 Complete the following phrase:  On the morning that the Space Shuttle Challenger was due to launch on STS-51-L, Petrone and several of his colleagues were alarmed at the massive amount of ice that had built up overnight on the Orbiter due to unseasonably cold temperatures. Petrone feared that the ice could seriously damage the shuttles thermal protection system when it struck the tiles during launch. He told his managers at Cape Canaveral that Rockwell could not support launching because it viewed the amount of ice on the Orbiter as a launch constraint. This was not the cause, however, of the 