ACS3 (Advanced Composite Solar Sail System) is a technology demonstration designed to characterize solar sail structures technologies for future small spacecraft to engage in deep space missions requiring long-duration, low-thrust propulsion. Source: NASA NSSDCA Master Catalog 

The solar sail is designed to fit inside a 12-unit (12U) CubeSat, which measures approximately 9×9×13inches (23×23×34 centimeters), or about the size of a small microwave oven. The unfurled solar sail is approximately 30 feet (about 9 meters) on a side.

The primary objective of the ACS3 technology demonstration is the successful deployment of the composite boom solar sail in low-Earth orbit. NASA’s Advanced Composite Solar Sail System fully deployed its solar sail in space on August 29 after a successful test of its sail-hoisting boom system.