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.