Can you name this story / author? I read it maybe 15 / 20 years ago. It's about a bunch of people pulling a very heavy object down a long narrow corridor, for religious reasons. Eventually they reach the end of the corridor, celebrate briefly, then race back to their starting point with the object, which is suddenly much lighter. They then start pulling the now heavy object down the corridor all over again. As the story proceeds, we learn they've been doing this for multiple generations, for hundreds, if not thousands of years. Then we learn they are actually in a starship that has broken down for some reason, and the object they are pulling is some sort of switchable space-time anchor, and step by step they are hauling their entire starship across millions of miles back home. Any ideas?