EVA Walk-Back Limit Calculation Using the Virtual Spacesuit

In order to ensure astronaut safety during extravehicular activities (EVA) on planetary surfaces, the operational paradigm is to limit the distance crew members would have to walk back to a safe haven in case of a hardware failure. For the Apollo missions, this distance was calculated prior to the mission based on the average consumption of oxygen, sublimator feedwater and battery power and assuming a constant walking velocity of the astronaut between the break-down site of the lunar roving vehicle and the lunar module. During the actual EVA the walk-back distance was recalculated based on the actual consumption rates. This paper presents a method for the calculation of the walk-back limit for future human exploration missions that additionally takes additional, dynamic factors into account, for example the projected metabolic rate of the astronauts during the traverse back to the safe haven due to the slopes of the terrain. To achieve this, the Virtual Spacesuit (V-SUIT) is utilized, a dynamic EVA simulation system developed at the Technical University of Munich. Two case studies are presented: An EVA from the Apollo 17 mission and a notional exploration EVA at the lunar south pole using a current NASA spacesuit architecture. Results show that the walk-back limit used during Apollo 17 was conservative and they demonstrate the impact of new spacesuit technologies on the calculated distances.