U.S. Air Force Ponders New Upper-stage Rocket Engine

WASHINGTON — The U.S. Air Force is beginning to weigh options for developing a more capable and affordable upper-stage engine for the Atlas 5 and Delta 4 rockets the service uses to launch most national security payloads.

The Air Force Space and Missile Systems Center in Los Angeles is giving industry until Nov. 9 to submit ideas for building a next-generation upper-stage engine to replace by 2017 the two versions of the RL-10 engine Pratt & Whitney Rocketdyne builds for the Atlas 5 and Delta 4. A formal request for information the Air Force posted Sept. 27 on the Federal Business Opportunities website has garnered the attention of Pratt & Whitney Rocketdyne and its rival Aerojet, the other main U.S. producer of liquid-fueled rocket engines.

Originally developed under the Air Force’s Evolved Expendable Launch Vehicle (EELV) program as competing rockets, the Atlas 5 and Delta 4 are operated today by United Launch Alliance of Denver, a Boeing-Lockheed Martin joint venture. The rockets use slightly different versions of the liquid hydrogen-fueled RL-10 engine to power their upper stage. While the engine has evolved over the years, Pratt & Whitney Rocketdyne officials say engineers are reaching the limit of additional improvements that can be squeezed out of the 50-year-old engine design.

The Air Force plans to continue to rely heavily on the EELV rockets until at least 2030, and the service wants to have a new upper-stage engine produced and qualified by 2017 that uses the same cryogenic fuel as the RL-10, according to the Sept. 27 posting. The proposed next-generation engine “would use modern design and manufacturing methods. It is expected that the new engine will demonstrate state-of-the-art operating margin and reliability and minimize life-cycle costs,” the posting said.

The RL-10A-4-2 engine used in the Atlas 5 vehicle’s upper stage is more capable than its Delta 4 counterpart, the RL-10B-2 variant. The Atlas variant produces 24,750 pounds of thrust and has a specific impulse — a measure of the engine’s efficiency — of 465.5 seconds. The Air Force would like the next-generation engine to be as efficient as the current Atlas design and produce between 25,000 pounds and 35,000 pounds of thrust, the posting said.

Canoga Park, Calif.-based Pratt & Whitney Rocketdyne has encouraged the Air Force to invest in new engine development as a way to drive down the ever-increasing costs of the EELV program.

“We certainly have been advocating the need to go to a next-generation engine, not because we believe the RL-10 is necessarily a bad engine — it has a tremendous demonstrated reliability and has flown more than 500 times — but it’s based on technology that was formed in the late ’50s and early ’60s,” said Steve Bouley, Pratt & Whitney Rocketdyne’s vice president for launch vehicles and hypersonic systems.

“We see an advantage in making an investment now to go to a next-generation engine and leverage the ability to have the same kind of reliability and performance as a minimum and reduce the cost, improve the manufacturability and leverage the history of the RL-10,” he said.

Pratt & Whitney Rocketdyne in recent years has invested some $40 million in new technologies such as turbo pumps and new engine chamber and ejector designs, and it has presented the Air Force with a roadmap for moving to a next-generation engine design, Bouley said.

The other primary U.S. developer of liquid-fueled rocket engines, Aerojet of Sacramento, Calif., also plans to respond to the Air Force’s request for information.

“We’re pleased that advanced capabilities are being evaluated,” said Julie Van Kleeck, Aerojet’s vice president for space and launch systems. “We think anything to further the U.S. propulsion capability in terms of using modern manufacturing processes is a positive.”

More than improved performance, Van Kleeck believes the Air Force is most interested in developing an engine that will be more affordable while retaining the same level of reliability as the current designs.

“One of the things that is pretty clear within the industry is affordability is what we will all be living with and having to treat as the key criteria for any decisions that get made going forward,” she said. “As a company, we’ve been working on our competitiveness and affordability for quite some time, leaning out the operation and reducing the footprint, and so on. … We think there are some advances in technology that can improve the affordability and robustness in this product.”

Pratt & Whitney Rocketdyne and Aerojet face a measure of business uncertainty because both are developing propulsion systems for NASA’s Constellation program, which the White House is trying to cancel. Pratt & Whitney Rocketdyne, for example, has been developing the J2-X engines that would power the upper stages of the Ares 1 and Ares 5 rockets, and Aerojet has been developing multiple propulsion systems for the Orion crew capsule and escape system.

Air Force spokeswoman LaGina Jackson was unable by press time to provide further schedule and funding details related to the next-generation engine efforts.