If "hard" SF is created when a writer centers a story around plausible technology and real science, then I dub Red Thunder a prime example of "flaccid" SF.

I used to like John Varley a lot, but having recently reread some of his stories in The John Varley Reader, and having suffered through this, his most recent novel, I'm forced to conclude that he really isn't very good. Red Thunder is an implausible mess. Think of the movie "Space Camp", except that instead of accidentally launching the Space Shuttle, the misfit kids instead build a spaceship out of junk and travel to Mars to rescue the crew of a doomed mission. And without the benefit of Kelly Preston and Kate Capshaw.

Bottom line: don't bother.