A micro-thruster array measuring one-quarter the size of a penny, designed by a TRW-led team for use on micro-, nano- and pico-satellites, has successfully demonstrated its functionality in a live fire test aboard a Scorpius sub-orbital sounding rocket.

Individual micro-electromechanical system (MEMS) thrusters, each a poppy seed-sized cell fueled with lead styphnate propellant, fired more than 20 times at 1-second intervals during the test staged at the White Sands Missile Range. Each thruster delivered 10(-4) Newton seconds of impulse.

Photo shows the size of TRW's prototype digital propulsion micro-thruster relative to a penny. The micro-thruster consists of a three-layer sandwich of silicon and glass; the gold-color squares are the silicon nitride rupture diaphragms at the bottom of diverging nozzles. A layer containing cylindrical chambers filled with lead styphnate is bonded to the underside of the diaphragm layer. The bottom layer contains polysilicon resistors that initiate combustion of the fuel. The prototype micro-thruster shown in this photo contains 15 individual thrusters in the central three-by-five array. Photo: TRW

"The test proves the technology behind this micro-thruster is well along in its development," said David H. Lewis Jr., TRW's MEMS Digital Micro-Propulsion project manager. "We're very pleased with its performance at White Sands. We believe micro-thrusters have the potential to provide on-orbit propulsion for station keeping, orbital correction and attitude control for future, very small satellites weighing from less than a pound to as much as 50 pounds."

The MEMS design, based on silicon chip fabrication technology, offers several advantages over conventional thrusters: It has no moving parts, utilizes a variety of propellants, is scalable, eliminates the need for tanks, fuel lines and valves, and fully integrates the structure of the satellite with the propulsion to power it. The micro-thruster is being developed by TRW and teammates Caltech and the Aerospace Corp. under a contract from the Defense Advanced Research Projects Agency.

The MEMS micro-thruster arrays are fabricated as a three-layer silicon and glass sandwich, with the middle layer consisting of multiple small propellant cells sealed with a rupturable diaphragm on one side and an ignitor on the other. Each cell is a separate thruster, and when ignited, delivers one impulse bit. Delivering propulsion in discrete increments by igniting thrusters in controlled sequences has lent the technology the name "digital propulsion."

TRW Space & Electronics builds communications, scientific and defense spacecraft for military, civil and commercial customers; produces, integrates and tests payloads; develops advanced space instruments; and integrates experiments into spacecraft. It is an operating unit of TRW Inc., which provides advanced technology products and services for global automotive, aerospace, telecommunications and information systems markets.