{"id":793302,"date":"2025-02-04T08:51:03","date_gmt":"2025-02-04T13:51:03","guid":{"rendered":"https:\/\/spaceweekly.com\/?p=793302"},"modified":"2025-02-04T08:51:03","modified_gmt":"2025-02-04T13:51:03","slug":"lightsails-and-the-audacious-plan-to-reach-the-stars","status":"publish","type":"post","link":"https:\/\/spaceweekly.com\/?p=793302","title":{"rendered":"Lightsails, and the audacious plan to reach the stars"},"content":{"rendered":"
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\nIn recent decades, technological advances have opened up the possibility of light-powered space travel at a significant fraction of light speed. This involves a ground-based light beamer pushing ultra-light nanocrafts \u2013 miniature space probes attached to lightsails \u2013 to speeds of up to 100 million miles an hour (160 million kph). Such a system would allow a flyby mission to reach Alpha Centauri in just over 20 years from launch. Read about the reality of lightsails and star travel, below. Image via Breakthrough Starshot Initiative. Used with permission.<\/figcaption><\/figure>\n
Caltech published this article \u2013 written by Kimm Fesenmaier \u2013 on January 31, 2025. Edits by EarthSky.<\/p>\n
Lightsails to the stars<\/h3>\n
The idea of traveling through interstellar space using spacecraft propelled by ultrathin sails might sound like the stuff of sci-fi novels. But in fact, a program started in 2016 by Stephen Hawking and Yuri Milner known as the Breakthrough Starshot Initiative has been exploring the idea. The concept is to use lasers to propel miniature space probes attached to \u201clightsails\u201d to reach ultrafast speeds and eventually our nearest star system, Alpha Centauri.<\/p>\n
Caltech said on January 31, 2025, that it is leading the worldwide community working toward achieving this audacious goal. Harry Atwater of Caltech explained:<\/p>\n
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The lightsail will travel faster than any previous spacecraft, with potential to eventually open interstellar distances to direct spacecraft exploration that are now only accessible by remote observation.<\/p>\n<\/blockquote>\n
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Ultrathin membranes<\/h3>\n
Now, Atwater and his colleagues at Caltech have developed a platform for characterizing the ultrathin membranes that could one day be used to make these lightsails. Their test platform includes a way to measure the force that lasers exert on the sails and that will be used to send the spacecraft hurtling through space. The team\u2019s experiments mark the first step in moving from theoretical proposals and designs of lightsails to actual observations and measurements of the key concepts and potential materials. Atwater said:<\/p>\n
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There are numerous challenges involved in developing a membrane that could ultimately be used as lightsail. It needs to withstand heat, hold its shape under pressure, and ride stably along the axis of a laser beam. But before we can begin building such a sail, we need to understand how the materials respond to radiation pressure from lasers. We wanted to know if we could determine the force being exerted on a membrane just by measuring its movements. It turns out we can.<\/p>\n<\/blockquote>\n
A paper describing the work appears in the journal Nature Photonics<\/em>. The lead authors of the paper are postdoctoral scholar in applied physics Lior Michaeli and graduate student in applied physics Ramon Gao, both of Caltech.<\/p>\n
The work so far<\/h3>\n
The goal is to characterize the behavior of a freely moving lightsail. But as a first step, to begin studying the materials and propulsive forces in the lab, the team created a miniature lightsail that is tethered at the corners within a larger membrane.<\/p>\n
The researchers used equipment in the Kavli Nanoscience Institute at Caltech and a technique called electron beam lithography to carefully pattern a membrane of silicon nitride just 50 nanometers thick, creating something that looks like a microscopic trampoline. The mini trampoline, a square just 40 microns wide and 40 microns long, is suspended at the corners by silicon nitride springs. Then the team hit the membrane with argon laser light at a visible wavelength. The goal was to measure the radiation pressure that the miniature lightsail experienced by measuring the trampoline\u2019s motions as it moved up and down.<\/p>\n
How light pushes the sail<\/h3>\n
But the picture from a physics perspective changes when the sail is tethered, says co-lead author Michaeli:<\/p>\n
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In this case, the dynamics become quite complex.<\/p>\n<\/blockquote>\n
The sail acts as a mechanical resonator, vibrating like a trampoline when hit by light. A key challenge is that these vibrations are mainly driven by heat from the laser beam, which can mask the direct effect of radiation pressure. Michaeli said the team turned this challenge into an advantage:<\/p>\n
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We not only avoided the unwanted heating effects but also used what we learned about the device\u2019s behavior to create a new way to measure light\u2019s force.<\/p>\n<\/blockquote>\nHere\u2019s another artist\u2019s concept of a lightsail, also via the Breakthrough Starshot Initiative. Used with permission.<\/figcaption><\/figure>\n
Understanding the forces at play<\/h3>\n
The new method lets the device act additionally as a power meter to measure both the force and power of the laser beam. Co-lead author Gao commented:<\/p>\n
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The device represents a small lightsail, but a big part of our work was devising and realizing a scheme to precisely measure motion induced by long-range optical forces.<\/p>\n<\/blockquote>\n
To do that, the team built what is called a common-path interferometer. In general, motion can be detected by the interference of two laser beams, where one hits the vibrating sample and the other traces a rigid location. However, in a common-path interferometer, because the two beams have traveled nearly the same path, they have encountered the same sources of environmental noise, such as equipment operating nearby or even people talking, and those signals get eliminated. All that remains is the very small signal from the motion of the sample.<\/p>\n
Measuring the lightsail\u2019s motions<\/h3>\n
The engineers integrated the interferometer into the microscope they used to study the miniature sail and housed the device within a custom-made vacuum chamber. They were then able to measure motions of the sail as small as picometers (trillionths of a meter) as well as its mechanical stiffness, that is, how much the springs deformed when the sail was pushed by the laser\u2019s radiation pressure.<\/p>\n
Since the researchers know that a lightsail in space would not always remain perpendicular to a laser source on Earth, they next angled the laser beam to mimic this and again measured the force with which the laser pushed the mini sail. Importantly, the researchers accounted for the laser beam spreading out at an angle and therefore missing the sample in some areas by calibrating their results to the laser power measured by the device itself. Yet, the force under those circumstances was lower than expected. In the paper, the researchers hypothesize that some of the beam, when directed at an angle, hits the edge of the sail, causing a portion of the light to get scattered and sent in other directions.<\/p>\n
Future development<\/h3>\n
Looking forward, the team hopes to use nanoscience and metamaterials \u2013 materials carefully engineered at that tiny scale to have desirable properties \u2013 to help control the side-to-side motion and rotation of a miniature lightsail. Gao said:<\/p>\n
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The goal then would be to see if we can use these nanostructured surfaces to, for example, impart a restoring force or torque to a lightsail. If a lightsail were to move or rotate out of the laser beam, we would like it to move or rotate back on its own.<\/p>\n<\/blockquote>\n
The researchers note that they can measure side-to-side motion and rotation with the platform described in the paper. Gao explained:<\/p>\n
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This is an important stepping stone toward observing optical forces and torques designed to let a freely accelerating lightsail ride the laser beam.<\/p>\n<\/blockquote>\n
Bottom line: Lightsails for star travel sound like the stuff of science fiction. But, using funds from the Breakthrough Starshot Initiative, materials science researchers at Caltech have been studying the properties of potential lightsails in the lab.<\/p>\n
Source: Direct radiation pressure measurements for lightsail membranes<\/p>\n
Via Caltech<\/p>\n
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Deborah Byrd<\/h4>\n
View Articles\n <\/p><\/div>\n
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About the Author:<\/h6>\n
Our Editor-in-Chief Deborah Byrd works to keep all the astronomy balls in the air between EarthSky’s website, YouTube page and social media platforms. She’s the primary editor of our popular daily newsletter and a frequent host of EarthSky livestreams. Deborah created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n
![\"Lightsails:](\"https:\/\/earthsky.org\/upl\/2025\/02\/lightsail-breakthrough-starshot-e1738616035276.jpg\")