Beginning a Story

How does one begin a story? Not the opening paragraphs but the concept, the idea, the situation?

I am doing this now. I owe a story to a theme anthology, and all I have is the theme given to me by the editor (interstellar flight, done realistically). So far, these are the steps I've taken:

• Find information about proposed interstellar craft. It turns out a whole raft of scientists have workable ideas on this (no STAR TREK dilithium crystals). The editor sent me some articles. Some I got from the Internet. That led me to order the book ENTERING SPACE (Robert Zubin), which arrived yesterday and constitutes today's reading. Do I usually do this much research for a short story? No. But I really want to be in this anthology, and anyway the topic interests me.
• Read the material and mark up everything. Underlining for facts, notes in the margin for possible story ideas. This morning I waded through a technical article on lighting for agriculture aboard a long-term ship. Fortunately, I don't need to understand all the math.
• If any ideas strike a genuine spark, stop research, write it down, and continue research in light of that idea. So far, this has not happened.
• Go through a file I keep of interesting character sketches to see if any of them seem to mesh with my notes-for-an-idea-that-isn't-really-there-yet. Nope, nothing strikes me.

That's as far as I've gotten in the process. Let's hope a few more days produces a usable story idea. It has in the past, so I'm optimistic. They key criterion: I must be excited about the idea. Stay tuned.