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Sailing has been a mainstay of human history for millennia, so it\u2019s no surprise that scientists would apply it to traveling in space. Solar sailing, the most common version, uses pressure from the Sun to push spacecraft with giant sails outward in the solar system. However, there is a more technologically advanced version that several groups think might offer us the best shot at getting to Alpha Centauri \u2013 light sailing. Instead of relying on light from the Sun, this technique uses a laser to push an extraordinarily light spacecraft up to speeds never before achieved by anything humans have built. One such project is supported by the Breakthrough Starshot Initiative, initially founded by Yuri Milner and Stephen Hawking. A new paper by researchers at Caltech, funded by the Initiative, explores how to test what force a laser would have on a light sail as it travels to another star.<\/p>\n
<\/p>\n The general concept of pushing something with light seems simple enough, but the devil is in the details in terms of how it will operate in space. The laser and spacecraft have to synchronize over millions of miles. If either so much as slightly move the angle they are set to, perhaps because a micrometeoroid hit them, then the mission fails either because the craft ends up in a different part of the galaxy or the laser doesn\u2019t provide enough power to get it there in a reasonable amount of time.<\/p>\n Testing is the way to ensure such a disaster doesn\u2019t happen, but even understanding how the physics of a light sail will work over such large distances is difficult. So, the researchers at Caltech, led by postdoc Lior Michaeli and PhD student Ramon Gao, built a setup to test those physics.<\/p>\n Images provided as part of a press release to accompany their paper in Nature Photonics show a small square sample of light sail connected to a larger, hollowed-out square membrane by a set of four springs attached to each corner of the sample. What the images don\u2019t do a good job of capturing is just how small the sample is \u201440 microns by 40 micros isn\u2019t much compared to the 10 m2<\/sup> for the final light sail design.<\/p>\n But it is a start, and the test rig introduced some interesting engineering challenges. The square is only 50 nm thick and made of silicon nitride. The springs are made of the same material, and the overall setup \u201clooks like a microscopic trampoline,\u201d according to the press release.\u00a0<\/p>\n When the sample was subjected to an argon laser, it vibrated. The researchers knew that this vibration was caused primarily by heat from the laser, and they needed to differentiate the vibration caused by heating from the force applied by the light itself. To do so, they turned to an instrument commonly used in space exploration\u2014an interferometer.<\/p>\n \n
Credit \u2013 Michaeli et al. \/ Caltech<\/figcaption><\/figure>\n<\/div>\n