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June
26, 2008: "Hold your hands out to the sun. What
do you feel? Heat, of course. But there's pressure as well
– though you've never noticed it, because it's so tiny. Over
the area of your hands, it only comes to about a millionth
of an ounce. But out in space, even a pressure as small as
that can be important – for it's acting all the time, hour
after hour, day after day. Unlike rocket fuel, it's free and
unlimited. If we want to, we can use it; we can build sails
to catch the radiation blowing from the sun."1
These
words were spoken not by a NASA scientist but by a fictional
character – John Merton – in Arthur C. Clarke's short story
The Wind from the Sun. If all goes well, Merton's
prophetic words are about to become fact.
 NASA
researchers, thinking "out of the box" (or maybe
"out of the rocket") have long dreamed of the possibility
of sailing among the planets with sails propelled by sunlight
instead of by wind. Except
in works of fiction, though, no one has yet successfully deployed
such a sail anywhere beyond Earth.
Right:
An artist's concept of a sailing ship and a solar sail.
"There's
a first time for everything," says Edward "Sandy"
Montgomery of NASA's Marshall Space Flight Center.
Montgomery's
team and a team from Ames Research Center (led by Elwood Agasid)
hope to make history this summer by deploying a solar sail
called NanoSail-D. It will travel to space onboard a SpaceX
Falcon 1 rocket, scheduled for launch from Omelek Island in
the Pacific Ocean during a window extending from July 29th
to August 6th (a back-up window extends from August 29th to
September 5th).
"NanoSail-D
will be the first fully deployed solar sail in space, and
the first spacecraft to use solar pressure as a primary means
of attitude control or orbital maneuvering," says Montgomery,
who is NanoSail-D's payload manager.
"We
are always on the lookout for opportunities. Ames owns a slot
on the Falcon 1 launch and asked us if we wanted to go along.
We said, 'Yes!'
We'll use the Poly Picosatellite Orbital Deployer, or P-POD,
developed by the University of California Polytechnic Institute
to deploy our sail."
A
few years ago, the Planetary Society attempted a mission like
NanoSail-D called Cosmos I, but the launch vehicle failed
and destroyed the undeployed spacecraft. Montgomery and team
believe that NanoSail-D, however, will unfurl four gossamer
wings from its pod in the blackness of space like a butterfly
from a cocoon: movie.
"The
structure is made of aluminum and space-age plastic,"
says Montgomery. "The whole spacecraft weighs less than
ten pounds. We carry it around in a special suitcase -- airplane
carry-on luggage size." Fully opened, the kite-shaped
sail spreads out to about 100 square feet of light-catching
surface.
Above:
The Huntsville-based NanoSail-D team stands with the fully
deployed sail at ManTech SRS technologies on April 16, 2008,
after the successful deployment test.
"A
success would be huge for the future of space exploration,"
Montgomery believes.
Why
so important? Solar sails could extend our reach as far as
our dreams. Because there's no friction in space, once a solar
sail starts moving, it can go on forever. Indeed, long after
a rocket would run out of gas and begin to coast, a solar
sailship could still be accelerating, achieving speeds much
faster and covering distances far greater than any rocket.
No rocket in existence could carry enough fuel to reach the
outer solar system in as short a time. And like a marine sail,
a solar sail could also bring you home. You could use the
solar sail to tack
your vessel, making it travel "against the wind,"
back to Earth.
"It's
not so much about how far a sail will go compared to a rocket;
the key is how fast," says Montgomery. "The
Voyagers have escaped the solar system, and they were sent
by rockets, but it's taken more than three decades to do it.
A sail launched today would probably catch up with them in
a single decade. Sails are slower to get started though. So,
for example, between the Earth and the moon, rockets might
be preferred for missions with a short timeline. It's a trip
of days for rockets, but months for a solar sail. The rule
of thumb, therefore, would be to use rockets for short hops
and solar sails for the long hauls."
 Right:
University of Alabama research technician Doug Huie holds
the future in his hands. Folded-up, NanoSail-D occupies a
space no bigger than a bread box.
All
of this may sound like speculation, but NanoSail-D could show
that solar sails are truly feasible. And there's an added
bonus to this technology demo:
"Currently,
micro-satellites in orbit above a few hundred kilometers can
stay in orbit for decades after completing their mission,"
explains Montgomery. "This creates an orbital debris
collision risk for other spacecraft. NanoSail-D will demonstrate
the feasibility of using a drag sail to decrease the time
satellites clutter up Earth's orbit. Although our sail looks
like a kite, it will act like a parachute (or like a drag
sail) in the very thin upper atmosphere around Earth. It will
slow the spacecraft and make it lose altitude, re-enter the
Earth's atmosphere and burn off in a relatively short period
of time. A drag sail is a lighter alternative to carrying
a propulsion system to de-orbit a satellite."
And
finally, the question everyone wants answered: What does D
stand for?
"We
chose the 'D' in the name, not because it came after models
A, B, and C, but because it can stand for demonstrate, deploy,
drag, and/or de-orbit," says Montgomery.
Soon,
'D' may stand for something new: "DID IT!"
Check
Science@NASA post-launch and the meaning will be revealed.
SEND
THIS STORY TO A FRIEND
Author: Dauna Coulter
| Editor:
Dr. Tony Phillips | Credit: Science@NASA
| more
information |
| 1The
Wind from the Sun by Arthur C. Clarke was originally
published under the title Sunjammer in Boys' Life in
1964. A collection of Clarke stories called The
Wind from the Sun and containing the story was
published in 1972 by Harcourt, Brace, and Jovanovich.
The story also appeared in The Collected Stories
of Arthur C. Clarke, first published in January
2001 by Gollancz.
"Our
sails are not as high performing as John Merton's in
The Wind from the Sun," adds Montgomery.
"We really can't consider carrying people yet.
The size of his sail is tremendous, and he is right
that it would take sails that large to carry men in
a sun yacht race to the moon. But microelectronics have
been developed since Clarke's story was written that
make it possible to build a very small, but very smart
robotic spacecraft weighing a fraction of what a human
space vessel would weigh. The sail size needed is scaled
according to the weight of the payload it has to push
(or pull). We have discovered that, with modest sized
sails (tens/hundreds/thousands of square feet rather
than the 50 million square feet needed for Merton's
solar yacht), there are a number of interesting scientific
missions possible. Everything required for these missions
can be launched as small secondary payloads on a single
flight of most any launch vehicle flying today."
"And
it's safer than traditional rocket propulsion. Solar
sails don't involve any combustibles or high-speed machinery.
There are no fuels stored in tanks or burned, and the
potential for getting shocked is about like that of
a flashlight or cell phone."
SpaceX
-- home page
More
information on Cosmos
I
The
basics of solar sailing
NASA's
Future: US
Space Exploration Policy
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