I found this old link searching and it seems that they were using the *tile* method for thermal protection which protects up to 3000 degrees.

"The TPS material samples include metallic Inconel tiles, soft Advanced Flexible Reusable Surface Insulation tiles and sealing materials. They were flown attached to the forward-left side position of the F-15B's Flight Test Fixture II, a device attached underneath the aircraft to carry experiments. In-flight video from the aircraft's on-board video system, chase aircraft photographs and video cameras documented the condition of the TPS materials during flights.

If we ever revive the CRV program, I sure hope they don't use tiles for thermal protection.
SteveS