In human space flight, astronauts are the most precious "payload" and astronaut time is extremely valuable. Astronauts operate under unusual and difficult conditions since the absence of gravity makes some of simple tasks tedious and cumbersome. Therefore, computer interfaces for astronauts are generally designed first for safety and then for functionality. In addition to general constraints like mass, volume, robustness, technological solutions need to enhance their functionality and efficiency while not compromising safety. Brain-machine interfaces show promising properties in this respect. It is however not obvious that devices developed for functioning on-ground can be used as hands-free interfaces for astronauts. This paper intends to address the potential of brain-machine interfaces for space applications, to review expected issues related with microgravity effects on brain activities, to highlight those research directions on brain-machine interfaces with the perceived highest potential impact on future space applications, and to embed these into long-term plans with respect to human space flight. We conclude by suggesting research and development steps considered necessary to include brain-machine interface technology in future architectures for human space flight.