Preliminary Investigation on Battery Sizing Investigation for Thrust Vector Control on Ares I and Ares V Launch Vehicles

Abstract An investigation into the merits of battery powered Electro Hydrostatic Actuation (EHA) for Thrust Vector Control (TVC) of the Ares I and Ares V launch vehicles is described. A top level trade study was conducted to ascertain the technical merits of lithium-ion (Li-ion) and thermal battery performance to determine the preferred choice of an energy storage system chemistry that provides high power discharge capability for a relatively short duration. Introduction Historically, missiles and launch vehicles have employed hydrazine (N 2 H 4 ) to feed into an auxiliary power unit which provides turbine power to operate hydraulic pumps for the TVC servo actuators. The actuators mechanically position the solid rocket nozzle to steer the vehicle to the correct trajectory. While this approach has been used successfully with a high reliability, NASA is interested in pursuing a less toxic, electric power approach that offers lower cost and improved operability. Figure 1 depicts the overall architecture associated with the EHA system and the interfaces with a launch vehicle. The Flight Control Computer (FCC) communicates via the 1553 data bus to the Booster Control Unit (BCU) to command the Motor Control Unit (MCU). The MCU provides the necessary position and torque values to the electric motor to drive the hydraulic pump and ultimately drive the actuator which directs the thrust from the launch vehicle to obtain the proper yaw and pitch trajectory. The electrical energy necessary to power the EHA is derived from the high voltage battery system. The selection of the appropriate 270 V battery Line Replaceable Unit (LRU) is the focus of this paper. Ground Support Equipment (GSE) interfaces to the battery to provide state-of-health monitoring, proper temperature control, and power to recharge the batteries. The current TVC architecture was based upon the following assumptions:  4 battery channels in parallel  4 Motor Control Units  2 TVC actuators each with a dual redundant internal design  The 4 batteries are each tied to a single motor control unit. Each motor control unit provides input power to one channel of each actuator. Battery requirements:  The maximum power output of the actuators is expected to be 57 horsepower (hp). This corresponds to a 92 hp maximum output of the electric motors. Using a 70 percent efficiency of all components back to the battery, this is equates to a 100 kW output requirement at the batteries. Two batteries summed together must supply this power.  Each battery should be designed for 270 +80/–30 VDC nominal operating range.  Total energy requirement is 5110 hp-sec (1058 Wh) at the electric motor for two batteries based on mission duty cycle.  5110 hp-sec energy with a 70 percent power management and distribution efficiency yields 7300 hp-sec (1512 Whr).  Two fault tolerant battery systems imply two batteries must supply the total energy demand.  Each battery is therefore required to deliver 3650 hp-sec or 756 Whr.