Breakthrough Starshot ‘Sprites’ in Orbit

If Breakthrough Starshot succeeds in launching a fleet of tiny probes to Proxima Centauri in 30 or 40 years, their payloads will be highly miniaturized and built to specifications far beyond our capabilities today. But the small ‘Sprites’ launched into low Earth orbit on June 23 give us an idea where the research is heading. Sprites are ‘satellites on a chip,’ growing out of research performed by Mason Peck and his team at Cornell University, which included Breakthrough Starshot’s Zac Manchester, who used a Kickstarter campaign to develop the concept in 2011 (see Sprites: A Chip-Sized Spacecraft Solution for background on the Cornell work).

Breakthrough Starshot executive director Pete Worden refers to Sprites as ‘a very early version of what we would send to interstellar distances,’ a notion that highlights the enormity of the challenge while pointing to the revolutionary changes that may make such payloads possible. The issues multiply the more you think about them — chip-like satellites in space have no radiation shielding and are susceptible to damage along the route of flight. But missions like these will help us analyze these problems and refine the technology.

Consider communications. In an email yesterday, Mason Peck told me that the Cornell team has juiced up the networking capabilities of the tiny spacecraft. “Now we have them talking to each other in a peer-to-peer network, and this demonstration shows how they synchronize like fireflies,” Peck said, a lovely image that points to what is becoming possible. Instead of a single large probe, think of a cluster of them, a fleet of spacecraft on chips, each carried by a sail. Losses along the route are assumed, but they are overcome by sheer numbers.

And as Peck, himself a key player in Breakthrough Starshot, goes on to point out, we’re beginning to learn how such chips can work among themselves:

This [peer-to-peer networking] capability would allow many of them to share science data, for example, or to create a persistent virtual senor out of many discrete sensors-on-chip. Also, in principle, their transmitting simultaneously could amplify the signals, enabling them to be heard from farther away. Or they could each transmit part of a dataset — say part of a large image.

We’ve never launched fully functional space probes as small as these, each 3.5-by-3.5 centimeter probe built upon a single circuit board and weighing in at just four grams. A Sprite can contain solar panels, computers, communications capability and an array of sensors. The tiny spacecraft’s electronics all function off the 100 milliwatts of electricity each generates.

The Sprites went into space aboard an Indian rocket as supplementary payloads. Now in orbit, the Latvian Venta satellite and the Italian Max Valier satellite, operated by OHB System AG, each have a Sprite attached to the outside, while the Max Valier satellite contains four more Sprites that are be deployed into space for subsequent study of their orbital dynamics.

Breakthrough Starshot is saying that communications from the mission show the Sprites are performing as designed, although Lee Billings, in a Scientific American post, has noted that the Sprites aboard the Max Valier satellite are problematic, with mission controllers thus far unable to establish communications with the external Sprite.

That could mean trouble for deploying the Max Valier’s four internal Sprites, but the stable orbits of the satellites give time for attempted fixes. Zac Manchester tells Billings that controllers have picked up signals from one external Sprite but are not sure which one it is. Even so, adds Manchester: “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.”

You may recall that Sprites have had their day aboard the International Space Station, being mounted for a long-term experiment outside the station before being returned to Earth undamaged from the exposure. Making a point that resonates with yesterday’s post on deorbiting space debris, Billings adds that the 2014 attempt to put 100 Sprites into orbit aboard a crowd-funded KickSat raised concerns over space debris; in any case, the Sprites were not deployed. Sprites will continue to be tested in space, but for now they will need to operate no higher than 400 kilometers above Earth, below which their orbits decay quickly.

How Sprites will evolve as Breakthrough Starshot continues to examine the technology remains to be seen. But remember that along the way, we have numerous potential uses for the tiny spacecraft here in our own system. Mason Peck has even talked about letting Sprites become charged through plasma interactions and then using a huge magnetic field like Jupiter’s as a particle accelerator to push the chips to thousands of kilometers per second.

That’s actually another way to get a payload to Proxima Centauri, though one that would take decades to get up to speed, and would still require several centuries for the journey. Even so, the idea of swarms of Sprites as interstellar probes, each communicating with the others like fireflies, has a surreal kind of beauty. In the meantime, could we use Sprites for interplanetary missions? Peck pointed out in a 2011 IEEE Spectrum article that the chips could use radiation pressure from the Sun to move around the Solar System. Let me quote him:

If a Sprite could be made thin enough, then its entire body could act as a solar sail. We calculate that at a thickness of about 20 micrometers—which is feasible with existing fabrication techniques—a 7.5-mg Sprite would have the right ratio of surface area to volume to accelerate at about 0.06 mm/s2, maybe 10 times as fast as IKAROS [the Japanese solar sail]. That should be enough for some interplanetary missions. If Sprites could be printed on even thinner material, they could accelerate to speeds that might even take them out of the solar system and on toward distant stars.

Image: Artist’s conception of a cloud of Sprite satellites over the Earth. Credit: Space Systems Design Studio/Cornell University.

Zac Manchester makes the same case, adding that Sprites can also be used to form three-dimensional antennas in deep space to monitor the kind of space weather that can damage power grids and orbiting satellites. Flying aboard larger spacecraft, they could be deployed as a rain of small probes to coat distant planetary surfaces with sensors.