Larry,

We're getting close to beating this one to death. This will be my last
response concerning X-38 and then I'll let it go.

> ... an Apollo Command Module was 3.9 meters in diameter and 3.5 meters
>tall. That doesn't include the Service Module. Since the CM didn't
>have deorbit engines, you'd need some form of SM to perform the burn. It
>could probably be something similar to what was used in the Gemini program.

The retro-stage as used on Gemini would be a good design choice. Such a
stage could also provide additional RCS capability like it did for
Gemini. Such a stage would add about a meter to the height of the rescue
vehicle.

>So, we've started with a deviation from the Apollo baseline by creating a
>new type of deorbit engine. We may well have to modify the dimensions so
>it can fit in the payload bay or to optimize it for the additional crew
>seats. We're talking about a different internal arrangement to seat more
>people, different avionics to replace the obsolete stuff, new heat
>shields, etc. Just what are we reusing from Apollo?
The original CM dimensions should be preserved so the Apollo flight data
could be reused. Such data is sensitive to real gas effects and turbulent
transition. The Skylab rescue version of the Apollo CM was built to
hold 5 people. I believe(?) that vehicle is on display in a museum (the
Smithsonian??). That basic design should be reused.

>It sounds like we're quickly developing a new spacecraft here as the
>ripple effects from changes start multiplying.

Happens all the time. I recently sized the TPS thickness for the Mars
2003 lander aeroshell. To save cost, the original design was specified as
"build to print" based upon the Mars Pathfinder drawings. However the
rover's mass kept growing so we had to slowly diddle the aeroshell's design
to reduce mass and reset the center of mass. Superficially the aeroshell
looks like Mars Pathfinder's and no doubt the NASA spin machine will say
it is. In terms of materials and internal dimensions, it's a different
beast. However the exterior shape is identical to Pathfinder's so the
aerodynamics did not have to be recertified. That represented
a significant cost savings and enhanced confidence in the design.

>One of the advantages of a lifting body design is greater crossrange
>capability during reentry. This could make the difference when it comes
>to being able to deorbit quickly or having to wait an extra rev or two
>to get within range of land.

Lifting bodies are much harder to design and fly. A lifting body is to
a blunt body what an airplane is to a parachute. Development and
manufacture costs would be significantly reduced by going with a blunt body.

>Your "two is better than one" argument falls short in one respect. If
>one of the modified Apollo capsules is damaged, the other wouldn't be
>big enough to hold everyone. Who gets left behind?

So one is better than two? If the single lifting body fails then all the
astronauts are dead. At least with two vehicles they can draw straws or
slug it out.

A parting shot on this: Ocean ships (cruise ships or freighters) don't
have fancy life boats. Often times they're just inflatable things. The
reason for this is mainly cost. However there is also the realization that
a rescue team will come for the survivors. The CRV should have a similar
design approach.

Gary