Note from mfb: This thread is a fork of our Dawn and Ceres thread, as we got multiple posts about potential missions to Mars and Ceres and further exploration. End note. Part of astrophysics is being able to calculate---things like the altitude of a geosynchronous satellite, for example. Even if you deplore futuristic visions---which can easily become self-indulgent and speculative---I think there is a real place for the solid analysis that can be motivated by related questions. It's a learning experience, and can mobilize mental resources. I was impressed by a new person who showed up in the Ceres thread and calculated the altitude of a geosynch. satellite on Ceres(!) And compared that with the height of a geosynch. satellite on Mars. Whatever you think about the MOTIVATION (consider the feasibility of a space elevator able to bring things down from orbit and get things up into orbit slowly and deliberately without chemical rocket...) I think the underlying analysis is valuable and would like it to have a place in Astrophysics forum. But it does not exactly fit in the Dawn mission Ceres thread. So at Mfb's suggestion I want to start a thread where we can continue discussion that got started in the Dawn thread. Actually it was not just one person, it was several, and they weren't all newcomers. I'll get links to a few of the posts in that other thread. It's pretty interesting, actually.