A project to develop diffractive solar sails has advanced to the third and final phase of NASA’s advanced concepts program. The team behind the project now has two years to further develop this unconventional means of space propulsion.
In addition to the two-year extension, the diffractive lightsails projectled by Amber Dubill of the Johns Hopkins University Applied Physics Laboratory, was awarded an additional $2 million, NASA announced today. The phase 3 funding was granted through the space agency’s Innovative Advanced Concepts (NIAC) program. With the extra time and cash, Dubill and her colleagues will now work toward a demonstration mission.
“As we venture farther out into the cosmos than ever before, we’ll need innovative, cutting-edge technologies to drive our missions,” NASA administrator Bill Nelson said in the statement. “The NASA Innovative Advanced Concepts program helps to unlock visionary ideas—like novel solar sails—and bring them closer to reality.”
The diffractive solar sails project graduated to NIAC phase 2 status in 2019. Rochester Institute of Technology engineer Grover Swartzlander led the first two NIAC phases of the project and will now continue as a co-investigator.
Solar sails work by using sunlight to propel vehicles through space, similar to how wind pushes sailboats along the water. Instead of using reflective sails like the one developed by the Planetary Society, the system being proposed would use diffractive sails. A desirable attribute of diffraction is that it causes light to spread out when it travels through a small opening. Here’s how Swartzlander described the concept back in 2019:
We’re beginning on a new age of space travel that makes use of solar radiation pressure on large, thin sail membranes. The conventional idea for the last 100 years has been to use a reflective sail such as a metal coating on a thin polymer and you unfurl that in space, but you can get a force based on the law of diffraction as well. In comparison to a reflective sail, we think a diffractive sail could be more efficient and could withstand the heat of the Sun better. These sails are transparent so they’re not going to absorb a lot of heat from the Sun, and we won’t have the heat management problem as you do with a metallic surface.
Shortcomings of the conventional reflective design include sails that are big and thin. They’re also limited by the direction of sunlight, which serves to constrain either power or navigation, as you can’t have both. Diffractive lightsails, by comparison, employ tiny grates on the sail material to diffract light in all directions. As NASA says, this will allow spacecraft to “make more efficient use of sunlight without sacrificing maneuverability.” The design being proposed by Dubill could result in smaller and nimbler sails. And as a fun side effect, the sails would be rainbow-patterned, similar to how CDs look when held to light.
Under NIAC phase 1 and 2, the team designed, created, and tested various diffractive sail materials. The team also ran tests and developed navigation and control schemes specific to a future solar mission. Indeed, diffractive sails could enable a constellation of satellites in orbit around the Sun’s polar regions. Zipping over the Sun’s north and south poles, the solar satellites, with a perpetual source of propulsion, would perform unprecedented scientific observations.
“Diffractive solar sailing is a modern take on the decades old vision of lightsails,” Dubill explained in the NASA statement. “While this technology can improve a multitude of mission architectures, it is poised to highly impact the heliophysics community’s need for unique solar observation capabilities.”
Now in phase 3, Dubill and her team will attempt to improve the solar sail material and run ground experiments to further test the feasibility of the concept. Should all go according to plan, the concept could result in an actual space-based mission and the proposed solar satellites.
“With our team’s combined expertise in optics, aerospace, traditional solar sailing, and metamaterials, we hope to allow scientists to see the Sun as never before,” said Dubill.