Complex sentence: The first public version was released digitally on Squad's "Kerbal Space Program" storefront on 24 June 2011, and joined Steam's early access program on 20 March 2013.
Split into simpler sentences: The first publicly available version was released digitally on Squad's "Kerbal Space Program" storefront on 24 June 2011. The game became available on Steam's early access program on 20 March 2013.