In a full 500 second test firing, the J-2X engine – a key part of the evolved Space Launch System (SLS) – has been put through its paces at NASA’s Stennis Space Center (SSC). Up to three of the powerful engines will power the Upper Stage of the Heavy Lift Launch Vehicle (HLV), in configurations which includes sending humans and cargo to Mars.
There will be two major roles for SLS, one is to launch cargo and one to launch the Orion (MPCV) on Beyond Earth Orbit (BEO) missions.
The core stage is an 8.4m diameter “External Tank” heritage system, with the top converted to host the Upper Stage structure, and the aft restructured to house the Main Propulsion System (MPS) – which will drive what will initially be three – or four, based on ongoing trades – Space Shuttle Main Engines (RS-25Ds), before existing stocks are exhausted, allowing for the transition to the expendable version of the SSME, known as the RS-25E.
The core will also support two boosters, initially hosting two five segment Solid Rocket Boosters (SRBs) from ATK, with an industry competition determining the the long term design, which may result in a transition to liquid (RP-1) based boosters.
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The vehicle will initially be able to fly without the Upper Stage, and in some cases would fly with a smaller replacement in the form of a Delta IV “Kick Start” Upper Stage system.
For the massive 130mt, fully evolved, Block II SLS – which will be a natural advancement on the opening Block I and Block IA configurations – an extra 80 feet in length will provide room for the main Upper Stage, which will – as currently baselined – utilize three J-2Xs as the Earth Departure Stage (EDS).
Development of the engines – which Wednesday’s test is a major part of – and the Upper Stage stage hardware will continue alongside the SLS work, prior to being held back until the Block II is ready to fly. As NASA documentation (L2) noted: “Complete J-2X and put ‘on the shelf’ for later use with SLS Block II. Move Integrated Stack avionics to this stage. This Upper Stage burns out prior to orbit insertion (ala Saturn V).”
The J-2X engine is being developed for the Marshall Space Flight Center (MSFC) SLS Program by Pratt & Whitney Rocketdyne of Canoga Park, California – who are also the manufacturer for the RS-25s.
Initially starting life for a role as a single engine on the Ares I Upper Stage, work began on the engine in 2006, based on engineering which reached back as far as the 1960s with the original J-2 engine – five of which powered the SII Second Stage of the Saturn V.
This latest variant is capable of generating 294,000 lbf (1,310 kN) of thrust, and is being tested at the new A2 test stand at Stennis Space Center. Testing began with P&W Rocketdyne successfully evaluating the initial J-2X gas generator design in 2008, followed by the completion of a second round of successful gas generator tests in 2010.
On June 11, the J-2X Development Engine E10001 was lifted into position using the Vertical Engine Installer (VEI) and successfully installed into the A-2 test stand at Stennis Space Center. This installation followed a close call that occurred on June 1, when the extended hydraulic cylinder on the VEI retracted unexpectedly, causing a sudden one-foot descent of the engine and its VEI mounting plate.
After the hardware was checked, a July 14 “burp” test – as it was called – of engine E10001 briefly produced 30,000 pounds of thrust, during a combined chill test and 1.9-second ignition test.
The second test firing of J-2X development engine E10001 occurred on July 26. The planned duration of the firing was to be seven seconds. However, the test was shutdown after 3.72 seconds due to a high pressure measurements in the main combustion chamber.
On August 17, the J-2X team conducted test A2J005. The test was terminated early (32.2 seconds of a planned 50-second run) for high thrust because the gas generator oxidizer orifice discharge coefficient was slightly larger than predicted. Valuable thrust balance data was obtained which allowed the team to make the necessary modifications. However, the outcome was a decision to remove the engine from the test stand.
“The decision was made by the J2X Project to pull engine 10001 from the test stand at Stennis Space Center after the engine hotfire on August 17th due to cracks noted in the Main Oxidizer Valve (MOV) seal in several places,” noted an update from the L2 J-2X Status Updates.
“There was also a piece of seal estimated at 0.75” to 1” long that was missing. Additional borescope inspections revealed a single piece of FOD (Foreign Object Debris) inside the ball shaft. MOV and MOV actuator removal is now complete. Failure investigation and anomaly resolution continues.”
With a new MOV assembled and acceptance tested, the J-2X engine was returned to the A-2 test stand, ahead of another hot-fire test on September 28, which conducted the pre-planned 40 second firing.
On October 25, a full 500 second test was planned, known as Hotfire Test 7. However, this test was halted after 140 seconds into the firing.
“The test, scheduled for 500 seconds duration, was prematurely stopped at 140 seconds due to a TCON (test controller) redline limit violation. Initial investigation indicated that the early termination was caused by a pump discharge pressure redline violation,” added the J-2X Updates.
“Additional evaluation revealed that the minimum redline limit, which was activated specifically for this test at engine start plus 140 seconds to guard against pump cavitations, was inadvertently set in the TCON software as a maximum (instead of a minimum). No hardware damage was noted. Preliminary results indicate that the primary objectives (i.e. flow meter and engine calibration at mainstage power level) of the test were achieved.
“A corrective action team has been formed and will work to determine root cause and corrective action prior to the next hotfire that is tentatively scheduled for November 9th.”
Once again, the experienced teams of Stennis showed their value, successfully working the data in readiness for Wednesday’s live firing, which lasted for the full duration of 499.7 seconds, followed by managers noting the quick look data appears to be good.
“The J-2X engine team and the SLS program as a whole are extremely happy that we accomplished a good, safe and successful test today,” said Mike Kynard, Space Launch System Engines Element Manager at MSFC. “This engine test firing gives us critical data to move forward in the engine’s development.”
“The J-2X engine is critical to the development of the Space Launch System,” added Dan Dumbacher, NASA’s deputy associate administrator for exploration systems development, said after the test at NASA’s Stennis Space Center in Mississippi. “Today’s test means NASA is moving closer to developing the rocket it needs if humans are to explore beyond low-Earth orbit.”
E10001 is one of five development engines, which will provide the data for two certification engines, prior to the move to actual flight engines which will ride with SLS. Managers noted that – for this class of engine – this is the least number of units used to test and develop towards the flight-ready engine.
“Today we made smoke and fire with a rocket engine yet again. The Stennis Space Center in Mississippi, long the front line in testing NASA’s propulsion systems from the Apollo to the shuttle era, is now helping us understand the J-2X engine. The J-2X will power the upper stage of our new Space Launch System (SLS), which will carry the Orion spacecraft, its crew, cargo, equipment and science experiments beyond Earth orbit,” added NASA Administrator Charlie Bolden.
“Today’s engine test fire – at nearly 500 seconds, the longest one to date – is one in a series of tests that will provide critical data to help fine tune the engine to maximize performance and provide the SLS with the capability to take humans to new destinations. And it’s not the only activity that NASA has going on around the nation as we open the next great chapter of space exploration.”
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