How do you balance speculative imagination with scientific plausibility?

You have to envision what mankind will need in the future to survive life on other planets, as well as life on future spaceships.

 To begin with, I considered how we would survive on other planets? Not everything needs to be chemical or mechanical. I have my characters bodies filled with nanites, thousands of them. They're self-replicating. And they will be made from your own DNA. By using your body's DNA, it will keep your bodys from rejecting your nanites.

  These nanities will also protect you from radiation poisoning, as well as from alien diseases. And alien poisons, too.

We will also have to figure out artificial gravity. And energy fields that will protect our ships from being destroyed by material particles in space. (Author Arthur Clarke, in one of his science fiction novels envisioned a giant iceberg preceding a generations-long trip of a star ship. The ice was harder than diamonds.)

  Current scientists are working on all kinds of ideas. They're putting their imaginations to work on all kinds of ideas.

  Sometimes, it's hard to keep up with all these ideas by modern-day scientists.