Minimizing EVA Airlock Time and Depress Gas Losses

This paper describes the need and solution for minimizing EVA airlock time and depress gas losses using a new method that minimizes EVA out-the-door time for a suited astronaut and reclaims most of the airlock depress gas. This method consists of one or more related concepts that use an evacuated reservoir tank to store and reclaim the airlock depress gas. The evacuated tank can be an inflatable tank, a spent fuel tank from a lunar lander descent stage, or a backup airlock. During EVA airlock operations, the airlock and reservoir would be equalized at some low pressure, and through proper selection of reservoir size, most of the depress gas would be stored in the reservoir for later reclamation. The benefit of this method is directly applicable to long duration lunar and Mars missions that require multiple EVA missions (up to 100, two-person lunar EVAs) and conservation of consumables, including depress pump power and depress gas. The current ISS airlock gas reclamation method requires approximately 45 minutes of the astronaut's time in the airlock and 1 KW in electrical power. The proposed method would decrease the astronaut's time in the airlock because the depress gas is being temporarily stored in a reservoir tank for later recovery. Once the EVA crew is conducting the EVA, the volume in the reservoir would be pumped back to the cabin at a slow rate.

Various trades were conducted to analyze this method, which include time to equalize the airlock with the evacuated reservoir versus reservoir size, pump power to reclaim depress gas versus time allotted, inflatable reservoir pros and cons (weight, volume, complexity), and feasibility of spent lunar nitrogen and oxygen tanks as reservoirs.