Bombs in orbit? Verification and violation under the Outer Space Treaty

Screenshot from a Russian video showing a missile concept that could place nuclear weapons on orbital trajectories to approach the US from the south. (credit: Russia 1)

On March 1, Russian President Vladimir Putin provided details, mostly in the form of artist’s impressions, on a variety of provocative weapon systems under development. One of them, the RS-28 Sarmat, was depicted as placing a nuclear weapon into a presumably orbital trajectory that could strike targets by traveling the long way around the globe (in this case, with fictionalized land masses, but later depicted as descending on Florida).

The US State Department condemned the development of Russia’s new weapon systems as violations of the Intermediate-Range Nuclear Forces (INF) Treaty but did not allege a violation of Article IV of the UN 1967 Outer Space Treaty (OST).1 Why?

The answer may be in part because, 50 years ago, the Johnson Administration set the precedent that testing such a weapon system would not be a violation when it stated publicly that the Soviet Union’s “Fractional Orbital Bombardment System (FOBS),” based on the predecessor to the RS-28, did not violate the treaty. Before and after the treaty’s signing, the administration internally debated the activities it would permit and their ability to verify compliance, ultimately concluding that the treaty was intended to prohibit a different type of weapon system.

A binding prohibition

Article IV requires signatories “not to place in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner,” among other prohibitions. The US and USSR had already publicly stated their intention not to station nuclear weapons in space, on the Moon, or on other celestial bodies in 1963 through UN Resolution 1884, but because the 1963 statement was not legally binding, the US was not obligated to verify that the USSR was honoring the agreement. By contrast, in preparation for the legally binding 1963 Partial Nuclear Test Ban Treaty, which prohibited exo-atmospheric nuclear testing, the US deployed the Vela surveillance satellites to detect the characteristic radiation from exo-atmospheric (and later, atmospheric) nuclear explosions.

In fact, the Soviets only agreed to the 1963 proposal on the condition that measures such as pre-launch inspection of payloads would not be required, and that the US would be satisfied by using its own national technical means for verification. However, elevating the 1963 statement to a legally binding instrument raised questions about the US ability to verify that other countries were in compliance, and events soon after the signing forced them to consider what would constitute a violation.

Establishing a threshold for violation

Two incidents in 1967 forced the Johnson Administration to establish a threshold for violation of the treaty that hinged on the interpretation of placing nuclear weapons in orbit around the Earth or stationing such weapons in outer space.

The first incident was in response to a June 1967 New York Times article reporting alleged Pentagon plans to develop a nuclear-tipped orbital ABM system. The State Department, who was generally tasked with interpretation of the treaty, stated internally that such a system would violate the treaty because it permanently stationed nuclear weapons in orbit, and it would be impossible to differentiate offensive from defensive orbiting nuclear weapons.2 The explicit inclusion of nuclear weapons in Article IV in addition to weapons of mass destruction prevented the introduction a loophole that the Joint Chiefs of Staff had sought in the 1963 statement in order to allow developing just such an ABM system.3

The second incident was in November 1967—a month after Congress ratified the treaty–when Secretary of Defense McNamara announced that the Soviets had tested a FOBS. The weapon consisted of a modified R-36 missile (the R-36ORB) that placed a two- to three-megaton warhead into an orbital trajectory over the southern hemisphere in order to evade US early warning radar (and possibly ABM) systems by flying lower and approaching from the south, using a retrorocket to de-orbit itself.4 When Secretary McNamara announced the tests, he argued that they did not violate the treaty because 1) they did not involve a warhead, so no nuclear weapon entered orbit; 2) the test vehicle was de-orbited before it achieved a full orbit; and 3) weapon development was not prohibited by the treaty.5

Yet Secretary McNamara’s interpretation angered some members of Congress, who argued that the FOBS represented a violation and questioned Soviet commitment to the treaty. US allies also privately raised concerns, and US the intelligence community suggested it could presage development of a multi-orbit bombardment system. State Department officials, who had not been notified in advance about Secretary McNamara’s announcement, argued internally that nothing in the treaty limited it to full orbits. This internal discord was picked up and reported by the famous Murrey Marder at the Washington Post in a pointed piece titled “Orbital Bomb Rationalizing Jolts Officials.”6

But the State Department was overruled and subsequently adopted the administration’s position, later noting that even if the tests had involved a nuclear weapon, they would not be considered a violation because a “true” orbital bombardment system was imagined to station nuclear weapons in orbit on a more permanent basis.7 Even the name, FOBS, was carefully employed to ensure that the weapon would not be considered a violation.

So it was that the Johnson administration set the bar in 1967: violation would need to entail space-based nuclear weapons, not ground-based systems that temporarily placed prohibited weapons into orbit. This interpretation owed more to the administration’s other needs—in particular, the need for Soviet cooperation to finalize the far more consequential Nuclear Non-proliferation Treaty—than to a close reading of the text or concern about space-based weapons. However unlikely it was that space-based nuclear weapons would be deployed, government officials nevertheless dutifully prepared for verifying compliance with this prohibition.

Inferring the right to inspect satellites

The treaty does not include an explicit permission for inspection of spacecraft to ensure compliance. During negotiations in 1966, the US delegation pushed for all facilities on celestial bodies to be open to all parties, akin to the 1958 Antarctic Treaty, but the Soviets resisted on the grounds that such access could be unsafe, and that access should only be permitted on a pre-arranged, reciprocal basis. The US delegation eventually accepted this limitation under the belief that any effort to evade inspection on these grounds would be obvious.8

Neither the US nor the USSR proposed requiring or even allowing access to spacecraft in orbit, and no such measure was included in the treaty—and in fact, US negotiators were instructed to abandon the talks if access to satellites became a requirement.

As a result of this omission, the US had to establish that the treaty did not prohibit inspection of spacecraft for the purpose of verifying treaty compliance. Consequently, Johnson administration officials argued that the treaty implicitly permitted the use of national technical means to verify compliance:

Thus, provided the close inspection does not involve “potentially harmful interference with activities of other States Parties in the peaceful exploration of outer space,” there is no prohibition against such action. In this context, visual inspection would not be considered as “potentially harmful.” Furthermore, a “bomb-in-orbit” would not be regarded as peaceful and therefore there would be no restraints against inspecting it.9

A more detailed interpretation reasoned that while the treaty did not generally permit physical access to satellites, it “does not contain any provision prohibiting steps to ascertain whether there has been a violation… If any presumption against a right of inspection is raised… this would be overcome if there were strong reason to believe that an orbiting space vehicle was carrying a prohibited weapon,” at which point other rights afforded to states under international law, such as self-defense, would take precedent. Any state would be entitled to challenge a state suspected of violating the treaty, and if doubts could not be addressed, “to take appropriate steps to protect itself against the effects of a Treaty violation.”10

Looking for “bombs-in-orbit”

The administration maintained publicly that the US possessed capabilities for verifying compliance with the treaty that were “sufficient for national security.”11 But the Joint Chiefs of Staff dissented in 1966, noting that while they accepted the treaty, “the United States does not now have the capability to verify the presence of weapons of mass destruction in orbit. The Joint Chiefs of Staff are seriously concerned about this lack of verification capability, and they believe that continued effort should be expended toward its attainment.”12 Although the Air Force did possess a system for the visual inspection of satellites known as Project 437 available by at least 1965, as Dwayne Day has pointed out it had limited capabilities and was cancelled soon after.13 Their dissent may have been due in part to a belief that a binding treaty presented opportunities to advocate for systems such as the Air Force’s planned Manned Orbiting Laboratory (MOL).

A February 1967 memo to prepare for questions from Congress noted that the US could detect all satellites, including a “bomb-in-orbit,” very easily at low orbits, and that higher orbits such satellites would have comparatively long time de-orbiting times. They also noted that they had “a very high confidence of being able to detect a satellite when it is launched” and that a number of ground-based radar and laser facilities under development would add to this capability.14

The memo added, however, that distinguishing nuclear weapon-carrying satellites still posed a significant technical challenge and a disguised weapon could be impossible to be identify. As a contingency, capabilities for physical inspection of spacecraft and facilities were evaluated. The Department of Defense reported that Gemini spacecraft had demonstrated the capability to rendezvous with satellites, and proposed that the MOL could be called on to conduct inspection missions within its limited delta-V. NASA did not volunteer any specific systems but noted many difficulties if it was called on to inspect satellites, including “the availability of ‘booby trap’ devices in the spacecraft to be inspected,” and concluded that “it appears that inspection capabilities in space could be limited.”15

Interestingly, NASA also considered their ability to inspect facilities on the lunar surface, since they were the only agency with the means to do so, even though they had not yet landed astronauts on the Moon. In the extremely unlikely scenario that they would be called on to inspect lunar facilities, NASA noted that: “for the present our manned inspection capabilities are essentially limited to the equatorial plane of the moon but with an accuracy to target area which is expected to be some hundreds of feet and an extravehicular range up to one-half mile. The basic capability through lunar orbiter photographic reconnaissance seems very good, with resolution of one foot and the ability to cover any spot on the moon.”16

Despite technical limitations, the administration concluded in 1966 that they maintained capabilities sufficient for national security because ultimately:

A single weapon in space would not upset the [strategic] balance. “Bombs in Orbit” are complex weapons systems which to be practicable involve large numbers of weapons and associated supporting activities. It would be extremely difficult to conceal such a program. When viewed in this light, it is clear that our national capabilities will provide us the necessary information for protecting our security interests. The real verification question hinges on our ability to know of an adversary’s space activities in sufficient depth to take the necessary actions prior to his attaining any strategic advantage through the weapons-in-space route. This is clearly within U.S. capabilities.17

A later memo to the Secretary of Defense asserted more directly that national capabilities would ensure that compliance with the treaty could be effectively monitored and admitted that while a small number of nuclear weapons could be orbited without detection, a large number could be easily detected.18

Does the Johnson Administration’s interpretation of 50 years ago still stand? No action taken so far after Putin’s address suggests that the current administration has adopted a more restrictive stance. But how this interpretation may have changed in the intervening half century, particularly in relation to some of the proposals of the Strategic Defense Initiative, and with the emergence of new actors and technologies (and artist’s impressions), awaits further research.


  1. State Department. Department Press Briefing – March 1, 2018.
  2. Leonard Meeker to Paul Warneke, ‘Outer Space Treaty and ABM Systems,’ 7 June 1967, Legislative Background Outer Space Treaty History Box 2, Folder “The Senate Considers the Treaty and Gives its Advice and Consent,” LBJ Library.
  3. Raymond Garthoff, A Journey through the Cold War: A Memoir of Containment and Coexistence, Brookings Institution Press: Washington, DC, 2001, p. 162.
  4. Asif Siddiqi, “Cold War in Space: A Look Back at the Soviet Union,” Spaceflight vol. 40, February 1998.
  5. ‘News Conference of Secretary of Defense Robert S. McNamara at Pentagon,’ 3 November 1967, National Security File, Files of Charles E. Johnson, Box 11, Folder 4 “Bombs in Orbit – General (Ballistic missiles in orbit, FOBS, MOBS, etc),” LBJ Library.
  6. Murrey Marder, “Orbital Bomb Rationalizing Jolts Officials,” Washington Post, November 5, 1967.
  7. Dean Rusk to US mission NATO, November 1967, National Security File, Files of Charles E. Johnson, Box 11, Folder 4 “Bombs in Orbit – General (Ballistic missiles in orbit, FOBS, MOBS, etc),” LBJ Library.
  8. Arthur Goldberg to State Department, 4-7 October 1966, LBJ Library.
  9. John S. Foster, “Memorandum for the Assistant Secretary, ISA,” February 2, 1967, Legislative Background Outer Space Treaty History Box 1, Folder 12, “The Treaty is Open for Signature and Goes to the Senate for Advice and Consent,” Folder #2, LBJ Library.
  10. “Memorandum of the Legal Adviser,” April 13, 1967, Box I:46, “The Papers of Arthur Goldberg,” Folder 3, Library of Congress.
  11. No title, January 16, 1967, Legislative Background Outer Space Treaty History Box 1, Folder 10, “The Treaty,” LBJ Library.
  12. “Talking Paper for the Chairman, JCS, fur [sic] use at a meeting of the National Security Council on 15 September 1966,” September 15, 1966, “Legislative Background Outer Space Treaty History Box 1, Folder 9, “The Second and Final Negotiations,” LBJ Library.
  13. Day, Dwayne. “Close encounters of the top secret kind.” The Space Review, October 20, 2014.
  14. Foster, “Memorandum for the Assistant Secretary, ISA,” LBJ Library.
  15. “Inspection,” undated, Folder, “Outer Space Treaty (1962) – NASA response and comments to Proposed Treaty, 17368,” NASA History Office archives.
  16. “Inspection,” NASA History Office archives.
  17. “Verification of the ‘No bombs in Orbit’ Portion of the Space Treaty,” December 28, 1966, Legislative Background Outer Space Treaty History Box 1, Folder 10, “The Treaty,” LBJ Library.
  18. “Memorandum for the Secretary of Defense,” February 9, 1967, Legislative Background outer Space Treaty History Box 2, Folder “The Senate Considers the Treaty and Gives its Advice and Consent,” LBJ Library.