Sometime this week, the wispy atmosphere 68 miles above the Earth will begin to bend back the fragile solar panels on the Russian space station Mir - gently at first, like a dog's ears in the wind.
But then it will rip them off, and break the obsolete, 148-ton Mir station into a formation of 1,500 white-hot, aluminum and titanium meteors. Whatever doesn't burn up or melt will be hell-bent for a deep-ocean grave in the remote southeastern Pacific.
That's if the Russians' plans to ditch Mir go as advertised.
If they don't, sometime no later than March 28, close to 27 tons of searing metal debris will come screaming out of the sky on its own, landing somewhere between 51 degrees north and south latitudes.
That encompasses almost anyplace in the inhabited regions of the world, including the United States. But American officials say there is little reason for worry.
"The Russians have done this many, many times. We have every reason to believe they will do this successfully," says Nicholas L. Johnson, NASA's chief scientist and program manager for orbital debris.
"The Russians have dropped five other stations in the same area [of the Pacific] and 80 Progress [supply] vehicles," including two since January, he said. "It's seen as a very responsible way of getting rid of things that might otherwise be a hazard to people around the world."
Only last June, the U.S. successfully de-orbited the 14-ton Compton Gamma Ray Observatory after a gyroscope failure made the 9-year-old satellite difficult to control. Its remains plunged safely into the Pacific 2,400 miles southeast of Hawaii.
One group of entrepreneurs is so sure Mir's de-orbiting maneuver will work they have invited scientists, cosmonauts and paying adventurers to watch the spectacle from an airplane flying alongside the re-entry corridor.
Still, Mir is the largest and most unwieldy man-made object that's ever fallen from Earth orbit. And not even the Russians know precisely how it will behave.
Just in case, the Russian Space Agency this month paid a $1 million premium to buy $200 million in civil liability insurance. The policy, backed by a group of international insurers, will cover any damages caused by Mir debris. The Russians say they acted mostly to reassure the international community.
It's hard to shake memories of Mir's previous accidents -- a terrifying 14-minute fire in 1997 and a nearly fatal depressurization that same year after a collision with a supply craft. Crews and ground controllers have also grappled with a series of life-support, power, computer and communications failures.
Mir's glory has long been exaggerated by the Russian press, said Roald Sagdeev, the Soviets' former chief of space science. He's now director of the East-West Space Science Center at the University of Maryland, College Park.
At its launch in 1986, Mir's scientific instrumentation was already a decade old. It could not compete in astronomy or materials science research, he said.
"When the time came for an update, say, in 1990, the Soviet Union was on the verge of dissolution. There were tremendous financial problems," Sagdeev said. Mir's story became a continuing fight for survival.
"It was great for engineers," he said. "They learned how to supply the station with repairs, sometimes very sophisticated. And they required from the crew to learn how to do this job in extravehicular walks."
But Mir's scientific accomplishments, he said, were "more or less mediocre."
Its most lasting contribution has probably been the years of experience in long-duration space flight gained by Russian and later American crews.
"Biomedical science, the behavior of the human body in space -- that was prospering," Sagdeev said. "And during the few years of very active NASA participation, NASA made very important contributions."
NASA had nothing like it. The U.S. space agency managed only 171 days of manned experience aboard its 1970s Skylab space station.
Mutant dragonfly
Built to last five years, Mir survived and grew for 15. The sixth and final Mir module, Priroda, was added in 1996. With five pairs of solar arrays, Mir took on the appearance of a mutant dragonfly.
Over the years Mir hosted 42 Russians and 63 foreign guests -- seven of them U.S. astronauts. But in the end, the $4 billion station became too noisy, dirty and dangerous for important scientific work, and too costly for the struggling Russian state to maintain.
After flirting briefly with private entrepreneurs who wanted to lease Mir for space tourism, the Russians decided last fall to bring it down.
"It's long overdue," Sagdeev said. "Mostly it was kept by a group of so-called patriotic-minded Russians arguing this is a matter of national pride. It's almost like keeping Lenin's body in the mausoleum in Red Square. My proposal is he should be launched to orbit. It would be a compromise."
As with anything in low Earth orbit, Mir is already falling, slowed by atmospheric drag. Early last year, Mir was a respectable 245 miles above the Earth. Then the Russians stopped sending spacecraft to push it higher. By last week it was no higher than 150 miles.
Sometime in the next few days, with Mir somewhere over Africa, the Russians plan to begin firing braking rockets on an unmanned Progress supply ship clamped to the station. After the final push, Mir will have begun a shallow dive into the atmosphere at close to 17,000 mph. The death plunge will last about 45 minutes.
At an altitude of 68 miles, NASA's Nicholas Johnson said, Mir's five pairs of solar panels will fold back or break away and burn up. At 56 miles, the six main modules, and the Progress supply craft, will begin to separate as deceleration forces and tumbling rip apart their docking ports.
"When you get down to about 80 kilometers [48 miles], individual modules start to come apart in a major way," Johnson said. "There's a lot of melting, and a lot of force because of deceleration. You start to see a lot of big pieces shed."
Meltdown
Mir's aluminum components will begin to melt first, at 1,220 degrees Fahrenheit. Beryllium and titanium -- with melting points above 2,300 and 3,000 degrees respectively -- will begin melting later, and will make up the bulk of what reaches the surface.
When the Compton observatory fell, Johnson said, "it looked like a very bright, intense comet where the main body was." Leading a long train of glowing debris, it crossed the sky for a minute or more. "Mir may have six or more big pieces coming down side by side."
In all, the Russians estimate that 1,500 fragments totaling 27 tons might survive the fall. The largest is likely to weigh 1,500 pounds. It will all hit the water at a "terminal velocity" of 150 mph.
Airmen and mariners in the South Pacific will have been warned to steer clear of a vast impact "footprint" 3,700 miles long and 124 miles wide.
Because the Russians lack a worldwide tracking network, they have asked the United States for data to help precisely time Mir's final rocket firings.
The U.S. Space Command routinely tracks more than 10,000 satellites and pieces of space junk larger than a baseball.
But not even the Space Command can say when or where Mir will land once it begins to fall. Irregularities in the Earth's gravity field or transient changes in the contours of the atmosphere can skew the equations and send the debris far off-target.
Scientists remain confident that people are safe, if only because three-quarters of the planet is ocean, and only a quarter of the land mass is inhabited.
A few close calls
Since 1957 the U.S. military has tracked the re-entry of more than 17,000 man-made objects. None has ever injured anyone. But there have been a few scares:
In 1978, the Russians lost control of a Cosmos 954 military satellite with a nuclear reactor on board. It fell to Earth near the Great Slave Lake in Canada. Searchers found much of the radioactive debris. No one was hurt.
In July 1979, NASA lost its grip on the Skylab space station. Most pieces fell into the Indian Ocean, but some landed in the Australian outback. No one was hurt there either.
In 1996, the Russian Mars 96 spacecraft failed to reach Earth orbit on launch, and fell into the eastern Pacific. Some of the debris may have fallen in South America.
A malfunction of the Progress rockets or an ill-timed loss of radio contact could spell trouble for Mir. "There are no guarantees," Johnson said.
"But there would have to be a serious malfunction early on for Mir to hit Baltimore."
Frank D. Roylance is a science reporter for The Sun.