 Although the Heliogyro design has no mass advantage over a square sail, it remains attractive because the method of deploying large sail blades is simpler than a strut-based design.Blade stiffness is achieved by spinning the spacecraft (centrifugal force) with its rotational axis generally pointing at the Sun.The University of Illinois together with CU Aerospace designed this mission to demonstrate deployment and to measure the thrust on a 7.7 cm × 250 m membrane (about 20 m2) made of aluminized mylar.