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Outer Space Treaty

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Outer Space Treaty

The foundational multilateral treaty of international space law. Full name: *Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies*. Signed 27 January 1967; entered into force 10 October 1967. As of October 2025, 118 state parties have ratified or acceded; 20 more are signatories. All major spacefaring nations are parties.

Referenced in outer-space as the framework establishing that space is not subject to national sovereignty.

Core Principles

Per the UN Office for Outer Space Affairs:

  • Exploration and use of outer space shall be for the benefit and in the interests of all countries — outer space is "the province of all mankind"
  • Outer space is free for exploration and use by all states
  • Outer space is not subject to national appropriation by sovereignty, use, occupation, or any other means
  • States shall not place nuclear weapons or weapons of mass destruction in orbit, on celestial bodies, or elsewhere in space
  • The Moon and other celestial bodies shall be used exclusively for peaceful purposes — no weapons testing, military maneuvers, or military bases
  • Astronauts shall be regarded as envoys of mankind
  • States are responsible and liable for national space activities, whether governmental or private
  • States shall avoid harmful contamination of space and celestial bodies

What It Permits

The treaty does not prohibit conventional weapons in space, military personnel supporting peaceful activities, or military space forces. Anti-satellite weapons (ASAT) tests by the US, USSR, China, and India (2019) remain legal under the treaty, though they create hazardous space-debris.

Legal Lineage

Drew heavily from the Antarctic Treaty (1961). The OST was the cornerstone of a network of Cold War space law:

Treaty Year Subject
Rescue Agreement 1968 Safe return of astronauts
Space Liability Convention 1972 Liability for spacecraft damage
Registration Convention 1976 Registration of space objects
Moon Treaty 1979 Jurisdiction over celestial bodies

The Moon Treaty has only 18 parties — no spacefaring nation has ratified it.

Gaps and Tensions

Silent or ambiguous on: asteroid and lunar resource mining, commercial space activities, space-debris liability, and military activities short of WMD. These gaps are increasingly contested as commercial spaceflight expands.