IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) that was a demonstrator of the critical technologies of the solar power sail was launched on May 2010 from Tanegashima Space Center using H-IIA rocket. The solar power sail utilizes two kinds of forces; one by solar photon from sun and another from high performance ion engine. Minimum mission success was the deployment of the membrane and the generation of the electricity by means of the thin film solar array on the membrane within several weeks. Also, acceleration and navigation using the solar sail will be demonstrated within half year. This paper describes the structure, the space environmental evaluation of the thin film solar array and the initial results of the solar array installed on the IKAROS in the orbit.