[January 10, 2024 by Marni Ellery in Berkeley Engineering]
Nearly 70 years after the launch of the first satellite, we still have more questions than answers about space. But a team of Berkeley researchers is on a mission to change this with a proposal to build a fleet of low-cost, autonomous spacecraft, each weighing only 10 grams and propelled by nothing more than the pressure of solar radiation. These miniaturized solar sails could potentially visit thousands of near-Earth asteroids and comets, capturing high-resolution images and collecting samples.
Led by Kristofer Pister, professor of electrical engineering and computer sciences, the researchers seek to leverage advancements in micro-scale technology to make interplanetary space exploration more cost-effective and accessible — and to accelerate new discoveries about our inner solar system. They describe their work, the Berkeley Low-cost Interplanetary Solar Sail (BLISS) project, in a study published in the journal Acta Astronautica.
The BLISS project brings together researchers from the Department of Electrical Engineering and Computer Sciences and the Department of Mechanical Engineering, as well as the Berkeley Sensor and Actuator Center and the Space Sciences Laboratory. Their work builds on other small spacecraft projects, including CubeSats, ChipSats, and the Breakthrough Starshot Initiative, while seeking to improve solar sail maneuverability and further reduce fabrication costs by using low-mass consumer electronics.
In addition to Pister, the team includes lead author and mechanical engineering doctoral student Alexander Alvara and co-authors Lydia Lee, Emmanuel Sin, Nathan Lambert and Andrew Westphal.
In a recent conversation, Pister and Alvara shared their group’s vision for this project with Berkeley Engineering.
Your latest paper focuses on fleets of small solar sails. What advantages do solar sails have over other types of spacecraft?
Alexander: Solar sails use a non-consumable propulsion force. They are propelled by sunlight, similar to how a sailboat is propelled by wind. So, unlike other spacecraft, solar sails can travel around the galaxy, or, more specifically, our solar system, without having to carry any fuel or worry about refueling.
Kris: The magic is that light, even though it doesn’t have mass, has momentum. When light bounces off a mirror, you get a force due to that change in momentum. And on a square meter sail, that force is tiny. It’s about the weight of a grain of sand, but you get it for free. And you get it for as long as you want, as long as you’re sitting in space with the sunlight striking you.
Could you tell us about the Berkeley Low-cost Interplanetary Solar Sail, or BLISS, project? What was the genesis of this project and what are its goals?
Kris: It started several years ago, when friends of mine were exchanging emails about an object, called Oumuamua, that was moving through our solar system. Some people were saying that maybe it’s an alien solar sail, and then [physicist] Dick Garwin sent around a paper that he had written in 1959 about solar sails. It said that you can use this light pressure to move out, away from the sun, which makes sense — the light pushes in that direction. But you can also use it to move in. It’s kind of like tacking against the wind in sailing. Light is much more like wind, and you can tack using solar radiation pressure.
So this lightbulb went off in my brain. All the work we do in my group is focused on miniaturizing things, and I thought we could miniaturize a solar sail spacecraft. Seeing that you can tack against light pressure made me realize that we could make spacecraft [weighing] 10 grams with almost all off-the-shelf technology. And our latest study provides evidence that this is feasible.
Our initial goal for the BLISS project was simple: capture images of all the near-Earth asteroids, starting with the biggest ones. Roughly a thousand near-Earth asteroids are bigger than a kilometer in diameter. And we have pictures, usually fuzzy pictures, of maybe 10 of them. We were excited by the idea that you could potentially take an iPhone camera, orbit around one of these things, take a thousand high-resolution color photographs from a very close distance and then beam that information down.
Speaking of miniaturizing things, why make the solar sails small in the first place?
Alexander: A smaller size allows the spacecraft to be more agile. We don’t have to worry about buckling of the sail, which is just one square meter. This is a huge issue with larger solar sails. Imagine taking a solar sail that is 50 square meters into space, then having unfolding components spreading out like origami. It’s still relatively small compared to other spacecraft, but the unfolding components add weight. And, as Kris mentioned, you’re getting the force of a grain of sand continuously on your sail, the light pressure, so you want to have a solar sail close to that mass. You don’t want something that’s huge, or it will take forever to move, and it’s going to be less easy to maneuver.
Kris: Cost is another advantage to going small. We’re proposing to start at about 10 grams for an interplanetary spacecraft. If we do everything right, the cost of the solar sails will be a thousand dollars or less. We could then put thousands of these tiny spacecraft in a little package, the size of a small satellite, and launch them into space.
Alexander: So, for the cost of a single launch, we could send out thousands of these solar sails and accomplish multiple missions.
See more pictures and read the rest of the article by Marni Ellery in Berkeley Engineering.
