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AJ-26 Engine for future Antares Launch fails during Testing
May 23, 2014
An Aerojet Rocketdyne AJ-26 engine assigned to a future Antares launch to the International Space Station failed on Thursday during a test firing at NASA’s Stennis Space Center in Mississippi. The failure is currently under investigation and potential impacts are being assessed.
The AJ-26 engine that was being test-fired on Thursday as part of a standard acceptance firing was planned to fly in 2015 aboard Orbital Sciences’s Antares launch vehicle, lofting a Cygnus spacecraft to orbit for a resupply mission to the Space Station. Aerojet Rocketdyne confirmed that there were no injuries from Thursday’s mishap and that an investigation into the failure was being started. Unknown at this time is whether the engine failure will impact the next launch of Antares that is currently planned for June 10. The AJ-26 engine is a modified NK-33 engine – built by the Kuznetsov Design Bureau for the Soviet N1 Moon Rocket in the 1960s and 70s and imported into the United States by Aerojet in the 1990s. NK-33 has been derived from the NK-15 engine that was used on the ill-fated N1 moon rocket. The four N1 flights that took place from 1969 to 1972 used the NK-15 while later flights were planned to use the NK-33, but were canceled after the program turned out to be a failure and the race to the Moon was lost to the United States. The existing NK-33 engines ended up in a warehouse where they were sitting for 30 years before being considered for use on modern launch vehicles. Aerojet purchased 43 NK-33 engines in the 1990s for conversion to the AJ-26 variant to be used on U.S. launch vehicles. Orbital Sciences acquired 20 engines for ten flights of the Antares launcher – two test flights and eight operational Cygnus missions to the Space Station under the NASA Commercial Resupply Services Contract. |
AJ-26 at Stennis E-1
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Before being used on Antares, each AJ-26 engine completes an acceptance firing at the E-1 Test Stand at the Stennis Space Center supported by NASA, Aerojet Rocketdyne, Orbital Sciences and Lockheed Martin personnel. Starting in 2010, AJ-26 engines have been routinely tested at Stennis. On Thursday, another AJ-26 was being put through its paces as part of a planned 54-second burn to qualify it for use on Antares in 2015. Thirty seconds into the burn, the test was terminated prematurely during which the engine sustained extensive damage. Some sources reported that the engine exploded.
The extent of damage to the engine and its test stand is currently unknown. It will likely take several days until the initial investigation of the failure can be completed and impacts on upcoming Antares operations can be assessed. The launch vehicle for the Orb-2 mission planned to launch on June 10 has already been integrated at the Wallops Flight Facility using two engines which passed their acceptance firings earlier.
NK-33 on Soyuz 2-1v
AJ-26 Testing
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NK-33 is a regeneratively cooled staged combustion engine with oxygen-rich preburners to drive the turbopumps. The engine operates at a high chamber pressure of 145 bar and provides a maximum sea level thrust of 1,630 Kilonewtons with length of 3.7 meters, an engine diameter of 1.45 meters and dry weight of 1,235kg. The engine can lift 137 times its weight and provides a vacuum impulse of 331s. Maximum vacuum thrust is 1,815kN.
In terms of thrust-to-weight ratio, the engine is one of the most powerful in the world, only falling short to the SpaceX Merlin 1D engine that is used on the Falcon 9 rocket. NK-33 provides throttle capability from 56 to 108% of rated performance, however its full thrust setting during flight is usually 105%. In tests, NK-33 achieved 135% of rated performance thrust without failing. NK-33 uses Kerosene as fuel and requires sub-cooled Oxygen with a temperature below its boiling point of -183-degrees Celsius to cool the turbopump bearings that would otherwise fail. To convert an NK-33 to the AJ-26, Aerojet Rocketdyne implements a number of modifications on the engine. These include the addition of US electronics, the implementation of electromechanical valve actuators in the propellant system, modifications to the fuel systems, the removal of the engine harness and the installation of gimbaling equipment. The two AJ-26 engines of Antares are mounted on a thrust frame and each engine is equipped with independent Thrust Vector Control Systems for vehicle control during ascent. Engine gimbaling is controlled by a Moog hydraulic TVC system. The two engines are fed by two separate LOX/RP-1 feed systems and have independent electrical hardware. The propellant inlets of the two engines are flexible to allow the engines to move relative to the core structure for Thrust Vector Control. The engine controllers are built by Orbital, but also incorporate engine sensors and propellant utilization systems provided by Yuzhnoye – the manufacturer of the first stage of Antares. The AJ-26 engines on Antares have shown a flawless performance on their previous assignments that began with test firings in 2012/13 on the newly built Pad 0B at the at the Mid-Atlantic Regional Spaceport located at the Wallops Flight Facility, Virginia. Antares made its first test launch on April 21, 2013 carrying a dummy payload into orbit before launching the first Cygnus spacecraft on its successful demonstration mission to ISS on September 18, 2013. |
Earlier this year, Antares launched the Cygnus Orb-1 mission – the first operational Cygnus mission to the Space Station under NASA’s Commercial Resupply Services contract. Orbital’s $1.9 billion CRS contract includes eight resupply flights through 2016.
A previous AJ-26 test failure occurred in 2011 when an engine caught fire after an aborted test due to a Kerosene leak within an engine manifold. This failure was traced back to stress corrosion cracks in the metal of the high-pressure system of the engine.
In parallel with AJ-26 test firings in the United States, original NK-33 engines were test fired in Russia in preparation for the maiden flight of the Soyuz 2-1v launcher that uses the NK-33 on its first stage along with an RD-0110R steering engine. One prior test failure in Russia has been reported, but NK-33 was not at fault as that failure was caused by problems with ground support equipment. Determining the cause of Thursday’s failure will be a priority to clear the Antares launch vehicle for its upcoming flights in case the problem was specific to the engine that was tested and not an issue that could occur across the engine family. Repairs on the E-1 test stand are also important to consider when looking at future missions of Antares. AJ-26 engines for the next two Antares launches have finished acceptance testing and are ready for flight leaving the option of a shortage of engines if testing suffers an extended interruption due to repairs at Stennis. Officials said it was to soon to tell whether any Antares launches would be delayed as a result of Thursday’s test failure. |
AJ-26 on Antares
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Previous AJ-26 Tests
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