This paper is to promote investigation into the nuclear rocket engine (NRE) propulsion option that is considered as a key technology for manned Mars exploration. Russian NRE developed since the 1950s in the former Soviet Union to a full-scale prototype by the 1990s is viewed as advantageous and the most suitable starting point concept for manned Mars mission application study. The main features of Russian heterogeneous core NRE design are described and the most valuable experimental performance results are summarized. These results have demonstrated the significant specific impulse performance advantage of the NRE over conventional liquid rocket engine (LRE) propulsion technologies. Based on past experience, the recent developments in the field of high-temperature nuclear fuels, and the latest conceptual studies, the developed NRE concept is suggested to be upgraded to the nuclear power and propulsion system (NPPS), more suitable for future manned Mars missions. Although the NRE still needs development for space application, the problems are solvable with additional effort and funding.

Small (<100 kg) spacecrafts are being developed in many countries but their propulsion systems still have many challenges. Although there is demand for small spacecraft propulsion, the number of missions at present is small due to several commercial and technical reasons. Poor performance of existing small spacecraft propulsion systems is one of the main reasons for the small number of missions. Several reasons are given for the poor performance of existing small spacecraft propulsion. Suggested improvements focus on small spacecraft and propulsion hardware mass optimization rather than on specific impulse enhancement. Propellantless propulsion systems are also recommended for small spacecraft interplanetary missions.