SCIENCE / MEDICINE : Space...
Every space scientist knows it is bound to happen sometime:
A piece of space junk the size of a walnut will rip through an orbiting satellite, or worse still, a manned spacecraft, placing craft and crew in grave danger.
A piece of debris no bigger than the end of your thumb traveling at orbital velocity poses a threat roughly equivalent to being hit by a 400-pound safe moving at 60 miles an hour, experts say. And there are thousands of such particles traveling around the Earth, remnants from past launches, any one of which could wreck a craft, from a small communications satellite to the $30-billion manned space station that the National Aeronautics and Space Administration hopes to have in orbit by the year 2000.
Increasingly concerned over the threat, NASA is trying to develop an early warning system that would at least give astronauts enough time to batten down a few hatches and seek refuge in the safest part of the craft.
“There is a real hazard here,” said Faith Vilas, a scientist who heads a team of scientists and engineers at NASA’s Johnson Space Center in Houston seeking an innovative solution. “It could be catastrophic.”
Vilas is working on the development of a small telescope that would extend the vision of the astronauts far enough ahead to identify small particles in time to take some action. She hopes to fly the scope aboard the space shuttle in a few years as part of a program to develop the technology that could someday avert a tragedy in space.
It is not possible to equip a spacecraft with a radar system like that used aboard an aircraft because the energy required to run such equipment is too great, she said. But a telescope that could identify hazardous debris at least a minute before impact would require very little energy.
David L. Talent of Lockheed Engineering and Sciences Co., Lockheed’s principal scientist on the project, said that once the telescope identified a hazard it could turn on a radar system that would lock on the debris and warn the astronauts how much time they would have before impact.
“If I were in the space station, I would want to know if something nasty is coming my way,” Talent said during a recent international meeting of the Society for Optical Engineering in Tucson.
And Talent warned that this is no idle exercise.
“It is estimated that the space station will take two to five hits that would be dangerous during the functional life of the station (about 30 years),” he said in an interview.
“The number (of bits of debris in orbit) will increase with every launch,” said Connie Tritsch, an optical engineer with Lockheed who is also working on the project.
“There’s going to be a lot of stuff out there,” she added.
Air Force officials are tracking about 6,600 larger pieces in Earth orbit, down slightly from last year because of solar storms that increased the drag on some debris, causing it to tumble toward the Earth and burn up in the atmosphere. But for the unknown number of smaller pieces that are too tiny to track, the astronauts will be on their own.
The telescope Lockheed is working on under contract with NASA would operate both at optical and infrared wavelengths so that it could pick up objects in sunlight as well as when the craft is in the darkness of the Earth’s shadow. Debris traveling through space emits some heat, which could be picked up by infrared sensors, Talent said.
He compared the situation to driving down the highway during a snowstorm. Looking straight ahead, most of the snowflakes appear to curve to either side as the vehicle approaches because they are not on a collision course.
Snowflakes likely to hit the windshield would appear stationary because they would be dead ahead.
“It’s the one that doesn’t move that you need to do something about,” he said.
A telescope aboard a manned space vehicle could identify small objects that are approaching on a collision course, he added. It would not be possible to move something as massive as the space station in time to dodge the bullet, he said, but it would at least give the crew time to do something.
Ironically, larger pieces of debris are less likely to surprise the crew because big hunks of junk--such as expended rocket bodies--are tracked by the Air Force, and NASA would be warned well enough in advance to take evasive action.
It is the smaller stuff, the nuts and bolts and small pieces of shrapnel, that could suddenly loom out of the dark to the surprise and horror of the astronauts. And the problem will get worse as time goes on.
Tritsch said that known space junk includes active payloads (5%), such as communications and spy satellites; rocket bodies (15%); launch debris (16%); inactive payloads (21%), such as dead satellites; and fragmentation debris (43%), such as bits of shrapnel left over from exploding or disintegrating payloads.
The space station will be strong enough to withstand the impact from the tiniest particles, but massive shielding that would protect the vehicle from larger pieces of junk would be so heavy it would greatly increase the cost of the program and is not considered practical.
NASA’s Vilas believes a telescope with a 60-inch mirror would be able to identify particles as small as 1/25th of an inch at least one minute before impact.
“That would give the crew time to power down some systems, close some hatches and then seek safe haven,” she said. Some areas in the station would be better protected than others.
“Then they would just have to wait and see what happens,” she added.
And Talent noted that the space station, with its four habitable modules, will be a very fat target: It will have a surface area of more than 50,000 square feet.
What’s Up There? Fragmentation Debris (Shrapnel left over from exploding or disintegrating payloads): 43% Inactive Payloads (Dead satellites): 21% Launch Debris: 16% Rocket Bodies: 15% Active Payloads (Communications and spy satellites): 5%
