NASA missions, past, present and planned – http://www.nasa.gov/missions/index.html
Representative questions that can be answered with this resource:
- What was the purpose of NASA’s Gravity Probe B?
- When was the last transmission from Pioneer 10?
- What are the current locations of Voyagers 1 and 2?
- Where did the Mars Viking Lander land?
Like the page says, links to mission factsheets and/or websites (when available). Available information varies widely by mission. Some missions will have multimedia.
Probably most useful in stories set in the era of the mission, or in the far future when the aging spacecraft gets recovered by a starship.