"Jeff Findley" wrote in message
...

The velocity of a vehicle reentering coming from the moon is *a lot*
higher than the velocity of a vehicle reentering coming from low earth
orbit. Given the shape and density of the Orion (similar to Apollo CM),
I've got to believe that the shuttle TPS materials simply aren't good
enough.

There's nothing wrong with the shuttle TPS for LEO work, but might not make
the grade for Lunar returns.

Three questions:

1 Will the Orion heat shield be in two thicknesses; one for LEO and one
for Lunar missions?

2 Is there a mass advantage to using an ablator over re-useable TPS?

3 Is there a cost advantage to ablator over re-useable TPS?