Complex sentence: The launch was originally scheduled 18 August 1994, but there was an RSLS abort at T-1.9 s after all three main engines ignited-the fifth (and final) time in the shuttle program where an RSLS abort occurred after main engine ignition.
Split into simpler sentences: The launch was originally scheduled 18 August 1994, but there was an RSLS abort at T-1.9 s after all three main engines ignited. This is the fifth time in the shuttle program where an RSLS abort has occurred after main engine ignition.