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.
“I am beyond thrilled to join the group of imaginative and creative people who make up NIAC Fellows. I’ve actually been on different NIACs since 2017 in various capacities, but being able to lead one is an honor I could only have dreamed of,” Dubill wrote to me in an email. “I was mentored by my [co-investigators] for years and it means a lot that they trusted me to lead this one and continue to develop this research in an institution that encourages this type of innovation.
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.
Defects of conventional reflective design include large, thin sails. They’re also limited by the direction of sunlight, which serves to limit power or navigation, because you can’t have both. Diffractive light sails, in comparison, use tiny grids on the sail material to diffract light in all directions. As NASA puts it, this will allow spacecraft to “make more efficient use of sunlight without sacrificing maneuverability.” Dubill’s proposed design could result in smaller, more nimble sails. And as a fun side effect, the veils would have a rainbow pattern, similar to how CDs look when held up to the light.
As part of NIAC Phases 1 and 2, the team designed, created, and tested various diffractive sail materials. The team also performed tests and developed navigation and control schemes specific to a future solar mission. Indeed, diffractive sails could allow a constellation of satellites to orbit the polar regions of the Sun. Gliding over the north and south poles of the Sun, solar satellites, with a perpetual source of propulsion, would perform unprecedented scientific observations.
“The diffractive solar sail is a modern take on the decades-old vision of light sails,” Dubill explained in the NASA release. “While this technology can enhance a multitude of mission architectures, it is poised to have a significant impact on the heliophysical community’s needs for unique solar observing capabilities.”
Dubill describes two main objectives for the next two years: to develop the sail diffractive itself and developing the solar polar orbiter constellation mission with diffractive sailboat.
“We plan to design, optimize, and fabricate sample diffractive sail materials that we want to characterize with optical testing and subject to spatial environmental testing,” Dubill told me. “In parallel, we plan to evolve the vision of a solar polar-orbiting sailboat mission by establishing optimal trajectories and sail attitude control to achieve the solar observations of a suite of payloads dictated by our heliophysicists.”
SIf all goes according to plan, the concept could lead to a real space mission and the proposed solar satellites.
“By expanding the diffractive sail design and developing the overall sail concept, the goal is to lay the foundation for a future demonstration mission using diffractive light sail technology.”
This post has been updated to include email comments from Amber Dubill.