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Dashing and Coasting to the Interstellar Finish Line

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Dashing and Coasting
to the Interstellar Finish Line

NASA Funds Advanced Propulsion Concept

August 19, 1999: A race to the edge of the solar system and into interstellar space could come out of a grant awarded recently by NASA for the University of Washington to develop an innovative space propulsion concept. Under a two-year, $500,000 grant from NASA's Institute for Advanced Concepts, Dr. Robert Winglee of the University of Washington will continue work on the Mini-Magnetospheric Plasma Propulsion - M2P2 - concept that he discussed at last April's Advanced Propulsion Research Workshop in Huntsville.

Right: A computer model depicts the "magnetic wall" that the M2P2 spacecraft would form around itself. Credit: University of Washington

The first four manmade objects to head for the edge of the solar system are the Pioneer 10 and 11 probes (launched March 3, 1972 and April 6, 1973, respectively) and the Voyager 1 and 2 (Sept. 5 and Aug. 20, 1977, respectively). None has yet reached the heliopause, the tenuous shock wave in deep space where the solar wind encounters the interstellar medium that permeates our galaxy.

Winglee's M2P2 concept would use the solar wind to push on a small imitation of the Earth's magnetosphere and accelerate the spacecraft to overtake the Pioneers and Voyagers and become the first manmade object to leave the solar system.

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Since the mid-1980s, scientists have been considering sailing to the stars with a "breeze" produce by lasers or microwave transmitters. But sails are bulky and require devices to deploy them.

"The enabling technology [for M2P2] is pretty much available today," said Winglee, who works in Washington's geophysics program which studies the magnetosphere, the region of space around the Earth where the solar wind is deflected by the Earth's magnetic field.

"What we're proposing to do is create a magnetic bubble to deflect the solar wind," Winglee explained.

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M2P2 would generate a magnetic field and then inject plasma (ionized gas) that would drag the magnetic field lines out and form a plasma bubble 30 to 60 km (18-36 mi) in diameter.

This is similar to the Earth's magnetic field trapping a large volume of electrified gas - thus forming the magnetosphere - and forcing the solar wind to flow around it. The wind actually pushes on the Earth through the magnetic field lines, but the push is so tiny compared to the Earth's mass that it has no effect.

Above: What looks like a computer depiction of Earth's magnetosphere forcing the solar wind to flow around the Earth is actually a graph of the solar wind flowing around the proposed M2P2 deep space probe. Credit: University of Washington

For the M2P2 spacecraft, a magnetic field of 0.1 Tesla (about 1000 times stronger than Earth's magnetic field) could be generated by a conventional solenoid. The helicon plasma source "is amazingly simple."

With a bottle of just 3 kg (6.6 lb) of helium as the plasma fuel, the magnetic bubble could be operated for three months. The size of the bubble would expand and contract with variations in the solar wind, so the force on the 100 kg spacecraft would stay constant at 1 Newton (about a quarter of a pound). The 3 kilowatts of electricity to run the magnet and plasma generator would come from solar cells.

Left: Drawing of the prototype M2P2 thruster which would be about the size of a pickle jar. Credit: University of Washington

There is enough power in the solar wind to accelerate a 136 kg (300 lb) spacecraft to speeds of up to 288,000 km/h (180,000 mph) or 6.9 million km (4.3 million mi) a day. By contrast, the space shuttle travels at about 7.7 km/s (17,300 mph) or 688,000 km (430,000 mi) a day.

Web Links
Setting sail for the stars talks about solar sail work that Winglee and other scientists presented at the Advanced Space Propulsion Workshop in April.
For the nitty-gritty of Winglee's work, the NASA Institute for Advanced Concepts has posted his abstract and his June 1999 project report (the latter as a 411K Acrobat PDF document).
Winglee's home page at the University of Washington carries more information about his research in geophysics and other areas, including two large (4.7 and 7.8 MB) MPEG computer simulation movies.
Space Plasma Physics Group at NASA/Marshall describes the magnetosphere and NASA research in this area where Earth meets space.
Winglee calculates the specific impulse (a measure of efficiency), would be tens of thousands of seconds. That's 10 to 20 times better than the Space Shuttle Main Engine.

"We can go faster and lighter than anyone else," Winglee said.

How fast?

If launched in 2003, M2P2 would go past the heliopause, where the solar wind runs into the interstellar wind, by 2013. That's a distance of more than 150 times the distance from the sun to the Earth. Voyager 1, launched in 1977, will get there in 2019.

Winglee said that adding dust particles to the magnetic bubble would enhance the thrust, and accelerate the M2P2 even faster for a mission to another star.

After giving his briefing in April, Winglee received a glowing recommendation from sail advocate Dr. Robert Forward: "I just love the audacity of that concept."

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