Godspeed by Charles Sheffield

Cut off suddenly, unexpectedly, from interstellar trade, the colony of Erin found itself confined to the slow in-system shuttles and asteroid miners that were the only spaceships left at Muldoon Port. The human population slowly dwindled, unable to thrive in Erin's marginal ecosystem.
Jay Hara grew up on isolated Erin, longing for the legendary days when the Godspeed ships spanned he galaxy, and a young man's dreams could take him to the stars. So when an old, sick spacer named Paddy Enderton shows Jay some very strange devices and tells him that he has found a Godspeed base out in the asteroid belt, Jay was eager to believe.