Optimum Design of a Fault Tolerant Linear Electromechanical Actuator for the Lower Stage Thrust Vector Control of a Satellite Launch

This paper summarizes the design and development of a fault tolerant linear electromechanical actuator for the lower stage thrust vector control of a satellite launch vehicle. Power electronics and electric machine technologies have evolved to the point that high-power electromechanical actuators present a viable alternative in applications historically served by hydraulic devices. In selecting control actuators for thrust vector control (TVC) application of a satellite launch vehicle, there is a critical need to reduce the weight and size while providing better reliability. By incorporating functional redundancy, the actuator can tolerate up to two failures in its critical components. The direct connection of motors to the movable nozzle without any mechanical coupling or gears helps to attain a remarkable level of reliability, efficiency and backlash free performance of the actuators. The actuator is configured using a brushless DC motor with quadruplex sets of windings and triplex sets of hall sensors. The triplex ratiometric LVDT having three independent sets of windings and probes are used for position feedback. Rollerscrews are used to convert the rotary motion to linear. A unified design methodology is followed so as to use this high power electromechanical Actuator in the lower stages of ISRO’s launch vehicles, GSLV, PSLV and the new generation vehicle LVM3. Two actuators are required its second stage liquid engine and four actuators for the liquid stage boosters. This paper discusses on the mechanical configuration of the actuator, optimum design of power plant, fault tolerance capability, criteria of selection of the critical components and the qualification tests that the actuator needs to undergo before flight acceptance. The first and second stages of the launch vehicle are denoted as stage-1 and stage-2.