Radiation Pressure Propulsion of Structurally Stable Lightsails with Embedded Payloads

When and Where

May 11, 2022
10:30am - 10:45am

Hawai'i Convention Center, Level 3, 316C

Presenter

Michael Kelzenberg

Ramon Gao

Harry Atwater

Co-Author(s)

Michael Kelzenberg¹,Ramon Gao¹,Harry Atwater¹

California Institute of Technology¹

Abstract

Michael Kelzenberg¹,Ramon Gao¹,Harry Atwater¹

California Institute of Technology¹

We have developed a time-domain simulation tool to study the structural viability of ultralight membrane-like laser-driven lightsail space probes, which have been proposed as a technologically viable means of achieving relativistic propulsion for interstellar exploration. [1,2] While recent efforts have discussed the optical and material property requirements for lightsail membranes [3-5], identifying various shapes and nanophotonic designs for beam-riding stability [6-8], considerably less is known about the structural viability of the proposed sailcraft, which must be self-supporting membranes and also capable of carrying a scientific payload. We have identified several routes to achieving structurally stable sailcraft based on the mechanical and optical properties of real materials including Si and SiNx, taking into account the challenge of propelling a lightsail with an inhomogeneous mass distribution resulting from carrying a payload -- without introducing collapse, rupture, overheating, or destabilization of the lightsail membrane. Our results pertain both to shaped specular lightsails as well as flat membranes with self-stabilizing nanophotonic designs. By modelling lightsails as flexible meshes rather than rigid bodies, we can investigate topics such as shape deformations, tensile strength limits, nonuniform mass distributions, temperature gradients, and internal reflections of light within the sail envelope. For example, we have studied specular curved lightsail shapes such as cones, paraboloids, and hemispheres of up to 10 m2 aperture area, and found that while many can provide beam-riding stability when spin-stabilized on the order of 100 Hz, many such shapes cause reflected light to become highly focused onto other portions of the sail, causing local temperature excursions exceeding 300K above the average sail temperature. Other designs are too weak to allow adequate spin-stabilization or attachment of a discrete payload. We have simulated several payload integration schemes including tethered (trailing) payloads, lumped centrally attached payloads, and distributed payloads, identifying viable approaches for carrying payloads up to 1 g in mass. Such nonuniform mass distributions require careful attention to the lightsail membrane and connecting structures to prevent tensile failure of the membrane at the points of attachment. We will also present our ongoing efforts to develop nanophotonic optical and thermal shielding for sailcraft payloads, which is required to prevent damage to conductors and semiconductor materials in the intense propulsion beam. Our presentation will include a discussion of various design regimes to ensure sailcraft stability and survivability, including simulated trajectories and animations of shape deformations. 1. Lubin, P. JBIS 2016, 69, 40-72. 2. Breakthrough Starshot Initiative. https://breakthroughinitiatives.org/initiative/3 3. Atwater, H. A.; Davoyan, A. R.; Ilic, O.; Jariwala, D.; Sherrott, M. C.; Went, C. M.; Whitney, W. S.; Wong, J. Nat Mater 2018, 17, (10), 861-867. 4. Brewer, J.; Campbell, M. F.; Kumar, P.; Kulkarni, S.; Jariwala, D.; Bargatin, I.; Raman, A. P. arXiv preprint 2106.03558 2021. 5. Ilic, O.; Went, C. M.; Atwater, H. A. Nano Letters 2018, 18, (9), 5583-5589. 6. Ilic, O.; Atwater, H. A. Nature Photonics 2019, 13, (4), 289-295. 7. Swartzlander, G. A. J. Opt. Soc. Am. B 2017, 34, (6), C25-C30. 8. Salary, M. M.; Mosallaei, H. Laser & Photonics Reviews 2020, 14, (8), 1900311.