Planetary ExtraVehicular Activity (EVA) Scenarios, Costs, and Benefits

This paper considers the cost and benefit of planetary surface ExtraVehicular Activity (EVA) on the Moon and Mars. The Exploration Systems Architecture Study (ESAS) scenarios are used as a basis. The benefits of surface EVA depend on the number of sites visited, the total duration of EVA, and the maximum distance of exploration. The costs of EVA are measured by the total emplaced mass required to support a sortie mission or to establish and support a long term base. The later lunar sorties described in the ESAS have longer duration and use rovers not provided earlier, so they are more cost-effective in surface exploration. The planned permanent lunar base provides one-sixth the cost per EVA hour and a thirty percent lower cost per kilometer of explorable distance, but exploration is limited to a single site. There is an important trade-off between the number of different sites explored and the total time spent in surface exploration. Assuming that exploring different sites is an important goal, the permanent lunar base is much less cost-effective than lunar sorties for exploration. A Moon base is more suited for its main purpose, to prepare for Mars. It is planned that Mars will be explored from a single surface base over eighteen months. The same Mars surface mass might support five Martian sorties to five different sites, each visited for a week. The total EVA hours provided by these sorties could be a significant fraction, more than one-third, of those planned at the Mars outpost.