Each advancement Pyongyang makes causes worry in Washington and among North Korea's neighbors. In 2010, U.S. Secretary of Defense Robert Gates warned that within five years the North could develop an intercontinental ballistic missile capable of reaching the United States.
But experts say the North must still surmount tough technical barriers to build the ultimate military threat: a sophisticated nuclear warhead small enough to mount on a long-range missile, something experts say will be the focus of future nuclear tests.
And despite Wednesday's launch, Pyongyang is also lacking the other key part of that equation: a reliable long-range missile.
"If in the future they develop a nuclear warhead small enough to put on a rocket, they are not going to want to put that on a missile that has a high probability of exploding on the launch pad," David Wright, a physicist with the Union of Concerned Scientists who has written extensively about North Korea's missile program, said in an email.
To create a credible missile program, experts say, North Korean technicians need to conduct many more tests that will allow them to iron out the wrinkles until they have a missile that works more often than it fails. Pyongyang's past tests have been somewhat scattershot, possibly because of the heavy international sanctions the rocket and nuclear tests have generated.
North Korea must build a larger missile than the one launched Wednesday if it wants to be able to send nuclear weapons to distant targets, analysts said.
The satellite North Korea mounted on the rocket weighs only 100 kilograms (220 pounds), according to the office of South Korean lawmaker Jung Chung-rae, who was briefed by a senior South Korean intelligence official. A nuclear warhead would be about five times heavier.
Other missing parts of the puzzle include an accurate long-range missile guidance system and a re-entry vehicle able to survive coming back into the atmosphere at the high speeds — 10,000 mph — traveled by intercontinental ballistic missiles, said Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics in Massachusetts.
Both are seen as being years off.
History also shows that first-generation, long-range missiles need dozens of test flights before they are accurate enough to be deployed.
The world's "ICBM club" has just four countries: the United States, Russia, China and France, according to Markus Schiller, an analyst with Schmucker Technologie in Germany and a leading expert on North Korean missiles.
If North Korea "really intended to become a player in the ICBM game, they would have to develop a different kind of missile, with higher performance," Schiller said. "And if they do that seriously, we would have to see flight tests every other month, over several years."
Wright said the Unha-3 rocket launched Wednesday has a potential range of 8,000 to 10,000 kilometers (4,970 to 6,210 miles), which could put Hawaii and the northwest coast of the mainland United States within range.
But even if North Korea builds a ballistic missile based on a liquid-fueled rocket like the 32-meter (105-foot)-tall Unha-3, it would take days to assemble and hours to fuel. That would make it vulnerable to attack in a pre-emptive airstrike. Solid-fueled missiles developed by the U.S. and Soviet Union are more mobile, more easily concealed and ready to launch within minutes.
Money is another problem for Pyongyang. A weak economy, chronic food shortages and the sanctions make it difficult to sustain a program that can build and operate reliable missiles.
"I don't think the young leader has any confidence that the home economy could afford a credible deterrent capability," said Zhu Feng, deputy director of the Center for International and Strategic Studies at Peking University.
Weeden said North Korea may want to create the perception that it poses a threat to the United States, but "I don't think that perception will be matched by the actual hard work and testing needed to develop and field a reliable, effective weapon system like the ICBMs deployed by the US, Russia and China."
North Korea already poses a major security threat to its East Asian neighbors. It has one of the world's largest standing armies and a formidable if aging arsenal of artillery that could target Seoul, the capital of South Korea. Nearly 30,000 U.S. forces are based in South Korea, a legacy of the 1950-53 Korean War that ended with an armistice, not a formal peace treaty.
The North's short-range rockets could also potentially target another core U.S. ally, Japan.
Daryl Kimball, executive director of the nongovernmental Arms Control Association, said those capabilities, rather than the North's future ability to strike the U.S., still warrant the most attention.
Pennington reported from Washington. Associated Press writers Liz Sidoti in Washington, Alexa Olesen in Beijing and Jenni Sohn in New York contributed to this report.
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