• On-orbit medical emergency • Habitation or medical facility emergency • A grounded primary crew transport vehicle In the event of a medical emergency beyond the scope of on-orbit facilities, a crew member may have to be returned to Earth. A proposal for Space Station Freedom is for an Apollo style capsule, outfitted for patient stabilization and carrying up to six crew members (Barratt, 1992). The G forces on reentry must be minimized, to not more than 3G, for the safety of an already compromised patient, and only in the most physiologically tolerable (+Gx) body axis. For Space Station Freedom construction, NASA proposes the ability to remain in orbit for eight hours in order to permit splashdown within 100 miles of a medical care facility and a time of 3.5 hours from splashdown to medical center. Similar concepts should be adopted for an SSPP medical facility and crew habitat. In the event of a facility or primary transport vehicle contingency (fire, loss of power, toxic exposure, loss life support, orbital debris damage of spacecraft, etc.) the emergency return vehicle could be used as a lifeboat until the other crafts regain function. Life Support System The proposed life support for the habitation/medical facility is that of a standard physical/chemical partially closed loop system that is supplied with food from Earth. Solid waste is stored. This is used for both Mir and Space Station Freedom design. Oxygen can be regenerated by electrolysis of water and water is reclaimed and purified by physical/chemical means. Other systems such as bioregeneration capabilities should be considered as they become available. Extravehicular Activity Man and Machine Coordination In the construction of a large solar power satellite, a choice must be made concerning EVA activities to be carried out by man and those by machine. The cost and risk of manned EVA using current suits, dictates that the project must attempt to minimize this time [Barratt, 1992], Zimmerman et al. [1985] have proposed useful criteria for Task Automation vs. Human Performance: 1. to avoid perceptual saturation 2. to reduce concurrent tasks 3. tasks on compressed timelines 4. to avoid human bandwidth limitations 5. routine tasks 6. memorization tasks 7. sequential and time tasks 8. monitoring tasks 9. time consuming, boring, and unmotivating tasks 10. emergency -prevention devices 11. complex mathematical or logical tasks 12. complex tasks that must be performed rapidly 13. to enhance system reliability 14. safety endangering tasks 15. systems with consideration to crew acceptance The limiting factor of automated systems thus far has been a lack of dexterity. Telerobotic systems under development include the Flight Telerobotic Servicer, the Special Purpose Dexterous Manipulator, the Remote Manipulator System, and the Japanese Experimental Module servicing arms [Barratt, 1992]. These systems can incorporate the benefits of both man and machine while avoiding the risks of manned EVA. Today however, humans remain “easier to program or reprogram than any system of comparable capability”. [Loftus, 1986] The exact construction tasks for SSPP will need to be outlined and the benefits of man or machine will need to be considered for each before the man - machine interactions are detailed.
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