7. C4 t thickness (m) R density of steel (7860 kg/m 3 ) .04m V radius of affected region (m) mass of steel R t 7860 ¾(.04) 3 energy for melting Total energy required .395 kg= 395 gm 1370°C x .11 + 65 = 215 cal/gm 84925 calories= 3.55xl0 5 joules Only 8-10% of this energy is needed to cause cracking (7.C2) K.E. of meteoroid= 3.16xlo 4 joules For a velocity of 30000m/sec a meteoroid will have a mass of .070 grams in order to have a kinetic energy of 3.16xl0 4 joules. (This assu~es that all the kinetic energy is used in raising the· energy level of the hull's impacted region.) Going back to the impact probability equation or to Figure 7.Cl, a fragment of this mass will hit approximately once per year. This is a tolerable level of outer hull plate failures due to meteoroid impact.
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