An improved APU for the Space Shuttle Orbiter

The Space Shuttle Orbiter Auxiliary Power Unit has operated successfully on all four orbiter vehicles and all missions. The current Auxiliary Power Unit (APU) operational life is limited to 12 missions, and the APU turnaround time between flights is longer than originally anticipated. The objective of the Improved APU program is to increase life to 50 missions, reduce installed vehicle weight by 134 lb., and reduce turnaround time. This paper describes the design changes incorporated into the improved APU and the associated development testing.