Active cooling heat protection.

Active cooling systems are of special interest for use in severe thermal and shear stress environments. The active systems of interest include transpiration cooling, distributed film cooling, partial film cooling, and film cooling that utilizes various coolants such as N2, He, H2O, and others for special applications. The performance and feasibility of each system has been obtained in ground facilities including those that have relatively severe thermal environments. It is believed that the distributed film cooling and partial film cooling systems show special advantage and warrant further consideration.