By "gravitational braking" do you mean a reverse slingshot around the
Moon?

Another possibility is 'air braking' by extending ceramic slabs into
the hypersonic plasma.  This would protect some of the surface skin
while increasing drag, thus slowing the vehicle more rapidly.

The Space Shuttle has shown that reentry heat is the frontier of space
at present.  Because of differing planetary velocities a returning
vehicle has to have thermal protection beyond anything now imagined.


tomcat