scope:

Description of Driving Event:

Ice debris created by the STS 51-L launch was greater than predicted by pre-launch analysis. The trajectories of wind-driven ice falling from the Fixed Service Structure/Rotating Service Structure (FSS/RSS) were predicted using aerodynamic analysis methods. These methods accounted for drag retarding the fall and wind velocity imparting a lateral velocity component. The effects of plume aspiration and particle rebound off the mobile launch platform were not included in the analysis. Launch films show that the vehicle rising off the launch pad caused considerable aspiration. This effect drew ice toward the Solid Rocket Booster (SRB) PLUME, with some ice striking the left hand SRB. The actual FSS/RSS ice movement, as observed on the photographic documentation, did not conform to the predictions in two important respects: 1) the ice generally did not release until after main engine ignition, and 2) the ice translated further toward the vehicle than predicted.