Contacts: Daryl Kimball, Executive Director, (202) 463-8270 x107
Updated: August 2017
The 1967 Outer Space Treaty bans the stationing of weapons of mass destruction (WMD) in outer space, prohibits military activities on celestial bodies, and details legally binding rules governing the peaceful exploration and use of space. One hundred and five countries are states-parties to the treaty, while another 26 have signed it but have not yet completed ratification.
The treaty forbids countries from deploying "nuclear weapons or any other kinds of weapons of mass destruction" in outer space. The term "weapons of mass destruction" is not defined, but it is commonly understood to include nuclear, chemical, and biological weapons. The treaty, however, does not prohibit the launching of ballistic missiles, which could be armed with WMD warheads, through space. The treaty repeatedly emphasizes that space is to be used for peaceful purposes, leading some analysts to conclude that the treaty could broadly be interpreted as prohibiting all types of weapons systems, not just WMD, in outer space.
The treaty's key arms control provisions are in Article IV. States-parties commit not to:
- Place in orbit around the Earth or other celestial bodies any nuclear weapons or objects carrying WMD.
- Install WMD on celestial bodies or station WMD in outer space in any other manner.
- Establish military bases or installations, test "any type of weapons," or conduct military exercises on the moon and other celestial bodies.
Other treaty provisions underscore that space is no single country's domain and that all countries have a right to explore it. These provisions state that:
- Space should be accessible to all countries and can be freely and scientifically investigated.
- Space and celestial bodies are exempt from national claims of ownership.
- Countries are to avoid contaminating and harming space or celestial bodies.
- Countries exploring space are responsible and liable for any damage their activities may cause.
- Space exploration is to be guided by "principles of cooperation and mutual assistance," such as obliging astronauts to provide aid to one another if needed.
Like other treaties, the Outer Space Treaty allows for amendments or member withdrawal. Article XV permits countries to propose amendments. An amendment can only enter into force if accepted by a majority of states-parties, and it will only be binding on those countries that approve the amendment. Article XVI states a country's withdrawal from the treaty will take effect a year after it has submitted a written notification of its intentions to the depositary states-the United States, Russia, and the United Kingdom.
Talks on preserving outer space for peaceful purposes began in the late 1950s at the United Nations. The United States and its Western allies submitted proposals in 1957 on reserving space exclusively for "peaceful and scientific purposes," but the Soviet Union rejected these efforts because it was preparing to launch the world's first satellite and test its first intercontinental ballistic missile.
In 1963, the UN General Assembly approved two resolutions on outer space that subsequently became the basis for the Outer Space Treaty. UN Resolution 1884 called on countries to refrain from stationing WMD in outer space. UN Resolution 1962 set out legal principles on outer space exploration, which stipulated that all countries have the right to freely explore and use space.
The United States and Soviet Union submitted separate draft outer space treaties to the UN General Assembly in June 1966. A mutually agreed treaty text was worked out over the next six months, and the UN General Assembly gave its approval of the treaty on December 19, 1966. The treaty opened for signature in Washington, Moscow, and London on January 27, 1967 and entered into force October 10, 1967.
—Research assistance by Ben Rusek