Everyone knows that solar energy is free and almost limitless here on Earth. The same is true for spacecraft operating in the inner Solar System. But in space, the Sun can do more than provide electrical energy; it also emits an unending stream of solar wind.<\/p>\n
Solar sails can harness that wind and provide propulsion for spacecraft. NASA is about to test a new solar sail design that can make solar sails even more effective.<\/p>\n
<\/p>\n Solar pressure pervades the entire Solar System. It weakens with distance, but it\u2019s present. It affects all spacecraft, including satellites. It affects longer-duration spaceflights dramatically. A spacecraft on a mission to Mars can be forced off course by thousands of kilometres during its voyage by solar pressure. The pressure also affects a spacecraft\u2019s orientation, and they\u2019re designed to deal with it. <\/p>\n Though it\u2019s a hindrance, solar pressure can be used to our advantage. <\/p>\n A few solar sail spacecraft have been launched and tested, beginning with Japan\u2019s Ikaros spacecraft in 2010. Ikaros proved that radiation pressure from the Sun in the form of photons can be used to control a spacecraft. The most recent solar sail spacecraft is the Planetary Society\u2019s LightSail 2, launched in 2019. LightSail 2 was a successful mission that lasted over three years. <\/p>\n Solar sail spacecraft have some advantages over other spacecraft. Their propulsion systems are extremely lightweight and never run out of fuel. Solar sail spacecraft can perform missions more cheaply than other spacecraft and can last longer, though they have limitations.<\/p>\n The solar sail concept is now proven to work, but the technology needs to advance for it to be truly effective. A critical part of a solar sail spacecraft is its booms. Booms support the sail material; the lighter and stronger they are, the more effective the spacecraft will be. Though solar sails are much lighter than other spacecraft, the weight of the booms is still a hindrance.<\/p>\n \u201cBooms have tended to be either heavy and metallic or made of lightweight composite with a bulky design \u2013 neither of which work well for today\u2019s small spacecraft.\u201d<\/p>\n Keats Wilkie, ACS3 principal investigator, NASA<\/cite><\/p><\/blockquote>\n<\/figure>\n NASA is about to launch a new solar sail design with a better support structure. Called the Advanced Composite Solar Sail System (ACS3), it\u2019s stiffer and lighter than previous boom designs. It\u2019s made of carbon fibre and flexible polymers. <\/p>\n Though solar sails have many advantages, they also have a critical drawback. They\u2019re launched as small packages that must be unfurled before they start working. This operation can be fraught with difficulties and induces stress in the poor ground crew, who have to wait and watch to see if it\u2019s successful. <\/p>\n ACS3 will launch with a twelve-unit (12U) CubeSat built by NanoAvionics. The primary goal is to demonstrate boom deployment, but the ACS3 team also hopes the mission will prove that their solar sail spacecraft works. <\/p>\n To change direction, the spacecraft angles its sails. If boom deployment is successful, the ACS3 team hopes to perform some maneuvers with the spacecraft, angling the sails and changing the spacecraft\u2019s orbit. The goal is to build larger sails that can generate more thrust. <\/p>\n \u201cThe hope is that the new technologies verified on this spacecraft will inspire others to use them in ways we haven\u2019t even considered.\u201d<\/p>\n Alan Rhodes, ACS3 lead systems engineer, NASA\u2019s Ames Research Center<\/cite><\/p><\/blockquote>\n<\/figure>\n The ACS3 boom design is made to overcome a problem with booms: they\u2019re either heavy and slim or light and bulky. <\/p>\n \u201cBooms have tended to be either heavy and metallic or made of lightweight composite with a bulky design \u2013 neither of which work well for today\u2019s small spacecraft,\u201d said NASA\u2019s Keats Wilkie. Wilke is the ACS3 principal investigator at Langley Research Center. \u201cSolar sails need very large, stable, and lightweight booms that can fold down compactly. This sail\u2019s 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.\u201d<\/p>\n ACS3 will be launched on an Electron rocket from Rocket Lab\u2019s launch complex in New Zealand. It\u2019ll head for a Sun-synchronous orbit 1,000 km (600 miles) above Earth. Once it arrives, the spacecraft will unroll its booms and deploy its sail. It\u2019ll take about 25 minutes to deploy the sail, with a photon-gathering area of 80 square meters, or about 860 square feet. That\u2019s much larger than Light Sail 2, which had a sail area of 32 square meters or about 340 square feet. <\/p>\n As it deploys itself, cameras on the spacecraft will watch and monitor the shape and symmetry. The data from the maneuvers will feed into future sail designs.<\/p>\n \u201cSeven meters of the deployable booms can roll up into a shape that fits in your hand,\u201d said Alan Rhodes, the mission\u2019s lead systems engineer at NASA\u2019s Ames Research Center. \u201cThe hope is that the new technologies verified on this spacecraft will inspire others to use them in ways we haven\u2019t even considered.\u201d<\/p>\n ACS3 is part of NASA\u2019s Small Spacecraft Technology program. The program aims to deploy small missions that demonstrate unique capabilities rapidly. With unique composite and carbon fibre booms, the ACS3 system has the potential to support sails as large as 2,000 square meters, or about 21,500 square feet. That\u2019s about half the area of a soccer field. (Or, as our UK friends mistakenly call it, a football field.)<\/p>\n With large sails, the types of missions they can power change. While solar sails have been small demonstration models so far, the system can potentially power some serious scientific missions. <\/p>\n \u201cThe Sun will continue burning for billions of years, so we have a limitless source of propulsion. Instead of launching massive fuel tanks for future missions, we can launch larger sails that use \u201cfuel\u201d already available,\u201d said Rhodes. \u201cWe will demonstrate a system that uses this abundant resource to take those next giant steps in exploration and science.\u201d<\/p>\n Solar sail spacecraft don\u2019t have the instantaneous thrust that chemical or electrical propulsion systems do. But the thrust is constant and never really wavers. They can do things other spacecraft struggle to do, such as taking up unique positions that allow them to study the Sun. They can serve as early warning systems for coronal mass ejections and solar storms, which pose hazards. <\/p>\n The new composite booms also have other applications. Since they\u2019re so lightweight, strong, and compact, they could serve as the structural framework for lunar and Mars habitats. They could also be used to support other structures, like communication systems. If the system works, who knows what other applications it may serve? <\/p>\n \u201cThis technology sparks the imagination, reimagining the whole idea of sailing and applying it to space travel,\u201d said Rudy Aquilina, project manager of the solar sail mission at NASA Ames. \u201cDemonstrating the abilities of solar sails and lightweight, composite booms is the next step in using this technology to inspire future missions.\u201d<\/p>\n \n\n
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