Shortly before sunrise on Sept. 22, 1979, a U.S. surveillance satellite known as Vela 6911 recorded an unusual double flash as it orbited the earth above the South Atlantic. At Patrick Air Force Base in Florida, where it was still nighttime on Sept. 21, the staff in charge of monitoring the satellite’s transmissions saw the unmistakable pattern produced by a nuclear explosion—something U.S. satellites had detected on dozens of previous occasions in the wake of nuclear tests. The Air Force base issued an alert overnight, and President Jimmy Carter quickly called a meeting in the White House Situation Room the next day.
Nuclear proliferation was just one of the Carter administration’s headaches in late 1979. The president was dealing with a slew of foreign-policy dilemmas, including the build-up to what would become the Iran hostage crisis. Carter was also preparing for a reelection campaign in which he had hoped to showcase his foreign-policy successes, from brokering Israeli-Egyptian peace to successful arms control talks with Moscow. The possibility that Israel or South Africa, which had deep clandestine defense ties at the time, had tested a nuclear weapon threatened to tarnish that legacy. And the fact that South Africa’s own nuclear weapons program, which the Carter administration was seeking to stop, was not yet sufficiently advanced to test such a weapon left just one prime suspect: Israel. Leading figures within the administration were therefore keen to bury the story and put forward alternative explanations.
Those alternative explanations were widely dismissed by many members of the scientific and intelligence community at the time; four decades years later, they look even more questionable.
On the 40th anniversary of the Vela event, Foreign Policy has assembled a team of scientists, academics, former government officials, and nonproliferation experts to analyze the declassified documents and data in the public domain, explain the political and strategic objectives of the key players at the time, and argue why a mysterious flash 40 years ago still matters today.
On Sept. 22, 1979, the U.S. Vela satellite recorded the telltale light signal from a nuclear test using detectors called bhangmeters. The satellite, known as Vela 5B or Vela 6911, was one of a number launched in the wake of the 1963 Partial Test Ban Treaty (PTBT), which banned nuclear tests in the atmosphere, underwater, and in outer space. The detected signal was a “double flash” characteristic of nuclear test signals recorded on 41 previous occasions by Vela satellites.
A nuclear explosion light signal typically starts with a powerful millisecond-long light spike from the surface of the explosion’s dense early fireball, followed by a dark period of several milliseconds as the fireball expands and its surface temperature drops, and then a drawn-out powerful light as the expanding fireball becomes transparent and radiates a light signal from its interior as well. The signal is usually drawn on a graph using logarithmic scales on both axes, where it appears to have two comparable humps, hence a characteristic double hump. Nothing in nature produces such a double-humped light flash. The spacing of the humps gives an indication of the amount of energy, or yield, released by the explosion (see below).
The United States had launched the Vela satellites, orbiting as far as one-third of the way to the moon, to monitor compliance with the PTBT. Until 1979, they had not detected any illicit explosions among the 41 recorded nuclear events. The satellite in question, Vela 6911, had in fact been retired. Although not all of its systems were operable, the two principal light detectors were still functioning. It had previously distinguished itself mainly for detecting strong gamma-ray bursts from distant galaxies, an important scientific discovery. When it recorded a double flash in 1979, the signal could have come from anywhere within a diameter of several thousand miles.
Suspicion quickly fell on South Africa, which was known to be working on a bomb, and even more so on Israel, which had close military connections with South Africa and had an untested nuclear arsenal. U.S. President Jimmy Carter wrote in his diary for Sept. 22, 1979: “There was indication of a nuclear explosion in the region of South Africa—either South Africa, Israel using a ship at sea, or nothing.”
An Israeli test would force him to deal not only with violation of the PTBT, but also with U.S. nonproliferation legislation.
An Israeli test would force him to deal not only with violation of the PTBT, but also with U.S. nonproliferation legislation. The 1977 Glenn Amendment to the Arms Export Control Act mandated an end to arms assistance, and an automatic application of extensive U.S. sanctions, if the president determined any state (other than the nuclear states authorized by the Nuclear Non-Proliferation Treaty) detonated a nuclear explosive after 1977. To complicate matters, the second round of Strategic Arms Limitation Talks between the United States and the Soviet Union was at that moment held up in the Senate, in part because of concerns about the United States’ technical capacity for verification. An inability to identify the culprit of the apparent nuclear test would strengthen the hand of the agreement’s opponents.
The Carter administration set about developing a public relations strategy in case the information leaked. They believed their problems would go away if they could cast doubt on the satellite data. That is, if it could be argued there was no characteristic bomb signal, then there would have been no nuclear explosion, and therefore no need to do anything. That became the administration’s line.
In October, the president’s science advisor, Frank Press, a distinguished geophysicist but also an official tuned to his boss’s interests, set up a panel of scientific experts to examine the Vela event, and in particular whether the observed flash could have a non-nuclear explanation. The panel consisted of eight respected physicists and engineers, including a Nobel Prize winner, and was led by Jack Ruina, a professor at the Massachusetts Institute of Technology with long experience as a government advisor on weapons systems.
The panel issued its final report in May 1980, after just three meetings. It concluded, “It is our collective judgment that the September 22 signal was probably not from a nuclear explosion.” Its members dismissed all evidence that suggested otherwise. This included the Naval Research Laboratory’s analysis that had located the blast’s ground zero near the Prince Edward Islands, about 1,000 miles from South Africa’s southern coast, using hydroacoustic (underwater sound) data, and claims regarding possible detection of radioactive iodine-131 in thyroids of Australian sheep, which if established could only have come from a bomb test (see following article).
The prevalent view among White House insiders was clearly very different from the one they put out for public consumption.
The prevalent view among White House insiders was clearly very different from the one they put out for public consumption. Carter, obviously influenced by the NRL’s analysis, wrote in his diary for Feb. 27, 1980: “We have a growing belief among our scientists that the Israelis did indeed conduct a nuclear test explosion in the ocean near the southern end of Africa.”
Yet the panel decided to ignore both hydroacoustics and radioactivity, arguing that the apparent explosion-identifying signal could not be distinguished from the background “noise.” Its report did remark in passing, in reference to possible detection of radioactive products of nuclear fission, that “positive results from the debris collection effort would provide conclusive evidence of a nuclear explosion.”
But instead of seriously evaluating the hydroacoustic and radioactive fallout data, as Lars-Erik De Geer and Christopher Wright would later do, the panel put forward at some length, a rather contrived alternative explanation—speculating that a micrometeor impact on the satellite might have ejected a shower of smaller particles that reflected sunlight in just the right way to mimic the light signal from a nuclear explosion. In the end, though, they did not stand behind it: “We do not maintain that this particular explanation is necessarily correct,” they wrote. Later analysis showed it was essentially impossible.
But the for the Carter White House, all that mattered was the panel’s “probably not.” It classified key documents and closed the book on the subject.
Perhaps the most important document it classified was the Naval Research Laboratory’s 300-page June 1980 report. The highly regarded research organization tasked several dozen staff members with an analysis of the hydroacoustic signals.
While the NRL report remains classified, the gist of it can be gleaned from a Dec. 11, 1980 letter NRL research director Alan Berman sent to the White House after a futile attempt to draw the panel’s attention to his report. Berman was confident that the Navy’s sensors had indeed picked up the hydroacoustic signals of a nuclear explosion and that, taking into account the speed of sound in the ocean and the potential paths from the Prince Edward Islands, it came at a time consistent with the satellite observation of the light signal. According to Berman, “There was a large impulsive release of energy which coupled acoustic energy into the deep South Atlantic Sound channel.” Moreover, he wrote, the hydroacoustic signal stood out prominently from the random background noise.
The Carter administration was so afraid to enforce the PTBT against Israel’s 1979 violation that it did what it could to erase or keep hidden evidence of its detection of a test. Subsequent administrations, Republican and Democratic alike, went along with this, and the U.S. government still pretends it knows nothing about any Israeli nuclear weapons.
The longstanding U.S. refusal to acknowledge Israel’s nuclear arsenal has destroyed its credibility on nonproliferation.
It is an outcome—and a danger—that an arms control expert foresaw long ago. In the period before the PTBT, when the debate over nuclear nonproliferation agreements centered on the adequacy of technical means to detect Soviet cheating, Fred Iklé, in a classic 1961 Foreign Affairs article, reminded the arms control community that while technical means to verify performance are essential, compliance ultimately depends on a willingness to respond to detected violation. Iklé worried that, for political reasons, a democracy like the United States might decide to overlook an arms-control treaty violation. Most important, Iklé wrote, was to make sure a would-be violator could not expect to benefit from a violation.
That’s not what happened after the Vela event. Israel’s nuclear program went on to acquire weapons deliverable by land, sea, and air, with the means of delivery provided by French-designed missiles, German submarines, and American airplanes. If anything, Israel’s nuclear weaponry gained a stronger political position vis-à-vis the United States. A June 2018 New Yorker article reported that Israel demanded, and got, secret letters from U.S. Presidents Bill Clinton, George W. Bush, Barack Obama, and Donald Trump, which Israeli leaders interpreted as a U.S. promise to protect their nuclear weapons. And indeed, these U.S. presidents did protect Israel’s nuclear weapons from scrutiny and criticism in the United Nations and other international forums. It is part of a pattern that has destroyed America’s credibility on nonproliferation.
What Israel says—or doesn’t say—about its nuclear weapons is its own affair. But the United States should not agree to muzzle itself. It was always a humiliating role that opened the United States to the charge of hypocrisy. Now, in the face of strong confirmation of Israel’s violation of the Partial Test Ban Treaty, it has become an insupportable one.
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