Two officials said that the United States briefly considered going in to retrieve the downed drone, or to destroy it, as first reported Wednesday by The Wall Street Journal, but the operation was deemed too risky. There are questions about whether Iran could reverse-engineer the technology, though they certainly could sell the vehicle to China, Russia or other countries with a deep interest in it.

“The flights from Moscow and Beijing to Tehran were probably quite full the last few days,” said P. W. Singer, who studies military robotics at the Brookings Institution…

While an orbiting surveillance satellite can observe a location for only a few minutes at a time, a drone can loiter for hours, sending a video feed as people move about the site. Such a “pattern of life,” as it is called, can give crucial clues to the nature of the work being done, the equipment used and the size of the work force.

“It’s basically like staking out a Mafia social club,” said John Pike, who tracks military technology at the Web site GlobalSecurity.org. “If I’m just looking at brick-and-mortar targets, satellite’s fine. But if I want to see what people are doing all day, the drone is a whole lot better.”