New trade tree for manned mars missions

• The number of astronauts is the key driving parameter of the mission.
• An important finding of the study was the impact of the crew size.
• An important parameter is the strategy for the return from Mars orbit to Earth orbit.
• There is still place for other interesting architectures.

Recent studies on human missions to Mars suggest revisiting the parameters that have the most important impact on the complexity, the initial mass in low Earth orbit, the risks and the development costs for the first journey to the red planet. In the last NASA reference mission, a trade tree is proposed.At first level, the parameter is the class of mission, e.g., conjunction (long surface stay) or opposition (short surface stay). This parameter is important but there is an agreement on the best option (conjunction). It is therefore not a relevant parameter of the decision tree. For the other levels, the parameters are as follows:
• Launching sequence: pre-deploy or all-up.
• Mars orbit insertion: aerocapture or propulsive.
• Exploitation of local resources: yes/no.
• Propulsion for interplanetary flight: chemical/nuclear thermal/electric.The relevance of these parameters is questionable. It is proposed to reexamine all parameters of the mission and to study their interdependency and the complexity and the costs of possible options. The first important parameter should be the size of the crew. It should be assigned to the top node of the tree, because its impact on the initial mass in low Earth orbit, costs and risks is probably higher than any other parameter. Another parameter is the strategy for Mars orbit insertion. It is suggested here that aerocapture is very important and that it brings acceptable constraints for the architecture of the mission. The third parameter should be the strategy for entry, descent and landing. The mass of the landing vehicle is very important, because it is tightly linked to the complexity of the entry, descent and landing phase. With a low mass, a capsule shape and a rigid heat shield can be chosen for this maneuver (lowest risk, highest technology readiness level). With a heavy vehicle, an inflatable heat shield might help but the qualification of the systems would be very difficult and the entry, descent and landing phase would be more complex. This parameter is clearly a driving parameter for the design of mission architecture because this part is one of the riskiest (clearly established in the NASA report), one of the most expensive in terms of development and tests costs and there are obvious impacts on other parameters of the mission. The fourth parameter should be the strategy for the return and the preparation of the Earth return vehicle. According to our study, this vehicle is the heaviest of the mission. Critical choices can be made here and can make a scenario simple or very complex.Interestingly, a small crew size facilitates the reduction of the mass for the landing vehicles, which in turn suggests simple solutions for the aerocapture of all vehicles and the preparation of the Earth return vehicle without requiring the development of nuclear propulsion systems. All in all, this study shows that the choices made for the NASA reference mission are systematically suboptimal and that new options deserve to be explored.