Solar sails have long promised to harness sunlight for space exploration,
just as early sailing ships harnessed the wind. Now the Planetary Society hopes
to refit a NASA sail design and make a third U.S. attempt to fly the first
solar sail in space.
Never before has a vehicle successfully flown in space using
a solar sail as its primary means of propulsion. But it hasn't been for a
lack of trying.
The California-based Planetary Society attempted to fly its Cosmos-1
solar sail in 2005, but it foundered because of a Russian
rocket malfunction. Then NASA's NanoSail-D was lost in the third failed
flight of SpaceX's Falcon 1 rocket in 2008.
Japan managed to deploy solar sail materials from a sounding rocket in
2004, but did not attempt to demonstrate controlled flight. The Planetary
Society's new venture could combine technologies and lessons from both earlier
spacecraft.
"In Cosmos-1 we had a more conventional spacecraft, but the
technology has moved ahead now," said Louis Friedman, executive director
of the Planetary Society in Pasadena, Calif. "You can actually get a
higher performance sail with a lower mass spacecraft."
NASA's spare sail
NanoSail-D may provide the foundation design for that future, smaller
spacecraft. The sail was meant
to test both solar wind pressure and Earth's atmospheric drag, but lacked
actual maneuvering capabilities for controlled solar sailing. By contrast,
Cosmos-1 had a radio system, imaging system and a micro-accelerometer to enable
control over the spacecraft.
NASA has backup NanoSail-D hardware in storage on Earth and a Planetary
Society working group could make a decision by the end of summer on how best to
integrate that design with its goals. Any future design may also come
significantly cheaper than the roughly $4 million price tag on Cosmos-1.
"If we can reduce it by half, we'd be pretty happy," Friedman
told SPACE.com. However, he added that the size reduction would not come
with performance reduction, and expects acceleration "at least as good and
maybe better" compared to Cosmos-1.
That equal or better speed boost becomes possible because acceleration
is proportional to area divided by mass, and so a smaller spacecraft mass can
make do with a smaller sail. Another mini-sail suggestion for the Planetary
Society comes from Russian researchers at the Space Research Institute in
Moscow, who also collaborated on Cosmos-1.
Small sails, big possibilities
A smaller-sized solar sail also opens up new launch possibilities,
ranging from the Russian Soyuz rockets to private launch firms in the United
States and elsewhere. The sail could likely hitch a ride as a secondary
payload, similar to the smaller cubesat missions which have allowed scientists
to launch numerous experiments into space.
Ideally, a companion spacecraft could also launch with the solar sail
and watch while the sail unfurls, Planetary Society officials said. That would
also provide researchers with valuable data on how the thin, gossamer-like sail
structure behaves in microgravity.
Figuring out how solar sails operate in space could eventually lead to
spacecraft which maneuver as confidently as sailing ships on Earth, and even
allow for sailing or "tacking" into the face of the sun's oncoming
solar wind.
The new endeavor may still face some friendly competition from a Finnish
solar
sail concept under development. That solar sail uses a slightly different
concept of electrical charge repulsion, which takes advantage of charged solar
particles.
Planetary Society officials have said they plan to announce the results
of their feasibility study once this summer's analysis of NASA's spare
NanoSail-D and Russia's mini-sail concept is complete.
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