I read this decades ago and cannot remember the author, title, or detail enough to find it on Google. The protagonist is a super soldier, killed repeatedly in drills, regenerated constantly, and conditioned to ignore fear of death. He is chosen to go through a very small wormhole to a new colony planet. (If the wormhole is bigger, it can cause stars to go supernova.) Help?
That's The Space Eater by Dave Langford. The wormhole through which the hero is sent is about two centimetres wide, so it's lucky that they have very good regeneration tanks.
The Space Eater by David Langford was the author's first straight science fiction novel, making use of various alarming side effects of an imagined matter transmission technology, and featuring perhaps the most unpleasant means of interstellar travel in SF. There are also high-tech soldiers and a variety of boys' toys in the form of exotic weaponry, ranging from handguns to planet-wreckers.