Rocket Lab, a launch service provider based in Long Beach CA, launched a rideshare payload on April 23 from its launch complex in New Zealand. I’ve been tracking that launch because aboard the Electron rocket was an experimental solar sail that NASA is developing to study boom deployment. This is important stuff, because the lightweight materials we need to maximize payload and performance are evolving, and so are boom deployment methods. Hence the Advanced Composite Solar Sail System (ACS3), created to test composites and demonstrate new deployment methods.

The thing about sails is that they are extremely scalable. In fact, it’s remarkable how many different sizes and shapes of sails we’ve discussed in these pages, ranging from Jordin Kare’s ‘nanosails’ to the small sails envisioned by Breakthrough Starshot that are just a couple of meters to the side, and on up to the behemoth imaginings of Robert Forward, designed to take a massive starship with human crew to Barnard’s Star and other targets. Sail strategies thus move from using them as propulsive projectiles (Kare) to full-blown interstellar photon-catchers for high-speed star travel.

With ACS3, we’re at the lower end of the size spectrum and digging into such fundamental matters as composite materials and boom deployment engineering. Entertainingly, the Electron launch vehicle was named ‘Beginning of the Swarm,’ doubtless a nod to the primary payload, which is a South Korean imaging satellite that will be complemented by 10 similar craft in coming years. But I also like to think that ‘swarms’ of small solar sails like the twelve-unit (12U) CubeSat used for ACS3, will eventually offer options not only for near-Earth but also outer system observation and exploration. But first, we have to nail down those tricky deployment issues. Keats Wilkie is ACS3 principal investigator at NASA Langley in Hampton Virginia:

“Booms have tended to be either heavy and metallic or made of lightweight composite with a bulky design – neither of which work well for today’s small spacecraft. Solar sails need very large, stable, and lightweight booms that can fold down compactly. This sail’s booms are tube-shaped and can be squashed flat and rolled like a tape measure into a small package while offering all the advantages of composite materials, like less bending and flexing during temperature changes.”

Image: On 24 April 2024, Rocket Lab launched the ACS3 & NeonSat-1 missions from Onenui Station (Mahia Peninsula), New Zealand. In this image, engineers at NASA’s Langley Research Center test deployment of the Advanced Composite Solar Sail System’s solar sail. The unfurled solar sail is approximately 30 feet (about 9 meters) on a side. Credit: NASA Ames.

ACS3 reached its final orbit a little less than two hours after liftoff, after earlier deployment of the South Korean NEONSAT-1 via a kick stage that changed orbit for the second of the deployments. The craft is now roughly 1000 kilometers up, and if everything goes well, full deployment of the composite booms spanning the diagonals of the sail will give us an 80 square meter sail as bright as Sirius in the night sky. Digital cameras onboard should provide imagery of the sail before and during deployment. No signs of sail deployment yet but the satellite is being observed at numerous sites.

The polymer from which the composite booms are made is reinforced with carbon fiber and flexible enough to allow it to be rolled for compact storage. According to Alan Rhodes, lead systems engineer for the mission at NASA Ames, seven meters of deployable booms can roll up into a shape that fits into the hand. Note too that these booms are 75 percent lighter than previous metallic deployable booms and should experience far less in-space thermal distortion during flight. A new tape-spool boom extraction system is being tested which will, engineers hope, minimize the possibility of the coiled booms jamming during the deployment. We shall see.

Animation: Deployment of the ACS3 sail. Credit: NASA Ames.

We’re getting pretty good at miniaturization, as shown by the fact that the 12-unit CubeSat carrying ACS3 into orbit measures roughly 23 centimeters by 34 centimeters, which makes it about the size of the microwave oven sitting on my kitchen counter. Refining the material and structure of the booms is another step toward lower-cost missions which we can eventually hope to deploy in networked swarms. Imagine a constellation of exploratory craft to targets like the ice giants. Larger sails using these technologies may eventually fly the kind of ‘sundiver’ missions we’ve often discussed here, deploying at perihelion for maximum thrust to deep space.