Scientists propose sailing to the stars on celestial wind
An artist's concept of a space sail
(CNN) -- Four hundred years after Johannes Kepler suggested
that ships might someday sail on "heavenly breezes" beyond
the Earth, his dream is on the verge of becoming reality.
|CNN's Allard Beutel looks at the 'space sail' interstellar mission.|
Within the decade, NASA scientists think they can demonstrate
a revolutionary propulsion system, an immense,
super-lightweight sail that harnesses the power of solar photons to
propel spacecraft faster and farther than ever.
NASA thinks the technology could push an interstellar probe
at five times the speed of current propulsion systems,
meaning it could cover the distance between New York and Los
Angeles in less than a minute.
"This will be humankind's first planned venture outside the
solar system," said Les Johnson, manager of Interstellar
Propulsion Research at NASA's Marshall Space Flight Center in
Conventional spacecraft need too much fuel to push their own
weight into interstellar space, but space sails require no
fuel, except for the sun, he said.
Searching for the heliopause
A probe advancing past the edge of the solar system would give scientists a remarkable glimpse into the composition of the universe.
Les Johnson of NASA's Marshall Space Flight Center displays a carbon fiber that holds promise as material for a giant space sail
"We hope to look at what the composition is beyond our solar
system. All of our measurements are in some way part of our
planetary system," said Paulett Liewer, a physicist at NASA's
Jet Propulsion Laboratory in Pasadena, California, which is
working with the Marshall center on interstellar probe
Liewer and others want to search interstellar space for signs
of organic matter and to study the interaction between
interstellar space and the solar system.
The Stardust probe earlier this year gathered samples of a thin interstellar dust stream drifting in the inner solar system. The preliminary data indicated the presence of complex carbon molecules. But the solar wind likely filters out the larger particles, meaning scientists can only guess how dense interstellar space is, according to Liewer.
"We have no idea what the mass density is. That will be a big
surprise," she said.
The heliopause is the outermost boundary of the solar wind,
where the interstellar medium restricts the outward flow of
the solar wind. The space within the boundary of the
heliopause, containing the sun and solar system, is referred
to as the heliosphere.
The exact location and shape of the heliopause is a
mystery. Scientists think it is teardrop-shaped or roughly
circular and exists some 90 to 120 astronomical units from
The resilient Voyager probe passed the planets years ago and
continues to beam back scientific information. But its
instruments are not ideal for collecting the kind of data deep
space scientists need, Johnson said.
If NASA launched a probe with a solar sail in 2010,
traveling at 150,000 mph (km/h), it would pass Voyager in
2018, despite the fact the latter would have had a 41-year
The spacecraft could travel more than 23 billion miles (37
billion km), or 250 astronomical units (AUs), said Johnson. In
comparison, Neptune orbits the sun at about 30 AUs. One AU is
93 million miles (150 million km), the distance between the
Earth and sun.
It could extend far beyond the heliopause in 15 years, a
definite plus for professional research.
"Now if you launch with conventional propulsion, most of the
scientists would be retired or dead" when such a probe reached its
target distance, Johnson said. But event at such a vast range, the
probe could beam back transmissions to Earth in several
Twice as large as the Superdome
Solar sails would require a thinness that rivals cellophane,
the strength to withstand intense solar heat and barrages of
micrometeors, and an extremely large surface area: 440 yards
(402 meters) wide, twice the diameter of the Louisiana Superdome.
A highly reflective coating would harness the momentum of
photons streaming from the sun.
Constructing the sail is daunting but doable, NASA
scientists said. Researchers believe they're close to
breakthroughs with lightweight composites, including a carbon
fiber material developed by Energy Science Laboratories in
San Diego, California. Its density is the equivalent of a
raisin flattened to 1 square yard (0.8 square meter),
according to NASA.
"It looks like it has the right thermal properties, so it can
go near the sun and not overheat," Johnson said.
To generate serious speed, a sail probe must first travel to
the vicinity of the sun, where it juices up on solar photons.
On its way out of the system, it would cast off the sail near
Jupiter, where the stream of sun particles peters out.
"All of the thrusting is in the inner solar system, then it
coasts," said Johnson.
Miles of sail squashed in tiny can
Creating a solar sail is difficult enough, but hoisting it
could prove an even greater feat.
"I am confident that we can get the materials, but packaging
and deployment will be the biggest nut to crack," Johnson
One JPL scientist who studies advanced propulsion concepts
describes the challenge ahead: "We have miles of sail, that
must be squashed inside an itty bitty can and placed in a
launch vehicle," Robert Frisbee said.
Because of atmospheric drag, a NASA spacecraft would have to
travel hundreds of miles from Earth before it could unfurl a
solar sail, Frisbee said.
Space scientists are considering several methods to deploy a
giant sail, he said. One would be to fold it like a sheet of paper,
then extend it out with mechanical booms. Another is using
an inflatable structure, like a long balloon, that inflates
with a tiny amount of gas and in so doing pulls out the sail.
Decades after solar sails ply the celestial seas, they could
rely on more than the sun for power, according to Johnson.
Lasers or microwave beams, perhaps originating from
satellites placed strategically around the solar system,
could give spacecraft critical boosts on journeys to the
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NASA's Marshall Space Flight Center
NASA Jet Propulsion Laboratory
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