 June 29 | Cosmos 1579 | Tsyklon 2 | 914 | 970 | 65.10 | 103.90 |
| 1984 October 31 | Cosmos 1607 | Tsyklon 2 | 908 | 994 | 65.00 | 104.10 |
| 1985 August 1 | Cosmos 1670 | Tsyklon 2 | 893 | 1,007 | 64.90 | 104.10 |
| 1985 August 23 | Cosmos 1677 | Tsyklon 2 | 880 | 1,001 | 64.70 | 103.90 |
| 1986 August 20 | Cosmos 1771 | Tsyklon 2 | 909 | 1,000 | 65.00 | 104.20 |
| 1986 March 21 | Cosmos 1736 | Tsyklon 2 | 936 | 995 | 65.00 | 104.40 |
| 1987 December 12 | Cosmos 1900 | Tsyklon 2 | 696 | 735 | 66.10 | 99.10 |
| 1987 June 18 | Cosmos 1860 | Tsyklon 2 | 900 | 992 | 65.00 | 104.00 |
| 1988 March 14 | Cosmos 1932 | Tsyklon 2 | 920 | 1,008 | 65.10 | 104.40 |