Monday, 23 January 2012
Analysis of the March 30, 2011 Hail Event At Shuttle Launch Pad 39A
Hall E (New Orleans Convention Center )
During the late afternoon of March 30, 2011 at approximately 21:25 GMT, hail monitor stations at Pad 39A recorded pea size hail while STS-134 Endeavour was preparing for its final flight into space. The duration of the hail event was approximately five minutes. The maximum hydrometeor size detected by the composite measurement of the three hail disdrometers and three hail pads surrounding the launch pad structure was estimated to be no larger than 12 mm, corresponding to the 6 sq. ft. total sensor measurement area. The 12 mm maximum size was measured by the active impact sensor at Station-2, located on the west side of the shuttle launch pad. High winds from the west produced a few elongated dents in the hail pads. High winds were also responsible for damage to facilities near hail monitor Site-2, where a dumpster was overturned and a picnic table roof was demolished. NWS radar volume scan showed 60-65 dBZ reflectivity values in the lowest four scan elevations around and over the pad 39A area. Some of the larger passive hail pad dents were shallower than what would be expected from solid frozen ice hydrometeor dents. Therefore, it is possible that the larger pea size hail may have been softer than the smaller rice size hail, consistent with partial melting before reaching the shuttle's fragile external tank outer shell.