Abstract
In order to investigate the behavior of suspended particulate matter (SPM) in the 1/6 gravity (1/6 G) environment, simulated lunar dust was diffused in a chamber, realizing quasi 1/6 gravity environment with a parabolic flight. The effect of 1/6 G environment on the atmospheric suspension was evaluated by means of the cutoff value of an elutriator; the cutoff value in the 1/6 G should be √<6> times larger than at the earth's surface. As a result, we experimentally confirmed that the falling velocity of SPM in a 1/6G is approximated to Stokes' law, and the falling time is inversely proportional to the gravity. Numerical computation suggested that residual SPM in a convection-free room becomes high in a low gravity environment or in a high ceiling room. These results announced that, once the lunar dust intruded into the lunar bases, it would take much longer time to clean up. Since the suspension time of SPM is different by the particle size, the exposure risk of SPM will also be varied to the particle size. Considering the risk depends only on the drifting time, actual influence by the low-gravity will be nonsense on the fine particles (D_p ≤ 1.0 μm in diameter) and on the large particles (D_p > 10 μm) in a 1/6G. In contrast, for medium sized particles (2.5 < D_p ≤ 10 μm) the difference in the drifting time between that on the earth and on the lunar surface is much larger than can be confirmed with the senses. Safety precautions used for this size of particle on the earth should be altered on the lunar surface.
