sail in the early 2000s. That effort, paid
for mainly by an entertainment company
led by Carl Sagan’s widow, ended with a
splash in 2005 when the Russian rocket it
was supposed to ride from a nuclear submarine failed to reach orbit.
After licking his wounds, Friedman
decided to work with NanoSail-D in its
initial stages. That restored his enthusiasm and inspired LightSail. “We got so
interested in the design that we said we’ll
go further: We’ll instrument the craft and
build in attitude control and a telemetry
system,” says Friedman. Thanks to CubeSats, the sail could be built for less money
than the society’s last, failed attempt.
LightSail’s design calls for the main
CubeSat bus to unfold four rectangles
covered with solar panels, then unfurl
blades of Mylar film to form a kite 5. 6
meters on a side. It will have cameras
to photograph itself, accelerometers to
measure solar pressure and a motor to
help keep it pointed on course. As it goes
around the Earth, the sail will have to
turn 90 degrees twice every 90 minutes.
And this time, just in case, the society is
building two copies: Twin LightSails are
in the final stages of construction at Stellar Exploration in San Luis Obispo, Calif.
Finding a ride is next. To get above
825 kilometers in altitude, where solar
radiation pressure begins to dominate
over atmospheric drag, LightSail needs
a launch vehicle that goes higher than
most CubeSat launches. The project is
now waiting for that lift, Friedman says.
Never one to give up dreaming, Friedman envisions two other LightSails to
come. LightSail- 2 would aim to do a
longer flight in a higher Earth orbit, and
LightSail- 3 would fly to the gravitationally stable L1 Lagrangian point between
the Earth and sun.
Future seas
Over the next few years, a handful of other
solar sails under development may see
the light of space, each proving in its own
way that sailing on sunshine is possible.
In England, a consortium from the University of Surrey and its industry partner Astrium is building two prototypes
for yet another CubeSat-based solar sail
5 meters on a side, called CubeSail. Engineers have constructed one sail that relies
on booms of metal tape that unroll like
party poppers, and a second that uses rigid
carbon fiber booms that unfold directly.
The team will test both in the laboratory
and by December decide which design to
fly, says project leader Vaios Lappas of the
University of Surrey. He expects CubeSail
to launch in early 2012.
Lappas’ team is also working on a
larger European Union–funded project, called DEORBIT SAIL, for launch
in 2014, and an inflatable sail for launch
that year or the next. As its name suggests, DEORBIT SAIL’s main objective
is to get decommissioned space junk out
of orbit. Though garbage cleanup may
sound like a pedestrian task for a glorious
solar sail, such applications may be what
gets sails built and flown in the years to
come, Lappas says. Tens of thousands of
large pieces of spent rockets and other
trash drift dangerously in low-Earth
orbit, threatening collisions with pricey
working satellites. Some countries are
beginning to require spacecraft designers to install a way to deorbit satellites
after their useful life has ended.
One cheap and lightweight way would
be to stick a solar sail on board, which
could unfurl at the end of the mission and
gently guide the craft down to incineration. Or a sail could go pick up the trash
directly: “We want to develop a system
where we can take our deorbiting system
to pieces of space debris, dock with them
NanoSail-D, shown over Finland in February, can be seen streaking across the
sky as it gradually falls out of orbit.
and bring them to the atmosphere and
let them burn up,” Lappas says.
Yet another approach to solar sails is
taking shape in a clean room in an Illinois laboratory. Researchers there have
designed a sail that would unfurl from
bobbins into a giant space ribbon 250
meters long, says Victoria Coverstone,
an aerospace engineer at the University
of Illinois at Urbana-Champaign. This
project, also dubbed Cube Sail, is basically ready to fly, she says, if the team can
find money for a launch and to upgrade
the Mylar film that makes up the sail. The
Illinois group next aims to test a spinning
deployment of sail blades, on the way to
an ambitiously large spinning sail whose
rotating blades could measure up to 5 or
even 10 kilometers long.
Meanwhile, the German space agency
DLR and the European Space Agency are
planning their own series of solar sails
dubbed Gossamer. The first of these
would launch a 25-square-meter sail
into Earth orbit in 2014, followed by
bigger ones over the next several years.
How all these new projects come
together may shape the future of solar
sailing for decades. “I think there’s a lot
that will happen in the next two to three
years that could essentially define how
solar sails take off from Earth and go into
space,” Lappas says.
In the longer term, solar sails will move
forward only if the scientific community
promotes them for missions where no
other propulsion technology can do the
job, says Colin McInnes, director of the
Advanced Space Concepts Laboratory at
the University of Strathclyde in Glasgow,
Scotland. It may seem a practical end
to a romantic concept, but “in the long
term that’s how it’s going to advance,”
he says. “The advocates of solar sailing
have to identify what the really compelling science or operational missions are
where solar sailing outcompetes other
propulsion technologies. It’s not going
to advance just because it’s such a neat
idea.” s
Explore more
s IKAROS: bit.ly/28yGED
s NanoSail-D: 1.usa.gov/qgNF8Z
September 10, 2011 | SCIENCE NEWS | 21
