Larry J asked:

>I know that no one has tried it yet, but what is your opinion about
>the difficulty of achieving aerocapture using the Earth's atmosphere
>instead of a direct reentry? If the CEV were designed to be
>captured into Earth orbit, then perhaps the heat shield design
>problem wouldn't be as severe. There would be some issues
>with getting rid of the heat absorbed while decelerating from
>13 km/sec to orbital velocity.

Great minds work alike. When the bosses first asked me to use
an Apollo CM for Mars return and I then showed them the entry
corridor was too small and the decelleration too great, the bosses
then said "Okay, run a simulation to aerocapture". I then showed
them that an aerocapture trajectory with a reasonable entry corridor
put the CEV into an orbit taking it in and out of the radiation
belts (the apoapsis was smack-dab in the middle of the worst of
the van Allen belts).

>Of course, we have to consider what happens if aerocapture fails >and the thing reenters anyway. Safe engineering would allow for
>a heat shield that could withstand that contingency (within some l
>limits), negating any benefit from aerocapture. How safe is safe >enough?

If direct entry fails, the astronauts are cooked to a golden brown. One must design lots of redundancy into an earth return vehicle and
[very important] provide lots of opportunity for manual over-ride by the astronauts. It was that manual over-ride capability that saved
Apollo 13. The Apollo CM had entry angle guide lines etched into
the window over the CM pilot's couch. If worst came to worse, the CM pilot could save his life by using the RCS to keep the correct line on the horizon. The CM would have landed in an unexpected place but the astronauts would have survived.

Gary