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In days gone by, explorers traveled into the unknown by sailing on the wind, and the robotic explorers of the future may do some sailing of their own. NASA is on the verge of launching a next-generation solar sail. If successful, this test could lead to cheaper, lighter spacecraft for long-duration missions that don’t need traditional fuel or engines. NASA says this technology could also be key to expanding our understanding of the Sun and wider solar system—as long as it works.
The next-gen sail is known more accurately as the Advanced Composite Solar Sail System (ACS3). The pressure of the solar wind is small but constant. That means a solar sail gets a continuous nudge that can accelerate it to high speeds over time, provided it has enough surface area. That won’t be a problem for the ACS3, which measures about 30 feet (9 meters) across. It won’t have a lot of mass to drag around in this test, either. NASA has mounted the sail on a 12U Cubesat from NanoAvionics that is about the size of a large microwave.
Even that modest payload would have been hard to maneuver with older solar sail designs. It’s a balancing act between ensuring the sail has enough surface area to generate thrust and keeping it compact and light enough that it can be mounted on a small spacecraft. Older sails used frames made from heavy metal or bulky but lightweight composite. Neither of those have given NASA engineers the kind of performance they need, but the ACS3 takes a different approach.
The booms that extend to support the sail are composed of flexible polymers and carbon fiber. They are reportedly stiffer and lighter than comparable designs. “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,” said mission leader Keats Wilkie.
Testing the boom is the mission’s primary goal after reaching orbit with the aid of a RocketLab Electron rocket later in April. The spacecraft will make its way to a sun-synchronous orbit of 600 miles (about 1,000 kilometers) before it begins unrolling the sail. It will take about 25 minutes to fully unfurl ACS3, which is about the size of six standard US parking spots. The spacecraft may be visible from Earth when the sun hits it just right, but there will be cameras on board for close-up monitoring of the deployment.
After verifying correct sail deployment, the team hopes to be able to test the sail’s performance as a means of propulsion. NASA engineers estimate this same flexible but sturdy booms could support a sail up to 21,500 square feet (2,000 square meters), which is 25 times larger than the Advanced Composite Solar Sail System. Solar sails could become common for future robotic missions of all sizes if the demo is successful.