/  News   /  THE VELA INCIDENT


By: David Rilley-Harris, Curator, DITSONG: National Museum of Military History (DNMMH)


Vela satellites prior to launch

(Picture: National Security Archive.


In 1963, numerous countries signed or acceded to the Partial Test Ban Treaty (PTBT), including the USA, USSR, South Africa, and Israel. The treaty banned nuclear weapons tests in Earth’s atmosphere, in space, and in the oceans. Only underground nuclear weapons testing would be allowed. At the time, South Africa and Israel were two of the latest countries suspected to have joined those possessing nuclear weapons. To monitor compliance with the treaty, the USA initiated the Vela Program which included Vela orbital satellites with the capacity to detect evidence of nuclear weapons detonations. The picture above shows two of those Vela satellites in May 1969, prior to their launch. The satellites were launched in pairs designed to separate once in orbit. On 22 September 1979, satellite Vela 6911 detected a probable nuclear detonation somewhere between Africa and Antarctica. The satellites which the USA had launched with concern to prevent the USSR from breaking the PTBT had instead spotted a possible contravention by an allied nation.

It was shortly before sunrise when Vela 6911 detected evidence of two bright flashes of light. The double flash was a sign of a nuclear weapon detonation with the first flash appearing with the initial shockwave and the second flash being caused by the fireball which follows. The satellite signal was transmitting to Patrick Air Force Base in Florida, the USA, where it was still the middle of the night. With the Vela satellites having picked up forty-one previous detonations which had all been confirmed as known nuclear weapons tests, the signal was initially assumed to be a positive detection of an unauthorized detonation. The Vela satellites were not designed to pinpoint the location of a detonation and so the exact location could only be surmised from the position of the satellite in orbit at the time it detected the double flash. Vela 6911 had been slightly west of half-way between the southern tip of Africa and the coast of Antarctica. The detonation would then have occurred within a 2 400 km radius covering parts of the Atlantic and Indian Oceans. This area included the Prince Edward Islands which were owned by South Africa, and the Crozet Islands which were owned by France. Not far east of the area was also the Kerguelen Islands, also owned by France. The explosion was thought to be a neutron bomb of around two or three kilotons. The air force base issued an alert and US President Jimmy Carter called for a meeting in the White House Situation Room the next day. Over the following seven days the US Air Force flew twenty-five sorties over the area to test the atmosphere for further evidence of a nuclear detonation, but no evidence was picked up or released to the public.

Given the extent of each nation’s development of nuclear weapons, Israel was initially suspected as having been responsible, with assistance from South Africa. The first official reports, however, called the Vela 6911 detection inconclusive as to whether a nuclear detonation had occurred at all. Doubt was cast on the reliability of the double flash detection partly because the Vela satellites were two years past their planned operational life span and were listed as having been retired. The satellite instruments could also be deceived by a collision with a meteorite causing the instruments to pick up small changes of light from debris alongside the satellite. Whoever was responsible, they may have believed that the blast would not be detected with the assumption that the Vela satellites were no longer transmitting data. There was also stormy weather in the area which may have been thought to obscure evidence of the blast. President Carter had only just completed negotiating a treaty between Israel and Egypt and he needed the Partial Test Ban Treaty to be upheld by the USSR. Admitting that Israel had broken the treaty would have angered nations in the Middle East and would have undermined the PTBT. It was, however, known that Israel had purchased 550 tons of uranium from South Africa for its Dimona nuclear plant. It is believed that in exchange for the uranium Israel provided South Africa with nuclear weapon designs and materials. Under international pressure to investigate, President Carter set up a committee to report on the Vela data. The Massachusetts Institute of Technology (MIT) professor of electrical engineering, Jack Ruina, was selected to head the committee and the Ruina committee was asked to disregard all political pressures and focus only on evidential analysis. This also meant that the committee would be able to ignore contextual evidence outside of the Vela data. On 23 May 1980, the committee found that the Vela data did not absolutely prove that there had been a nuclear detonation as other possible explanations for the data were conceivable. In defence of the committee findings, it was pointed out that no alternative method of detection had confirmed the Vela data. It has since been discovered that the White House had likely been privy to information regarding the detection of radioactive substances in New Zealand rainwater days after the Vela flash.


Left: The position of the satellite at the time of the flash. Right: The likely path of radioactive contamination.

(Picture: The Collector.


Recent years have yielded previously secret documents about the Vela incident released under the US Freedom of Information Act. One file revealed that the US Air Force Technical Applications Centre (AFTAC) had sent a Col Robert McBryde to New Zealand in November 1979 to confirm New Zealand’s Institute of Nuclear Science (INS) reports regarding their rainwater. His report described the INS information as “flimsy”. It has also been revealed that radioactive isotope iodine-131 was found in the thyroids of Australian and Tasmanian sheep slaughtered in October and November 1979. No iodine-131 was found in New Zealand’s sheep. Other declassified information reveals that a listening station in the Ascension Islands picked up evidence of a detonation in the direction of the Prince Edward Islands. Similar evidence was picked up by an underwater sound surveillance system near Newfoundland. The hydroacoustic data positioned the blast in shallow waters between the Prince Edward and Marion Islands. On the day of the Vela flash, Arecibo Observatory in Puerto Rico also picked up ionospheric disturbance which corresponded to that seen in conjunction with Soviet nuclear tests in the early 1960s. A 2022 study of old data from a NASA satellite, Nimbus-7, showed evidence that 16 minutes and 44 seconds after the blast traces of the shockwave moved through the ozone layer. President Carter’s diaries, published in 2010, show that the initial suspicions of an Israeli nuclear weapons test supported by South Africa were only increasingly confirmed and declassified documents from the time show that the CIA believed that the chance that it was a nuclear detonation was at 90%. A day-long oral history conference on the Vela incident held in Washington in 2019 included some people who had been involved. There were recollections that South Africa was initially believed to have conducted the test, but that South Africa would have needed help. The fissile material was thought to have originated from the Apollo Plant in Pennsylvania, USA. There was also recollection of a 1981 supplementary report of the Ruina committee regarding sheep thyroids.

Western political interests around the Vela incident have been to obfuscate the question of who was responsible for the nuclear detonation. While it is now clear that a nuclear weapon test did occur, it is still inconclusive as to who was responsible for carrying out or assisting with the test. The suspects remain South Africa, Israel, the USA, or even France.

Ditsong Logo