A mission can fail at the interfaces even when every component works alone.

Assembly and integration connect propulsion, structures, software, power, communication, crew systems and ground interfaces into one vehicle and mission system.

• Do physical interfaces fit?
• Do electrical and data interfaces agree?
• Can one subsystem disturb another?
• Does the combined system still meet mission limits?
• Can configuration changes be traced?

Integration is where local correctness must become whole-system correctness.