Advanced composite solution: using sunlight to power deep space exploration
NASA is developing new deployable structures and materials technologies for solar sail propulsion systems destined for future low-cost deep space missions. Just as a sailboat is powered by wind in a sail, solar sails employ the pressure of sunlight for propulsion, eliminating the need for conventional rocket propellant. NASA’s Advanced Composite Solar Sail System, or ACS3, mission uses composite materials – or a combination of materials with different properties, in its novel, lightweight booms that deploy from a CubeSat. Data obtained from the ACS3 mission will guide the design of future larger-scale composite solar sail systems that could be used for space weather early warning satellites, near-Earth asteroid reconnaissance missions, or communications relays for crewed exploration missions.
The composite materials boast light weight, flexibility, and rigidity: qualities that make them easily stowable and also less prone to bending when heated by the sun.
The primary objective of the ACS3 mission is to demonstrate the successful deployment of the composite boom solar sail in low-Earth orbit. After reaching space, the mission’s CubeSat spacecraft will deploy its solar power arrays and then begin unfurling its solar sail via four booms that span the diagonals of the square and unspool to reach 7m in length. After approximately 20 or 30 minutes when the solar sail is fully deployed, the square-shaped solar sail measures approximately 9m per side (or about the size of a small apartment). A suite of onboard digital cameras will obtain images of the sail during and after deployment to assess its shape and alignment.
The ACS3 mission’s sails are supported and connected to the spacecraft by booms, which function much like a sailboat’s boom that connects to its mast and keeps the sail taut. The composite booms are made from a polymer material that is flexible and reinforced with carbon fibre. This composite material can be rolled for compact stowage but remains strong and lightweight when unrolled. It is also very stiff and resistant to bending and warping due to changes in temperature. Solar sails can operate indefinitely, limited only by the space environment durability of the solar sail materials and spacecraft electronic systems. The ASC3 mission will also test an innovative tape-spool boom extraction system designed to minimise jamming of the coiled booms during deployment.
Interest in solar sailing as an alternative to chemical and electric propulsion systems continues to increase. Using sunlight to propel small spacecraft in lieu of consumable propellants will be advantageous for many mission profiles and offers flexibility in spacecraft design to help NASA meet its missions’ objectives most efficiently.
This is the first use of composite booms as well as sail packing and deployment systems for a solar sail in orbit. These composite booms are 75% lighter and experience 100 times less in-space thermal distortion – change of shape under heat – than previously flown metallic deployable booms.
The solar sail is designed to fit inside a 12-unit (12U) CubeSat, which measures approximately 23cm x 23cm x 34cm, or slightly larger than a toaster oven. The composite boom technology used for this ACS3 mission can be used in future missions for solar sails up to 500m3 – about the size of a basketball court. Follow-on composite boom technologies now in development will enable solar sails as large as 2,000m2. The ACS3 mission is scheduled to launch no earlier than mid-2022.