ACS3, NASA’s Advanced Composite Solar Sail System


  • NASA’s Advanced Composite Solar Sail System, or ACS3, is a solar sail spacecraft launching to Earth orbit as early as mid-2022.

  • Solar sails harness the gentle push of sunlight for spacecraft propulsion.

  • ACS will test sail boom materials that could enable much larger solar sails.

What is ACS3?

NASA’s Advanced Composite Solar Sail System, or ACS3, is a solar sail mission that will test out new sail boom materials in Earth orbit. Scheduled to launch as early as mid-2022, ACS3 will deploy a sail about the size of a small apartment from a toaster oven-size spacecraft.

Solar sails harness the power of sunlight for spacecraft propulsion. Space missions like The Planetary Society’s LightSail 2 spacecraft have demonstrated that small spacecraft can use solar sails to change their orbits, expanding their possible uses. NASA’s NEA Scout will use a solar sail to visit a near-Earth asteroid, while the agency’s Solar Cruiser mission will create an artificial orbit between the Earth and Sun that could be used to watch for harmful solar storms.

Future solar sail missions will need bigger sails and lighter materials to maximize their performance. ACS3 will use lightweight carbon fiber sail booms instead of traditional metal booms. This will be the first test of this technology in space, and success will pave the way for future missions to use even larger sails.

ACS3 Solar Sail
ACS3 Solar Sail An artist's concept of NASA's ACS3 solar sail spacecraft in Earth orbit.Image: NASA

What is solar sailing?

Light is made up of particles called photons. Photons don’t have mass, but they have momentum. As sunlight reflects off a shiny solar sail, some of its momentum gets transferred, giving the sail a small push. This push is slight but continuous, and over time can impart more thrust to a spacecraft than traditional chemical rockets.

Solar sails can reach unique destinations that are difficult or impossible to access with other propulsion systems. They may also be our best option for interstellar travel.

How will ACS3 advance solar sailing?

The acceleration a solar sail spacecraft receives from sunlight depends on the size of the sail and the mass of the spacecraft. To increase performance, mission designers must look towards bigger sails and lighter spacecraft.

Solar sails require long booms to hold them taut. LightSail 2 and other solar sail spacecraft use metal booms, which are heavy and can warp unpredictably due to the hot-and-cold temperature swings they experience in space. ACS3 will use composite booms made of carbon fiber reinforced polymer. CFRP materials have high strength and low weight, and can be found in numerous aerospace, automotive, and medical applications.

Each ACS3 sail boom measures 7 meters (23 feet) long, but weighs just 900 grams, or 2 pounds, making them 75% lighter than metallic booms. NASA says they are 100 times less susceptible to warping under extreme temperature swings.

The CFRP booms are strong enough to hold the sail tight, yet flexible enough to wrap neatly around a central spindle for launch. NASA is also investigating the use of CFRP materials to build human habitats on the Moon or Mars. If ACS3 is successful, NASA says composite sail booms could be used for follow-on missions with sails as large as 2,000 square meters (21,500 square feet).

How ACS3 works

At its core, ACS3 is a CubeSat — a small satellite built to standardized dimensions. LightSail 1 and 2 were 3-unit CubeSats about the size of a loaf of bread. ACS3 is a 12-unit CubeSat about four times larger than LightSail.

The composite sail booms deploy from tape measure-like central spindles, just like LightSail. The booms pull out four triangular sails to form a kite shape when fully deployed, measuring 9 meters (30 feet) per side. With a cutout for the center core, the total sail area is about 80 square meters (860 square feet).

ACS3 will launch into Earth orbit via a rideshare rocket that deploys multiple satellites. A launch vehicle has yet to be selected, but the mission team is looking for a ride to an orbit with an altitude roughly between 700 and 900 kilometers (435 and 560 miles). Once ACS3 successfully deploys its solar sail, the spacecraft will attempt a series of orbital changes to demonstrate its capabilities.

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