Proliferation: A flash from the past
t 3 o'clock in the morning of September 22, 1979, a U.S. Vela satellite detected a brief, intense, double flash of light near the southern tip of South Africa. Did it signal a low-yield nuclear explosion? Will we ever know for sure?
The controversy over the mysterious flash, which has never been settled, was raised again last April when South African Minister Aziz Pahad was quoted in Ha'aretz, an Israeli daily paper, as calling the incident "definitely a nuclear test."
The Ha'aretz report continued: "This was the first time an official spokesman of [Nelson] Mandela's government had admitted that the flash was in fact the result of a nuclear test, thereby contradicting declarations made by Mandela's predecessors that South Africa had never conducted such tests." Although the article did not explicitly say so, it also implied that the test might have been conducted with Israel.
Pahad's office responded that his remarks were taken out of context. For example, his press secretary told the Albuquerque Journal in an article dated July 11 that Pahad had said only that there was a "strong rumor" that a test had taken place, and that it should be investigated.
But it was no use. Also on July 11, Los Alamos National Laboratory issued a press release touting Pahad's original statement as confirming the lab's long-stated position that the 1979 flash indicated a nuclear test. Of course, not correcting the statement may have been part of Los Alamos's current campaign for funds to put a new generation of detection equipment on future satellites.
Despite Pahad's correction, a widely reported story in the July 21 Aviation Week & Space Technology led with the statement that a "South African government official has confirmed that his nation detonated a nuclear weapon in the atmosphere in September 1979."
According to the International Atomic Energy Agency (IAEA), however, South Africa did not construct its first nuclear explosive device until November 1979, two months after the mysterious flash. But the IAEA has not investigated allegations that the event was an Israeli test, perhaps conducted with South Africa's knowledge.
An awkward signal
Based on the characteristics of the light signal recorded by Vela, the United States estimated that the flash could have come from a test with a yield of two to four kilotons.
In addition to its light sensors, or "bhangmeters," the satellite also had sensors that could have detected electromagnetic pulses (EMPs) from an atmospheric explosion. But at the time of the flash, the satellite was two years beyond its life span, and its EMP sensors had failed.
At an altitude of 60-70,000 miles, the satellite could only place the possible explosion within a 3,000-mile radius. This area included portions of the Antarctic, southern Africa, and large portions of the Atlantic and Indian Oceans. Some analysts placed an explosion at approximate sea level near Prince Edward Island in the Indian Ocean. Prince Edward is a South African possession, far from shipping or commercial air routes.
Because of the location, South Africa quickly emerged as a prime suspect, although the South African government just as quickly denied that it had conducted a test. The nuclear weapon states also denied conducting tests in the region.
Soon after, rumors emerged that Israel had conducted the test, either alone or in cooperation with South Africa. Other rumors named Taiwan as a possible third partner.
South Africa and Israel, both of whom had signed the Partial Test Ban Treaty, would have been in violation of international law if it could have been proved that they had conducted a test. More important, the Carter administration was acutely aware that clear evidence of a test could seriously disrupt U.S. diplomatic efforts in the Middle East or in southern Africa. And it could have led to a cutoff in military aid to Israel.
A confirmed Israeli test would also have disrupted the Camp David peace accords, concluded in March 1979. The Christian Science Monitor reported a few months later that before the Camp David meetings, Egypt, Syria, and Iraq all said that confirmation of a test would push them to seek an Arab nuclear capability, if not war.
After the flash
Soon after the sighting, the Carter White House assembled a distinguished panel of non-government scientists to assist in determining whether the light signal indicated a nuclear explosion. In addition to studying the satellite data, the panel also reviewed possible corroborating information.
The panel's public report, which was released in the summer of 1980, concluded that the "signal was probably not from a nuclear explosion," although it did not "rule out the possibility."
The panel also suggested other explanations. It ultimately concluded that the signal was of unknown origin--a "zoo event." The group also suggested that the optical data could have been generated by a small meteoroid hitting the satellite, although the probability of such an event was very low.
The panel's conclusions were hotly contested by several government agencies, particularly the CIA, the Naval Research Laboratory, Los Alamos, and the Defense Intelligence Agency. They believed that the data indicated a nuclear explosion. The Naval Research Laboratory's 300-page report, the only comprehensive and original government analysis, concluded that there had been a nuclear event near Prince Edward Island or Antarctica.
Because the political stakes were so high, many critics of the White House panel accused the Carter administration of a cover-up.
Nevertheless, some on the "it-was-a-test" side now concede that the data would not have been persuasive enough to levy sanctions against Israel or South Africa. David Simons, a Los Alamos physicist who had just joined the lab's verification program in 1979, was quoted in the July 11 Albuquerque Journal article: "Even we felt the United States would be putting itself in an awkward position. To stand up and force some kind of political sanctions with that kind of data would have been very difficult."
An atmospheric nuclear explosion emits an intense light flash that has a distinctive double-hump signature with a dimmer, but still luminous, trough. Both of the Vela's bhangmeters detected a double flash of light.
In addition to having the right double-hump, the flash also had the right duration. However, the White House panel found another characteristic that led them to conclude that the signal was probably not from a nuclear explosion. The two light sensors did not record roughly parallel intensities of light, as would be expected for light emitted from a distant event. The difference in the intensity of light recorded by the two bhangmeters led the panel to conclude that the event--whatever it was--was much closer to the satellite and more in view of one sensor than the other.
Classification rules have prevented the other side of the debate from releasing any detailed alternative explanations of this anomaly, although the rules have not prevented the critics from expressing their disagreement. In the Los Alamos press release of July 11, Simons said similar discrepancies had been observed in Vela signals from earlier atmospheric tests. And one expert who helped design the satellite said the panel's explanation of how a near-perfect image of a nuclear explosion could be caused by a meteoroid strained credulity. He added that when an explanation was needed, "the zoo animals come marching out of the woodwork."
The debate also focused on other monitoring data that seemed to confirm an explosion. In addition to light and EMPs, nuclear tests in the atmosphere produce fission products and generate a variety of disturbances--hydroacoustic waves, acoustic waves, seismic signals, traveling ionospheric disturbances, and magnetic signals.
Soon after the event, underwater hydrophones picked up hydroacoustic (sonar) pulses similar to those known to be caused by nuclear detonations. The Naval Research Laboratory analyzed these signals, concluding that they had traveled on a direct path from a source near Prince Edward Island and were reflected off the Antarctic ice shelf. The intensity of this signal was consistent with that of a small explosion on or slightly beneath the ocean's surface. But the White House panel rejected this study, saying it used non-standard methods of analysis and was incomplete.
One White House staffer has said that if an explosion had occurred near the island, it would also have been recorded by another Vela satellite, which was not the case. Critics have responded that the second satellite may not have been working properly.
Additional evidence came from researchers at a new, highly sensitive radio-telescope in Arecibo, Puerto Rico, which detected a traveling ionospheric disturbance--a ripple in the Earth's upper atmosphere--moving from southeast to northwest in the early morning of September 22. But Los Alamos space scientist Lew Duncan, one of the researchers who originally connected the ionospheric disturbance to the event that night, said recently that he is still not fully convinced that what the dish at Arecibo detected was a nuclear test.
After the flash was detected, the U.S. government made an effort to collect fission products--but the planes doing the sampling did not enter the low-pressure air mass in which the explosion was thought to have occurred.
One indication of possible fallout was found in samples of sheep thyroids in Western Australia. These samples were examined by a University of Tennessee scientist a few months after the event, but the results were not revealed until after the White House panel had completed its work.
The samples showed slightly elevated levels of iodine 131, a short half-life radioactive material. Meteorological studies confirmed that wind and weather patterns could have carried radioactive fallout from the area of the flash, which could have rained over Western Australia in late September. However, the levels of radioactive iodine were very low, sparking a debate over their significance. In the end, this indicator was regarded as inconclusive.
The ships at sea
If a test was conducted in or above the ocean, several naval ships would have been in the area--to see that the device was deployed safely and to provide security. Early reports indicated that a contingent of the South African Navy was in the South Atlantic at the time. But no evidence ever emerged to link these ships to a nuclear event.
The most troubling report comes from Commodore Dieter Gerhardt, a convicted Soviet spy who at the time of the suspected test was the commander of the Simonstown naval base near Cape Town. He said that a fleet of Israeli ships had made a port call at Simonstown shortly before the mysterious flash.
Gerhardt is convinced that a test occurred that night. He does not claim to have been involved, but he says that the flash was produced by an Israeli-South African explosion, code named "Operation Phenix." In February 1994, Gerhardt told the Johannesburg City Press: "The explosion was clean and was not supposed to be detected. But they were not as smart as they thought, and the weather changed--so the Americans were able to pick it up."
Whether or not an explosion occurred, it should be possible to find out what ships were in the area. South Africa tracked and identified all commercial and military shipping around the Cape. From a sophisticated maritime communications and surveillance center near Simonstown, it monitored 20 million square miles of ocean, pinpointing the location of every ship and identifying it by type, country of origin, and on-board armaments.
Is it time to reopen the investigation?
The U.S. government has ample reason to reopen the investigation of the event. Neither side in the controversy has marshaled compelling evidence for its case, leaving the issue to fester. In addition, the White House panel did not study all the evidence. If the investigation is resumed, the United States should seek the cooperation of South Africa, which under Nelson Mandela's leadership should be interested in discovering the true story behind the mysterious flash.
But the recent controversy shows that the South African government needs to take careful stock of what it knows. Too often African National Congress officials have been quick to repeat apartheid-era rumors about the old regime's nuclear activities without taking the time to determine the facts.
The U.S. government should declassify additional information about the event. A thorough public airing of the existing information could resolve the controversy.
The only apparent reason not to reopen the investigation is the fear that it could uncover an Israeli test. But today, few doubt that Israel has nuclear weapons, and that knowledge has not seemed to diminish U.S.-Israeli ties.
David Albright, a Bulletin contributing editor and a physicist, is president of the Institute for Science and International Security (ISIS) in Washington, D.C. Corey Gay is a policy analyst at ISIS.
November/December 1997 pp. 15-17 (vol. 53, no. 06) © 1997 Bulletin of the Atomic Scientists