Considerations for Thrust Vector Control (TVC) In-Flight Load Predictions

Nathaniel A Stepp

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NASA NTRS · 20240010637

Considerations for Thrust Vector Control (TVC) In-Flight Load Predictions

Nathaniel A Stepp

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Abstract

This presentation communicates an overview of a methodology developed by the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center (MSFC) Thrust Vector Control (TVC) Systems Integration & Components Branch (MSFC-ER63). The methodology is based on NASA heritage TVC design practices and is designed to analyze the summation of static and quasi-static environments acting on a gimbaled rocket engine/motor system. The analysis determines the maximum overall expected induced torque acting on the rocket engine/motor system about the gimbal center of rotation and assumes a mathematical 3-Dimensional (3D) 2-Degree-of-Freedom (DOF) rigid-body pendulum model over a predefined range of angular motion. Additionally, it calculates the associated reaction force acting along a TVC actuator line-of-action (LOA) to maintain thrust vector holding operations. This methodology is particularly useful for determining maximum overall design loads for TVC actuator design-space shaping and requirements determination.

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Thrust Vector Control TVC Actuator Loads Gimbal Propulsion TVC Actuator Loads Load Modeling Load Prediction Launch Vehicle Steering Liquid Rocket Engine Solid Rocket Engine SSME Booster Core-Stage Flex-Bearing

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Nathaniel A Stepp. 2024-08-22. Considerations for Thrust Vector Control (TVC) In-Flight Load Predictions. https://ntrs.nasa.gov/citations/20240010637

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NASA NTRS2024

MSFC-TVC | TB-03: Derivation of Thrust Vector Control (TVC) Actuator-Force / Gimbal-Torque Transformation Matrix

Thrust vector control (TVC) systems for rocket engine propulsion traditionally use a simple linear relationship to convert between actuator forces and torques about the engine gimbal’s center-of-rotation (COR). As shown in Equation (1), the torque about the gimbal COR is proportional to the applied actuator force and the TVC moment arm (MA)—the perpendicular distance between the TVC actuator’s line-of-action (LOA) and the engine gimbal’s COR. While this fundamental relationship remains valid and accurate in a two-dimensional (2D), one-degree-of-freedom (1-DOF) context—particularly in its non-linear formulation as described in the ER63 Technical Bulletin TB-02 (Derivation of Thrust Vector Control (TVC) Engine-Gimbal / Actuator Moment-Arm Geometry)—it becomes limited when extended to three-dimensional (3D), two-degree-of-freedom (2-DOF) analyses. In 3D, out-of-plane angular displacements can arise, causing the gimbaled engine plane-of-motion to become non-coplanar with the respective actuator plane-of-motion. Such misalignments occur due to the rod-end (RE) and/or tail-stock (TE) mounting geometry of individual TVC actuators. These geometric complexities lead to inaccuracies in calculating engine torques and corresponding actuator forces if only the traditional TVC MA relationship is employed. For higher gimbal angular displacements (e.g., greater than 5 degrees), these inaccuracies become more pronounced, necessitating a more robust mathematical framework. This document presents a comprehensive 3D (2-DOF) derivation of a transformation matrix that accurately converts between gimbaled engine torques and TVC actuator forces. By incorporating the necessary geometric and rotational considerations, this new approach corrects the limitations of the traditional TVC MA method. Subsequent sections compare the newly formulated approach to the traditional method, demonstrating its enhanced accuracy and reliability for a broad range of gimbaled engine conditions.

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Core Stage TVC Systems Engineering Challenges in Reusing Heritage Hardware

The Space Launch System (SLS) Core Stage (CS) Thrust Vector Control (TVC) system is comprised of 8 mechanical feedback Shuttle heritage Type III TVC actuators and four RS-25 engines, each attached to a Shuttle heritage gimbal block/bearing. Two actuators are used to move each engine in two planes perpendicular to one another (i.e., pitch and yaw). The TVC system design leverages hardware from the Space Shuttle program as well as new hardware designed specifically for the Core Stage. The Space Shuttle heritage hardware directly reused on SLS includes the Orbiter TVC hydraulic servo-actuators (with two slight design modifications), the Orbiter hydraulic circulation pumps, the Orbiter gimbal block/bearing, and the Solid Rocket Booster hydraulic pumps. The Core Auxiliary Power Unit (CAPU) is derived from the Orbiter Auxiliary Power Unit (APU). The Orbiter and Solid Rocket Booster APU turbines are powered by hot gas produced by catalyzed hydrazine decomposition. On the SLS Core Stage, the CAPU turbine is spun using cold gas tapped-off from the RS-25 to CS liquid hydrogen autogenous pressurization line. While direct reuse or slight modification of existing hardware may seem to be a triple-win for a program in cost, schedule, and technical risk mitigation, those benefits can only be realized when its degree of application in a new system is carefully and thoughtfully managed. The heritage hardware reuse should be prescribed within the heritage design capability and reuse environments must lie within the envelope of heritage qualification testing. Despite the significant test and flight experience of the Shuttle heritage hardware components, successful integration with the newly designed CS TVC components and incorporation into the stage design proved to be a challenge which required re-qualification of the heritage hardware as well as thorough integrated testing to support flight certification. Examples of the challenges that were overcome include: re-qualifying heritage hardware to survive new shock and vibration environments, certifying performance of extensively modified heritage hardware, regenerating design insight due to lack of available heritage vendor data, showing compliance to modern structural design standards, translation of heritage requirements for analog avionics to modern digital avionics, and interfacing heritage mechanical hardware with newly designed avionics. This paper is the second installment in a seven-paper series surveying the design, engineering, test validation, and flight performance of the Core Stage Thrust Vector Control system. This paper will discuss several engineering challenges encountered during the development process for SLS CS TVC and how they were successfully overcome to reach flight readiness.

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Overview of the SLS Core Stage Thrust Vector Control System Design

The Space Launch System (SLS) Core Stage (CS) Thrust Vector Control (TVC) consists of four independent hydraulic systems. The SLS CS TVC system is comprised of 8 mechanical feedback Shuttle heritage Type III TVC actuators and four RS-25 engines, each attached to a Shuttle heritage gimbal block/bearing. Each hydraulic system nominally provides hydraulic power to one RS-25 engine and two actuators. Additionally, each system provides redundant control capability to one actuator on each of its neighboring systems. The RS-25 uses hydraulic power to control propellant valves, and the TVC actuators are used to move the engine in the pitch and yaw gimbal planes. The TVC system design leverages hardware from the Space Shuttle program as well as new hardware designed specifically for the Core Stage. The Space Shuttle heritage hardware directly reused on SLS includes the Orbiter TVC hydraulic servo-actuators (with two slight design modifications), the Orbiter hydraulic circulation pumps, the Orbiter gimbal block/bearing, and the Solid Rocket Booster hydraulic pumps. The Solid Rocket Booster APU turbines are powered by hot gas produced by a catalyzed hydrazine decomposition. The SLS Core Auxiliary Power Unit (CAPU) is derived from the Space Shuttle Orbiter Auxiliary Power Unit (APU); on the SLS Core Stage, the CAPU turbine is spun using cold gas tapped-off from the RS-25 to CS liquid hydrogen autogenous pressurization line. The remaining hardware in the TVC system (hydraulic Filter Manifold (FM), hydraulic Supply Accumulator (SA), hydraulic Return Accumulator (RA), Hydraulic Reservoir, Exhaust Gas Heat Exchanger (EGHE)) as well as the avionics providing control and telemetry (TVC Actuator Controller (TAC) and CAPU Controller (CAPUC) are new components developed for SLS. This paper is the first installment in a seven-paper series surveying the design, engineering, test validation, and flight performance of the Core Stage Thrust Vector Control system. In this paper, the overall design architecture of the CS TVC is presented, with a focus on the interfaces between the TVC actuators, the engines, their hydraulic power systems, and the avionics that provide commands from the SLS Vehicle Management (VM) software to effect stable and robust flight control for the integrated SLS launch vehicle.

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