Robert Silverberg - Next Stop The Stars

Voyagers of Time
One man with the chance to save a dark future of warring tribes, dead cities, mutants, and killer robots, all under the heels of invading giants.
One man with the chance to destroy a gentle future of childlike singers.
One man with the chance to use the past to save - or destroy - a desperate present.
Voyagers of Space
One man whose talents may make hime a psychic victim.
One man whose faults may make him a space hero.
NEXT STOP
THE STARS