Antares AJ-26 engine fails during Stennis testing

One of the AJ-26 engines set to launch with a future Antares rocket has failed during testing at the Stennis Space Center on Thursday. Sources claim the engine “exploded” on a Stand located in the E Complex at the famous rocket facility. The failure is currently under evaluation, although it may delay the next Antares launch that is tasked with lofting the the ORB-2 Cygnus to the International Space Station (ISS).

AJ-26 Failure:

The Antares launch vehicle has enjoyed a highly successful early life, launching three times without incident, with her debut during the A-ONE test flight in April, 2013.

The rocket safely lofted two Cygnus spacecraft into orbit for their missions to the International Space Station (ISS), the first as a COTS demo flight – known as ORB-D, soon followed by the ORB-1 mission that was the first under their Commercial Resupply Services (CRS) contract with NASA.

The Antares launch vehicle’s main engine is the Aerojet produced AJ-26 – a rebuilt version of Soviet NK-33, originally intended for the massive N-1 launch vehicle.

The tanking for the Antares was contracted to the Yuzhnoye Design Bureau from the Ukraine. Yuzhnoye has extensive knowledge in producing kerosene rocket bodies as the producer of the Zenit launch vehicle.

Orbital originally conceived of a core with a single NK-33 derived engine combined with strap-on solid boosters. However a second engine was ultimately added to the core and the boosters were removed from the final design.

The Antares’ AJ26-62 main engines running with a LOX/RP comination, producing 3,265kN of thrust at Sea Level.

Aerojet originally purchased approximately 40 NK-33 engines in the mid-1990s and, under contract with Orbital, the company has modified the engines specifically for its Antares rocket.

Throughout the years, more than 200 NK-33 engines were built and 575 engine tests conducted, totaling more than 100,000 seconds of test time.

Aerojet has been developing design modifications to the NK-33 since that time to ensure that the AJ-26 was suitable for commercial launchers.

Engine testing ahead of flight is conducted at the Stennis Space Center, specifically on the E-1 Test Stand. NASA – and its commercial partners – has tested AJ-26 engines at Stennis since November 2010.

“Each test of an AJ-26 engine is exciting and affirming because it is in direct support of NASA’s commercial space flight efforts, as well as a continuation of a very successful Stennis partnership with Orbital and Aerojet Rocketdyne,” Stennis Director Rick Gilbrech recently noted after the E-15 AJ-26 test in January of this year.

It is not yet known which AJ-26 was being tested at Stennis on Thursday. However, L2 sources note the engine failed mid way through it firing, some claiming it actually exploded, during the test that occurred sometime around 7pm UTC.

The condition of the Test Stand following the failure is currently unknown. However, no one at the test site was injured.

“During hot-fire testing earlier today at NASA’s Stennis Space Center, Aerojet Rocketdyne’s AJ26 engine experienced a test anomaly. There were no injuries,” noted Aerojet Rocketdyne spokesperson Jessica Pieczonka to NASASpaceflight.com

“The company is leading an investigation to determine the cause.”

A previous failure of an AJ-26 occurred in June, 2011 – when the fourth Antares engine caught fire on the E-1 Test Stand. The fire was caused by a kerosene fuel leak in an engine manifold, with the root cause was subsequently determined to be stress corrosion cracking of the 40-year old metal.

The engine had to be replaced with another unit from downstream in the manifest. The replacement engine was successfully hot-fire tested on September 28, 2011 after improved inspection protocols had been implemented.

It will likely take some days for the failure to be investigated, prior to any decision on a potential impact to the next Antares launch.

Both engines on the fourth Antares – that will be tasked with lofting the ORB-2 Cygnus to the ISS – successfully passed through their test requirements at Stennis.

The ORB-2 mission is currently manifested for launch on June 10, at 06:07 GMT, from Pad 0B at the Mid-Atlantic Regional Spaceport located at the Wallops Flight Facility in Virginia.

(Images: L2 Special Sections, Orbital and NASA)