Breakthrough Starshot, the $100 million initiative aiming to send robotic missions to nearby stars by the mid-21st century, has achieved what might prove to be a "Sputnik moment" in successfully lofting its first spacecraft — the smallest ever launched and operated in orbit.
In 1957, the Soviet Union shocked the world by flying the first artificial satellite, Sputnik 1, a 183-lb. (83 kilograms) metallic orb about twice the size of a basketball that broadcast a radio message to anyone listening down on Earth. On June 23, Breakthrough Starshot sent not one but six satellites into low-Earth orbit, riding as supplementary payloads on an Indian rocket launching two other educational satellites built by the European space company OHB System AG.
These six satellites are comparatively dainty, but punch far above their weight. Called "Sprites," each is a 0.14-ounce (4 grams) flake of circuit-board just 1.4 inches (3.5 centimeters) on a side, packing solar panels, computers, sensors and communications equipment into an area equal to a U.S. postage stamp. Representatives of Breakthrough Starshot, which is funded by the Russian billionaire Yuri Milner, brokered the deal that sent the Sprites piggybacking to orbit. They also worked with the U.S. State Department to ensure the project did not violate strict federal regulations limiting exports of spaceflight hardware. [Breakthrough Starshot in Pictures: Laser Sail Nanocraft to Explore Other Star Systems]
Manufactured in bulk, low-cost Sprites could be deployed and networked by the hundreds or thousands to create space-based sensor arrays of unprecedented breadth, with each craft so lightweight that it could operate without propellant, shifting or maintaining its orbit solely through the radiation pressure of starlight or the forces imparted by a planet's magnetic field. More wildly, future iterations of Sprites could become Breakthrough's hoped-for "StarChips" — spacecraft integrated with gossamer-thin, meter-wide "lightsails" that would travel at 20 percent the speed of light to Alpha Centauri or other nearby stars, propelled by high-powered pulses of photons from a gargantuan ground-based laser array. Progress toward this starry-eyed goal is slow but steady, Breakthrough representatives say, and the organization is set to solicit research proposals for the associated "grand challenges" in optics, communications, materials science and other disciplines later this year.
"This is a very early version of what we would send to interstellar distances," says Pete Worden, Breakthrough Starshot's executive director and former director of NASA's Ames Research Center. "In addition, this is another clear demonstration that it is possible for countries to work together to do great things in space. These are European spacecraft with U.S. nanosatellite payloads launching on an Indian booster — you can't get much more international than that."
For now, much like Sputnik of yore, each of the Sprites in low-Earth orbit carries a radio transmitter that almost anyone might tune in to with relative ease, serving as a real-world demonstration of emerging spaceflight capabilities that could prove revolutionary. [Gallery: Visions of Interstellar Starship Travel]
The Sprites' revolution, however, is not being televised, and is presently struggling just to be heard on the radio. One Sprite apiece is attached to the outside of each mothership — the Latvian Venta satellite and the Italian Max Valier satellite, the latter of which also holds four additional Sprites awaiting deployment into space as wholly independent spacecraft. Radio telemetry from minuscule magnetometers and gyroscopes on the deployed Sprites would then be used to track the spacecraft as they shift, spin and tumble, to better understand their orbital dynamics. Ground stations in California and New York have received radio signals from at least one of the exterior-mounted Sprites, but mission controllers are struggling to establish communications with the Max Valier, which may have failed to deploy its own radio antenna. Without that communications link, Max Valier's payload of Sprites cannot be deployed, and uncertainty lingers over whether both exterior Sprites are actually transmitting.
"We've gotten signals from at least one Sprite, but we're not sure which because we haven't received two signals simultaneously," says Zac Manchester, a post-doctoral researcher at Harvard University who is helming the project for Breakthrough Starshot. Manchester began work on the Sprites in 2007 while earning his PhD at Cornell University, laboring alongside Cornell professor Mason Peck and another doctoral student, Justin Atchison.
Despite the setback, Worden is bullish on the mission's value. "Our primary objective was to show that a Sprite's communications and power systems could work in space — that's the baseline data we need to pursue further steps," he says. "From our perspective, this experiment has been 100 percent successful."
Manchester is similarly ebullient: "This is the first time we've successfully demonstrated Sprites end-to-end by flying them in space, powering them with sunlight and receiving their signals back on Earth." Each Sprite, he says, generates only 100 milliwatts of electricity in direct sunlight. That's scarcely enough to sustain a typical wireless router's antenna, but sufficient in ideal circumstances to transmit data down from low-Earth orbit at a rate akin to that of a fax machine. More impressively, those 100 milliwatts are also enough to operate Sprite's onboard microprocessors, which surpass many full-sized satellites from the 1990s in terms of raw computing power.
Both motherships are in stable orbits, Manchester says — offering enough time for mission controllers to attempt various fixes — and Sprites have previously withstood long-term exposure to space. In 2011 during its penultimate mission the space shuttle Endeavour delivered three to the International Space Station (ISS), where they were mounted outside for three years as part of a materials-science experiment. That mount faced away from Earth, preventing their signals from reaching the planet. But once brought back from space the Sprites were still in working order, happily chirping in radio when bathed in a sunlamp's glow on a lab bench.
Another demonstration attempt occurred in 2014, when a crowd-funded, shoebox-sized "KickSat" ferried a hundred of the featherweight spacecraft into orbit. But those Sprites could not be deployed from the short-lived KickSat due to concerns that they might create (or become) uncontrollable pieces of space debris that could pose grave risks to astronauts who were in a Soyuz rocket en route to the ISS at the time. (The U.S. Air Force uses powerful radars to catalog and track most space debris to provide early warnings for astronauts and satellites, but Sprites are so small that they can slip through that surveillance unseen.) [Photos: Space Debris Images & Cleanup Concepts]
Fears of nigh-invisible debris swarms place a ceiling of sorts on Sprites and similarly-sized nanosatellites, which U.S. federal officials have informally forbidden from venturing higher than 250 miles (400 kilometers) above Earth. Below that threshold, the spacecrafts' orbits decay relatively quickly, allowing them to harmlessly re-enter and burn up in the atmosphere within weeks or months. "That's the unofficial comfort zone for the foreseeable future," Manchester says, adding that he and his collaborators are nevertheless working on methods to make Sprites easier to register on radar. "But if we could send these outside of Earth orbit," he adds, "all bets would be off."
Before they ever reach the stars, Manchester says, Sprites are more likely to first form three-dimensional antennas in deep space to monitor space weather that could threaten Earthly power-grids and orbiting spacecraft. He believes larger interplanetary probes could deploy swarms of Sprites to pepper promising asteroids, moons and planets with sensors seeking out mineral deposits or signs of extraterrestrial life.
According to Worden, that would be a powerful new paradigm for space science. "Eventually, every mission that NASA does may carry these sorts of nanocraft to perform various measurements," he says. "If you're looking for evidence of life on Mars or anywhere else, for instance, you can afford to use hundreds or thousands of these things — it doesn't matter that a lot of them might not work perfectly. It's a revolutionary capability that will open up all sorts of opportunities for exploration."
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