Electronic Design

Electromechanical Actuator Reaches New Heights—Literally

A tiny part is destined to have a big effect on the space program. NASA's Marshall Space Center in Huntsville, Ala., is preparing an electromechanical actuator that's going to save time and money in designing and maintaining second-generation reusable launch vehicles (see the figure). That's because electromechanical actuators have a number of advantages over their hydraulic counterparts, which have been successfully used in rocket propulsion systems.

First, hydraulic actuators are filled with fluid, which can leak when high pressure is exerted on them. These leaks require substantial maintenance and support equipment. Technicians have to dismantle significant amounts of hardware to find and fix the leaks. They also must clean up the spill and check the remaining fluid for possible contaminants. All of this adds up to time and money that electromechanical actuators simply don't require.

Second, hydraulic systems must sustain typical hydraulic pressures between 3000 and 6000 psi in rocket engines, regardless of the demand for power. Electromechanical actuators use power only when they're needed. Third, electronic actuators weigh less than hydraulic systems. "When designing propulsion systems to leave Earth's gravity," says Charlie Nola, integrated vehicle health management and avionics subsystems manager for the space center, "anytime you can save weight you're also saving money."

The actuator was designed as part of the Second Generation Reusable Launch Vehicle Program. This project is trying to vastly improve safety and reliability while cutting the high cost of space travel from today's $10,000 per payload pound to $1000 per pound.

As part of this program, NASA's Stennis Space Center in Mississippi recently performed a series of tests on a set of engines that included these electromechanical actuators. Twin Linear Aerospike XRS-2200 engines were fired for 90 seconds, reaching a planned maximum power of 85%.

"The series of engine firings tested the actuator control system in what we call a 'real condition of use' environment," said Donald Chenevert, electromechanical actuator project manager at the Stennis Center. "Firing allows us to see how the integrated system handles the extreme cold of cryogenic propellants, the stress loads of the propellants pushing through the valves, and the dynamic response to commanded flow rate changes." According to Chenevert, all test objectives have been met.

With these results, the electromechanical actuator's future in the space program looks pretty secure. For details, go to www.msfc.nasa.gov, or to www.slinews.com.

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