World leaders have expressed concern for weeks over the possibility of a North Korean missile test. Beyond satellite images of the missile launch base, however, relatively little is known about Pyongyang's prospective launch plan.
Weapons experts in South Korea and the United States think the ballistic missile sitting on a North Korean launch pad is a Taepodong-2.
Kim Taewoo, of the Korea Institute for Defense Analyses in Seoul, says there are more than three decades of history behind the Taepodong.
"North Korea began indigenous development of missiles during the 1970s. During the '90s, North Korea successfully developed the Rodong missile," said Kim Taewoo. "And then, we witnessed the test-firing of the Taepodong-1 missile in 1998."
That Taepodong-1, which flew 1,300 kilometers directly over Japan, is believed to have had a range of about 2,000 kilometers. Experts think the Taepodong-2 missile now on the launch pad may have double that range - meaning it could reach as far as the U.S. state of Alaska.
North Korea has not fired a long-range missile since 1999, although it has tested several smaller rockets.
The possibility of a North Korean launch has unsettled its neighbors and the United States. Despite being extremely poor, the communist state has a large military and is suspected of having an arsenal of thousands of missiles and rockets that can go a few hundred kilometers, as well as several mid-range weapons.
Pyongyang, which says it is threatened by the United States, has frequently said it is prepared to use its weapons.
A launch would complicate efforts to restart negotiations on ending Pyongyang's nuclear weapons programs. North Korea has refused to return to talks with the United States, China, Russia, Japan and South Korea.
Some political analysts think North Korea is using the threat of a launch to push the United States into bilateral talks. Washington says it will only talk to Pyongyang within the framework of the six-party negotiations.
Whatever Pyongyang's motives, technical experts say there are likely to be certain clues to indicate a launch is about to take place.
Chae Yeon-seok, former director of the Korea Aerospace Research Institute in Seoul, says first, the launch area would be cleared.
He says the framework supporting the missile would first be taken away, allowing the missile to stand on its own. Though the removal of the structure may difficult to see from satellites, he adds, it would be a clear indication a launch is imminent.
L. David Montague, former president of the missile division of the U.S. company Lockheed Martin, says there may be other signals as well.
"They're going to be monitoring telemetry and that sort of thing so you would expect to see an increase in activity in radio traffic. Presumably they might even put a ship out there somewhere, to observe," he said.
Many news reports have quoted intelligence estimates of the missile's fuel status. Montague rejects speculation that fueling the missile puts pressure on Pyongyang to launch to avoid having the fuel degrade. He says the missile probably uses fuel that would allow it to sit on the launch pad indefinitely.
"As far as I know they're using kerosene and some oxidizer that is not unstable, so I just can't imagine that there's any specific time limit there," he added.
Chae, of the Korea Aerospace Research Institute, agrees the missile's tanks can be filled or emptied as North Korea chooses. He adds that the fuel probably weighs about 50 tons - about 90 percent of the missile's total weight.
He says most missile frames have pipelines through which fuel can be directly injected into the rocket. If there is no such pipeline, it is an indication the launch facility is antiquated.
Recent reports have cited satellite images of dozens of trucks believed to be fueling the North Korean missile.
The Taepodong-2 is a multi-stage rocket, meaning it sheds empty sections as fuel is depleted. It should exit the earth's atmosphere quickly before descending in a gradual curve back to earth.
David Montague thinks the international community is becoming unduly alarmed by the possible test. He says a single test cannot produce a serious advancement in Pyongyang's missile capability.
"One test means nothing in the grand scheme of things," he continued. "Typically in the United States, if we were building a ballistic missile we wanted to have confidence in, we would have 20 flight tests before we were satisfied we had found all the design flaws, so to speak."
Instead, says Montague, a North Korean missile launch could yield a windfall of information for the United States intelligence community.
Among other things, it would reveal how far North Korean missile technology has progressed, and how much further it has to go before the communist nation becomes a more serious threat.
Weapons experts, diplomats and intelligence officials in Asia and the United States say until there is a launch, there is no way to know exactly North Korea's plans, motives or abilities. One senior U.S. diplomat in Seoul said Wednesday that Pyongyang may be hesitating about a launch because of international pressure.