Sun puts chill on space missions


Dangers: Solar storms are speeding the demise of the Russian Mir space station and posing a radiation hazard for the International Space Station that is under construction.

April 01, 1999|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

When Icarus flew too close to the sun, the heat melted the wax that held his homemade wings together and sent him plummeting to his death.

The sun's energy still poses significant, unseen hazards for those who fly too high.

Take Russia's aging Mir space station. Launched 13 years ago, Mir has outlasted computer crashes, a fire, a collision with an unmanned supply ship, its five-year life expectancy and even the Soviet Union that designed and built it.

More than 100 people, including seven U.S. astronauts, have visited Mir for research in science, engineering and long-term weightlessness. Stargazers around the world have watched at dawn or dusk as Mir coasted silently across the sky.

But rising solar activity, combined with gravity and Russia's financial problems, have apparently doomed Mir to a fiery plunge to Earth this year.

Mir is already falling, scientists say. From an altitude of 240 miles a year ago, the 130-ton space station has fallen to 212 miles despite two boosts from rocket "tugs" sent to push it higher. And its descent is accelerating.

"This is no normal decay. Mir is coming down faster than they thought," says Jesco von Puttkamer, a program manager with NASA's office of space flight.

Blame the sun, which next year will reach the peak in its 11-year cycle of activity. As this "solar maximum" approaches, the sun is heating the upper atmosphere and causing it to expand.

Mir is feeling the added "drag," which is slowing it like a car in rising water. And as it slows, it falls.

Russian Prime Minister Yevgeny M. Primakov has said that Mir could operate for three more years if someone came up with $250 million in operating expenses, part of which would be used to boost the station to a higher orbit. No one has volunteered the money.

"They've given themselves until April, and if they can't find the money they will start planning to bring it down," von Puttkamer says.

The two Russians and one Frenchman on board Mir are scheduled to depart Aug. 23. But von Puttkamer suspects Mir won't last that long. "They would need a re-boost to get to August," he says. He thinks the crew will be brought down earlier and that the station will fall in July or August.

Much of Mir would burn up in the plunge, but parts are likely to survive. The Russians must engineer a "controlled de-orbit" so that the parts don't fall on populated areas. Using the thrusters on a Progress supply ship, the Russians will try to steer Mir toward an empty ocean.

With Mir gone, attention will shift to the new International Space Station, under construction 250 miles above the Earth. Astronauts there will face another hazard from the sun: radiation.

Every day, the sun blows billions of tons of ionized gas, electrons and protons into space -- the "solar wind." Sometimes, especially near the solar maximum, this wind is punctuated by squalls and storms of dangerous high-energy particles.

The Earth is shielded from most of this radiation by its atmosphere and its magnetic field, or magnetosphere. But astronauts, especially those who might venture to the moon or Mars, could face potentially lethal radiation.

In 37 years of spaceflight, the National Aeronautics and Space Administration says, no astronauts have been overdosed, sickened or killed by solar storms. But there have been close calls.

"During Apollo, we really lucked out," says Michael Golightly, chief of space science at the Johnson Space Flight Center in Houston.

"One of the biggest solar storms ever recorded occurred on the 4th of August, 1972," Golightly says. There was another in October that year. Both storms occurred between the Apollo 16 and 17 lunar landing missions. "But it wasn't due to planning," he says.

Had explorers been caught on the moon's surface with nothing to shield them but their spacesuits, they probably would have died, the National Oceanic and Atmospheric Administration's Space Environment Center says.

Shuttle astronauts are generally safe from solar storms because they usually orbit near the equator, where the Earth's magnetic field affords the best protection. Exposures are higher nearer the poles.

"We've had two [shuttle] missions where there were solar particle events that could have caused concern," Golightly says.

A solar proton event in May 1989 -- during the last solar maximum -- found the shuttle Atlantis and its crew in orbit. They were too near their scheduled return to make a quicker, emergency landing. Radiation levels climbed in parts of the spaceship, but "crew exposure was very minimal," Golightly says.

Another Atlantis flight, in October 1989, also encountered a large proton event. But the shuttle's orbital path kept the crew far from the poles, deep within the protection of the magnetosphere. Radiation on board stayed low.

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