Another explanation could be rockets designed to fire into space — though this is not necessarily benign. Countries will often develop space-launch rockets as a kind of test model for intercontinental ballistic missiles. North Korea and India both started their ICBM programs this way.
Mr. Lewis estimated that Shahrud’s casting or curing pits could produce three rockets per year — not enough for an arsenal, but the right amount for a space-launch program. This could develop the technical know-how for an ICBM without one actually being built.
A Revolutionary Guards officer named Majid Musavi, who is thought to be Mr. Moghaddam’s successor, seemed to suggest as much in his only known interview. A space program, Mr. Musavi said in 2014, allowed the scientists to continue their work while complying with orders from Iranian leaders not to produce missiles over 2,000 kilometers in range.
Still, Shahrud’s focus on solid-fuel engines suggests that any space program there is intended for missile technology, said David Wright, a missile expert at the Union of Concerned Scientists.
“If the goal is to launch satellites, it makes more sense to use liquid-fuel rockets,” he said. Solid fuel brings few upsides for civilian use, he said, but is “a convenient way to also develop the technology for a solid ICBM.”
It is difficult to assess whether Iran would develop this technology as a precaution in case tensions spike with the United States, as leverage for future negotiations or as experimental testing for missiles that are still years away.
Work at the facility is most likely intended as “a hedge” should the nuclear agreement collapse, said Dina Esfandiary, an Iran expert at the Center for Strategic and International Studies. The country does not appear to be sprinting toward a long-range missile, but preparing the ground in case Iranian leaders should one day deem that necessary.