The quest to solve one of the persistent barriers to citizen space exploration
On June 7, in the sky somewhere over Baja California, Mexico, a small satellite opened and extended a wide, thin mylar membrane, like a curious flower blooming, or a space-soaring butterfly emerging from its cocoon. Launched on an Atlas V, a two-stage, 190-foot rocket with expandable payload, the LightSail had floated, dormant, in free fall in an orbit between 350 and 700km around the planet for 18 days. It was a culmination of decades of effort, and a concerned crew of scientists and observers worked out bugs and tracked its location.
Bill Nye — he of Science Guy fame — was quick to tweet: “Sail has Deployed!” Though the effort to launch a solar sail pre-existed Nye’s tenure as CEO of The Planetary Society, it was thanks in part to him that LightSail reached the sky — and the hearts and minds of a new generation of space enthusiasts. It represents, according to project manager Doug Stetson, an important step: A compact, cheap, indefinite supply of propulsion for space vehicles — and not just NASA-sized spacecraft.
“Democratization of space is really the ability to be able to send those small exploration spacecraft beyond Earth, which is something that’s been, really, not possible before,” Stetson says.
With solar sailing technology, Stetson explains, it’ll be possible to send small (cheap) spacecraft beyond Earth orbit. “One could envision a day when small organizations, universities, student groups, nonprofits, things like that could actually have their own interplanetary exploration spacecraft to send to the moon, or near earth asteroid, or even Mars.”
DO IT YOURSELF SPACE PROBES
Nye, Stetson, and The Planetary Society leveraged Kickstarter, as well as modern tech like CubeSats and microcontrollers, to make LightSail happen. The 18.4’×18.4′ sail packed down to the size of a loaf of bread to fit in the standardized, 3U-size CubeSat case, and deployed in a controlled manner so as not to rip the thin, 4.5μ mylar apart.
Once unfurled, the LightSail remained in orbit for barely a week before burning up on reentry. After all, it was just a trial run to test deployment. At its highest — still in low-earth orbit — the sail was still subject to too much drag, thanks to the atmosphere, to take advantage of the solar push. Next year, The Planetary Society plans to launch a similar sail, but to nearly 800,000 feet — more than half the height of the ISS — where it’ll actually be able to sail on solar wind. As it orbits Earth, crew on the ground will adjust its orientation, using a momentum wheel to make it tack across the solar photon stream, or run along with it. If it goes well, the next version will stay active for up to six months, eventually reentering once its motion is no longer controlled.
THE PROPULSION PROBLEM
The LightSail, both this year’s launch and next year’s controllable flight, represents a particular advancement for anyone who wants to run their own experiments in space. Between CubeSats and the miniaturization of control technology (see “Space Chase,” Make: Volume 46), it’s easier than ever to get your experiments into orbit. (Still not easy, many would point out. Just easier.) What hasn’t gotten easier is moving them around once they’re there.
“The real limitation has been propulsion, because typically, propulsion is very heavy,” says Stetson. “And that’s where LightSail comes in. It’s the chance to put inside of a CubeSat its own intrinsic propulsion.”
Traditional propulsion has been chemical — that is, fuel based — and is still necessary to lift LightSail and other solar sails to space. Though it does provide quick acceleration, fuel is heavy and gets used up. With a solar sail, the acceleration comes from photons — which have energy and momentum — striking a reflective surface and transferring tiny bits of momentum to it. The sail accelerates slowly, but indefinitely, making it ideal for extreme long distances and lightweight, low-cost missions.
In fact, the LightSail is not a new concept. Quite the opposite: As space propulsion goes, solar sailing is one of the most venerable goals of astronomers and engineers, dating back as far as Galileo. A new generation’s love affair with space shows the cyclical curve of history wending back to the era of our parents, when the U.S., the USSR, and NASA threw money at the sky and anything was possible. It still is — it just costs a lot less. For LightSail, The Planetary Society estimates around $5.5 million, raised mostly through private donations and grants, and offset by a million-dollar-plus Kickstarter that coincided with the trial run. (Low cost is a relative term when we’re talking about space.)
“It’s always been the case that until a technology like that is demonstrated in orbit, it won’t reach the mainstream,” says Stetson. “Organizations like NASA will not be willing to commit large amounts of money to missions in the solar system until those key technologies are proven.”
That’s a gap The Planetary Society intends to fill, and the ultimate goal for LightSail. The 2016 edition won’t go interplanetary, nor will it have a particular mission. It will act as proof of concept, relaying information about how the sail moves when photons are acting upon it.
A COSMIC FIX
The 25 days LightSail spent in orbit were filled with a series of triumphs and pitfalls. Remember that controlled deploy? It ran on common hardware. Designer Chris Biddy used brushless DC motors with a planetary gear set, driven by a PIC controller programmed by Alex Diaz. Hall effect sensors tracked the deployment so the operators could know how far it had extended, and a worm gear held it in place during idle times.
But for a controlled deploy to work, you need to be able to control it. And one of the first things that happened was LightSail’s communication went dark. It froze up while sending data packets home — the satellite equivalent of the blue screen of death or the dreaded spinning beach ball. Engineers on the ground can’t exactly hold down the power button, but each time the satellite passed over Cal Poly or Georgia Tech — the two schools partnered with The Planetary Society — the team sent a reboot command.
Eight days later, LightSail began sending data again, although it seems that wasn’t because of earthbound attempts. Instead, the reboot was likely caused by a stray cosmic ray, which strike the satellite’s electronics with surprising regularity.
Operating on the “photos or it didn’t happen” principle, LightSail began sending garbled jpegs home, a bit at a time, each time it passed Cal Poly or Georgia Tech. Then, after the external panels swung open, it delivered a low-battery signal and went silent again.
“It was a roller coaster for sure,” says Biddy. “You go into the weekend thinking, man, it didn’t make it. Such a bummer. And then I got a text or something from one of the operators saying, hey, it’s back.”
Like the journey of LightSail itself, but expanded over decades rather than days, The Planetary Society’s trajectory is a long slog full of struggles, fails, and false starts. Founded in 1980 by Carl Sagan, Louis Friedman, and Bruce Murray because NASA scrapped plans for its own solar sail, the society relies on private funding to pursue its exploratory space missions. (It’s also the organization responsible for the Search for Extraterrestrial Intelligence, or SETI, and Planetary Defense asteroid tracking.) So when funding fell through or launches got postponed, or even exploded after liftoff — a 2005 solar sail was lost when the Cosmos 1 rocket it was on exploded — the project sat, not so much gathering dust as awaiting technological and sociological advances, and funds.
Kickstarter, CubeSats, and the Science Guy provided the oomph. And in space, LightSail’s battery stabilized, and the team initiated deployment. Over the next few days, the satellite gradually beamed back photos indicating that it had indeed stretched out. Then, a few days later its orbit fully deteriorated and LightSail disintegrated. Time of death: 1:23 pm EDT, June 15, 2015. LightSail Two, time of launch: Coming September 2016.