Detection
The "double flash" was detected on September 22, 1979, at 00:53 GMT, by the American Vela satellite 6911, which carried various sensors that had been designed specifically to detect nuclear explosions. In addition to being able to detect gamma rays, X-rays, and neutrons, the satellite also contained two silicon solid-state bhangmeter sensors that would be able to detect the dual light flashes associated with an atmospheric nuclear explosion: the initial brief, intense flash, followed by the second longer flash.
The satellite reported the characteristic double flash of a small atmospheric nuclear explosion of two to three kilotons, in the Indian Ocean between The Crozet Islands (a very small, sparsely inhabited French possession) and the Prince Edward Islands which belong to South Africa at 47°S 40°E / 47°S 40°E / -47; 40Coordinates: 47°S 40°E / 47°S 40°E / -47; 40. The previous 41 double flashes that the Vela satellites detected were all subsequently confirmed to be nuclear explosions.
There was, and remains, much doubt as to whether the satellite's observations were accurate. The Vela Hotel 6911 satellite was one of a pair that had been launched on May 23, 1969, over ten years before the "double-flash" event, and this satellite was already more than two years beyond its so-called "design lifetime". This satellite was known to have a failed electromagnetic pulse (EMP) sensor, and it had developed a fault (in July 1972) in its recording memory, but that fault had cleared itself by March 1978.
Additionally, early technical speculation also examined the possibility that the Vela had recorded a combination of natural phenomena, such as lightning in conjunction with a meteor strike. Other early news media articles of the time discussed the possibility of a large extraterrestrial object strike, such as an asteroid, occurring. The Vela satellite's flash detectors were sensitive to lightning superbolts, which resulted in two scientists, John Warren and Robert Freyman from the Los Alamos National Laboratory (then called the Los Alamos Scientific Laboratory), immediately flying to and investigating a rare, overland superbolt occurrence on Bell Island, Newfoundland, in April 1978. Their observations of the event, called the 'Bell Island Boom', noted building structural damage, dead farm animals and destroyed electrical devices amongst other evidence (the superbolt's blast was heard 55 kilometers away in Cape Broyle, Newfoundland). The Bell Island Boom was among some 600 "mystery booms" that occurred along the North American eastern seaboard from late 1977 to mid‑1978.
Nonetheless, the initial assessment by the United States National Security Council (NSC), with technical support by the Naval Research Laboratory in October 1979 was that the American intelligence community had "high confidence" that the event was a low-yield nuclear explosion, although no radioactive debris had ever been detected, and there was "no corroborating seismic or hydro-acoustic data." A later NSC report revised this position to "a position of agnosticism" about whether a test had occurred or not. The NSC concluded that responsibility for a nuclear explosion, if any, should be ascribed to the Republic of South Africa.
Several U.S. Air Force WC-135B surveillance aircraft flew 25 sorties over that area of the Indian Ocean soon after the "double flash" was reported, but they failed to detect any sign of nuclear radiation. Studies of wind patterns confirmed that fall-out from an explosion in the southern Indian Ocean could have been carried from there to southwestern Australia. It was reported that low levels of iodine-131 (a short-half-life product of nuclear fission) were detected in sheep in the southeastern Australian States of Victoria and Tasmania soon after the event. Sheep in New Zealand showed no such trace.
The Arecibo ionospheric observatory and radio telescope in Puerto Rico detected an anomalous ionospheric wave during the morning of September 22, 1979, which moved from the southeast to the northwest, an event which had not been observed previously by the scientists.
Read more about this topic: Vela Incident