Complex sentence: The TR-201 or TR201 is a hypergolic pressure-fed rocket engine used to propel the upper stage of the Delta rocket, referred to as Delta-P, from 1972 to 1988.
Split into simpler sentences: The TR-201 or TR201 is a hypergolic pressure-fed rocket engine. It was used to propel the upper stage of the Delta rocket, referred to as Delta-P, from 1972 to 1988.