NASA pushed back the lift-off of the space shuttle Discovery from late May to mid-July due to concerns about ice buildup on the giant external fuel tank, which occurs even in hot weather because supercold liquid hydrogen and oxygen powers the shuttle into space, according to The New York Times.
Recent studies had given engineers a new appreciation of the hazards of ice forming on the cold surfaces of the external fuel tank, according to NASA officials. Reviews of the hazards from the debris of launching indicated that the ice buildups that shook free in flight posed more of a danger than previously believed.