Anti-satellite weapons (ASAT) are designed to incapacitate or destroy satellites for strategic military purposes. Currently, only the United States, the former Soviet Union, and the People's Republic of China are known to have developed these weapons.
The development and design of anti-satellite weapons has followed a number of paths. The initial efforts by the USA and the USSR were using ground-launched missiles from the 1950s; many more exotic proposals came afterwards.
U.S. programs 
In the late 1950s the U.S. Air Force started a series of advanced strategic missile projects under the designation Weapon System WS-199A. One of the projects studied under the 199A umbrella was Martin's Bold Orion air-launched ballistic missile (ALBM) for the B-47 Stratojet, based on the rocket motor from the Sergeant missile. Twelve test launches were carried out between 26 May 1958 and 13 October 1959, but these were generally unsuccessful and further work as an ALBM ended. The system was then modified with the addition of an Altair upper stage to create an anti-satellite weapon with a 1100-mile (1700-km) range. Only one test flight of the anti-satellite mission was carried out, making a mock attack on the Explorer 6 at an altitude of 156 miles (251 km). To record its flight path, the Bold Orion transmitted telemetry to the ground, ejected flares to aid visual tracking, and was continuously tracked by radar. The missile successfully passed within 4 miles (6.4 km) of the satellite, which would be suitable for use with a nuclear weapon, but useless for conventional warheads.
A similar project carried out under 199A, Lockheed's High Virgo, was initially another ALBM for the B-58 Hustler, likewise based on the Sergeant. It too was adapted for the anti-satellite role, and made an attempted intercept on Explorer 5 on 22 September 1959. However, shortly after launch communications with the missile were lost and the camera packs could not be recovered to see if the test was successful. In any event, work on the WS-199 projects ended with the start of the AGM-48 Skybolt project. Simultaneous U.S. Navy projects were also abandoned although smaller projects did continue until the early 1970s.
The use of high altitude nuclear explosions to destroy satellites was considered after the tests of the first conventional missile systems in the 1960s. During the Hardtack Teak test in 1958 observers noted the damaging effects of the electromagnetic pulse (EMP) caused by the explosions on electronic equipment, and during the Starfish Prime test in 1962 the EMP from a 1.4 Mt warhead detonated over the Pacific damaged three satellites and also disrupted power transmission and communications across the Pacific. Further testing of weapons effects was carried out under the DOMINIC I series. An adapted version of the nuclear armed Nike Zeus was used for an ASAT from 1962. Codenamed Mudflap, the missile was designated DM-15S and a single missile was deployed at the Kwajalein atoll until 1966 when the project was ended in favour of the USAF Thor-based Program 437 ASAT which was operational until 6 March 1975.
Another area of research was directed into energy weapons, including a nuclear-explosion powered X-ray laser proposal developed at Lawrence Livermore National Laboratory (LLNL) in 1968. Other research was based on more conventional lasers or masers and developed to include the idea of a satellite with a fixed laser and a deployable mirror for targeting. LLNL continued to consider more edgy technology but their X-ray laser system development was cancelled in 1977 (although research into X-ray lasers was resurrected during the 1980s as part of the SDI).
ASATs were generally given low priority until 1982, when information about a successful USSR program became widely known in the west. A "crash program" followed, which developed into the Vought ASM-135 ASAT, based on the AGM-69 SRAM with an Altair upper stage. The system was carried on a modified F-15 Eagle that carried the missile directly under the central line of the plane. The F-15's guidance system was modified for the mission and provided new directional cueing through the pilot's heads up display, and allowed for mid-course updates via a data link. The first launch of the new anti-satellite missile took place in January 1984. The first, and only, successful interception was on September 13, 1985. The F-15 took off from Edwards Air Force Base, climbed to 38,100 feet (11,613 m) and vertically launched the missile at the Solwind P78-1, a U.S. gamma ray spectroscopy satellite orbiting at 555 km (345 mi), which was launched in 1979. Although successful, the program was cancelled in 1988.
Soviet Union 
The origins of the Soviet anti-satellite weapon program are unclear. According to some accounts, Sergei Korolev started some work on the concept in 1956 at his OKB-1, while others attribute the work to Vladimir Chelomei's OKB-52 around 1959. What is certain is that at the beginning of April 1960, Nikita Khrushchev held a meeting at his summer residence in Crimea, discussing an array of defense industry issues. Here, Chelomei outlined his rocket and spacecraft program, and received a go-ahead to start development of the UR-200 rocket, one of its many roles being the launcher for his anti-satellite project. The decision to start work on the weapon was made in March 1961 as the Istrebitel Sputnik (IS) (Interceptor of satellites, or literally "Destroyer of satellites").
The IS system was "co-orbital", approaching its target over time and then exploding a shrapnel warhead close enough to kill it. The missile was launched when a target satellite's ground track rises above the launch site. Once the satellite is detected, the missile is launched into orbit close to the targeted satellite. It takes 90 to 200 minutes (or one to two orbits) for the missile interceptor to get close enough to its target. The missile is guided by an onboard radar. The interceptor, which weighs 1400 kg, may be effective up to one kilometer from a target.
Delays in the UR-200 missile program prompted Chelomei to request R-7 rockets for prototype testing of the IS. Two such tests were carried out on November 1, 1963 and April 12, 1964. Later in the year Khrushchev cancelled the UR-200 in favor of the R-36, forcing the IS to switch to this launcher, whose space launcher version was developed as the Tsyklon 2. Delays in that program led to the introduction of a simpler version, the 2A, which launched its first IS test on October 27, 1967, and a second on April 28, 1968. Further tests carried out against a special target spacecraft, the DS-P1-M, which recorded hits by the IS warhead's shrapnel. A total of 23 launches have been identified as being part of the IS test series. The system was declared operational in February 1973.
Testing resumed in 1976 as a result of the U.S. work on the Space Shuttle. Elements within the Soviet space industry convinced Leonid Brezhnev that the Shuttle was a single-orbit weapon that would be launched from Vandenberg, maneuver to avoid existing anti-ballistic missile sites, bomb Moscow in a first strike, and then land. Although the Soviet military was aware these claims were false, Brezhnev believed them and ordered a resumption of IS testing along with a Shuttle of their own. As part of this work the IS system was expanded to allow attacks at higher altitudes and was declared operational in this new arrangement on July 1, 1979. However, in 1983, Yuri Andropov ended all IS testing and all attempts to resume it failed. Ironically, it was at about this point that the U.S. started its own testing in response to the Soviet program.
The Soviet Union also experimented with large, ground-based ASAT lasers from the 1970s onwards (see Terra-3), with a number of U.S. spysats reportedly being 'blinded' (temporarily) during the 1970s and 1980s. The USSR had also researched directed energy weapons, under the Fon project from 1976, but the technical requirements needed of the high-powered gas dynamic lasers and neutral or charged particle beam systems seemed to be beyond reach. The USSR also experimented with military space stations with a capability for anti-satellite duty in its Almaz program.
In the early 1980s, the Soviet Union also started developing a counterpart to the U.S. air-launched ASAT system, using modified MiG-31 'Foxhounds' (at least six of which were completed) as the launch platform.
ASAT in the era of strategic defense 
The era of the Strategic Defense Initiative (proposed in 1983) focused primarily on the development of systems to defend against nuclear warheads, however, some of the technologies developed may be useful also for anti-satellite use.
After the Soviet Union collapsed, there were proposals to use this aircraft as a launch platform for lofting commercial and science packages into orbit. Recent political developments (see below) may have seen the reactivation of the Russian Air-Launched ASAT program, although there is no confirmation of this as yet.
The Strategic Defense Initiative gave the US and Russian ASAT programs a major boost; ASAT projects were adapted for ABM use and the reverse was also true. The initial US plan was to use the already-developed MHV as the basis for a space based constellation of about 40 platforms deploying up to 1,500 kinetic interceptors. By 1988 the US project had evolved into an extended four stage development. The initial stage would consist of the Brilliant Pebbles. defense system, a satellite constellation of 4,600 kinetic interceptors (KE ASAT), of 100 lb (45 kg) each, in Low Earth orbit, and their associated tracking systems. The next stage would deploy the larger platforms and the following phases would include the laser and charged particle beam weapons that would be developed by that time from existing projects such as MIRACL. The first stage was intended to be completed by 2000 at a cost of around $125 billion.
Research in the U.S. and Russia was proving that the requirements, at least for orbital based energy weapon systems, were, with available technology, close to impossible. Nonetheless, the strategic implications of a possible unforeseen breakthrough in technology forced the USSR to initiate massive spending on research in the 12th Five Year Plan, drawing all the various parts of the project together under the control of GUKOS and matching the U.S. proposed deployment date of 2000.
Both countries began to reduce expenditure from 1989 and the Russian Federation unilaterally discontinued all SDI research in 1992. Research and Development (both of ASAT systems and other space based/deployed weapons) has, however, reported to have been resumed under the government of Vladimir Putin as a counter to renewed U.S. Strategic Defense efforts post Anti-Ballistic Missile Treaty. However, the status of these efforts, or indeed how they are being funded through National Reconnaissance Office projects of record, remains unclear. The U.S. has begun working on a number of programs which could be foundational for a space-based ASAT. These programs include the Experimental Spacecraft System (XSS 11), the Near-Field Infrared Experiment (NFIRE), and the space-based interceptor (SBI).
Recent ASATs 
At 5:28 p.m. EST January 11, 2007, the People's Republic of China successfully destroyed a defunct Chinese weather satellite, FY-1C. The destruction was reportedly carried out by an SC-19 ASAT missile with a kinetic kill warhead similar in concept to the American Exoatmospheric Kill Vehicle. FY-1C was a weather satellite orbiting Earth in polar orbit at an altitude of about 537 miles (865 km), with a mass of about 750 kg (1,650 lb). Launched in 1999, it was the fourth satellite in the Feng Yun series. The missile was launched from a mobile Transporter-Erector-Launcher (TEL) vehicle at Xichang ( ) and the warhead destroyed the satellite in a head-on collision at an extremely high relative velocity.
United States 
USA-193 was an American spy satellite, which was launched on 14 December 2006 by a Delta II rocket, from Vandenberg Air Force Base. It was reported about a month after launch that the satellite had failed. In January 2008, it was noted that the satellite was decaying from orbit at a rate of 1,640 feet (500 m) per day. On 14 February 2008, it was reported that the U.S. Navy had been instructed to fire an SM-3 ABM weapon at it, to act as an anti-satellite weapon.
According to the U.S. Government, the primary reason for destroying the satellite was the approximately 1,000 lb (450 kg) of toxic hydrazine fuel contained on board, which could pose health risks to persons in the immediate vicinity of the crash site should any significant amount survive the re-entry. On February 20, 2008, it was announced that the launch was carried out successfully and an explosion was observed consistent with the destruction of the hydrazine fuel tank.
Experts debated whether the hydrazine tank would have survived an uncontrolled reentry. However, if it had, any human fatality would still have been very unlikely. Although hydrazine is toxic, a small dose would not have been immediately lethal. The chance of the (assumed intact) hydrazine tank landing close enough to at least one person for that person to be killed if he or she lingered in the vicinity of the crash site was about one percent, while the cost of the intercept was about $100 million.
The intercept, however, was widely interpreted as a demonstration of U.S. capabilities in response to the Chinese anti-satellite test a year earlier. The intercept was different from typical ASAT missions in that it took place at a much lower altitude (133 nautical miles or 247 kilometers) than would normally be the case, and the SM-3 missile as currently deployed would not have adequate range and altitude reach for typical ASAT missions in low-Earth orbit. However, the warhead was shown capable of hitting a satellite at orbital closing speeds.
ASAT development 
In a televised press briefing during the 97th Indian Science Congress in Thiruvananthapuram, the DRDO Director General Rupesh announced that India was developing the necessary technology that could be combined to produce a weapon to destroy enemy satellites in orbit.On February 10, 2010, DRDO Director-General and Scientific Advisor to the Defence Minister, Dr VK Saraswat stated that India had "all the building blocks necessary" to integrate an anti-satellite weapon to neutralize hostile satellites in low earth and polar orbits.
In the early 1980s, the Soviet Union used modified MiG-31 'Foxhounds' as a launch platform for an Anti-Satellite weapon system. After the collapse of the Soviet Union, this project was put on hold due to reduced defense expenditures. However, in August 2009, the Russian Air Force had announced the resumption of this program. Further reports in May 2010 based on statements from Col. Eduard Sigalov in Russia's air and space defense forces, indicated that Russia was "developing a fundamentally new weapon that can destroy potential targets in space." The Sokol Eshelon is a prototype laser system based on an A-60 airplane which is reported to be restarting development in 2012.
See also 
- Anti-ballistic missile
- High-altitude nuclear explosion
- Kessler syndrome, in which runaway ablation could render Earth orbit uninhabitable for centuries
- Kill vehicle
- Militarisation of space
- Outer Space Treaty
- Multiple Kill Vehicle
- Martin WS-199B Bold Orion
- Grier, Peter."The Flying Tomato Can." Air Force magazine, February 2009. Retrieved: 9 February 2013.
- Kestenbaum, David (January 19, 2007). "Chinese missile destroys satellite in 500 mile orbit". NPR.
- Shuttle Buran, see chronology section
- IS anti-satellite system
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- "U.S. plans for falling satellite". CNN. January 30, 2008. Archived from the original on 2008-01-31.
- Associated Press – Broken Satellite Will Be Shot Down
- "Navy missile hits dying spy satellite, says Pentagon". CNN. February 21, 2008.
- "US shoots down toxic satellite". Daily telegraph (Australia). 2008-02-20. Archived from the original on 2008-12-22. Retrieved 2008-02-20.
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- "Is Russia ready for Star Wars? | Features & Opinion | RIA Novosti". En.rian.ru. Retrieved 2012-11-17.
- ria novosti 11/08/2009
- "Russian officer says developing new weapon for space defense". RIA Novosti.
- Podvig, Pavel (13 November 2012). "Russia to resume work on airborne laser ASAT". Russian Strategic Nuclear Forces. Retrieved 17 November 2012.
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