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Diffractive solar sail

From Wikipedia, the free encyclopedia
Concept art for a diffractive lightsail

A diffractive solar sail, or diffractive lightsail, is a type of solar sail which relies on diffraction instead of reflection for its propulsion.[1][2] Current diffractive sail designs use thin metamaterial films, containing micrometer-size gratings based on polarization or subwavelength refractive structures, causing light to spread out (i.e. diffract) and thereby exert radiation pressure when it passes through them.[2][3]

History

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The idea of using diffraction for a solar sail was first proposed in 2017 by researchers at the Rochester Institute of Technology.[4] This was enabled in part by advances in material design and fabrication (particularly of gratings), and optoelectronic control.[5] In 2019 a diffractive solar sail project from the Rochester Institute of Technlology suggested a solar polar orbit mission with diffractive sails that could reach a higher solar inclination angle and smaller orbital radius than one with reflective sails, reaching NASA's NIAC phase II.[1][2][6] In 2022 the NIAC project reached phase III and gained US$2 million of support from NASA, with involvement of researchers from both Johns Hopkins University and the Rochester Institute of Technology.[7][8]

Advantages over reflective sails

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Reflective solar sail designs tend to consist of large, thin reflective sheets. By the law of reflection, the forces acting on them will always be normal to the sheet surface; the sheets must therefore be tilted during navigation, which poses structure and control challenges, and reduces the power reaching the sail.[2][5][7] These in turn can lower reliability, increase mass, and reduce acceleration.[2] Furthermore, reflective sails tend to absorb a reasonable proportion of the light hitting them, causing them to heat up; this can cause structural problems, particularly when the sail is repeatedly heated and then allowed to cool.[5] Also, each photon hitting the sail is used once, i.e. it's either reflected or absorbed.[5]

On the other hand, in a diffractive sail the grating can redirect light even when the sheet directly faces the sun, allowing much more efficient control with maximum power hitting the sail.[5][2] The diffractive film can be designed to allow for optoelectronic control of the gratings, thereby reducing mass and increasing reliability relative to mechanical control.[2] Since the film is translucent, most of the light just passes through the sail, reducing overall heating.[5] Photons can be reused: either by passing through a second diffraction grating for more thrust, or by going to a solar cell to provide electricity.[8]

References

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  1. ^ a b Dubill, Amber L.; Swartzlander, Grover A. (1 October 2021). "Circumnavigating the sun with diffractive solar sails". Acta Astronautica. 187: 190–195. Bibcode:2021AcAau.187..190D. doi:10.1016/j.actaastro.2021.06.036.
  2. ^ a b c d e f g Hall, Loura (8 April 2019). "Diffractive Lightsails". NASA. Retrieved 9 February 2023.
  3. ^ Swartzlander Jr, Grover A. (15 May 2018). "Flying on a Rainbow: A Solar-Driven Diffractive Sailcraft". arXiv:1805.05864 [physics.pop-ph].
  4. ^ Swartzlander, Grover A. (1 June 2017). "Radiation pressure on a diffractive sailcraft". Journal of the Optical Society of America B. 34 (6): C25–C30. arXiv:1703.02940. Bibcode:2017JOSAB..34C..25S. doi:10.1364/JOSAB.34.000C25. S2CID 118954811. Retrieved 9 February 2023.
  5. ^ a b c d e f Swartzlander, Grover (12 October 2017). "StackPath". www.laserfocusworld.com. Retrieved 9 February 2023.
  6. ^ Hall, Loura (8 April 2019). "NIAC 2019 Phase I, Phase II and Phase III Selections". NASA. Retrieved 9 February 2023.
  7. ^ a b Potter, Sean (24 May 2022). "NASA-Supported Solar Sail Could Take Science to New Heights". NASA. Retrieved 9 February 2023.
  8. ^ a b Sivarajah, Ilamaran; Thomson (review), Laura (29 June 2022). "The Diffractive Solar Sailing Project". AZoOptics.com. Retrieved 9 February 2023.