An amazing idea, pretty well executed; liked the idea of PCs flying around in old-school hardware doing what they do. Also, the locations are (reasonably) accurate (w/ the noted, purposeful exception of the Vulcanoids) and pretty playable. Disadvantages are as follows: you'd better have a good idea of the nature of the actually useful older craft in the space program, for realism's sake; a Mercury was not a useful spacecraft for anything but test flights by any means.
Also, they kind of wimped out on us, giving us the least-traffic region in the Solar system to deal with; what with Mercury a mine/prison and Venus a terraforming location; Mars or Ceres would have been a LOT more interesting and useful for an independent bunch of PCs.
Last, the downloads were sectioned rather oddly (TOC, Text Glossary, and Text) for useful reference. why?