Complex sentence: Changeout of the orbiter-side 17-inch umbilical assembly was made with one borrowed from the yet-to-arrive Shuttle "Endeavour"; the external tank was then fitted with new umbilical hardware.
Split into simpler sentences: Changeout of the orbiter-side 17-inch umbilical assembly was made with one borrowed from the yet-to-arrive Shuttle "Endeavour". The external tank was then fitted with new umbilical hardware.