The original Church of Humanity's colony ship had used fusion power, so why were the colonists' descendants using fission power nine hundred years later?

Humanity had abandoned fission power as soon as reliable fusion plants became available.

So for most of the human race, the very concept of fission power was something out of a dark, primitive, vaguely dangerous, and only dimly remembered past.

"It sounds impressive, Ma'am," he said after a moment, "but I don't know a thing about fission power."

For decades, Environment Guardian have been dissing nuclear fission power.

In fusion reactions, two light atomic nuclei fuse to form a heavier nucleus (in contrast with fission power).

Fusion powered electricity generation was initially believed to be readily achievable, as fission power had been.

Other technologies like fission power, fusion power, and solar power address the problem of a source of primary energy but not energy storage.

They had just about exhausted their easily worked areas of fossil fuels and relied heavily on nuclear fission power to provide motive transport.

This industrial district had been devoted largely to the production of spaceship equipment which the hyperdrive was making as obsolete as fission power.