Washington (CNN) -- The largest rocket ever launched from the West Coast went into space Thursday afternoon carrying a secret "national security" satellite, Vandenberg Air Force Base in California announced.

The 23-story tall Delta IV rocket blasted off on schedule at 1:10 p.m. PT (4:10 p.m. ET). With 2 million pounds of thrust -- 33 times the output of the Hoover Dam -- it delivered into orbit a satellite for the National Reconnaissance Office, the U.S. government agency that oversees the nation's satellites.

The NRO is staying mum about the satellite but noted this is the third in a series of six satellite launches happening over a seven- to eight-month period. The next launch is scheduled for February 5.

"We would like to keep our adversaries guessing on what our capabilities are," said Rick Oborn, a spokesman for the intelligence agency.

But some analysts say they believe the orbiter will be an imagery satellite capable of seeing images as small as a human fist from hundreds of miles away.

"It will be used to produce high-resolution imagery of military and terrorist facilities around the world," said Jeffrey Richelson, an expert on space reconnaissance with the National Security Archive.

According to experts, the satellite, known as a KH-11, is not capable of reading a license plate number or a newspaper headline, as seen in Hollywood movies. But due to its large size and bigger optics, the satellite has advanced resolution that can see much finer detail on the ground than anything similar.

"Being able to see things four inches across has tremendous value. If you're trying to assess what's the capability of a new missile on a launch pad in North Korea -- could it reach the U.S. for example -- if you could see that rocket with enough precision, enough detail to get accurate dimensions, you can then determine what its capabilities are," said Ted Molczan, an amateur astronomer who specializes in tracking satellites in secret orbits.

Molczan said there are currently 3 KH-11s in orbit and he believes the purpose of this launch is to replace one that has been in orbit since 2001.

While this is the first Delta IV rocket to launch from Vandenberg Air Force Base, about 150 miles up the coast from Los Angeles, it is the fifth launch in the program's history. The others have previously launched from Cape Canaveral, Florida.

The Delta IV is some 91 feet taller than the Titan IV-B -- the old Vandenberg workhorse that was retired in 2005 -- and has a maximum low-earth-orbit payload capacity nearly 2,000 pounds greater than its predecessor, the Air Force said.

The launch follows three years of preparations at Vandenberg and a $100 million infrastructure upgrade at the base to handle the massive rocket launch.

"The excitement and buzz on base today is reminiscent of the 1950s space excitement. Children are excited to see 'the big rocket.' It is a fun day to be in space operations," Lt. Ann K. Blodzinski, an Air Force spokeswoman, said before the launch.

Blodzinski expected crowds to fill viewing sites on and off base to watch the launch.