COLORADO SPRINGS, Colo. — With a large inventory of upper-stage engines for the Delta 4 rocket on hand, propulsion provider Pratt & Whitney Rocketdyne plans to convert some of that hardware for use aboard the Atlas 5 vehicle, company officials said.

Canoga Park, Calif.-based Pratt & Whitney Rocketdyne builds different versions of the RL10 upper-stage engine for the Delta 4 and Atlas 5, the workhorse launch vehicles of the U.S. Department of Defense. Both rockets, developed and funded under the U.S. Air Force’s Evolved Expendable Launch Vehicle (EELV) program, are built and operated by United Launch Alliance of Denver, a Boeing-Lockheed Martin joint venture.

In a press briefing here April 11, just prior to the start of the National Space Symposium, Steven A. Bouley, vice president of launch vehicle and hypersonic systems at Pratt & Whitney Rocketdyne, said the company recently received an order for 12 RL10A engines, the variant used on the Atlas 5, and anticipates an order for another five. Those could be the last of that variant built as Pratt & Whitney moves toward an RL10 variant that can be used on both the Atlas 5 and Delta 4.

ULA has been faced with higher-than-expected manufacturing costs on Atlas 5 and Delta 4, in part because of relatively low production rates but also because the end of the space shuttle program has forced up the cost of the RL10. Pratt & Whitney builds the space shuttle main engine, and with that program going away, the RL10 production program must bear a much higher portion of the company’s overhead costs. Moving to a common RL10 variant for both Atlas 5 and Delta 4 is seen as one way to drive down EELV program costs.

The Delta 4 and Atlas 5 were developed separately by Boeing and Lockheed Martin, respectively, during an earlier phase of the EELV program, when the commercial satellite market was expected to drive heavy demand for both vehicles. Boeing and Lockheed Martin were permitted to create ULA to merge their rocket manufacturing programs after it became clear that U.S. government market alone was not enough to sustain their respective rocket production lines.

Pratt & Whitney Rocketdyne has an excess inventory of RL10B engines, the variant used on Delta 4, because Boeing originally placed a large order of components for that system in anticipation of higher demand, Bouley said. That order has since been reduced, but there is still a large inventory on hand and some of those engines will be converted to the RL10C variant for use on the Atlas 5.

One of the key changes will be on the engine nozzle extension, a carbon-carbon composite structure that on the RL10B consists of three segments. For the RL10C, the nozzle extension will be reduced to just one segment, Bouley said.

The RL10C conversion program is funded under a line item in the Air Force budget request, and a critical design review — during which the design of a system is finalized — of the modified engine is scheduled for the week of April 18, Bouley said. Although the ultimate goal is to get down to a single RL10 variant, Pratt & Whitney Rocketdyne officials stressed that once converted to the RL10C variant, an engine cannot be used on the Delta 4.

Pratt & Whitney Rocketdyne hopes to complete qualification testing of the RL10C in 2012 or 2013, Bouley said. He said he did not know when the engine might make its first flight aboard an Atlas 5.



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