Researchers have written about some of the challenges involved in building a light sail suitable for Breakthrough Starshot, a project that would accelerate a gram-scale "chipcraft" using lasers so that it could travel interstellar distances in just decades:
A team of researchers at the California Institute of Technology has taken a hard look at the challenges facing efforts to carry out the Breakthrough Starshot project. In their Perspective piece published in the journal Nature Materials, the researchers outline the obstacles still facing project engineers and possible solutions.
The light sail would need to be made of a lightweight but reflective material able to withstand being bombarded by gigawatts of photons without melting. Graphene doesn't qualify. Many of the materials the researchers evaluated have only been studied in their bulk forms, rather than thin films, which can have different properties.
The researchers seem optimistic about the challenges. From the abstract (DOI: 10.1038/s41563-018-0075-8) (DX):
The Starshot Breakthrough Initiative established in 2016 sets an audacious goal of sending a spacecraft beyond our Solar System to a neighbouring star within the next half-century. Its vision for an ultralight spacecraft that can be accelerated by laser radiation pressure from an Earth-based source to ~20% of the speed of light demands the use of materials with extreme properties. Here we examine stringent criteria for the lightsail design and discuss fundamental materials challenges. We predict that major research advances in photonic design and materials science will enable us to define the pathways needed to realize laser-driven lightsails.
Also at Ars Technica.
Previously: Stephen Hawking and Yuri Milner's $100 Million Interstellar Spacecraft Plan
Related: NASA Plans to Launch an Interstellar Mission to Alpha Centauri in 2069
Related Stories
The BBC and the Guardian both carry stories about an unmanned interstellar spacecraft designed to reach the Alpha Centauri system "within a generation" (30 or so years).
The spacecraft would be miniaturised to the size of an average silicon chip, and be propelled by a solar sail which would receive a boost from a powerful laser on the Earth.
Milner's Breakthrough Foundation is running a project, backed by Hawking, to research the technologies needed for such a mission, which they think will soon be feasible.
takyon: The campaign is called Breakthrough Starshot. Breakthrough Initiatives also announced the release of initial observational datasets from the Breakthrough Listen 10-year SETI effort.
NASA thinks that the technologies needed to launch an interstellar probe to Alpha Centauri at a speed of up to 0.1c could be ready by 2069:
In 2069, if all goes according to plan, NASA could launch a spacecraft bound to escape our solar system and visit our next-door neighbors in space, the three-star Alpha Centauri system, according to a mission concept presented last week at the annual conference of the American Geophysical Union and reported by New Scientist. The mission, which is pegged to the 100th anniversary of the moon landing, would also involve traveling at one-tenth the speed of light.
Last year, Representative John Culberson called for NASA to launch a 2069 mission to Alpha Centauri, but it was never included in any bill.
Meanwhile, researchers have analyzed spectrographic data for the Alpha Centauri system and found that small, rocky exoplanets are almost certainly undiscovered due to current detection limits:
The researchers set up a grid system for the Alpha Centauri system and asked, based on the spectrographic analysis, "If there was a small, rocky planet in the habitable zone, would we have been able to detect it?" Often, the answer came back: "No."
Zhao, the study's first author, determined that for Alpha Centauri A, there might still be orbiting planets that are smaller than 50 Earth masses. For Alpha Centauri B there might be orbiting planets than are smaller than 8 Earth masses; for Proxima Centauri, there might be orbiting planets that are less than one-half of Earth's mass.
In addition, the study eliminated the possibility of a number of larger planets. Zhao said this takes away the possibility of Jupiter-sized planets causing asteroids that might hit or change the orbits of smaller, Earth-like planets.
(For comparison, Saturn is ~95 Earth masses, Neptune is ~17, Uranus is ~14.5, and Mars is ~0.1.)
Planet Detectability in the Alpha Centauri System (DOI: 10.3847/1538-3881/aa9bea) (DX)
(Score: 0) by Anonymous Coward on Wednesday May 09 2018, @04:28PM (4 children)
One thing I've never seen mentioned is a discussion of how a chip the size of a postage stamp flung by Proxima Centauri is supposed to phone home to tell us it got there. Wouldn't it need a big-ass antenna?
(Score: 2) by Grishnakh on Wednesday May 09 2018, @04:37PM
I've wondered the same thing. Radio transmissions are governed by the inverse-square law, so every time you double the distance, you need 4 times the transmitting power. Here on Earth, we could I guess build a really big-ass radio transmitter so these little things can still receive communications at Alpha Centauri, but things things surely won't have enough transmitting power to be heard from that distance without building a planet-sized radio dish. I'd really like to see the analysis they've done of this; without effective communications, these (or any) probes will be useless.
(Score: 5, Informative) by takyon on Wednesday May 09 2018, @04:51PM
https://www.popsci.com/three-questions-for-breakthrough-starshot [popsci.com]
If they did use electromagnetic communications instead, newer radio telescopes could use interferometry. They could be based in different locations in space, or on the Moon.
https://www.nextbigfuture.com/2017/04/planet-wide-millimeter-radio-telescope.html [nextbigfuture.com]
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 2) by HiThere on Wednesday May 09 2018, @05:38PM
I haven't looked at this design, but some of the designs I saw depended on using the secondary lightsail as an antenna. I suspect that they had solar cell driven amps built right into the base of the antenna. That's only a few transistors, and pretty light. It's a reasonable question to ask how far that signal would go, however, as even laser beams fall apart over enough distance.
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(Score: 1) by rumata on Thursday May 10 2018, @04:38AM
It's all in that magical light sail. Not only is it lots of 9s reflective on one side, a few 9s emissive on the other side, and has ludicrously high strength to weight ratio at high temperature and in a very thin film (so that you can dump lots of GW into a few square meters without vaporizing it or have it tear itself apart by the resulting acceleration). It can also be shaped into a diffraction limited mirror at the other end and be precision pointed back to earth so that you get respectable data-rates with very limited transmitter energy.
Now I'm not an elderly and distinguished scientist, but I'll flat out say this is going to be impossible for many moons to come, quite possibly forever. AFAIK we don't have anything currently that will fulfill any of the requirements, not even in micro lab-samples, let alone the combination, let alone packaged into something that can be shaped into a practical structure.
Cheers,
Michael