Puttering through the Van Allen Belts

(Mike Miller) writes:

For a hypothetical spacecraft (an Earth orbit-to-lunar orbit transfer
vehicle) that spends 10 hours accelerating to Earth escape velocity
(~0.01G from a high-Isp engine), is 1-meter of water shielding
sufficient to reduce the radiation exposure in the Van Allen belts to
levels safe enough for repeated human passage?

It is more than sufficient. Five centimeters of water would suffice
to keep the dose limit to roughly 1 rem (0.01 sievert) per passage.

The DOE limit for occupational exposure is 5 rem per year.


And note, if you want to reach escape velocity from low Earth orbit
in ten hours, you need ~0.02G of acceleration. The simple additive
model doesn't work unless your burn time is short compared to your
orbit period, and the long-burn trajectories are less efficient.
Simplistically speaking, an impulsive burn to escape involves
raising your apogee to infinity; a slow burn to escape requires
raising apogee *and perigee* to infinity, twice the delta-V.


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