The sail of the IKAROS is a huge square some 20 meters in a diagonal line, as thin as 0.0075 mm, and made of polyimide resin. On the membrane of the sail, thin film solar cells are attached as well as an attitude control device and scientific observation sensors. This thin and light solar sail membrane will be deployed using the centrifugal force of spinning the main body of the IKAROS before its tension is set. The deployment is in two stages. The first stage is carried out quasi-statically by the onboard deployment mechanism on the side of the main body. The second stage is the dynamic deployment. As this deployment method does not require a strut such as a boom, it can contribute to making it lighter and thus can be applied for a larger membrane.