Boeing Frontiers
March 2003
Volume 01, Issue 10
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Tech Talk

RS-84 forging a new direction


An artist's rendering of the RS-84A new reusable propulsion system is taking shape as a candidate for the next-generation rocket engine.

Designated the RS-84, the power plant is under development at Canoga Park, Calif.-based Rocketdyne Propulsion and Power, a business unit of Boeing Integrated Defense Systems' Launch and Satellite Systems.

"The biggest thing about the RS-84 is that it represents a true second-generation reusable engine," explained Program Manager John Vilja. "We can benefit directly from what we've done in the past in propulsion systems, while also taking advantage of emerging technologies to shape this as an engine for the future. NASA recognized that there was a need for this all along and has been working toward this for awhile."

The RS-84 will yield more than one million pounds of thrust and a specific impulse of 335 seconds in vacuum. It's on the drawing board as part of NASA's recently re-baselined Space Launch Initiative to identify and develop new technologies for advanced space flight.

Space Launch Initiative underwent a restructuring late last year as part of NASA's overarching blueprint called the Integrated Space Transportation Plan. The RS-84 now falls under the Next Generation Launch Technology program, which looks far into the future of space flight by investing in key technology areas such as airframe structures and propulsion.

The RS-84 is revolutionary in the United States, in that its propulsion relies on gaseous oxygen to drive the engine's turbo pumps (see "RS-84 explained" below).

The engine design also takes advantage of an Advanced Health Monitoring System, which monitors how well the engine is operating as it runs and can provide maintenance data before the vehicle lands.

"Computing technology has made huge leaps and bounds that allow us to incorporate these capabilities," Vilja said.

Finally, Rocketdyne is tapping into the huge wealth of experience that it has accumulated over the years from its work on other hydrocarbon-fueled engines such as the Delta RS-27 and Atlas MA-5A series, more recent efforts including the X-33 Aerospike, RS-68 and Integrated Powerhead Demonstration power plants, as well as the only other reusable rocket engine ever built, the Space Shuttle Main Engine.

Component testing on the RS-84 is under way and subscale testing will follow this summer at NASA's Stennis Space Center in Mississippi, where Boeing is the testing contractor. Major milestones for the RS-84 included a System Definition Review in February, which is like a status check of the overall concept with the NASA customer. The Preliminary Design Review follows in June, and at this juncture NASA will determine whether to proceed with the detailed design phase.

"We're aiming for a high degree of reliability and a low degree of cost with this new engine," Vilja said.

RS-84 explained

The RS-84 represents a new direction in propulsion for the United States, in that it uses gaseous oxygen—which also functions as the combustion oxidizer—to drive the engine's twin turbo pumps rather than kerosene (a hydrocarbon fuel) or liquid hydrogen, as is the case with other engines Rocketdyne has developed over the years. This creates what engineers call a gaseous oxidizer-rich environment.

Some Russian engines have traditionally operated as gaseous oxygen-rich, but the RS-84's reusability is just one of several significant differences between it and the Russian engines. The Russians have traditionally relied on coatings to protect metals from the harsh oxidizer-rich gases the combustion process generates.

Boeing is using newly developed proprietary metals that are immune to this demanding environment and don't require a coating.

Rocketdyne also elected to go with a single pre-burner, two turbo-pump configuration rather than the single pump, which is the Russian precedent.

"The result was pumps that were lighter, smaller and easier to handle," Program Manager John Vilja explained.


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