Next generation solar bimodal systems

One of the principal advantages of a solar thermal propulsion system as compared to a conventional chemical propulsion one is high specific impulse which is proportional to the square root of a propellant temperature. Obviously, next generation solar propulsion and bimodal systems must take advantage of high and ultra-high temperatures. This requires use of an appropriate energy conversion system capable to take advantage of high temperature potentially achievable in a solar receiver. High efficiency and power density of a high temperature thermionic converter open new perspectives in the development of advanced bimodal power systems having performance significantly higher than that achievable by the state-of-the-art technology. The paper presents an innovative concept of a cascaded solar bimodal power system with a high temperature Cs-Ba thermionic converter. The paper shows that the use of high temperature Knudsen cesium-barium thermionic converter in a solar bimodal system allows to eliminate thermal insulation sleeve, generate electrical power in the propulsion mode, and precise control thermal state of the solar receiver. In the Cs-Ba thermionic converter, an electron instability and high amplitude current oscillations develop. These effects can be used to obtain alternate current power directly in the converter. Possibility and potential advantage of such a generator are discussed