Abstract : The formation of frost, ice, and ice balls are common occurrences on the insulated External Tank (ET) of the Space Transportation System (STS) during National Aeronautics and Space Administration (NASA)-Kennedy Space Center (KSC), Florida launch preparations. The metal ET tank, 154 ft. tall and 27.5 ft. in diameter, is covered by insulating Sprayed On Foam Insulation (SOFI). However, internal ET fuel and oxidizer tanks contain large quantities of cryogens-in this case super cold liquid hydrogen (LH2) at minus 4230F and liquid oxygen (LO2) at minus 2970F. Complicating matters are Florida's humid and sometime cold weather that through condensation, support the formation of frost and ice. Although ice formation on the shuttle is more of a problem in the winter months, ice balls can form even in the hot summer months, because of cracks, voids, or other defects that may be present in the ET foam. Ice is a critical safety concern because of the possibility of it breaking off the ET at liftoff or during early vehicle assent. Falling ice could strike and possibly damage the Orbiter crew compartment windows, Reinforced Carbon-Carbon (RCC) panels on the leading edge of the Orbiter's wings, or its thermal protection tiles, thus placing the crew and vehicle at risk.