Shuttle astronauts plan an electrifying experience Experiment aims to generate current in space

February 23, 1996|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

In a dramatic update of Benjamin Franklin's famed 1752 experiment with lightning and a kite, Columbia astronauts this weekend hope to generate electrical current by floating a half-ton satellite 12 miles above the shuttle at the end of a slender cable.

The experiment was launched at 3:18 p.m. yesterday from the Kennedy Space Center in Florida, riding in Columbia's payload bay. The crew of four Americans, two Italians and one Swiss are to spend 14 days in space.

A 1992 attempt to fly the Tethered Satellite System (TSS) failed. If it works this time, it may lead to a technology that future spacefarers could use to produce electrical power and thrust for their spacecraft, without lugging chemical fuels into orbit.

"It is a completely new technology which we're trying to bring up," said Dr. Dennis Papadopoulos, the University of Maryland physicist who devised the $250 million experiment. "It's extremely exciting."

He spoke from the TSS control center at NASA's Marshall Space Flight Center in Huntsville, Ala.

It was an American Nobel Prize-winning chemist, Irving Langmuir, who asked a question in 1920 that Dr. Papadopoulos hopes to answer during Columbia's flight: What happens when an object becomes highly charged in a magnetic field with no walls?

Physicists say such a system should generate an electrical current. It's analogous to the way a copper coil spinning around a magnet will become an electrical generator, like those in cars.

The "Langmuir Problem" launched the study of plasma physics, but "the question has never been solved," Dr. Papadopoulos said. Experiments on Earth were always limited because scientists could not produce an experimental environment without walls.

"The current would flow through the walls," frustrating the studies, Dr. Papadopoulos said. "We want a very big laboratory."

Space being the biggest lab of all, Dr. Papadopoulos in 1983 proposed the tethered satellite experiment for a U.S. shuttle flight.

A tethered satellite racing through Earth's magnetic field should pick up loose electrons from the very thin, electrically charged gases, or plasma, that gather along the magnetic field lines in the ionosphere, where the shuttle flies. The electrons would then flow through the insulated copper wire in the tether, then back into the plasma, along the magnetic field lines. That would complete the circuit and create electric current.

Delays

NASA originally set a 1987 launch date for TSS, but the Challenger disaster in 1986 pushed the project back.

When it finally flew in 1992, the tether snagged on a protruding bolt added to the reel mechanism shortly before launch. The satellite moved only 295 yards from the shuttle and generated little electricity. This time, Dr. Papadopoulos said, the reel has been fixed and tested. And since then "nobody touched it."

The Italian-built satellite is an aluminum sphere, 6 feet in diameter, weighing 1,100 pounds. Four instrument booms will extend from the sphere as it deploys.

At 2 a.m. tomorrow, if everything works properly, tiny thrusters will push the satellite away from the shuttle's payload bay, while the reel mechanism plays out the tether. The diameter of a boot lace, the tether is made of copper wire, with Teflon insulation and braided Kevlar for strength.

Once the satellite has gone about a mile from the shuttle, centrifugal forces should take over and draw it out to the tether's full 12-mile length.

As electrons begin to flow through the wire, an electron gun on the shuttle similar to those in TV picture tubes will fire them back into space, completing the electrical circuit. The system could generate up to 5,000 volts and one-half ampere.

Instruments on the satellite and on the shuttle will beam the results to Huntsville, where Dr. Papadopoulos and his team of 15 scientists will collect data for seven days, in 12-hour shifts.

Light show

The astronauts may have quite a show as the system fires electrons into space.

"We expect a glow and a lot of luminous emissions very similar to lightning," Dr. Papadopoulos said. The discharges will come from both the electron gun and the shuttle itself. "The astronauts should be able to see them when [the satellite] is two to three kilometers away."

The electrical current poses no danger to the astronauts or the shuttle, he said, and the crew has also trained to deal with any swinging, bobbing or twirling that might develop in the system.

If the TSS proves the concept's feasibility, tethered satellites could produce some of the electrical power needed by space stations, reducing their reliance on solar panels or chemical fuels that are expensive to launch.

The TSS process could also be reversed to produce thrust, in the same way that a generator becomes an electric motor if electrical power is put into the system. Electricity from solar arrays or batteries could be sent up the tether, producing a magnetic force against the Earth's geomagnetic field strong enough to power small orbital maneuvers.

Dr. Papadopoulos also plans to try using the 12-mile tether as a giant antenna to transmit extremely low-frequency radio waves to listening posts in Australia, Puerto Rico and the Canary Islands.

Such signals can penetrate deep into the ground, and if this experiment works, they might one day be used like radar to do remote sensing. Perhaps, he said, they could be used to "explore the underground of the moon, or to look for water around Phobos," a moon of Mars.

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