Crew size impact on the design, risks and cost of a human mission to mars

Numerous scenarios have been proposed for a human mission to Mars. The crew size is typically between three and six astronauts. According to experts in human factors, a crew of three is possible but a crew of six is more appropriate. However, it is shown in this paper that the impact of the number of astronauts on the design, the risks, and the cost of the first mission might be much more important than expected. Different domains are considered: There is a direct impact on the consumables and astronauts´ affairs. Reducing the size of the crew from six to three astronauts allows an IMLEO (Initial Mass in Low Earth Orbit) reduction on the order of 34%. There is an important impact on the choice of EDL (Entry, Descent and Landing) systems. According to our calculations, reducing the size of the crew from six to three astronauts allows sufficient mass savings and volume reduction for the choice of large capsules with a 70° sphere cone heat shield. If it is confirmed, this choice enables important mass savings for EDL systems, on the order of 26% for the landing vehicles. Aerocapture would also be enabled for the interplanetary manned vehicle, allowing complementary mass savings. Finally, considering the total reduction of the payload that has to be sent to Mars, it might be possible to avoid the LEO (Low Earth Orbit) assembly and to send the interplanetary vehicles directly to Mars. All in all, reducing the size of the crew from six to three astronauts is probably a game-changing option. In addition, if six astronauts were the preferred crew size on the surface of Mars, the best option according to the IMLEO criterion would be, without question, a duplication of the scenario with three astronauts.