Modern control system theory has been applied to the design of the control system for the nerva nuclear rocket engine. Multiloop classical controls design approach has been used previously in the engine test program. The configuration and operation of the engine system with the resulting high degree of coupling and the multivariable nature of the system establishes a need for modern control techniques with considerable ad vantages over classical methods. The design procedure consists of system model linearization, system simplification, and the quadratic optimal control design. Transient performance results have been obtained from digital implimentation of the control system.