When Vladimir Putin announced a brand new globe-spanning missile powered by a mini reactor last year, it was supposed to be a crown jewel for Moscow’s military. But as President Trump tweeted late Monday, it’s increasingly looking like one of those missiles exploded during testing. So whose bright idea was it to slap a nuclear reactor on the back of a nuclear missile, why is Russia making one, and just how viable is a nuke-powered missile?

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Wait, there’s a nuclear reactor-powered missile? Kind of. The missile, dubbed the 9M730 Burevestnik (or “petrel” in English), is designed to carry a warhead—nuclear or conventional—around the globe and dodge American missile defenses. (NATO refers to the missile by a name more befitting its James Bond movie aura: Skyfall.) Putin hailed the weapon as a “a low-flying stealth missile carrying a nuclear warhead, with almost an unlimited range, unpredictable trajectory and ability to bypass interception boundaries.”