A story in your head isn't a story. It's just a daydream until you actually write it down. So write it down.
If you look up every last detail on your subject, you'll never finish.
There's nothing I would like more than to watch a manned Mars landing.
Don't tell your stories to anyone. You'll be more motivated knowing it's a prerequisite to having an audience.
Back in the days of Apollo, sending humans to the moon was the only viable way to get the scientific data we wanted. But now, with our computer and robotics technology, there's very little an astronaut can do on Mars that a well-designed rover can't.