Comment: I’ve been excited by LightSail 2 since before its launch. My interest in solar sails was sparked by Arther C. Clarke’s “The Sunjammer” when it appeared in Boys’ Life in 1964. The fact that LightSail 2 was the work of The Planetary Society done on the cheap with donations is just icing on the cake. For the last 30 months LightSail 2 has shown the world how to sail in space. NASA has learned a great deal in preparation for their future solar sail missions.
NEA Scout will be launched whenever the Artemis-1 Orion is launched to orbit the Moon. From near the Moon, NEA Scout will set sail towards a still to be determined near Earth asteroid. This uncertainty gives a “second star to the right and straight on ’til morning” air of adventure to the mission. This uncertainty is only tolerable because solar sails won’t run out of fuel. If NEA Scout ends up having to circle around to rendezvous with the asteroid, so be it. It might even take in more asteroids over its lifetime.
The Solar Cruiser will be the biggest sail yet, about a third the size of a football field. This craft should launch in 2025 or so and is destined to hover in an orbit staying on the Sun-Earth line just on the far side of the Sun-Earth Lagrange Point. A conventionally powered spacecraft would have to expend a lot of fuel to maintain that position. The Solar Cruiser can stay there indefinitely.
I finally found a simple description of how these solar sails are controlled on an episode of Planetary Radio where Les Johnson, NASA’s Principal Investigator for the NEA Scout and Solar Cruiser, explains how it’s done. Much like sailing a windsurfer, you change the center of effort of the sail in relation to the center of mass of the board. With a solar sail, you shift the mass of the craft in relation to the center of effort of the sail. One method is to physically adjust the location of the central part of the craft along the x and y axes. Another way, just developed by NASA, amounts to scandalizing a specific area of the sail with photovoltaic panels on the sail that can adjust the amount of light that is passed through without imparting momentum to that part of the sail. Japan came up with this concept for their pioneering IKAROS solar sail launched in 2010. Japan would not share the technology with NASA.
I think we’re going to see a lot more of these solar sails in space exploration, especially as we move towards more multi-year and multi-decade interstellar missions. It will be a new age of sail… and just as adventurous and exciting.
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