 The cigar shaped distribution profile and low density of the plasma reduces the instantaneous shock to the pusher plate.The pusher plate's thickness would decrease by, approximately, a factor of 6 from the center to the edge so that the net velocity of the inner and outer parts of the plate are the same, even though the momentum transferred by the plasma increases from the center outwards.At low altitudes where the surrounding air is dense gamma scattering could potentially harm the crew without a radiation shield, a radiation refuge would also be necessary on long missions to survive solar flares.