Imagine a fleet of light sails, imprinted with holographic messages, embarking from Earth to the stars beyond. This tantalizing vision is now actively being developed for potential use in projects like Breakthrough Starshot, an interstellar mission concept that aims to send 1,000 tiny spacecraft across four light years to Alpha Centauri, our nearest stellar neighbor.
Unveiled in 2016 by Yuri Milner and Stephen Hawking, Breakthrough Starshot envisions deploying a fleet of stamp-sized “StarChips” attached to light sails in orbit, and accelerating them to about 20 percent the speed of light using massive laser arrays on Earth.
As if that isn’t mind-bending enough, scientists and artists have recently started exploring the futuristic idea of embossing holograms on the light sails. This is not just to make the sails look trippy; it’s also a potential solution to the technical challenge of stabilizing and steering the sails.
To reach their target speeds, Starshot’s sails are supposed to be blasted for several minutes by 50 to 100 gigawatts of energy provided by a laser beam on the Earth’s surface (for comparison, the average nuclear power plant produces one gigawatt, according to the US Department of Energy). But because the laser would be moving due to the rotation of the Earth, some mechanism is needed to keep the sails within the beam as it drifts; otherwise they will float out of the light, failing to accelerate.
“The sail is so lightweight that you can’t really put a control system on there to fire little jets and otherwise correct for the relative position of the sail and the light,” Mason Peck, a professor of aerospace engineering at Cornell University, told me over the phone. “So rather than making the sail follow the light beam with some sort of robotic approach or thrusters, you might make it do so with optical or photon pressure.”
One approach to channel that photon pressure is to create sails with spherical or conical shapes—theoretical studies show that those shapes provide a self-correcting force that could nudge sails back into the beam if they begin to drift off. But spherical sails would more easily collapse under the intense pressures of heat and acceleration, compared to flat square sails.
That’s where the holograms come in. By embossing a hologram shaped like a cone or a sphere onto a flat sail, it might be possible to essentially trick photons into reacting as if the structure were really curved. Meanwhile, the flat design would be better equipped to withstand the enormous forces exerted by the beam.
“If [the hologram] is conical or spherical, that photonic force will push it back in the center [of the beam], but from the point of view of the inertial forces, it’s a flat shape, so it won’t collapse,” physicist Greg Matloff, a light sail expert who serves on the advisory board of Breakthrough Starshot, told me in a phone call.
In other words, a holographic image on a sail may prove to be the best of both worlds, though it will take many years of experimentation to find out for sure. But beyond the potential stabilization and propulsion applications, holograms are also a promising vector for sending messages from Earth into the wider universe.
Matloff and his partner, artist C Bangs, have been ruminating on holographic message plaques for nearly two decades. In 2002, at the suggestion of physicist Robert Forward, the pair co-authored a NASA proposal that detailed how images and information could be encoded into a hologram on a sail. It’s a similar concept to the Voyager Golden Records, the phonographs onboard the Voyager probes launched in 1977, except that a holographic message could contain far more information and would also serve as propulsion for the spacecraft.
Breakthrough Starshot has given Matloff and Bangs the opportunity to resurrect this concept in earnest. In 2017, they consulted with hologram expert Martina Mrongovius, the creative director of the NYC HoloCenter, about the potential to emboss holographic data and artwork onto light sails and other spacecraft platforms.
“It is a space probe tradition to include a message plaque,” Mrongovius told me in an email. “Holograms have a massive information capacity to open up the types of imagery we could send into space. With holographic imaging, you can multiplex hundreds images together and create animations as well as record depth and dynamics.”
Such a platform could contain mountains of data about humans, Earth, and any other subjects we’d want to send out into the cosmos on light sails. Whether or not these messages would ever be intercepted by an alien species that could interpret them is an open question, and also somewhat beside the point.
“Considering how other beings could sense is an aspect of designing deep space messages, as well as longevity,” Mrongovius said. “The more immediately addressable question is how we represent ourselves as inhabitants of Earth. Sending a message is an opportunity to collaborate and build our identity as a species. Sending these messages is humanity’s way of reaching out into space, of saying we understand propulsion, are creative creatures, and that we come in peace.”
Bangs shares this view. “Basically when we do message plaques, we’re doing them for ourselves—we’re not doing them for aliens,” she told me over the phone. “We’re talking about really representing who we collectively feel that we are, and sending it out there.”
This tantalizing idea is about to start earning real-world experimental stripes. Earlier this year, NASA greenlit the launch of the Alpha 1U CubeSat, a small satellite developed by Peck and his team at Cornell’s Space Systems Design Studio. On track for launch within the next year or two, the spacecraft will deploy four “ChipSats” attached to a light sail. Six holograms created by Bangs and Mrongovius will also be attached to the side panels of the square satellite, and perhaps even imprinted on the sail.
The iridescent images will be based on sculptures made by Bangs that depict DNA, a fish, a moth, and other life-centric themes. Mrongovius will create holograms based on photographs of these art-pieces. (Bangs and Matloff will be presenting a lecture on the project over the weekend in London, at a meeting for the Initiative for Interstellar Studies.)
“The holograms we are creating look very different to the robotic aesthetic of most satellites,” Mrongovius said. “The CubeSat rotates as it orbits so we are recording multiple images into each face that replay when illuminated by the sun at different angles.”
The team hopes that the project will inspire interdisciplinary ideas about holographic applications in space, beyond Breakthrough Starshot. “For the humans who inhabit the ISS and future space bases, interiors with holographic art can expand visual space, enable dynamic light, and bring the aesthetics of nature into small artificial environments,” Mrongovius said, noting the work of artists Setsuko Ishii and Betsy Connors.
“Holographic art is a confluence of physics and imagination—so is space exploration,” she added. “While enabled by technology, both endeavors are driven by curiosity and vision.”
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