Bermudez first located the site in early spring and they have tracked its construction using commercial and unclassified satellite imagery.
"The primary purpose of the facility is to test," Bermudez told The Associated Press in an interview last week. A base capable of a long-range test could obviously be used in wartime to launch a missile that carried a warhead.
"This is a clear indication North Korea is continuing its ballistic missile development program," Bermudez said.
Bermudez is also unveiling the images on the defense web site Janes.com and in the Sept. 17 edition of Jane's Defence Weekly.
He said the launch pad has been operational since 2005 but has not yet been used. He believes North Korea wants to use it to develop longer-range and more accurate ICBMs. It could also launch satellites into space.
Although North Korea has been long thought to want additional missile capability and test facilities, this is the first public disclosure of the new launch facility, according to Bermudez, Brown and John Pike, an imagery analyst with GlobalSecurity.org, who first reviewed the information last week.
Pike said the new facility represents a major step forward for North Korea's long-range missile program as it would allow multiple test flights in a short time, which is difficult at the smaller, original long-range missile launch site known as Musudan-ni.
"This would be a facility to conduct a real flight-test program and develop something that you have some operational confidence in," Pike told the Associated Press. "It would suggest they have the intention to develop the capability to perfect a missile to deliver atomic bombs to the United States."
"At the old facility, (a robust test program) just wasn't going to happen," he said.
Pike and Brown identified Musudan-ni nine years ago when they were both with the Federation of American Scientists in Washington.
A U.S. counterproliferation official said U.S. intelligence has been aware of the North Korean site for several years. He spoke on condition of anonymity to discuss classified information.
North Korea has not used the new site, but could at any time, U.S. intelligence officials and the outside analysts said.
"There is no reason they couldn't launch in the near future," Brown told The Associated Press.
Construction has continued even as the U.S. government renewed its attempt to persuade North Korea to shut down its nuclear weapons program. Those negotiations do not address North Korea's long-range missile program, but would give North Korea much-desired economic and political incentives in exchange for giving up nuclear weapons.
The deal's future may be in doubt with news this week that Kim Jong Il, who has held absolute rule in the impoverished, isolated Stalinist regime, may have been incapacitated by a stroke or other health crisis. North Korean authorities deny he is ailing.
The new launch facility exceeds in both size and sophistication the Musudan-ni base on North Korea's east coast, images from DigitalGlobe and GeoEye suggest.
North Korea launched a failed long-range Taepodong-2 space launch vehicle in 2006 from Musudan-ni. That test alarmed the world and gave new energy to the stop-and-start diplomacy over North Korea's nuclear program. It also conducted a surprise launch of a Taepodong-1 over Japan in 1998 from that east coast site.
Pyongyang has not yet attempted to launch the ballistic missile version of Taepodong-2, which is estimated to have a maximum range of about 2,500 miles, potentially threatening the western edge of Alaska. The range could be extended with engine improvements and light payloads.
The new launch facility is built on the site of a small village called Pongdong-ni which was displaced during construction. It includes a movable launch pad and 10-story tall tower capable of supporting North Korea's largest ballistic missiles and rockets. It also includes a rocket motor test pad, which Brown and Bermudez said is similar in size and design to a rocket test facility outside of Tehran, Iran. There are also support buildings.
"The discovery of this new facility demonstrates that North Korea is still conducting an ambitious ballistic missile program and may still have plans to launch satellites into space," Brown said.
Bermudez and Brown refer to the site as the Tongch'ang-dong launch facility, naming it after the closest village. U.S. intelligence does not use the same name for the site. Officials would not immediately divulge the term they use.
The base is not quite complete, according to Pike, who reviewed the most recent imagery Tuesday and said it is still missing a vertical assembly building where the missile would undergo its final assembly before being rolled to the launch site. Brown and Bermudez have not yet found optical or radar tracking facilities; they believe North Korea will rely on mobile or shipboard radar systems in tests. They have also not identified fixed air defense systems that would protect the facility from air attack.
But the site does have an engine test stand, a critical facility for measuring vibration from the engines and adjusting guidance systems to account for it, Bermudez said.
"The engine test stand means they now have the ability to increase the reliability of whatever system" they develop, he said.
Brown and Bermudez say the new launch facility is more protected from surveillance aircraft than Musudan-ni because it is mostly surrounded by hills. Its proximity to Chinese airspace could also discourage close observation by plane, as the U.S. military may want to avoid a repeat of the 2001 collision of a U.S. spy plane and a Chinese fighter.
North Korea is believed to possess up to a dozen nuclear warheads. The new launch pad would help in the development of missiles to carry them, he said. In 2006, North Korea conducted an underground nuclear test, removing any doubt it had the means to make a nuclear warhead. Its previous missile test showed it also had the means to deliver one.
North Korea has agreed in principle to forswear nuclear weapons and the plutonium used to fuel them. It placed its known plutonium-producing reactor out of commission earlier this year, but has recently backtracked by taking some equipment back out of storage in possible preparation to restart the reactor.
In June, North Korea destroyed the reactor's distinctive conical cooling tower as a symbolic show of good faith with the United States and other nations bargaining with it. But the deal has since stalled over North Korea's obligations to allow intensive international fact-checking of its past nuclear activities.
North Korea claims the U.S. has not held up its end of a nuclear disarmament deal because it has not removed the North from a list of state sponsors of terrorism.
