July 5, 2022

NASA Moves Ahead With Wild Solar Sail Concept

NASA Moves Ahead With Wild Solar Sail Concept

Artist's conception of a refracting light sail.  The rainbow-like patterns are similar to how CDs display similar patterns when placed under light.

Artist’s conception of a refracting light sail. The rainbow-like patterns are similar to how CDs display similar patterns when placed under light.
Clarification: Mackenzie Martin

A project to develop refracting solar sails has progressed to the third and final phase of NASA’s Advanced Concepts Program. The team behind the project now has two years to continue developing these unconventional means of space propulsion.

In addition to the two-year extension, the Refractive lights projectled by Amber Dobell of the Johns Hopkins University Applied Physics Laboratory, and raised an additional $2 million, NASA announce today. Phase 3 funding was granted by the space agency Advanced and innovative concepts Nyak program. With the extra time and money, Dobell and her colleagues will now work on a demonstration mission.

“As we go further into the universe than ever before, we will need innovative, cutting-edge technologies to propel our missions,” NASA Administrator Bill Nelson said in the statement. “The NASA Innovative Advanced Concepts program helps unleash future ideas – like new solar sails – and bring them closer to reality.”

The Solar Reflective Sails project graduated to NIAC Phase II in 2019. Rochester Institute of Technology engineer Grover Swartzlander led the first two NIAC phases of the project and will now continue as an Associate Investigator.

Solar sails work by using sunlight to propel vehicles through space, similar to the way winds push sailboats along water. Instead of using reflective sails like those advanced By the Planetary Society, the proposed system would use refracting sails. A desirable feature of diffraction is that it causes light to scatter as it travels through a small aperture. Here’s how Swartzlander describe it Return of the concept in 2019:

We are about to enter a new era of space travel that uses the pressure of solar radiation on large, thin sails. The traditional idea for the past 100 years has been to use a reflective sail like a metallic coating on a thin polymer, and then open it up in space, but you can get strength based on the law of diffraction as well. Compared with the reflective sail, we believe that the refractive sail can be more efficient and can withstand the heat of the sun better. These sails are transparent, so they won’t absorb much of the sun’s heat, and we won’t have the problem of managing heat as you do with metal roofs.

The shortcomings of the traditional reflector design include the large and slender sails. It’s also restricted towards sunlight, which restricts energy or mobility, since you can’t get both. In comparison, fission sails use small webs on the sail material to diffract light in all directions. As NASA says, this will allow the spacecraft to “make more efficient use of sunlight without sacrificing maneuverability.” Dobel’s proposed design could result in smaller, slender sails. And as a fun side effect, the sails will be rainbow-patterned, similar to the shape of CDs when placed in the light.

Under NIAC Phase 1 and 2, the team designed, engineered, and tested various refracting sail materials. The team also tested and developed navigation and control systems for a future solar mission. In fact, refracting sails can enable a constellation of satellites to orbit around the sun’s polar regions. By pressing on the sun’s north and south poles, solar satellites, with a constant source of thrust, will perform unprecedented scientific observations.

“A reflective solar sail is a modern version of a decades-old view of light sails,” Dobelle explained in a NASA statement. “While this technology can improve many mission structures, it is poised to significantly impact the solar physics community’s need for unique solar energy monitoring capabilities.”

Now in Phase 3, Dobell and her team will attempt to improve the solar sail material and conduct ground trials to further test the concept’s feasibility. Should things go according to plan, the concept could lead to an actual space mission and proposed solar satellites.

“With our team’s combined expertise in optics, space, conventional solar sailing, and metamaterials, we hope to allow scientists to see the sun like never before,” Dobell said.