Before revision: Controls Flattop consists of a hemispherical fixed reflector and two movable quarter-spheres of reflector that can close down on the central core.
After revision: Gibson, Marc A., Maxwell H. Briggs, James L. Sanzi, and Michael H. Brace, "Heat Pipe Powered Stirling Conversion for the Demonstration Using Flattop Fission (DUFF) Test," Nuclear and Emerging Technologies for Space (NETS-2013), American Nuclear Society, Albuquerque, February 25-28, 2013Controls Flattop consists of a hemispherical fixed reflector and two movable quarter-spheres of reflector that can close down on the central core.