Instead, all four launches of the mighty N1 Soviet rocket, which used an earlier iteration of the first-stage engines used in Thursday’s launch, failed between 1969 and 1972. And as the Soviet Union abandoned the idea of putting cosmonauts on the moon, those engines languished in Russia “without a purpose,” reported Space Lift Now.

That was until they were snapped up by Dulles-based Orbital Sciences, which built the rocket that exploded. It uses two modified versions of those Russian engines to propel missions to the International Space Station, according to the company’s user’s guide. To be clear, investigators say they do not know what caused Tuesday’s explosion, which destroyed hundreds of millions of dollars worth of equipment. But some observers are questioning those Soviet-era engines.

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On Tuesday night, an Orbital executive complained there aren’t more modern alternatives to the decades-old engines, the Guardian reported. “When you look at it there are not many other options around the world in terms of using power plants of this size,” said Frank Culbertson, the company’s executive vice president. “Certainly not in this country, unfortunately.” The first issues with the rocket appeared to arise, he said, during the rocket’s first stage, when it was powered by Soviet engines. “The ascent stopped [and] there was some, let’s say, disassembly of the first stage, after which it fell to Earth,” he said.

Regardless of the outcome of the investigation, the explosion is likely to stall the ambitions of Orbital Sciences, which has a $1.9 billion contract to make eight supply missions to the International Space Station. It shed $266 million in market value Tuesday night. What’s more, this is not Orbital’s only recent engine-related explosion.

In May, one of its refurbished Soviet engines failed at the Stennis Space Center in Mississippi. “Sources claim the engine ‘exploded,'” reported NASA Space Flight. “The failure is currently under evaluation.”

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Elon Musk, the chief executive of Orbital’s competitor SpaceX, has long warned against using such decades-old technology. Calling it one of the “pretty silly things going on in the market,” he told Wired last year some aerospace firms rely on parts “developed in the 1960s” rather than “better technology.” He called out Orbital Sciences in particular. It “has a contract to resupply the International Space Station, and their rocket honestly sounds like the punch line to a joke,” he said. “It uses Russian rocket engines that were made in the ’60s. I don’t mean their design is from the ’60s — I mean they start with engines that were literally made in the ’60s and, like, packed away in Siberia somewhere.”

That synopsis isn’t far from the truth. After the N1 rocket failed in the early 1970s, the Soviet Union pulled back on its space ambitions, and its engines went into hibernation, Space Flight Now reported. “After the engines were built, Soviet space dreams were adjusted to focus on Earth-orbiting space stations, leaving the engineering marvels in storage without a purpose.”

They were eventually brought to the United States in the 1990s for a California-based company looking to supply engines for the Atlas 5 rocket, but another engine was ultimately chosen, the news agency said. And the “NK-33 appeared to be left in the dust for a second time until Orbital Sciences came along.”

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The engines were far from perfect, but Orbital scientists nonetheless hailed them as unlike anything in the United States. “As we went through testing, we did discover there were some effects of aging since they had been in storage for awhile, including some stress corrosion cracking,” Culbertson conceded at the time. “That’s what we [corrected] with weld repairs and other inspections.” The company’s “user guide” boasts that the engines, “refurbished with modern components,” have “an extensive test history.”