Purdue Scientist to Lead Next Step in Solar Sailing

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A small satellite that will attempt the first controlled solar sailing in Earth orbit is a go for launch.

Purdue professor David Spencer is the lead for LightSail 2, part of a payload that is scheduled to launch June 22 on SpaceX’s Falcon Heavy rocket. The citizen-funded project from The Planetary Society is part of the U.S. Air Force’s Space Test Program-2 payload.

Solar sailing uses reflective sails to harness the momentum of sunlight for propulsion.

“While there have been several previous solar sail deployment demonstration missions, if all goes as planned LightSail 2 will become the first spacecraft to increase its orbital energy through controlling the sail orientation relative to the sun,” said Spencer, an associate professor in Purdue’s School of Aeronautics and Astronautics and project manager for LightSail 2.

Spencer has been involved with the LightSail program since 2010 and was mission manager for LightSail 1, which demonstrated solar sail deployment in 2015. Video Of the history of the LightSail program, courtesy of The Planetary Society.

LightSail 2 arrived at Kennedy Space Center in Cape Canaveral, Florida on May 21. It was integrated on May 7 with Prox-1, a satellite that includes a spring-loaded deployer, at the Air Force Research Laboratory in Albuquerque, New Mexico. Spencer led the development of the Prox-1 spacecraft while at Georgia Institute of Technology.

The Falcon Heavy will inject the combined Prox-1/LightSail 2 spacecraft into orbit at an altitude of about 450 miles. One week after launch, Prox-1 will deploy LightSail 2. Following a spacecraft checkout period, LightSail 2 will deploy its solar panels and then unfurl its four solar sail segments, providing a total sail area about the size of a boxing ring.

LightSail 2 will attempt to demonstrate solar sailing as a method for propulsion for CubeSats by performing two “slews,” or turns of the spacecraft, every orbit. The solar sail rotates edge-on and face-on to the Sun each orbit, giving the craft thrust to raise its orbit by about 500 meters per day during the early portion of the mission. The result is to increase the orbital energy about Earth, stretching the initial near-circular orbit into an ellipse.

“While solar sails have been described in literature for many decades, solar sailing technology is still in its infancy,” Spencer said. “Recently, solar sailing advancement has been enabled by miniaturized CubeSat technology.

“Through demonstrating controlled solar sailing, LightSail 2 provides an important advancement toward the realization of solar sailing’s potential for space science applications.”

There are a handful of long-term, visionary applications of solar sailing.

A fleet of solar sail-propelled spacecraft could monitor the space between the sun and the Earth to provide Earth an early warning for solar storms. A solar science mission could attempt to get into a polar orbit around the sun. Because of the limitless propulsion provided by solar photons, solar sailing has the potential to shorten the transfer times for missions that require large changes in velocity, including missions to the outer limits of the solar system and interstellar space.

“Solar sailing technology can enable missions to the extreme limits of our solar system with flight times of 25 years or less,” Spencer said.

Spencer’s research team will track LightSail 2, receiving the signal from the spacecraft as well as commanding the spacecraft during operations, from the Space Flight Projects Lab at the Purdue Technology Center. Justin Mansell, one of Spencer’s graduate students, is working on modeling and simulation of the mission and will compare that with actual flight data to evaluate the overall performance of the system.

Funding for the project has been through The Planetary Society’s members and private donors.

“The LightSail program was citizen-funded and implemented by a team composed of small companies and universities,” Spencer said. “The program demonstrates a new way of conducting space exploration, without relying on government agencies for funding.”