While America was looking forward to the July 4 holiday, the Russian space program was busy putting the final touches on its latest rocket launch. A Proton-M rocket carrying three satellites for the GLONASS navigation constellation (Russia's answer to GPS) launched on July 2, 2013, at 06:38:22 Moscow Time.

Just one problem: The rocket came crashing back down to Earth at 06:38:54—landing in a massive fireball. The crash marked another setback for the beleaguered Russian space program. There were fears that the massive quantity of propellant could leak, potentially creating a very toxic disaster for the local population. And there was no immediate explanation as to why the Proton-M failed so spectacularly, so fast.

But on Tuesday, Anatoly Zak reports on his own site, RussianSpaceWeb.com, that investigators have determined the culprit was the “critical angular velocity sensors, DUS, installed upside down.”

He writes:

Each of those sensors had an arrow that was suppose to point toward the top of the vehicle, however multiple sensors on the failed rocket were pointing downward instead. As a result, the flight control system was receiving wrong information about the position of the rocket and tried to "correct" it, causing the vehicle to swing wildly and, ultimately, crash. The paper trail led to a young technician responsible for the wrong assembly of the hardware, but also raised serious issues of quality control at the Proton's manufacturing plant, at the rocket's testing facility, and at the assembly building in Baikonur. It appeared that no visual control of the faulty installation had been conducted, while electrical checks had not detected the problem since all circuits had been working correctly.

Zak also added that Russian authorities have launched a criminal investigation.