^8 months, while the eyes limit extravehicular activity (EVA) to ^35 days/year (8 hours/day) if 1 gm/cm2 £s provided. Thus EVA will be the limiting factor, even if a space suit which affords 1 gm/cm effective shielding is provided. Fortunately, the eyes (which limit EVA) and the testes (which limit cabin occupancy) are small enough to be readily protected by extra shielding. However, even in that situation, special provisions must be made to provide improved space suits if much EVA is planned. The basic philosophy should be to limit radiation exposure whenever possible. Toward that end, the following criteria are suggested: • Need >10 gm/cm2 shielding for major solar flare events — Personnel to remain in storm shelter during such events; brief excursions outside storm shelter are possible for emergencies. Total time in storm shelter r$200 hr/year • Need >2 gm/cm2 shielding for normal activity — Personnel will receive <0.5 rem/day (skin); sleeping in storm shelter will help • Need £1 gm/cm^ shielding for space suit — Personnel will receive <0.5 rem/hr (skin) during EVA. EVA activity to be curtailed when sun is active (<100^ of time at solar max; <2% of time at solar min). Astronauts should have a heavily-shielded (^10 gm/cm) "storm shelter" (preferably lined with materials of high atomic number to limit the bremsstrahlung dose rate inside) into which they can retreat when sleeping or when a solar flare particle event is in progress. Such a shelter need provide only ^30 ft3/ man and can possibly be formed by life support storables (air, water, food, etc.). The cabin should have at least 2 gm/cm^ of effective shielding (and one thin spot is more significant than large areas of thick spots). Finally, EVA should be limited, insofar as possible, to periods of time when the sun is quiet. Even then, at least 1 gm/cm2 effective shielding should be provided. By providing these minimum amounts of shielding, careful scheduling of EVA, and rotating personnel, it should be possible to keep within the recommended dose limits. In summary: 1. Schedule most EVA activity when sun is quiet (solar minima expected 1986, 1997, etc.). 2. Line storm shelter with high-Z material (lead, gold, tungsten, etc.); this will decrease Van Allen produced bremsstrahlung. 3. Rotate personnel assignments to equalize radiation dose (use storm shelter for sleeping quarters). 4. Use storables (food, water, oxygen, waste products) for radiation shielding.
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