Orphanage — Robert Buettner

When earth needs heroes, whom will we call to valor? When mankind's enemy is beyond our worst imagination, who will be our champions? Will we pick the brightest and the toughest? Or the ones with nothing left to lose?

WAR IS AN ORPHANAGE
Mankind's first alien contact tears into Earth: projectiles launched from Jupiter's moon, Ganymede, have vaporized whole cities. Under siege, humanity gambles on one desperate counterstrike. In a spacecraft scavenged from scraps and armed with Vietnam-era weapons, foot soldiers like eighteen-year-old Jason Wander--orphans that no one will miss--must dare man's first interplanetary voyage and invade Ganymede.

They have one chance to attack, one ship to attack with. Their failure is our extinction.