On one of your slides you mention using Assembly at the subsystem level for HW to HW integration (I can see this for Payloads as those are usually stand alone),  however, for spacecrafts a lot of subsystems aren't integrated as a stand alone, are you overstating possible costs by doing at each subsystem vs. a spacecraft level assembly which would encompass the integration of all the subsystems at the spacecraft level?

A bus (or payload) can have just one subsystem-assembly pairing, with all components listed below, rather than multiple subsystems (or instruments) each with multiple separate pairings. 

In general, note that the Space Assembly under each Space Subsystem captures the support from the Subsystem to the Space System (S/C or Observatory), whether the Subsystem is integrated prior to system delivery or integrated directly to the S/C.   Not including a Space Assembly within each Subsystem would result in an overall I&T underestimate. 

To watch the "Best Practices using the TruePlanning Space Missions" Webinar, click here.