This year’s anticipated launch of the Planetary
Society’s “Cosmos 1” spacecraft may usher in the long-awaited age of
solar sailing. The performance of such spacecraft could be optimized
with a simple control strategy developed by scientists at the University
of Illinois.

“The concept of solar sailing originated in the 1920s, but only recently
has technology advanced far enough to turn this dream into reality,” said
Victoria Coverstone, a UI professor of aeronautical and astronautical

Powered by the sun, solar sails require no onboard propellant — making
delivery of huge payloads across vast distances of interplanetary space
possible. “For example, a solar-sail spacecraft could ferry provisions
and equipment to Mars in advance of a manned expedition,” Coverstone

In a project funded by the Jet Propulsion Laboratory, Coverstone and
John Prussing, also a professor of aeronautical and astronautical
engineering at the UI, investigated the feasibility of using a solar
sail to escape Earth orbit and venture out to the planets.

“The pressure of sunlight can indeed be used to gradually accelerate the
spacecraft until escape velocity is attained,” Prussing said. “But, to
achieve maximum performance, optimum orientation of the sail at each
point in the orbit is required.”

The researchers derived an efficient control algorithm to continuously
orient the sail in three dimensions in order to maximize the component
of sail force along the desired trajectory. They submitted their
findings to the Journal of Guidance, Control and Dynamics.

“The solar sail does not sail on the solar wind — the stream of charged
particles that produces the familiar glow of auroras,” Coverstone said.
“Instead, the solar sail uses sunlight in much the same way as a sailboat
uses wind. Sunlight striking the sail will apply a force, which can be
directed by tilting the sail. Because the force is small, however, the
sail must be quite large.”

When launched into Earth orbit, the Cosmos 1 spacecraft will unfurl a
solar sail consisting of 600 square meters of lightweight, aluminized
mylar. The sail will be divided into eight “blades” or “pedals” roughly
triangular in shape.

In April, the Planetary Society will test the deployment of two
solar-sail blades during a short, sub-orbital flight. The actual
mission — the first solar-sail flight of its kind — is scheduled for
launch between October and December of this year.

“The success of that flight, as well as the continued development of
efficient control strategies, could alter the course of future planetary
spaceflight,” Prussing said.

Headquartered in Pasadena, Calif., the Planetary Society was co-founded
by Carl Sagan, Bruce Murray and Louis Friedman in 1980 to advance the
exploration of the solar system. With more than 100,000 members in 140
countries, the society is the largest space interest group in the world.