Reviewed date: 2007 Jan 31
I read Tau Zero four or five years ago and it instantly became a favorite of mine. This is a hard sf novel, unlike many of Poul Anderson's other works. The Leonora Christine is an interstellar spaceship powered by a Bussard ramjet. The scientists and other specialists on board are prepared for a five-year journey to a nearby star where they hope to find an inhabitable planet to study. They may return to Earth, or they may choose to found a permanent colony.
But part-way through their trip, disaster strikes: an uncharted nebula--really just a thin cloud of gas in space--damages Leonora Christine's ramscoop, leaving the ship unable to reverse power for deceleration. Repairs cannot be made without shutting down the ramscoop, which cannot be done because the ramscoop's magnetic field is the only thing protecting Leonora Christine's crew from deadly cosmic radiation. The ship can continue accelerating, but can never slow down.
The crew decides their only chance is to head for inter-galactic space, where the level of radiation is low enough that they can turn off the ramscoop and effect repairs. The relativistic effects of near-light-speed travel mean that although the journey will take millions of years of Earth time, it will take only a few years of ship time.
Of course the crew of Leonora Christine runs into heaps of trouble along the way, not the least of which is loss of morale. Even if they survive, millions of years will have past, and mankind may even be extinct. Some crew members are not sure life is worth living.
Tau Zero was nominated for the Hugo award but lost to Ringworld. It's a shame, because Ringworld is a crummy novel. Tau Zero is the better story--which is not to say it has no faults. At 188 pages it is essentially a very long short story. The characters are not as fully developed and differentiated as they should be for a 1970 novel. Additionally, it stretches the limits of belief to imagine that the crew would go to pieces so quickly; after all, had the expedition succeeded they would never have returned to Earth anyway. But despite these quibbles, the final conclusion of Leonora Christine's circum-universal voyage is astounding. It blew me away, and makes Tau Zero an easy candidate for my highest rating: five.