[Space, Spaceships] Armor needed for Aerobraking/Re-entry

[thrash]

Originally Posted by Humabout

I simply contend that the figures you are using are misleading.

The figure that I proposed is pretty routine for these types of calculations. The SMAD III reference is standard and was simply easy for me to locate:

"The drag coefficient for satellites in the upper atmosphere is often approximately 2.2 (using a flat plate model). Spheres have Cd ~ 2.0 - 2.1." Vallado, Fundamentals of Astrodynamics and Aerodynamics, 3d ed., p. 549.

"...Cd is the coefficient of drag ~ 2.2, ..." Squibb, Boden, and Larson (eds), Cost Efficient Space Mission Operations, 2d ed., p. 359.

Your figures (0.4-0.04) are just way too low. The Apollo Cd values I've seen quoted are around 1.4-1.6. The "smooth airfoil" number is for a sub-critical angle of attack, which is specifically the way to minimize drag, not maximize it for braking effect. Once you exceed the critical angle, a wing surface acts more like a flat plate (though at a lower angle to the flow at that point).