Simple Control Strategy Derived For Solar-Sail Spacecraft

"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 engineering.

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 said.

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.