http://www.aviationnow.com/publication/awst/loggedin/AvnowStoryDisplay.do?pubKey=awst&issueDate=2005-02-14&story=xml/awst_xml/2005/02/14/AW_02_14_2005_p66-01.xml&headline=Rocketdyne+Tests+High-Performance+Thruster+Running+on+Low+Freezing-Point+Oxidizer

Propulsion Technology

Aviation Week & Space Technology

02/14/2005, page 66

Michael A. Dornheim

Los Angeles

Engine runs on freeze-resistant oxidizer that normally rips motors apart

Rocketdyne Tests New Thruster

Boeing Rocketdyne has tested a new high-performance 1,100-lbf. rocket engine the company believes is suitable for a wide range of applications.

The Multi-Use Thruster (MUT) can burn a special storable oxidizer with a freezing point lower than that of standard nitrogen tetroxide, simplifying storage on Earth and reducing the need for tank heaters on long space flights.

The MUT demonstrated a thrust-to-weight ratio (T/W) of 290, which is the highest performance in its thrust class, says William Brown, who led the demonstration program for Rocketdyne. A much higher T/W of 600 was also demonstrated using a composite nozzle and thrust chamber, but that material is more susceptible than metal to handling damage. All these figures were produced under vacuum conditions using nozzles with a 12:1 expansion ratio. Rocketdyne didn't reveal chamber pressure, but in tests of an earlier version of the engine it was roughly 500 psi.

For rough comparison, the 1970s-vintage Marquardt R-40A bipropellant thruster used on the space shuttle reaction control system produces 870-lbf. thrust and weighs 10 kg. (22 lb.), for a T/W of 40. It operates at a much lower 150-psi. chamber pressure, and its length is several times greater than the MUT.

Rocketdyne officials believe the 1,100-lbf. thrust level fills a hole in the market. Other engines are significantly smaller or larger, says Rees W. Padfield, Rocketdyne's chief engineer for attitude control systems and propulsion programs. To match MUT thrust with another engine, either two smaller ones will have to be used, or a larger one derated, he says.

The problem with MON combustion is it reacts more strongly to resonant pressure waves in the engine and can lead to runaway combustion instability capable of ripping an engine apart in milliseconds, Brown says. "No one else has been able to make an engine work on MON-25," Padfield says. A key achievement with MUT was mitigating MON-25 combustion instability.

The tests demonstrated a vacuum specific impulse of 292 sec. with the 12:1 nozzle and burning NTO. The engine is cooled by an internal film of fuel-rich gases and by external radiation. The overall mixture ratio is fuel-rich.

Throttling was demonstrated over a range of 50-115% of the 1,100-lbf. design thrust. Efficiency drops when throttled back, but the drop was less than usual, Brown says.

THE U.S. AIR FORCE FUNDED the tests to demonstrate the capability Rocketdyne claimed as possible. That capability was met, Padfield says. The tests were run around last September at NASA's White Sands Test Facility in New Mexico. Three engines were fired: one with metal construction and one with composites--both burning NTO--and a third unit burning MON-25 made out of metal. Modular construction allowed quick development of components such as valves and injectors.

Rocketdyne developed an earlier version of the engine on company funds, addressing a need they perceived for a high-thrust divert engine for complicated boost-phase intercept of ballistic missiles (AW&ST Jan. 12, 2004, p. 44). Rocketdyne envisions the multi-use thruster in a variety of applications, including missile defense, launchers, upper stages and weapons buses, interplanetary flight and hopping from point-to-point on other bodies.

http://www.aviationnow.com/media/images/awst_images/large/AW_02_14_2005_712_L.jpg Multi-use thruster is 8.5 in. long and produced up to 1,265-lbf. thrust at White Sands Test Facility. Rings at throat and partway along nozzle are for instrumentation.

Missile defense needs quick ramp-up and very short "on" times for precise control, and the tests showed MUT could achieve 90% thrust within "milliseconds," Padfield says. The ramp-up and minimum pulse time "significantly outclass any engine this size," Brown says. The engines also fired for long durations to represent other missions, such as interplanetary course corrections.