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North Korea launched its first Taepodong-2 in 2006, but it exploded just 40 seconds after liftoff. A follow-up attempt in 2009 got off the launch pad and successfully completed a tricky pitching maneuver, but analysts believe its third stage failed to separate properly, sending it and the satellite it carried into the Pacific.

Even so, physicists David Wright and Theodore Postol of the Union of Concerned Scientists say the 2009 launch displayed major strides over the Taepodong-1. If modified as a ballistic missile, they say, it potentially would give the North the capability to reach the continental United States with a payload of 1 ton.

In an analysis of the 2009 launch, Mr. Wright and MR. Postol suggested North Korea relies heavily on a stockpile of foreign components, likely from Russia. If data from the upcoming launch confirms that, it may mean Pyongyang’s missile program is severely limited by the isolated country’s ability to procure new parts from abroad.

That could figure into future arms talks. If North Korea is running out of the parts it needs, it isn’t likely to conduct frequent missile tests and may be more willing to agree to test moratoriums. More emphasis on blocking its imports also would make sense if the North cannot manufacture what it needs.

What analysts find out will figure into regional security planning for years to come — as North Korea’s first attempted satellite launch did in 1998.

Japan and the United States responded to that launch by pouring billions of dollars into the world’s most advanced ballistic missile shield. That shield includes a network of sea-based SM-3 interceptor missiles and land-based PAC-3 Patriot missiles.

Japan now is mobilizing PAC-3 units in Okinawa, which is near the path of the upcoming launch and is where more than half of the 50,000 U.S. troops in Japan are deployed. Japan also is mobilizing PAC-3 units in Tokyo, which is much farther from the rocket’s expected path. South Korea is taking similar steps — which it didn’t do in 2009.

The U.S. will be watching with equipment that was unavailable in 2009: a Sea-Based X-Band radar system aboard a Navy ship that left Pearl Harbor late last month.

U.S. officials claim the SBX system is so powerful it can track a baseball-sized object flying through space 2,500 miles away. Further, if U.S. military satellites detect a flash of heat from a missile launch in North Korea, within a minute computers can plot a rough trajectory and share that information with Japan.

Tokyo and Seoul warn they will use their interceptors on anything that threatens their territory, though that is highly unlikely. No country has ever shot at another country’s satellite launch, and, barring any major surprises, the North Korean rocket will be traveling mostly over water, not populated areas.

“Whether it comes close to our southwestern islands or not, this will have significant implications for our missile defenses and how they should be adjusted in the future,” said Hiroyasu Akutsu, a senior fellow and Korea expert with the National Institute for Defense Studies, a think tank run by Japan’s Defense Ministry.