Change causes massive ramifications throughout the system. Tightly controlled time schedules with little slack are sensitive to delays. Production sequences must be strictly followed. Substitutions are not easily accomplished and equipment breakdowns can bring the entire system to a halt. Safety features must be designed into the system because human intervention is not easily accommodated.
Trains run on time.
Management has limited flexibility in the use of tracks. Trains must be staggered and time buffers rigidly followed. Failures within the system are relatively easy to locate. Direct, on-line information sources exist. Once a spacecraft is launched, NASA is committed.