The Hidden War — Michael Armstrong

A harrowing and unforgettable story of an extraterrestrial threat to utopian existence, and the ensuing battle in space hidden from all of earth's inhabitants. 

Thanks to the wonder of the hide, no one starves or freezes or gets sick on the perfect worlds of the Solarian Alliance. Like a synthetic skin, the hide protects and heals, and can transform people into anything they want to be. Nothing threatens this utopian existence until an extraterrestrial message of unspeakable horror is received. An evil race terrorizes the galaxy, and it's coming toward Earth. . .  Into this world, the Solarian Alliance frees Krim, the last survivor of the Beat asteroid known as the Jack and a prisoner since he saw his world vanish into that strange other space known as Ur. Disgusted with this utopia, Krim enlists in a distant fight at the edge of the solar system, the battle no one on Earth may know about, lest it disrupt their perfect peace . . . the Hidden War.