The history of solar sailing. Source: The Planetary SocietyThe history of solar sailing. Source: The Planetary Society

Space exploration missions have been limited by the performance margins of state of-the-art chemical rocket engines and by the amount of fuel a spacecraft must carry, which can add up to 25% of the launch weight of typical planetary-exploration spacecraft. Researchers at NASA and the European Space Agency are developing a key in-space propulsion technology that could replace conventional chemical fuels with an inexhaustible natural resource: Energy from the sun.

Solar sail propulsion is envisioned as a way to give spacecraft more mobility and versatility during flight, and to open new regions of the solar system for exploration. The technology uses solar photons, which are reflected off giant, mirror-like sails made of lightweight, reflective material 40 to 100 times thinner than a piece of writing paper. Continuous photonic pressure provides enough thrust to perform maneuvers, such as hovering at a fixed point in space and rotating the space vehicle’s plane of orbit, which would require too much propellant for conventional rocket systems. The sun supplies the necessary propulsive energy, eliminating the need for onboard propellant and reducing payload mass.

In 2019, The Planetary Society launched LightSail 2 with an aluminized Mylar sail. The vessel is the first spacecraft to use solar sailing for propulsion in Earth orbit, the first small spacecraft to demonstrate solar sailing and the second solar sail spacecraft to successfully fly, following Japan's IKAROS, which launched with The ACS3 solar sail system fits within a 12U CubeSat at launch. Source: NASAThe ACS3 solar sail system fits within a 12U CubeSat at launch. Source: NASAa polyimide-based sail in 2010.

NASA engineers are currently planning a mission to advance the next generation of solar sail technology for small interplanetary spacecraft. As part of this development effort, the Advanced Composite Solar Sail System (ACS3) will demonstrate deployment of a 74 m2 composite boom (mast) solar sail system in low-Earth orbit, marking the first use of composite booms and sail packing and deployment systems for a solar sail in orbit. An innovative tape-spool boom extraction system has been designed to minimize blossoming, or jamming, of the coiled booms during deployment. The mission will serve as a technology pathfinder for a future 500 m2 composites-based small spacecraft solar sail system suitable for low cost heliophysics research and small body planetary science.

The ACS3 solar sail system is sized to fit within a 12-unit (12U) CubeSat. The solar sail consists of four, 20 m2 triangular aluminum-coated plastic membrane sails supported by four 6.5 m thin-ply collapsible composite booms. The thin-ply composite booms, which are 75% lighter and experience 100 times less in-space thermal distortion than the current state-of-the-art metal booms, are flattened and rolled onto spools for compact stowage within the spacecraft. NASA Ames Research Center has tapped NanoAvionics to design and build the 12U nanosatellite bus.

Experiments with a 3 mm wide piece of graphene convinced ESA researchers that a solar sail composed of the one atom-thick material would be effective. A series of 1 W lasers was directed at the graphene sample as it was dropped from a 100 m tall tower, which served to accelerate it by as much as 1 m/s². Under operating conditions in space, the graphene sails are expected to continue accelerating under solar exposure and increase the speed of its host craft. The researchers envision scaling up the material to assemble kilometer-wide sails.

In addition to benefitting space exploration missions, solar sail technology might be used in an advanced space-weather warning system to more quickly and accurately alert satellite operators and utilities on Earth of geomagnetic storms caused by coronal mass ejections from the sun. NASA researchers theorize that the technology also could help remove some of the thousands of pieces of orbital debris ringing the planet, conduct space station-keeping tasks or hover at high latitudes for communications and observation.

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