A new type of solar sail could allow us to explore hard-to-reach places in the solar system

Solar sailing technology has been a dream for many decades. The simple elegance of sailing on the waves of sunlight has a dreamy side that has captured the imaginations of engineers as well as writers. However, the practical aspects of the amount of energy received compared to that needed to transport useful payloads brought those dreams back to reality. Now, a team led by Amber Dubill of the John Hopkins University Applied Physics Laboratory and supported by the NASA Innovative Advanced Concepts (NIAC) program is developing a new solar sail architecture that may already have found its killer application – heliophysics.

The technique they use is known as refractive light sailing. It has significant advantages over current solar sail technology, including the ability to spin. This is a big problem for most solar sails, which lose their effectiveness if they are not facing the sun directly. Diffraction causes light to scatter as it passes through an aperture. Using this property of the solar sail material would allow the craft to move away from the sun while still being pressured by the light pushing it in whatever direction it was spinning.

To create such refractive pressure, the team created a material with very small gratings embedded in it to diffract light onto a surface that could still take advantage of the force generated when that light was absorbed. This would allow any spacecraft using a sail as a propulsion system to move away slightly from the Sun and take advantage of the powerful thrust from the photons of light.

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UT video describing solar cells.

To demonstrate this technology, the NIAC is supporting it with a Phase III grant after the successful completion of Phases I and II over the past few years. The third phase comes with $2 million in two-year funding to further develop the materials used in the solar sail, culminating in ground-based testing that could herald a move to use in deep space.

Deep space is the most likely place to apply such refractive sails. In particular, the researchers believe that they will be effective in solar physics. Conventional thrust techniques do not work well around the sun’s poles, due to magnetic interference in that space. Conventional solar sails will not work well either, because the light falling on them in these locations may push them away from the sun or not at all.

Weekly satellite hangout with UT Fraser Publisher Cain & Amber Dubill – Principal Investigator in Solar Refractive Technology.

Using a refracting solar sail, the spacecraft can still orient itself in the right direction while still using the force from the light to move effectively. This will allow a vehicle equipped with one to observe the sun from an angle like never before. But there is still a long way to go before any vehicle is equipped with one. The funding path after NIAC Phase 3 is ambiguous at best at the moment, and there will still be more development work to be done after another two years of development. But, with luck, a new type of solar sail may be linked to the next generation of the solar physics lab. It may eventually be used in many other programs as well.

Learn more:
NASA – A NASA-powered solar sail can take science to new heights
UT – Forget about interstellar flights. Small light sails can be used to explore the solar system today
UT – LightSail 2 sends new images of Earth
Utah – What is a solar sail?

main picture:
Artist’s depiction of refractive solar sails.
Credit – Mackenzie Martin