This story was updated at 4:51 p.m. EDT.
An electrically-charged solar sail with a possible
"turbo" option may be ready for its first space trials in three years
if scientists in Finland have their way.
The Finnish invention would use long, positively-charged
tethers to ride the solar wind, without the need for any sort of fuel or
propellant.
"A flight out of the solar system to measure the gas,
dust, plasma and magnetic field in the undisturbed interstellar space would
perhaps be the 'flagship' thing to do," said Pekka
Janhunen, a researcher developing the sail at the Finnish Meteorological
Institute.
The solar sail's debut would involve a smaller model with 5-mile
(8-km) long tethers riding in a high elliptical Earth orbit. That would allow
Janhunen and others to gauge the force of the solar wind on the spacecraft with
an accelerometer.
"The mission would validate and calibrate our theory
and enable us to design full-scale missions with accurate and experimentally
verified numbers for predicted thrust," Janhunen added.
Two solar panels would power an electron gun that keeps the
spacecraft tethers charged, creating propulsion from the similarly charged
solar wind pushing against the sail. Researchers are looking into aluminum or
copper alloy wires for the tethers.
The maiden mission would also test a concept to increase the
thrust from the solar wind, called radio frequency electron heating.
The subscale mission would also test a "turbo"
charge for the solar sail. Radio-frequency waves could excite the solar wind
particles through electron heating, which might boost the thrust created. The
concept is difficult to simulate or analyze in theory, but should be easy to
test in space, according to Janhunen.
Whether the first test gets off the ground depends on
securing almost $8 million USD (5 million euros). Researchers from Finland,
Germany, Sweden, Russia, and Italy are currently developing various components
of the solar sail.
Previous efforts to deploy and test solar sails foundered
due to launch failures and mishaps. A joint Russian-U.S.
effort in 2005 was doomed by rocket
booster failure less than two minutes after launch. Two previous Russian
efforts in 2001 and 1999 also failed, though Japan successfully deployed a
small solar sail prototype in 2004.
Other sail concepts have suggested using microwaves
beamed from Earth to push spacecraft up to record speeds, instead of riding
the solar wind.
However, a successful solar sail could have big payoffs by
making deep space missions cheaper without fuel requirements. A fleet of solar
sail spacecraft could also significantly lower the cost of transporting
material within the solar system.
"Fetching water ice from asteroids to produce rocket
propellant on Earth orbit would probably be one sensible application of that
capability," Janhunen told SPACE.com. "Producing rocket fuel
on orbit means that one doesn't have to lift it from Earth, which could make
all space activities cheaper - except for those in low-Earth orbit."
Solar sails alone will not pave the way for further space
exploration – other developments such as cheaper and more reusable launch
vehicles are necessary. But proving solar sail technology would help extend
mankind's reach into the solar system.
"Starting the long-awaited asteroid resource utilization
could be significant for the longer-term well-being and survival of our civilization
on this planet," Janhunen said.
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