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Meeting	ACGS Committee Meeting 130 - Missoula, MT - March 2023
Agenda Location	6 SUBCOMMITTEE B – MISSILES AND SPACE 6.1 Space Launch System Core Stage TVC Test and Flight Experiences
Title	Space Launch System Core Stage TVC Test and Flight Experiences
Presenter	John Wall
Affiliation	NASA MSFC (Mclaurin Aerospace/ESSCA)
Available Downloads*	presentation
	Downloads are available to members who are logged in and either Active* or attended this meeting.
Abstract	The SLS Core Stage Thrust Vector Control (TVC) system is comprised of 8 mechanical feedback Shuttle heritage actuators that vector the four Shuttle heritage RS-25 engines about a Shuttle heritage gimbal block/bearing. The actuators are powered by a newly designed hydraulic core auxiliary power unit (CAPU), and attached to a custom built core stage thrust structure, and commanded by all new digital/analog TVC Actuator Control (TAC) avionics. Despite the significant test and flight experience of the Shuttle hardware, the SLS Green Run ambient and hot fire test activities revealed a number of findings associated with the dynamic response of the TVC integrated system. Post test evaluations determined that the characteristics of the structure and gimbal friction are significantly influenced by the thrust loaded conditions and the command avionics exhibited a small but noticeable nonlinearity. A bounding approach to modeling the long neglected effects of friction and other test-observed phenomena showed a small but acceptable potential for Limit Cycle Oscillation (LCO) in the flight control loop, supporting confident rationale for first flight. Further study and refinements to the modeling of the TVC system led to an exacting understanding of the causes of test responses. The first highly successful flight of SLS’s Artemis I confirmed both the nature and acceptability of the findings revealed by the pre-flight Core Stage TVC test and analysis efforts.