"Inspiration Mars" has the idea to use a free return trajectory for a crew of two rounding Mars. While attractive in some ways, this free return trajectory has the disadvantage of ending up with a very high re-entry speed as it comes back to Earth's atmosphere. Heavy heat shields and/or lots of fuel for breaking rockets counterbalances some of the advantages.
It is often (always?) suggested to use adaptations of capsules like Orion (NASA) or Dragon (SpaceX) as re-entry vehicles. But they are greatly overdimensioned for a crew of two using it for a few hours as they approach Earth after having discarded the rest of their spaceship. I'm thinking of a claustrophobic cage like Gemini. They wouldn't need to operate anything. They would need none or minimal life support systems except their space suites.
Wouldn't these be some great advantages of a tiny REV?:
1) Smaller surface area of the capsule needs a smaller heat shield. But maybe the physics involved is not that simple?
2) Lower mass of capsule and heat shield makes the braking rockets and also the parachutes more efficient in slowing down the speed.
3) Tiny crewed re-entry vehicles were used about 50 years ago. Making them smaller than those used and planned today should make the challenge of high speed re-entry easier, even if a capsule design has to be made from scratch.
And finally, would a fast re-entry vehicle have any more generally useful application?
I've looked through some of the student contributions in the Mars Society / Inspiration Mars contest, so I feel like a rocket scientist now! :p Link (posted on marssociety.org Mar 28, 2014, 3:48 PM by M Stoltz): http://www.marssociety.org/home/press/announcements/marssocietypostsinspirationmarsstudentdesignreportsonline