Elon Musk is old news—or rather, old tech. That's the take by Vladimir Koshlakov, the head of Russia's Keldysh Research Center and a man who want to build a nuclear-powered rocket (you heard that right).

“Elon Musk is using the existing tech, developed a long time ago,” said Koshlakov, making his weird dig at the SpaceX found in an interview with state-owned Rossiyskaya Gazeta. “He is a businessman: he took a solution that was already there, and applied it successfully.”

Koshlakov, meanwhile, is leading the charge to build a new type of space vehicle called the Transport and Energy Module (TEM), featuring a nuclear-powered engine, according to state-owned media outlet Russia Today. However, Russia’s would-be nuclear engine makes use of technology almost as old as the chemical rockets currently in use. So what exactly does a nuclear rocket entail, and why don't we have them yet?

Both the United States and the old Soviet Union spent decades researching nuclear rockets, and this new design is a direct descendant of these programs.

The specific design of a nuclear-powered rocket engine can vary dramatically—one experimental U.S. program featured a rocket that would propel itself by setting off nuclear explosions behind it—but the most common version involves using a small nuclear reactor to generate immense amounts of heat. That heat is then transferred to some sort of fuel—typically hydrogen, although it’s not clear what the TEM rocket uses—and the rapid heating of that fuel causes it to expand and produce thrust.

The KIWI nuclear reactor engine preparing for a test in 1962, at Los Alamos. Los Alamos National Laboratory

In the United States, the first program to try to develop this type of rocket—called a nuclear thermal rocket—was Project Rover, started by NASA and the Atomic Energy Commission in 1955. Project Rover ran for two decades, producing a handful of test engines at Los Alamos.

Rover's first attempt at a nuclear engine was called KIWI, and it was focused on proving the concept. The next generation engine, called Phoebus, was designed to test how well the concept actually worked in practice, including simulating a space-like environment for the rocket during experiments. By 1972, the project had actually gotten as far as designing a small version of the engine, called Pewee, to use as a final stage for small satellites and spacecraft.

So what happened? Well, 1972 saw the last of the half-dozen Apollo moon landing.{public fascination with space was drying up. Federal funding, too. In 1972, Project Rover was canceled without ever actually launching a nuclear rocket into space.

A surviving RD-0410 nuclear rocket engine. Uncredited

Meanwhile, the Soviets were developing their own nuclear thermal rocket, the RD-0410. The RD was significantly smaller than any of Project Rover’s rockets, including the diminutive Pewee. Testing on the RD-0410 also didn’t begin until after Project Rover had ended; the first live-fire test of the rocket occurred in 1978.

But just like in the U.S., the Soviet project ran out of funding before it could be completed. In the early 1980s, just as the engine was nearing the first tests in space, the Soviet Union was beginning to collapse. The embattled government didn’t have the time or the money to entertain speculative rocket projects, and the RD-0410 was canceled by 1990.

The TEM Russian nuclear engine being developed today is a direct successor to the RD-0410. The project relies on modern materials and construction methods and borrows from the work done by both Soviet and American scientists. Despite what Koshlakov has said, nuclear rocket engines have a history about as long as any other kind of rocket. Perhaps with this new project, one of them will actually fly.

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