Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Monday, February 3, 2025

Riding on a light beam

Some of you probably have read about a project called Breakthrough Starshot that began perhaps eight years ago (and which was championed by none other than Stephen Hawking), which proposed sending small remote-controlled cameras to nearby star systems, powered by lasers that could propel them up to twenty percent of the speed of light.

If something like this were launched today, it would mean we could be getting photographs back from Proxima Centauri in twenty years.

[Image licensed under the Creative Commons ESO/M. Kornmesser, Artist's impression of the planet orbiting Proxima Centauri, CC BY 4.0]

It's an ambitious project, and faces significant hurdles.  Even if propelled by lasers -- which, being light, travel at the speed thereof -- navigation becomes increasingly difficult the farther away it gets.  Just at the distance of Pluto, our intrepid little spacecraft would be 4.5 light-hours from Earth, meaning if we tried to beam it instructions to dodge around an incoming meteor, it would be 4.5 hours until the command arrived, at which point all that would be left is intrepid scrap metal.  And Proxima Centauri is 4.3 light years away.

You see the problem.  The Starshot spacecraft would have to be able, on some level, to think for itself, because there simply wouldn't be time for Mission Control to steer it to avoid danger.

There are other obstacles, though.  Besides the obvious difficulties of being in the cold vacuum of interstellar space, contending with cosmic rays and the like, there's the problem engendered by its speed.  Assuming the estimate of a maximum velocity of twenty percent of light speed is correct, even tiny particles of dust would become formidable projectiles, so Starshot is going to require some heavy-duty shielding, increasing its mass (and thus the amount of energy needed to make it go).

Three years ago we got an encouraging proof of concept, when the group working on the mission -- Russian entrepreneur Yuri Milner's Breakthrough Foundation -- launched a test of the Starshot craft.  It was a tiny little thing, small enough to fit in your hand and weighing about the same as a stick of gum, designed and built by engineers at the University of California - Santa Barbara.  In the test flight it achieved an altitude of nineteen miles, all the while functioning flawlessly, returning four thousand images of the Earth taken from aloft.

And just last week, a paper in Nature Photonics describes further research on how to overcome the weight/propulsion issue, with the creation of a fifty-nanometer-thick membrane of silicon nitride that was tested to measure the actual thrust a laser could create on something that lightweight -- a feat that has never been done before.  The miniature sail passed with flying colors.

"There are numerous challenges involved in developing a membrane that could ultimately be used as lightsail," said Harry Atwater of Caltech, who led the study.  "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."

The most significant remaining hurdle is to design the laser system to make Starshot move -- lasers that are extremely powerful yet so finely collimated that they can still strike a ten-centimeter craft square-on from several light years away.  The engineering director for Breakthrough, Peter Klupar, is designing a 100,000 gigawatt laser -- to be located, he says, in Chile -- that could be the answer.  Of course, such a powerful device is not without its dangers.  Reflected off a mirror in space, Klupar says, such a laser could "ignite an entire city in minutes."

Not that there's a mirror out there.  So you shouldn't worry at all about that.

"You would think that this is all impossible, but we have folks at Caltech and the University of Southampton and Exeter University working on about fifty contracts on making all [of] this happen," Klupar said.  "No one has come up with a deal-breaker that we can find yet.  It all seems real."

All of which may seem like science fiction, but it's phenomenal how fast things go from the realm of Star Trek to reality.  Klupar compares his light sails to CubeSats, tiny (ten by ten centimeters, weighing a little over a kilogram) orbiting telemetry devices that are now common.  "It feels a lot like the way CubeSats felt twenty years ago," he said.  "People were saying, 'Those are toys, they're never going to develop into anything, there's no way I can see that ever working.'  And today and look them: hundreds of millions of dollars is being spent on them."

So keep your eye on this project.  If there's a chance at a remote visit to another star system, I think this is our best bet.  The Breakthrough Foundation estimates an actual, honest-to-goodness launch toward a nearby star as early as 2030.  Meaning perhaps we could get our first photographs of planets around another star by 2050.

I'll be ninety years old at that point, but if that's what I'm waiting for, I can make it till then.

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