The object of this work is a first assessment of the use of a pulsed nuclear thermal rocket for thrust and specific impulse (Isp) augmentation with particular reference to interplanetary travel. The basis of the novel space propulsion idea is the possibility of working in a bimodal fashion where the classical stationary nuclear thermal rocket (NTR) could be switch on or switch off as a pulsed reactor as desired by the mission planners. It was found that the key factor for Isp augmentation lies in the capability of rapid quenching of the fuel and working at low Fourier numbers where the energy from the pulse can be considerably larger than the stationary mode. The Isp enhancement is based on the instantaneous heating of the propellant by the intense neutronic flux generated by the pulse which is not limited by de second law of thermodynamics and then allowing a propellant hotter than the fuel. However, within the framework of this concept in application to Isp amplification, the energy from the fission fragments is an unwanted energy and must be evacuated by a solidary quenching system working in parallel with the propellant channel, which is in clear contrast with currents nuclear thermal rocket concepts. It was found that liquid metals are the only coolants which allow the fast quenching required and preliminary estimates reveal that lithium is featuring a remarkable performance for this purpose, albeit with the neutronic drawback associated with the isotope 6Li. In addition, thin geometrics of the fuel are mandatory to keep intimate contact with the quenching coolant. Theoretical treatment is properly developed for the basis of the concept and some preliminary thermohydraulics and neutronic simulations performed. The proposed pulsed mode could endows the classical NTR with the missing first gear necessary for interplanetary travel.

Peer Reviewed