reentry cavitator

The Russian Shkval (Squall) torpedo is built like a
rocket. It flies underwater in a cavity made by a so
called cavitator mounted on its nose. The cavity
drastically reduces viscous drag and enables the
torpedo to fly as fast as 100 meters per second.
http://www.diodon349.com/Kursk-Memor...underwater.htm

A spacecraft reentering the atmosphere moves much faster
than the speed of sound, so its aerodynamics is similar
to the aerodynamics of the cavitating torpedo. It may be
possible to reduce structural stress and temperature of
the reentering spacecraft with the help of the cavitator.
The cavitator would be made of pure copper, cooled, and
mounted on an actuator which controls the attitude and
trajectory of the spacecraft. If this idea does work,
the last stage of rocket launchers can be reusable.