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Diffractive lightsails use small gratings embedded in thin films to produce diffraction (which causes light to spread out when it passes through a narrow opening).

Diffractive light sails are a potential advance on traditional reflective light sails. They can redirect light (and therefore thrust) without attitude changes. They are “aimed” using optoelectronic control rather than mechanical control, so they remain square to the incident sunlight. Thus they maintain their full capture area without angling to redirect light.

Because all light is transmitted, heating issues are less than reflective sails and the transmitted photons can still be used for PV panels.

They have been proposed for a solar polar orbit (high ecliptic inclination), which are challenging to accomplish with chemical rocket propulsion.

The Diffractive Solar Sailing project was selected for Phase III study under the NASA Innovative Advanced Concepts (NIAC) program.

enter image description here https://www.nasa.gov/news-release/nasa-supported-solar-sail-could-take-science-to-new-heights

Wikipedia on diffractive solar sails: https://en.wikipedia.org/wiki/Diffractive_solar_sail

Circumnavigating the sun with diffractive solar sails: https://www.sciencedirect.com/science/article/pii/S0094576521003337

Are there plans for a demonstration mission?

Woody
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  • By transmitting rather than reflecting, they are a lot less effective as solar sails, there's a lot less $\Delta p$. But being actively steerable electronically (rather than by attitude changes of the big bulky-yet-delicate monster) sounds like a potentially big benefit in trade-off. BUT you mention the same spacecraft re-using the transmitted light for PV power generation and that seems to throw a monkey wrench into the diffractive sail as steerable propulsion, because of course the PV, presumably attached to the same spacecraft, absorbs all the remaining momentum of the photons anyway! – uhoh Nov 27 '23 at 23:04
  • And now since the center of the photon force on the PV array is likely moving around as the diffraction angle is changed, it's likely to just torque the spacecraft around or set it spinning. Is there really a plan to reuse the light in PV cells? Can you point out a link to where that implementation is outlined and explained? The image included in your post seems to be missing one more ingredient to make it whole - unicorns! – uhoh Nov 27 '23 at 23:06
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    @uhoh ... I'd hate to try sell you a used car. All good points. My Spidey Sense was tingling when I read you can eat your photons, and have them, too. But it said "NASA", so it must be true ! Maybe they meant to say the same structure could support both functions, but only one at a time. If photons were diffracted away from the PV panel, it provides propulsion. If not, the photon could hit the PV. – Woody Nov 28 '23 at 00:17
  • "But it said 'NASA', so it must be true..." Could the helical engine work? :-) – uhoh Nov 28 '23 at 05:12
  • @uhoh I would think you'd want some of each -- fully reflective film for the better propulsive force, and some diffractive panels for steering. – Darth Pseudonym Nov 29 '23 at 19:44

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