7 .Cl APPENDIX VII.C METEOROID IMPACT The location in free space subjects the colony to an isotropic mass flux of meteoroids defined by the following relationship (7.Cl): where: Log 10 N = -1.34 log 10 m -10.423 N = number of impacts/ft 2 /day m = mass of meteoroid (gms) Assuming the average density of a meteoroid to be 0.5 gm/cm 3 and the average velocity to be 30 km/sec (7.Cl) and basing the impacts on a colony surface' area of 2.202x10 6 ft 2 for 60 years (21,915 days), it is found that one impact will occur for a meteoroid with a mass of 1.565 grams. This meteoroid size becomes the design criterion for meteoroid impact. (Sixty years was chosen instead of the design life of thirty years as an added margin of safety since the above equation was empirically derived.) Figure 7.Cl shows the relationship between meteoroid mass and the expected number of impacts during a sixty-year period by a meteoroid of that mass. Figure 7.Cl shows the small probability of the colony being hit by a meteoroid of any substantial size. However, with a velocity of 30 km/sec even a relatively small meteoroid could inflict serious damage to a section of the hull. First it must be determined whether or not a 1.565 gram meteoroid can penetrate both the inner and outer hulls. Using the following expression derived from experimental data in References (7.Cl) and (7.C2):
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