How to design a sail that won’t tear or melt during interstellar voyages

Starshot LightSail Spacecraft Artist Concept Accelerating with Ground-Based Laser Array. The previous concept of LightSail envisioned being passively pushed by the light from the sun, but Starshot’s laser-based approach prevents the sail from melting or tearing during acceleration. It is necessary to reconsider the shape and composition of.Credits: Masumi Shibata, Breakthrough Initiatives

Astronomers have been waiting for decades for the launch of the James Webb Space Telescope, which promises to look into space more than ever. But if humans really want to reach our nearest stellar neighbor, they have to wait quite a long time: the probe sent to Alpha Centauri by rocket takes about 80,000 years to travel. I need it.

Igor Bargatin, an associate professor of mechanical engineering and applied mechanics, seeks to solve this futuristic problem with ideas from sails, one of humanity’s oldest transport technologies.

As part of the Breakthrough Starshot initiative, he and his colleagues are designing the size, shape, and materials of sails that are pushed by the wind, not the wind. Light..

Using thin materials and a powerful laser array for nanoscopic, such sails can carry microchip-sized probes at one-fifth the speed of light, and Alpha Centauri in about 20 years instead of thousands of years. It’s fast enough to travel to.

“To reach another star in our lives, we need something relativistic or close to the speed of light,” says Bargatin. “The idea of ​​light sails has been around for some time, but we are now thinking of ways to ensure that those designs survive the trip.”

Much of the earlier research in this area estimated that the sun passively provided all the energy needed for the sails of light to move. However, Starshot’s plans to make sails relativistic speed require a much more focused energy source. Once the sail is in orbit, a large array of lasers on the ground trains the beam on it, providing millions of times the light intensity of the Sun.

Given that the laser target is a structure that is one-thousandth the width of paper and three meters wide, finding a way to prevent the sail from tearing or melting is a major design challenge.

Bargatin, Deep Jariwara, Associate Professor of Electrical Systems Engineering, and Earth Waslaman, Associate Professor of Materials Science and Engineering, UCLA Sameri Faculty of Engineering, have published two papers in the journal. Nano letter I will outline some of those basic specifications.

A paper led by Bargatin proposed that Starshot’s lightsail (consisting of an ultra-thin sheet of aluminum oxide and molybdenum disulfide) does not remain flat, as many previous studies have assumed, but parachutes. It shows that it needs to be swirled.

“The intuition here is that very tight sails, whether sailboats or space, are much easier to weep,” says Bargatin. “It’s a relatively simple concept to understand, but it took a lot of complicated calculations to actually show how these materials work at this scale.”

Bargatin and his colleagues suggest that a curved structure, rather than a flat sheet, about the same depth as the width can best withstand the super-acceleration strain of the sail, which is a pull of thousands of times the Earth’s gravity. doing.

“Laser photons fill the sails in the same way that air inflates a beach ball,” said Matthew Campbell, a postdoctoral fellow in Bargatin’s group and the lead author of the first paper. “And we know that lightweight, pressurized vessels must be spherical or cylindrical to avoid crevices and cracks. Think of a propane tank or a rocket fuel tank.”

Another paper, led by Raman, is about nanoscale patterning in sails. Laser beam One million times more powerful than the sun.

“If the sail absorbs even a small portion of the incident laser light, it gets very hot,” Raman explained. “To ensure that they just do not collapse, we need to maximize their ability to radiate their heat, which is the only mode of heat transfer available in space.”

Previous studies of LightSail have shown that a photonic crystal design can be used to maximize the thermal radiation of a structure by perforating the “fabric” of the sail at regular intervals. The researcher’s new paper adds another layer of periodicity: canvas swatches were tied together in a grid.

The spacing of the holes that match the wavelength of the light and the spacing of the swatches that match the wavelength of the heat radiation allow the sail to withstand even stronger initial pushes, reducing the time it takes for the laser to stay on the target.

“A few years ago, even thinking about this type of concept and doing theoretical work was considered tremendous,” says Jariwala. “Currently, not only do we have a design, but the design is based on the actual materials available in our laboratory. Future plans are to create such a structure on a small scale, It is to test with a high power laser. “

Pawan Kumar, a postdoctoral fellow in Jariwala’s lab, and John Brewer and Sachin Kulkarni, members of Raman’s lab in UCLA Samueli, contributed to this study.

Issues not yet addressed in the Breakthrough Starshot project

For more information:
Matthew F. Campbell et al., Relativistic LightSail needs to make a big wave, Nano letter (2021). DOI: 10.1021 / acs.nanolett.1c03272

John Brewer et al, Multiscale Photonic Emissivity Engineering for Relativistic LightSail Thermal Control, Nano letter (2022). DOI: 10.1021 / acs.nanolett.1c03273

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How to design a sail that won’t tear or melt during interstellar voyages

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