Suit Design and Human Factors EVA during construction requires a suit that will support and protect the astronaut and as well allow enough flexibility for construction activity. The current Extravehicular Mobility Unit (EMU) used by the NASA consists of the Space Suit Assembly (SSA) and the Portable Life Support System (PLSS). The SSA consists of a hard upper torso and soft lower torso, arms, and legs. The suit pressure atmosphere is 29.6 kPa, thermally insulated and of nearly 100% O2. The Russian EVA suit operates at 40 kPa (but can be lowered to 30 kPa), and also consists of soft components except for a hard upper torso. Each suit can support EVA for about seven hours. The increase in EVA expected for large SPS construction will require a modification to these designs. The extended duration of the EVA's increases the risk of orbital debris or micro meteoroid encounter. The construction process itself will likely lead to a greater risk of orbital debris, regardless of the safeguards against it. These safety concerns can most effectively be addressed with the use of a “hard” EVA suit that would reduce this risk of suit penetration. Since the cabin pressure of the US Space Shuttle, Mir Space Station and proposed Freedom Space Station is 101.3 kPa, EVA activities in the lower pressure suits require either a lengthy (up to 4 hour) prebreath, or a lowering of cabin pressure hours before EVA to reduce the risk of DCS. Given the large proportion of EVA during construction, this difference between cabin and suit pressure must be minimized to increase safety and decrease preparation time. Since dexterity is generally sacrificed with increased suit pressure, using a low pressure cabin seems beneficial. However, if the habitat has other purposes such as conducting life science research as on current spacecraft, this permanent lowering of cabin pressure may not be possible and a high pressure suit may be required. Currently, hard shell / high pressure suits are under development. The Mark III is a composite rigid structure and fabric design [Kosmo et al., 1990]. NASA's AX - 5 is a constant volume, all metal suit that operates at 57.2 kPa, and a European rear entry hard suit under development will operate at 50 kPa [Svensson et al., 1986]. The AX-5 has joints that move by rotating bearings instead of fabric deformation. One further design is of a double hulled metal suit to protect against debris. Current suits provide aluminum equivalents of 0.5 g/cm2 (McCormack et al., 1989) while advance suits will provide 1.5 g/cm2. For EVA in Geostationary Earth Orbit, a suit of 1.62 g/cm2 is required [Thompson et al., 1986]. The major drawback of all EVA suits is glove design. Finger joints are difficult to move even in low pressure suits. Astronauts of the EASE (Experimental Assembly of Structures in Space - shuttle flight 61-B) project emphasized the fatigue felt in their hands and forearms [Cleave and Ross, 1986]. To achieve the necessary dexterity needed for construction, a better design is needed. In the construction environment, it is important that handrails, waist tethers, and footholds be among the first objects installed to facilitate construction. Advanced suits should also incorporate real-time monitoring of vital EVA signs (cardiovascular system, respiration, metabolism, suit temperature and pressure etc.) so support systems can be automatically or remotely immediately altered. It is suggested that a one-way, flow-controlled conduit be incorporated near the astronaut's mouth to handle any emetic episodes inside the suit which are presently life threatening. A wide field of view combined with a helmet mounted display with video telecommunications may aid in construction activities. Other areas of improvement are in the development of longer life, rechargeable batteries and recyclable air regeneration systems. Checkout time for the suits must be facilitated as to reduce downtime. For EVA activity above Low Earth Orbit, enhanced suit radiation shielding will be required. Tools should be designed for one-handed operation and for maximum ease of operation. Workplace and helmet mounted lighting should also be include. Regarding the amount of EVA activity with respect to DCS danger, Webb et al. [1988] report that 8 hours of EVA-level activity for five consecutive days at 65 kPa EVA simulation and breathing 100% O2 showed no evidence of either DCS of oxygen toxicity. 6.2.4 Lunar Operation Effects Utilizing lunar resources for manufacturing and construction of a large solar power satellite may decrease the project cost due to the much lower lunar launch expense as compared to Earth launch expense. Again, it is presumed that some manned activity will be necessary on the lunar surface. This introduces the need for crew habitat and medical facilities on the Moon. The increased distance from the Earth (as compared to construction in Geostationary or Low Earth Orbit), the introduction of approximately 0.16 of Earth's gravity, and the process of actual material manufacturing, poses a few distinct concerns and considerations to crew safety. As an extensive lunar presence is not planned for
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