* RS-68 is the initial engine version.

This contract modification will authorize Boeing to perform demonstration testing on a rebuilt RS-68 engine.

RS-68 being tested at NASA's Stennis Space Center.

Because of the trade-off, NASA would save an estimated USD $ 35 million by using simplified, higher thrust RS-68 engines ( reconfigured to fire and perform like the SSME ), while at the same time, eliminate the costly tests needed for an air-startable SSME for the Ares I ( as the J-2X and its predecessor were designed to be started in both mid-air and in a near vacuum ).

The RS-68 was developed at Rocketdyne Propulsion and Power, located in Canoga Park, Los Angeles, California, to power the Delta IV Evolved Expendable Launch Vehicle ( EELV ).

The RS-68A is an updated version of the RS-68, with changes to provide increased specific impulse and thrust ( to over at sea level ).

The modifications to the RS-68 for the Ares V include a different ablative nozzle to accommodate a longer burn, a shorter start sequence, hardware changes to limit free hydrogen at ignition, and changes to reduce helium use during countdown and flight.

NASA states several changes are needed to human-rate the RS-68, including health monitoring, removal of fuel-rich environment at liftoff, and improved subsystems robustness.

The Ares V will use stretched five or " five-point-five "- segment versions of the SRBs ; a new, larger tank using Shuttle External Tank construction and insulation technology ; and newer, cheaper expendable rocket engines ( the Pratt & Whitney Rocketdyne RS-68 engine, identical to those used on the Delta IV EELV ) located at the base of the new tank.

The in-line option originally featured five throw-away versions of the SSMEs on the core stage, but was changed later to five RS-68 rocket engines ( currently in use on the Delta IV rocket ), with higher thrust and lower costs, which required a slight increase in the overall diameter of the core.

Their Delta IV family of launch vehicles relies on a new core rocket engine technology called RS-68.

The Ares V design incorporated six RS-68 engines with assistance from a pair of 5. 5-segment SRBs.

Five Space Shuttle Main Engines ( SSME ) were originally planned for the Ares V, but the RS-68 engines are more powerful and less complex and therefore less expensive than the SSMEs.

After the change only the Delta IV's RS-68 engine was considered by NASA for the new cryogenically fueled Ares V rocket.

The Ares V first stage, which will be fitted with five RS-68 rocket engines ( the same engine used on the Delta IV rocket ), will be in diameter, as wide as the S-IC and S-II stages on the Saturn V rocket.

As originally envisioned, both the Ares I and Ares V would have used a modified " throw away " version of the SSME, but in due course, because of the need to keep R & D costs down and to maintain a schedule set by NASA Administration Michael D. Griffin to launch the Ares and Orion by 2011, NASA decided to switch to the RS-68 engine for the Ares V and to an uprated J-2 engine for the Ares I.

Because of the switch to the RS-68, the Ares V was widened from to accommodate the extra propellants, while the Ares I was reconfigured to incorporate a fifth solid-rocket segment as the J-2X, as the rocket engine is known, has less thrust than the SSME.

The engine has three versions: the original RS-68, the improved RS-68A, and the RS-68B for NASA.

The RS-68 is gimbaled hydraulically and is capable of throttling between 58 % and 101 % thrust.

A leading goal of the RS-68 program was to produce a simple engine that would be cost-effective when jettisoned after a single launch.

The benefit of the RS-68 is its reduced construction cost: To build an RS-68 for the Boeing Delta IV program costs about $ 14 million, compared to $ 50 million for the SSME.

While the SSME's higher costs were designed to be spread across multiple launches, the larger, less-costly, more powerful ( 50 % more thrust ) RS-68 was a more cost-effective engine for an expendable launch vehicle.

The RS-68 was certified for use on Delta IV in December 2001.

The RS-68 is part of the Common Booster Core ( CBC ) used to create the five variants of the Delta IV family of launch vehicles.

NASA chose the RS-68 because of its lower cost, about $ 20 million per engine after NASA upgrades.

Later the Ares V was changed to use six RS-68 engines.

The DIRECT alternative launch project included two or three RS-68 engines in " version 2. 0 " of the team's proposal, but switched to the Space Shuttle Main Engine ( SSME ) for " version 3. 0 ".

To achieve this, the RS-68 has 80 % fewer parts than the multi-launch Space Shuttle Main Engine ( SSME ).

The government has authorized work under the Assured Access to Space initiative to develop hardware that will reduce or eliminate these risks and increase the reliability of the RS-68 engine.

Other communities -- the ones to be aided most by the Senate bill -- have had difficulty starting such stations because of the high initial cost of equipment.

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In Goidelic languages the word was borrowed before these languages had re-developed the / p / sound and as a result the initial / p / was replaced with / k /.

Moderate Catholics felt that he had been a leading figure in attempts to reform the Church, while Protestants recognized his initial support for Luther's ideas and the groundwork he laid for the future Reformation.

Eusebius ' description of his own method —" I shall collect the entries from the whole of the divinely inspired Scriptures, and I shall set them out grouped by their initial letters so that one may easily perceive what lies scattered throughout the text "— implies that he had no similar type of book to work from ; his work was entirely original, based only on the text of the Bible.

" While there were some initial suspicions that she had been faking amnesia, some experts have come to believe that she genuinely suffered a protracted fugue state.

In April 2011, officials from Hamas and Fatah announced that both parties had reached an initial deal to unify into one government, with plans for elections to be held in 2012.