Complex sentence: The spacecraft uses solar sail technology initially developed for the successful IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun) that launched in 2010, whose solar sail was 14 m × 14 m in size.
Split into simpler sentences: The spacecraft uses solar sail technology initially developed for the successful IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun) that launched in 2010. Its solar sail was 14 m × 14 m in size.