Testing is due to get under way this fall on the RS-68A, an upgraded version of the cryogenic engine that powers United Launch Alliance‘s Delta 4 rocket.


Pratt & Whitney Rocketdyne is two years into the upgrade effort, which aims to boost the engine’s thrust and specific impulse to support the future launch needs of the U.S. Air Force and the National Reconnaissance Office.

The RS-68 is the largest liquid oxygen-liquid hydrogen booster in existence, currently capable of producing 663,000 pounds of thrust at sea level at 102 percent power. The space shuttle main engine, another Pratt & Whitney Rocketdyne product, produces only 418,000 pounds of thrust under comparable conditions.


upgrade effort, funded under a United Launch Alliance contract, is aimed at increasing the RS-68’s power level by six percentage points to 108 percent from the current 102 percent and making main injector changes to increase the engine’s specific impulse – a measure of the engine’s efficiency – to at least 414.2 seconds from the current 407.7 seconds.


NASA intends to use a variant of the upgraded RS-68A engines in clusters of five to power the main stage of its proposed Ares 5 heavy-lift rocket. Among some of the changes NASA wants Pratt & Whitney Rocketdyne to make to the engine are designing a different ablative nozzle to accommodate a longer burn, and shortening the engine’s start sequence. NASA also wants Pratt & Whitney Rocketdyne engineers to make hardware changes aimed at reducing the size of the fireball the engine produces at ignition. NASA also would like to see the RS-68 consume less helium during countdown and flight.


NASA has said it expects to pay around $20 million per copy for the upgraded engine, making it the cheaper alternative to the space shuttle main engine that had been the agency’s initial choice for the Ares 5 main stage.

Ron Ramos, director of expendable propulsion programs at Pratt & Whitney Rocketdyne, said during an interview at the National Space Symposium here April 10 that the company is two years into the RS-68 upgrade effort, which it is doing under the direct guidance of Denver-based United Launch Alliance. Development and certification testing is due to get under way this September at NASA’s Stennis Space Center in Mississippi.


Ramos said Pratt & Whitney Rocketdyne currently is on schedule to deliver the first RS-68A engines in 2010. “Typically, 18 months after that, they’d be ready to fly,” he said.

Although NASA and the Air Force agreed within the past year to cooperate on the RS-68 upgrades, work on the RS-68B is on hold until the space shuttle retires. Ramos said Pratt & Whitney Rocketdyne has been told to expect the funding to start to flow in fiscal 2011, the first year NASA’s budget includes significant money for the Ares 5 rocket.


In the meantime, Pratt & Whitney Rocketdyne is busy developing the J-2X engine NASA has chosen to power the Ares 1 upper stage and the Ares 5 Earth-departure stage. NASA officials readily acknowledge that the J-2X is smack in the middle of the critical path to the first flight of the Orion Crew Exploration Vehicle and its Ares 1 launcher.


That fact has caused the U.S. Government Accountability Office, the investigative arm of Congress, to question the technical feasibility of fielding Ares 1 as much as 18 months sooner than its planned March 2015 debut, something NASA has said it could do for an additional $2 billion.


In a report presented April 3 to the House Science and
Technology Committee, Cristina T. Chaplain, the Government Accountability Office’s (GAO) director of acquisition and sourcing management, expressed skepticism that the
J-2X development could be complete within seven years, noting that the space shuttle main engine took nine years to develop.


“Further, NASA anticipates that the J-2X engine is likely to require 29 rework cycles to correct problems identified during testing,” the report said. “Given the linear nature of a traditional test-analyze-fix-test cycle, even large funding increases offer no guarantee of program acceleration, particularly when the current schedule is already compressed and existing NASA test facilities are already maximized.”


Ramos acknowledged the GAO’s concern, but pointed out that it took Pratt & Whitney Rocketyne just five years to develop the RS-68, an effort that entailed 55 rework cycles.