The probe that fell to Earth

by James Oberg

New Scientist -- 6 March 1999

If a spacecraft carrying a deadly cargo of plutonium crashed in a remote area, you'd expect an international search effort to prevent it falling into the wrong hands. But you'd be wrong, says James Oberg
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WHILE CAMPING ONE WEEKEND in the mountains of southern Chile, John VanderBrink witnessed an extraordinary event. Late at night he saw a bright, slow-moving meteor low in the northwestern night sky, travelling horizontally from left to right about 10 degrees above the horizon. "The object was brighter than Sirius and had a luminous trail five degrees in length," recalls VanderBrink. He even saw sparkling fragments break away from the main object. He and his wife Katrina followed the object's path for almost a minute until it disappeared behind mountains to the north.

VanderBrink is an electronics specialist at the European Southern Observatory near La Serena and it was clear to him that this was no ordinary meteor. "I had no illusions that it was anything other than a piece of space debris," he says. A very large piece, as it would turn out. What the VanderBrinks saw that night was almost certainly the re-entry into the Earth's atmosphere of a failed Russian spacecraft called Mars-96 .

Although an unusual sight, the re-entry of a spacecraft would usually be of little interest. But Mars-96 was no ordinary vehicle. The spacecraft was carrying around 200 grams of plutonium, a hot radioactive element that was supposed to provide power on the cold Martian surface. Plutonium is considered to be one of the most poisonous substances known to humankind. In the wrong hands, it could be used as a spectacular weapon of terror.

Nobody knows exactly what happened to the spacecraft's deadly cargo. While governments prefer to think it is lying at the bottom of the Pacific Ocean, there is growing evidence--including thousands of eyewitness reports like the VanderBrinks'--that the plutonium fell intact into the Andes. It is almost certainly still lying there, probably somewhere near the border between Chile and Bolivia. And nobody seems to care who finds it.

Russia's Mars-96 probe was the most ambitious Russian interplanetary expedition ever and designed to solve many of the Red Planet's mysteries. The 7-tonne spacecraft actually consisted of five separate vehicles. The largest--a 5-tonne section--was designed to orbit the planet. Two landers, each weighing 50 kilograms, were designed to enter the Martian atmosphere and broadcast from the surface. Two "penetrators", shaped like golf tees and weighing 65 kilograms each, were even designed to survive the impact with the ground, sending them a few metres beneath the surface. The four landing craft carried a total of 18 small plutonium batteries to generate electrical power.

The launch was on Saturday, 16 November 1996, shortly after midnight from the Baikonur cosmodrome in Kazakhstan. The spacecraft was so big that to get it into a parking orbit 160 kilometres above the Earth required a huge three- stage Proton rocket as well as a kick from a fourth stage thruster that would remain attached to the vehicle. The fourth stage was then supposed to fire again an hour later to push the probe on its way to Mars. Even that would be insufficient to achieve the necessary escape velocity from the Earth's gravity. The probe would then separate from the expended fourth stage and fire its own small engine to complete the escape manoeuvre.

Vladivostok or bust

After the first burn of the fourth stage, Mars-96 reached its parking orbit 20 minutes after blastoff and as it crossed China, within direct radio contact of a Russian tracking site at Ussuriysk, near Vladivostok. It then crossed the Pacific from northeast to southwest, passing within 600 kilometres of the watching eyes of the American military space tracking site on Kwajalein Island in the mid-Pacific.

The second fourth-stage burn was supposed to occur as the spacecraft flew northeast over the coast of Uruguay on the eastern side of south America. Normally, the Russians would station a tracking ship off the coast of Africa to monitor this burn and provide extra commands if needed. But most of the tracking ships had been sold for scrap and the one remaining vessel was rusting in St Petersburg harbour. In the event, the fourth stage failed and the rocket and the Mars-96 probe remained in the parking orbit.

At the time, nobody knew it had failed. The probe's simple-minded autopilot never noticed the absence of the burn because a minute after the scheduled completion time, crossing the West African coast over the Côte d'Ivoire, it separated from the fourth stage and turned on its own small engine, as originally planned. This sent it into an elliptical orbit and towards its fiery demise.

None of this was yet known to the Russian trackers who had no contact with the spacecraft, nor to the American eavesdroppers who had seen a normal first orbit. Mars-96 finished its burn, obediently unfolded its solar arrays, and triumphantly broadcast its status: "insertion burn complete, spacecraft in interplanetary cruise configuration". At the main Russian space tracking facility at Yevpatoriya in the Crimea, the signal was received and for a few joyful moments the engineers thought that nothing was wrong.

But as the probe passed Yevpatoriya overhead, tracking data told the Russians the awful truth. The probe was trapped in an elliptical Earth orbit, with no possibility of an escape towards Mars. The mission was over. Only then began the desperate attempt to crash the space- craft safely. But within minutes it had passed beyond the range of the Crimean station, and no other Russian site ever heard from it again.

A few minutes later, the probe passed about 900 kilometres south of Kwajalein, but the Americans didn't even look for it, because they were expecting it to already be on its way to Mars. The probe soared out to a high point of perhaps 1500 kilometres over the Philippines. It crossed New Guinea, the northeast Australian coast to Brisbane, passed across Wellington, New Zealand, then out over the far southern Pacific until it approached the South American coast where the VanderBrinks were camping that night.

Meanwhile, the faulty fourth stage was still in its circular orbit with a small battery-powered beacon which the Russians were able to track. By the time American military space surveillance systems learnt that the probe had failed, the only object left in orbit was this fourth stage. Based on similar failures of Soviet interplanetary missions in the past, the US Space Command, which monitors all rocket launches, concluded that the probe and its plutonium were still attached to the rocket.

Alarm bells began ringing as the Americans suddenly realised that the plutonium was heading back towards Earth. As Sunday wore on, they calculated where the satellite would re-enter the atmosphere. By mid-afternoon Washington time, it looked as if Australia could be hit.

At this point, a full-blown Emergency Response Team had assembled in Washington, DC, and President Clinton personally telephoned the Australian Prime Minister John Howard to assure him of the Americans' full support in any search and recovery operation that might be necessary. But new tracking data soon showed the satellite overshooting Australia and briefly threatening New Zealand until the impact point moved far out into the southern Pacific Ocean. By Sunday evening, Washington time, the object had burnt up somewhere west of Chile, near Easter Island. The Americans concluded that whatever was left had ended up out of harms way on the ocean floor. The "emergency" was declared over and the specialists were sent home.

It was not until later that the Russians worked out what had really happened--and it was much later before the Americans found out. On Monday, 18 November, two days after the launch, the Russians held a sombre press conference in Moscow and revealed that the upper stage and the probe had separated at the very beginning of the flight. They admitted that they now believed that the object tracked on Sunday--the one that had caused the worldwide panic and warnings--was only the inert and plutonium-free fourth stage. As for the plutonium, all they could be sure about was that it had fallen to Earth somewhere along a track across the eastern Pacific, right across the middle of South America, and then into the mid-Atlantic. They could not be any more specific.

It wasn't until almost two weeks later that the US Space Command officially admitted its original error. It stated that a new analysis of infrared tracking data from spy satellites suggested where the probe had re-entered. The statement continued: "Any debris surviving the heat of this re-entry would have fallen over a 200-mile long portion of the Pacific Ocean, Chile, and Bolivia . . . [US Space Command] is not able to estimate what portion, if any, of the Mars-96 spacecraft might have survived re-entry . . . The Russians are in the best position to address the materials on board their spacecraft and whether any portion of the spacecraft might have survived."

White House spokesman David Johnson told reporters that this information was immediately passed on to the countries involved: "We informed the South American governments and the public as soon as we concluded that there was a possibility of something falling there," he stated, the week after the US Space Command's news release. However, this time there was no team of experts on standby, no emergency calls from the president and no offer of help.

Neither was there any help from the Russians. In Moscow, the head of the Russian Space Agency, Yuriy Koptev, met with ambassadors from Argentina, Bolivia, Chile, and Peru, to assure them that even though they were "adjacent to the crash site", there was no chance of any plutonium leakage. "There is no threat of radioactive contamination of the Pacific," he claimed.

The US Space Command's admission came as long-overdue reassurance to a lot of people in Chile. By chance, the probe had re-entered Earth's atmosphere after dark, when the sky happened to be completely clear. So thousands of people who were outside had seen the probe's final fall into the atmosphere. In the days that followed, many of these people tried to report their observations to the authorities. Yet the Chilean government, assured by Washington and Moscow that the probe had fallen into the ocean hundreds of kilometres away from their coastline, disregarded the stories and told the witnesses they had seen nothing important.

However, Luis Barrera also heard of the fireball and became suspicious. Barrera is directory of the Astronomy Institute at the Catholic University of the North in Antofagasta and immediately began to collect evidence. He visited each eye- witness, collected statements, visited the places where the sightings were made to take photographs and calculate the likely route of the fireball. He released his preliminary conclusions later in December. "Based on my studies of the reports, all confirm that the object exploded over the sea, and that the trajectory was southwest to northeast," he says.

NASA's studies of satellites entering the atmosphere show that they tend to break apart at about an altitude of 80 kilo- metres, while still moving almost horizontally at speeds of up to 7000 metres per second. At this speed, the surviving fragments could easily travel another 200 kilometres after a break- up. "The remains of the probe reached South America in the region of Tocopilla, Chile, in the direction of the city of Oruro, Bolivia," says Barrera.

Since Mars-96 carried four probes designed to enter the Martian atmosphere, they would almost certainly have survived entry into Earth's atmosphere. And the penetrators were designed to survive an impact with the ground.

The following March, under questioning from persistent private researchers, the US Space Command even acknowledged that it knew about the sighting reports from Chile. "We were aware of a number of eyewitness accounts of the re-entry event via the media several weeks after the re-entry occurred," wrote Major Stephen Boylan, Chief of the Media Division at the US Space Command in Colorado Springs. "Upon further analysis, we believe it is reasonable that the impact was in fact on land."

Given this conclusion, the lack of response is difficult to fathom. The US military has developed contingency plans for nuclear accidents. Depending on the level of contamination, these range from mass evacuations, mobilisations of thousands of shoulder-to-shoulder searchers, deployments of fleets of helicopters and ground sensors, and other responses ranging all the way down to putting up posters.

In January 1978, Kosmos 954, a nuclear-powered Soviet spy satellite, fell to Earth in northwestern Canada. Although this area is sparsely populated, several residents were accidentally exposed to radiation--none resulting in serious harm--before a major recovery effort succeeded in retrieving all the nuclear material.

But with Mars-96, the Americans and the Russians have opted to leave the plutonium where it lies. This may not be the wisest course of action. "It's a potentially hazardous material," says Otto Raabe, of the Institute of Toxicology and Environmental Health at the University of California in Davis.

Raabe concedes that the radiation from such a small amount of plutonium would not necessarily be dangerous. "Someone could receive some external radiation exposure from neutron and gamma radiation if close to the material, but it would not be at dangerous levels for such a small amount of plutonium." Radiation levels would probably be in the 0.01-0.02 milli-sieverts range. That would require keeping the battery next to the skin for a full year to accumulate the annual safe dosage for American radiation workers.

Although unlikely, this is a possibility. After the explosion of a rocket near the Baikonur cosmodrome in 1970, Soviet soldiers found a nuclear battery in the wreckage. Later, investigators looking for the battery discovered that the shivering soldiers had secretly kept it as a hand-warmer in their poorly heated guardhouse. In this case, the unit was spotted by one of the searchers and confiscated immediately.

In the Andes "altiplano", the high salt flats where it is bitterly cold even in mid-summer, one of the Mars-96 power units would seem like a perpetually warm "magic box". It would be of enormous value to anyone who found it. Each battery is the size of a 35-millimetre film cannister and contains about 12 grams of plutonium-238. The finder might even take it home and put it in his bed, or his children's bed--and would be careful not to tell anybody who might take it away.

The characteristics of the probable impact area make it likely that pieces of the probe will be found. Most of the land consists of high salt flats with little or no vegetation. It is lightly populated, but hunters, shepherds and prospectors wander around, as do army patrols. Life is hard enough in the Andes without the added risk of exposure to plutonium.

The biggest danger would be from plutonium dust, says Raabe. "For all practical purposes, the primary hazard from plutonium-238 dioxide occurs if it is somehow pulverised into very tiny particles--smaller than 5 micrometres in diameter--that are inhaled." This will not be easily achieved with plutonium pellets in Mars-96 which were formed at high tenperatures. "So it is not likely to pose a problem," Raabe says.

But one NASA doctor, who prefers to remain anonymous, says: "[Doing nothing] is a policy that places people at risk." These assurances rely on the assumption that the only threat to the containment of the plutonium is from the impact on landing. Far more plausible is the possibility that, if found, a probe would be deliberately broken open by the finder in search of valuable materials.

In the Brazilian city of Goiânia in 1987, four people died of radiation poisoning after breaking into an abandoned radiation therapy unit containing 100 grams of the highly radioactive element caesium-137. They used saws and sledgehammers to break open the machine's casing.

The most frightening scenario involves the plutonium from Mars-96 falling into the wrong hands. Although 200 grams of plutonium is far too little to be used in a nuclear weapon, it would be a valuable prize for terrorists. Used in a conventional weapon, the plutonium could be spread as dust over a major city.

The military specialists are aware of the danger. The only real threat of terrorist application is in deliberate contamination, says Colonel Dan Smith of the Center for Defense Information. But "that's enough of a use given the hype we've attached recently to the possibility of terrorists introducing nuclear materials into the US--it would drive governments around the bend if [terrorists] said they had found [Mars-96]".

In the recent past, governments have placed great emphasis on controlling plutonium. In 1994, the German police were very excited to confiscate 350 grams of plutonium from Russians trying to smuggle it through the country (This Week, 20 August, 1994, p 5). By this token, the 200 grams in the probe would seem more than enough to inspire attempts to retrieve it.

Somewhere between a policy of mass evacuations and the current "do-nothing and hope" approach, a balanced response to the Mars-96 plutonium has yet to be identified. Although the Russians are obliged by international law to pay for the search and cleanup, they cannot afford to, even if they were to admit that the Chilean witnesses really saw their falling spacecraft. As for the US, American officials are adamant: "It's not our vehicle," the then head of NASA space science, Wes Huntress, told New Scientist. "We have no responsibility for it."

Radiation experts in NASA's space programme say privately that while an active search would probably not be justifiable, a far more vigorous programme of local public warnings is needed. Notices would need to be posted widely, with full technical descriptions of the objects and with substantial cash rewards offered for information or for actual materials. Free medical screening would also be offered. Easy points of contact need to be established, either through military or police offices, or through a special-purpose recovery centre with full-time staff.

Barrera has long been saying the same thing. "We need international aid to investigate the most probable region, but the Chilean authorities have tried to minimise the problem by stating publicly there are no environmental risks or personal health risks." Barrera complains that nobody has even provided Chile with drawings of the space hardware. He says the longer it takes, the greater the risks become. "My fear is that we are going very slowly, very slowly."