New electronics technology is proving to be advantageous for the main
propulsion system planned for a second generation reusable launch vehicle.

The technology is the electro-mechanical actuator – an electronic system
that provides the force needed to move valves which control the flow of
propellant to the engine.

Hydraulic actuators have been used successfully in rocket propulsion
systems. However, when high pressure is exerted on such a fluid-filled
hydraulic system, it can leak.

“Electro-mechanical actuators are proving to be low maintenance, which can
translate into savings of time and money,” said Charlie Nola, integrated
vehicle health management and avionics subsystem manager for the Propulsion
Projects Office of the Second Generation Reusable Launch Vehicle Program at
NASA’s Marshall Space Flight Center in Huntsville, Ala.

“The electronic controller is a separate unit powering the actuator. Each
actuator has its own control box. So if we detect a problem in a controller,
we simply replace that one unit,” said Nola. “The control boxes are located
in an easy-to-reach area, so maintenance becomes a simple step performed
without dismantling the propulsion system or replacing the actuator.”

By comparison, hydraulic systems require significant maintenance and support
equipment. If a leak occurs, technicians must dismantle a significant amount
of hardware to find and fix the leak, as well as clean up the spill and
check the remaining fluid for possible contaminants that could hinder

Hydraulic systems also must sustain significant hydraulic pressures –
typically in the range of 3,000 to 6,000 pounds per square inch (210.9 to
421.8 kilograms per square centimeter) in rocket engines – regardless of
demand. Electro-mechanical actuators utilize power only when needed.

“The electronic actuator system also weighs less than a hydraulic system,”
said Nola. “When designing propulsion systems to leave Earth’s gravity,
anytime you can save weight you’re also saving money.”

The Second Generation Reusable Launch Vehicle Program goal is to
substantially improve safety and reliability while reducing the high cost of
space travel from today’s $10,000 per payload pound to $1,000 per pound.
Efforts are under way at every NASA Center to improve and develop all the
technologies required for future spacecraft.

A series of tests was recently performed on a set of linear aerospike
engines at NASA’s Stennis Space Center, Miss., to gather more data about
electro-mechanical actuators. Additional information about those tests, and
about the Second Generation Reusable Launch Vehicle Program, is available on
the Internet at: