A project to develop diffractive solar sails has moved into 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 light sails projectled by Amber Dubill of the Johns Hopkins University Applied Physics Laboratory, received an additional $2 million, NASA announcement today. Phase 3 funding was granted through the space agency Innovative Advanced Concepts (CANIA). With the extra time and money, Dubill and his colleagues will now work on a demonstration mission.
“As we venture further into the cosmos than ever before, we will need innovative and advanced technologies to carry out our missions,” NASA Administrator Bill Nelson said in the statement. “NASA’s Innovative Advanced Concepts program helps unlock visionary ideas — like new solar sails — and bring them closer to reality.”
The Diffractive Solar Sails Project moved to NIAC Phase 2 status in 2019. Rochester Institute of Technology engineer Grover Swartzlander led the first two phases of the NIAC project and will now continue as a co-investigator.
Solar sails work by using sunlight to propel vehicles through space, much like the wind pushes sailboats along water. Instead of using reflective veils like the one developed by the Planetary Society, the proposed system would use diffractive sails. A desirable attribute of diffraction is that it causes light to scatter as it passes through a small aperture. This is how Swartzlander describe the concept in 2019:
We are entering a new era of space travel that uses the pressure of solar radiation on large and thin sail membranes. The conventional idea for the past 100 years has been to use a reflective veil such as a metallic coating on a thin polymer and unroll it in space, but you can also get a force based on the law of diffraction. Compared to a reflective sail, we believe that a diffractive sail could be more efficient and could withstand the heat of the sun better. These sails are transparent so they won’t absorb a lot of heat from the sun, and we won’t have the problem of heat management like you do with a metal 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.
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