The cause of Tuesday's Antares 130 launch failure is not known. The builder and owner of the rocket, Orbital ATK, will lead an investigation of the accident, and it will be assisted by NASA and the FAA. All that is known for sure at this point was tweeted by Orbital ATK: "There has been a vehicle anomaly. The vehicle suffered a catastrophic failure."
Uh, yeah. That much seems painfully self-evident.
So what likely went wrong? Well, we know that the failure occurred 6-10 seconds after liftoff from Launch Pad-0A at the Mid-Atlantic Region Spaceport at Wallops Island, Virginia. We know that the first stage of the Antares is powered by two AJ26 engines, which are fueled by liquid oxygen (LOX) and kerosene (RP-1). We know that the burn time for the first stage is approximately 230-235 seconds, which means that we can exclude any problems with the second stage or the stage separation phase of the flight -- which is often when things tend to go wrong with rocket launches.
So the focus is on the first stage and its two engines. Usually, when a launch goes wrong just a few seconds after liftoff, the problem has something to do with an engine. Perhaps a fuel leak or a clogged fuel line.
For example, the explosion of the Sea Launch Zenit 3SL 3.9 seconds after liftoff on January 30, 2007 was caused by a malfunction of the vehicle's first stage engine, which was believed to have become clogged with debris -- possibly from the engine itself. Note that the failure of a Russian Proton M rocket in 1999 was traced to a second stage fire which was started by a stray aluminum particle in the engine caused by a faulty weld. Poor workmanship.
Another example was the failed launch of SpaceX's Falcon 1 on March 24, 2006, which occurred about 25 seconds after liftoff. An investigation attributed the failure to a fuel leak, which may have been caused by a broken B-nut on the engine's fuel pump inlet pressure transducer. The aluminum nut, designed to hold the fuel pipe fitting in place, is believed to have failed due to "inter-granular corrosion". In other words, stress may have led to structural cracking, which in turn caused fuel to leak onto the engine -- which then, of course, caught fire.
We know that the AJ26 engines were built by the Kuznetsov Design Bureau of Russia in the 1960s. But the engines -- originally designated NK-33 -- were bought by Aerojet Rocketdyne of California in the 1990s and completely refurbished, tested, and qualified, then sold to Orbital ATK. Lots of welding work, replacement of fuel lines, electronics upgrades, steering system modifications, and qualifying for US propellants. So, in essence, what was old was made new. Well, kind of. There's still just no getting around the fact that the engines were first built over 40 years ago.
There's also no getting around the fact that on May 22, 2014, an AJ26 engine undergoing "hot-fire" testing at the NASA Stennis Space Center in Mississippi failed, and may have even exploded. An investigation was conducted, but the results have apparently not been released to the public. But we do know that another AJ26 tested at Stennis in June 2011 also failed and caught fire. According to an article by Chris Bergin on the NASA Spaceflight.com website, "The fire was caused by a kerosene fuel leak in an engine manifold, with the root cause subsequently determined to be stress corrosion cracking of the 40-year old metal."
It will take days, maybe even weeks to determine the exact cause of the failed Antares launch. At the moment, though, it looks to me like that ol' Russian engine's got some issues.