From back cover of Avon paperback May 1974:

WHEN THE SUN EXPLODES

All life will end. No one will survive the blow-up; except the men and women who crowd into a few starships and fly away into space while there is still time, to look for a new home in the infinite void, a new planet on which to settle.

Jorn, unskilled, unemployed, seemingly a reject from society, finds that he has what it takes to become one of the brave survivors, blasting off in hastily built ships that have never flown before. Jorn and his companions begin a long search, threatened by repeated disasters and despair, but ultimately leading through to an expected climax for which no one is prepared.