They've used Whipple Shields at our ballistic range facility. They shoot a B-B from a light gas gun with a muzzle velocity of 7 km/sec at a slab of aluminum that's 4 inches thick. The entry hole is 1/4 inch in diameter while the exit hole is 4 inches in diameter (a conical cavity). The B-B created a shockwave on impact that vaporized the aluminum making the conical cavity. They then shoot another B-B with the same muzzle velocity but this time the target is a sheet of aluminum 1/8 inch thick followed by a 2 inch gap and then a second identical sheet of aluminum (classic Whipple shield). The first sheet has a nice clean 1/4 inch hole. However the second sheet is unpenetrated but has a circle of white ash and bits of vaporized aluminum (the impact shockwave did not propagate through the gap). If the B-B had been going at 0.5 C it would have vaporized into a glowing plasma. The important difference would be to make the gap large enough that the plasma could cool through radiation and expansion before reaching the second sheet of aluminum. Whipple shields work! Now getting to 0.5 C is another story....

Gary