Complex sentence: In the absence of an emergency, the LES was routinely jettisoned about 20 or 30 seconds after the launch vehicle's second-stage ignition, using aseparate solid fuel rocket manufactured by the Thiokol Chemical Company.
Split into simpler sentences: In the absence of an emergency, the LES was routinely jettisoned about 20 or 30 seconds after the launch vehicle's second-stage ignition. The jettison motor was a separate solid fuel rocket manufactured by the Thiokol Chemical Company.