You wrote: However I am concerned about where Bush's space exploration initiative is going. There was some talk that eventually we'd send people to Mars under Bush's plan. Unfortunately most of the Crewed Exploration Vehicle (CEV) designs that I have seen are not appropriate for Mars return. Lunar return trajectories come in around 11 km/sec while Mars return trajectories come in around 13 km/sec and higher. The Apollo Command Module (CM) was a simple design and just barely worked for lunar return. It will not work for Mars return because the entry corridor is too small for the Lift/Drag ratio of the Apollo CM. A significantly different CEV geometry from the CM is required for Mars return. Unfortunately all proposed CEV designs that I have seen are CM derivative. Either the folks in control do not realize that an Apollo CM will not work for Mars return --or-- they're not serious about sending people to Mars.

1. Would a design suitable for reentry from Mars also be suitable for reentry from the Moon?

I understand that a heat shield designed for a 13 km/sec reentry wouldn't have any trouble handling a 11 km/sec reentry. I'm asking about the geometry. My gut feeling is that it would be fine, just as the Apollo CM shields worked for reentry from Earth orbit as well as for lunar return.

2. While having a common vehicle is desirable to the greatest possible extent, would it be better to go primarily for commonality of the really expensive parts like systems and software and be less concerned about the less costly parts like structure, thermal control systems, and the heat shield.

I'm thinking of the Joint Strike Fighter model, where 3 variations of the basic design are optimized for the Air Force, Navy, and Marine/British requirements but share common engines, avionics, and primary systems.

For the CEV, the reentry and thermal requirements are much more rigorous for the moon as compared to the Mars environment. Like I said, a vehicle optimized for the Mars mission might be well suited for the moon mission as well, but it might also be overbuilt and considerably more expensive. Since the moon missions are intended to precede the Mars mission by several years, they could serve as a good proving ground for the critical systems while continued development goes on for the more challenging mission.

Besides, this would give you the opportunity to design 2 heat shields instead of 1! Can you tell that I'm a defense contractor who works on space systems?