Existing launch vehicles utilize hydraulic systems for thrust vector control (TVC) gimbaling of engines and aerosurface control. These systems, as in the case of the Space Shuttle and its Solid Rocket Boosters (SRBs), have performed successfully in flight. They do, however, have high pre-flight operation, maintenance, and refurbishment costs. The next generation of launch vehicles propose to use electromechanical actuators (EMA's) for engine gimbaling and aerosurface control to eliminate hydraulics and its associated systems and problems.The new actuation systems are not without their own challenges, with the power source being one of the largest. The power demands for electromechanical actuation can be met by existing battery technology, however, it is done so with a significant weight penalty. An EMA's duty cycle has two components: a high power pulse to initiate and perform the actuation, and a nominal load to maintain position. Conventional batteries must be sized (Amp-hour rating) to meet the pulse power requirement while maintaining a bus voltage in range to satisfy the needs of the EMA control electronics, and therein lies the problem. Restricting the voltage sag limits the discharge rate (C rate) of the battery and therefore requires an increase in the Amp-hour rating, which relates directly to an increase in weight.An option to lower power source weight is a hybrid source consisting of a conventional battery and a capacitor bank. A hybrid source of this type would utilize the power density strengths of a capacitor bank to meet thehigh power pulse demands, and the energy density strengths of a battery to provide average power and capacitor recharging, resulting in a smaller, lighter, and more efficient power source.Testing has been performed at NASA's Marshall Space Flight Center (MSFC) with support from Auburn University's Space Power Institute to investigate the validity of the hybrid power source concept. This proof-of-concept testing used chemical double layer (CDL) capacitor technology in the form of a ≈5 farad - 270 volt capacitor bank, standard deep cycle marine lead-acid batteries, and a 25 horse power EMA developed at MSFC. The test data was used to size a flight type silver-zinc (Ag-Zn) battery to perform the same task in a battery only configuration, and also size a battery for a hybrid configuration.Test results and analysis show that a greater than 50% weight savings can be realized by utilizing this type of hybrid power source configuration with no negative effect on performance. These positive results support the need for further development in the area of CDL capacitors and hybrid configurations to meet the needs of the next generation launch vehicles' electromechanical actuators.
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