More than 950 operating satellites currently orbit the Earth, providing information and other services essential to our civilian, scientific, and economic life, as well as our military operations. As their importance increases, so do concerns about keeping them safe—because for as long as there have been satellites, there have been plans for interfering with them.
A History of Anti-Satellite Programs describes the major motivations and milestones in the development of anti-satellite (ASAT) weapons, from the years of the first satellites to the present day. (To read the report in its entirety, please download A History of Anti-Satellite Weapons.)
The Risks of Anti-Satellite Weapons
The act of destroying a satellite can damage the space environment by creating a dangerous amount of space debris. What's more, the impairment or loss of a satellite, such as one used for reconnaissance, can quickly escalate a conflict or generate other unpredictable and dangerous consequences. And short of an actual attack on a satellite, even the targeting of satellites or the construction of space-based weapons could precipitate an arms race with its own damaging and far-reaching consequences.
To better understand these risks, it's important to assess the historical developments that have led to the development of and restrictions on ASAT technology.
A Timeline of Anti-Satellite Technologies and Policies
1950s–1960s: Nuclear-Tipped Interceptors and the Outer Space Treaty
The United States and Soviet Union developed early ASAT capabilities as dedicated systems and as residual capabilities of systems developed for other purposes, notably defense against ballistic missiles. Because of the limitations of interceptor guidance systems, early U.S. and Soviet missile interceptors were tipped with megaton-class nuclear weapons—the large lethal range would permit a successful ASAT or anti-ballistic-missile (ABM) attack without precision guidance.
Such interceptors have long been recognized as a poor ASAT option, in part because nuclear explosions in space are indiscriminate and would destroy all nearby satellites in their line of sight. In the weeks after detonation, many more satellites would also be damaged by the increased radiation in low earth orbits.
In 1967, the United States and Soviet Union signed the Outer Space Treaty (OST), which bans orbiting nuclear weapons and provides that all countries are free to use space for peaceful purposes as long as they respect the interests of other space users and operate in accordance with international law. It does not, however, explicitly prohibit deliberate attacks on satellites or prevent ASAT weapons tests.
1960s–1970s: Co-Orbital ASAT Weapons and U.S.-Soviet Bilateral Agreements
Russia's only dedicated ASAT system used a co-orbital strategy, in which a weapon armed with conventional explosives is launched into the same orbit as the target satellite and moves near enough to destroy it. The 1,400-kilogram Russian Co-Orbital ASAT weapon, for example, was designed to approach a satellite within one or two orbits (1.5 - 3 hours), then detonate an explosive that would damage the target with shrapnel. After conducting a series of seven tests from 1963–1971—including five interceptor detonations—the Soviet Union declared the system operational in 1973.
The 1972 U.S.-Soviet Treaty on the Limitation of Anti-Ballistic Missile Systems (the ABM treaty) prohibited interfering with "national technical means of verification" of treaty compliance, which implicitly protected reconnaissance satellites. Protections also began to be formally extended to other types of satellites through the 1971 Accident Measures Agreement and Hotline Modernization Agreement, which protected satellites essential to U.S.-Soviet communications in the event of a crisis.
The Soviet Union resumed testing of its Co-Orbital ASAT system in 1976, which reportedly extended the range of the system and reduced attack time by enabling the interceptor to reach its target in a single orbit. Testing continued until 1982 and the system remained operational until 1993.
1980s: Air-Launched ASAT Systems and the U.S. Strategic Defense Initiative
In 1982, the United States announced its intention to test the Air-Launched Miniature Vehicle (ALMV), a two-staged missile launched from an F-15 aircraft flying at high altitude. The missile would ascend to a a target satellite in low earth orbit and destroy or disrupt it in a high-speed collision, a technique known as a "kinetic kill" or "hit-to-kill" strategy. Though more technically challenging than a co-orbital strategy, the ALMV offered several advantages, including the flexibility to launch an ASAT attack at any time with significantly reduced time between missile launch and target destruction.
The U.S. tested its ALMV system several times beginning in 1984, including a 1985 test that destroyed an aging satellite at an altitude of 555 km. The test highlighted the consequences of destructive ASAT technologies: the destroyed satellite generated more than 250 pieces of persistent space debris large enough to be tracked, as well as more than 800 smaller pieces. In December 1985, Congress banned further testing of the system on satellites. The Air Force discontinued the ALMV program in 1987.
In the spring of 1983, President Reagan gave his "Star Wars" speech and announced that he intended to focus U.S. resources on developing a large-scale missile defense system. This Strategic Defense System (SDI) was expected to develop several types of space-based interceptors with intrinsic ASAT capabilities. The Soviet Union responded by restarting research on its own missile-defense systems and also made diplomatic overtures, proposing a ban on space-based weapons and declaring a unilateral moratorium on its ASAT weapons tests.
1980s–1990s: The U.S. MIRACL and KE-ASAT Systems, Soviet Laser ASAT System
Ground-based ASAT weapons based on directed electromagnetic energy (such as lasers) offer the potential to attack satellites with differing levels of intensity: low-powered lasers can merely "dazzle" (temporarily overwhelm) or "blind" (permanently damage) parts of a satellite's sensor, while high-powered lasers can disable, damage, or destroy a satellite.
In the late 1980s, the Air Force and Navy began developing an anti-satellite ground-based laser system, in part due to intelligence reports suggesting that the Soviet Union had developed a working laser system that could pose a significant threat to both satellites and ballistic missile.
The Navy coupled its megawatt-class Mid-Infrared Advanced Chemical Laser (MIRACL) to the Sea Lite beam director, a large and agile mirror that can direct the MIRACL's beam, but Congress banned tests of the system following revelations that the Soviet laser system posed no significant threat. The ban lapsed in 1996, and in 1997 the MIRACLE system appeared to be successfully used to dazzle or damage a satellite's sensor at an altitude of 420 km.
During this period, the U.S. Army accelerated plans for its own ground-based ASAT system, known as the kinetic-energy ASAT (KE-ASAT) program. The Department of Defense terminated the program in 1993, but Congress resurrected it in 1996 and authorized funding of the program from 1996 - 1998, and then again in 2000 and 2001. No funding has since been authorized and the KE-ASAT system was never tested on a space-borne object, though three "kill vehicles" were completed and placed in storage; two have since been dismantled for other uses.
2000s: Satellite Jamming, Renewed U.S. Interest in ASAT Capabilities, and ASAT Efforts from China and India
Satellite jamming—interfering with radio communications between a satellite and users on the ground—is another potential ASAT technology. Both the United States and Russia likely have jamming capabilities effective out to geosynchronous orbit. In 2002, the United States deployed the ground-based Counter Communications System, but little is publicly known about its specific capabilities.
The U.S. and other countries are actively developing other ASAT-related technologies, including satellites that can maneuver and approach targets and advanced ground-based laser systems that can more effectively interfere with a satellite's sensors.
In 2007, China used a mobile, ground-based missile to launch a homing vehicle that destroyed one of its aging weather satellites by direct impact, or "kinetic kill"—and created more persistent debris than any other event in space. In 2008, the U.S. demonstrated the ASAT capabilities of its sea-based Aegis missile defense interceptors by destroying a non-responsive U.S. satellite at an altitude of 240 km. In 2010, India announced its intentions to develop a hit-to-kill ASAT system.
Future Diplomatic Efforts
In 2008, Russia and China presented a draft treaty—the Treaty on the Prevention of the Placement of Weapons in Outer Space— to the Conference on Disarmament, the primary international body through which arms control are negotiated. It would place important limits on the use of ASAT weapons, but offers little to slow their development or deployment.
In 2010, the European Union publicly presented a draft Code of Conduct for Outer Space Activities and began consulting with potential signatories, who would be responsible for preventing harmful interference with space objects and refraining from intentional damage to satellites. Development and deployment of ASAT weapons would not be constrained, but their use would be prohibited.
The draft EU Code of Conduct represents a modest step forward in improving the safety of space operations and protecting the space environment, as well as setting the reasonable expectation that space assets should not be a target of aggression. In January 2012, the United States announced that in lieu of signing the EU code, it would work with the European Union to develop an International Code of Conduct for Outer Space Activities.