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NASA drops Ares I upper stage engine

NASA has stopped developing the 274,000lb-thrust (1,220kN) J-2XD engine version for its Ares I crew launch vehicle (CLV) and will use its 294,000lb-thrust J-2X powerplant for the CLV and the Ares V cargo launch vehicle upper stages.

The liquid-oxygen, liquid-hydrogen-fuelled J-2X, named after the Apollo programme upper-stage J-2 engine, will start 133s into the flight at an altitude of 194,000ft (59,000m) and will have a mass of about 2,450kg (5,400lb). Every element of the original powerplant's design will be altered to achieve the higher Ares launchers' thrust needs.

To ensure the required 448s specific impulse, the engine will also use a version of the NASA/Lockheed Martin X-33 advanced technology demonstrator's J-2S engine's turbopump. That will be tested in October as part of the J-2X powerpack at NASA's Stennis Space Center. Flight revealed this parallel development last year and now only the J-2X will be available from 2013.

As well as a larger nozzle extension, the J-2X will have to use new materials because the J-2 used out-of-date aluminium alloys, its thermal protection system is no longer available, and other components have since been outlawed by the US Environmental Protection Agency.

More up-to-date manufacturing technologies will also be employed, including the hot isostatic pressing bonding method used to produce the Pratt & Whitney Rocketdyne RS-68 engine's milled channel combustion chamber.

The current J-2X preliminary design review will also decide whether the engine faces 280 or 220 tests.

"We had looked at the 274,000lb engine during development...we decided to upgrade when we saw we could do that," says NASA Marshall Spaceflight Centre-based Exploration Launch Projects Office manager, Steve Cook.

Despite the adoption of the Ares V engine for the CLV, the J-2X requirements still include the ability to provide a circularisation burn and to cope with a cold soak of up to 95 days in low-Earth orbit. Cook expects to verify those in 2012-13.

The need for a cold soak-capable Ares I J-2X engine seemed to confirm information obtained by Flight that the agency had considered shifting the Orion crew exploration vehicle's service module propulsion functions to the Ares I upper stage - it would be left attached while Orion was at the International Space Station.

This information had been corroborated by a NASA foam debris reduction report passed to Flight, which says that the Ares I's upper-stage insulation would have to operate for more than 90 days in orbit and that the vacuum environment would see small foam pieces liberated.

But Cook denies that any such Orion ISS flight study, using the upper stage, had taken place.

On 17 July, NASA announced its award to P&WR of the $1.2 billion J-2X design, development, testing and evaluation contract that will run to 31 December 2012. The $1.2 billion includes payment for work done since the June 2006 preliminary letter contract and requires eight engines to be supplied.

One will be a flight model, another will be an engineering model for the main propulsion test article, and the other six will be for ground testing. The first ground test is planned for March 2010. The US agency expects to award the Ares I upper-stage production contract next month.

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