still ^10^ rem/5 years for 10 gm/cm2. This is true both during a large (e.g., August, 1972) solar flare particle event and when there is no flare, because the bremsstrahlung produced by the Van Allen belt electrons is so difficult to shield. By way of comparison, typical EVA space suits have <0.2 gm/cm^ effective shielding, the LEM (Lunar Excursion Module) had ^2 gm/cm^ effective shielding, while the Gemini and Apollo spacecraft had ^3.5 gm/cm2 and ^4.5 gm/cm2, respectively. It is interesting to note that if a low-altitude Earth orbit is considered, the tissue dose for 1 gm/cm2 at ^800 nmi (Figure 6.1-5) approximates that for geosynchronous orbit in the absence of a flare (the solar flare particle dose for low altitude, low-inclination earth orbits is very small because of the shielding effect of the geomagnetic field). However, for VL0 gm/cm in the absence of a flare, an altitude of ^500 nmi is more comparable because at low altitudes the Van Allen particles (especially the protons) are more difficult to shield out than at synchronous orbit. The recommended radiation dose limits for astronauts are listed in Table 6.1-2. These dose limits run from 0.1 rem (1 year daily average to the testes) to 1,200 rem (career maximum to the skin). The career maxima are ^5.3 times the yearly maxima for all critical organs, which are ^2.1 times the quarterly maxima, which are ^1.4 times the 30-day maxima (Table 6.1-3). Based upon these recommended dose limits and the calculated radiation environments or geosynchronous orbit, the testes limit cabin (2 gm/cm^) occupancy to Figure 6.1-5. Low-Altitude Van Allen Orbit Doses
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