A powerful Delta 4 rocket roared to life and climbed away from the Cape Canaveral Air Force Station Sunday evening on a high-priority mission to boost a National Reconnaissance Office spy satellite into orbit.

Because the NROL-32 payload is classified, United Launch Alliance halted commentary about seven minutes after liftoff, just after the protective nose cone fairing separated and fell away. The vehicle was performing normally at that point, but no other updates were expected.

The payload is believed to be an electronic eavesdropping satellite with a huge collecting antenna. In a September address to the Air Force Association, NRO Director Bruce Carlson said the Delta 4 was carrying “the largest satellite in the world.”

“I believe the payload is the fifth in the series of what we call Mentor spacecraft, a.k.a. Advanced Orion,” Ted Molczan, a respected satellite tracker, told Spaceflight Now. “They are among the largest satellites ever deployed.”

Once on station, the satellite presumably will unfold a huge, lightweight antenna to tap into targeted military or civilian communications networks.

“The satellite likely consists of sensitive radio receivers and an antenna generally believed to span up to 328 feet to gather electronic intelligence for the National Security Agency,” Molczan told Spaceflight Now.

(Read More: CBS News)