The head of a U.S. missile defense advocacy group warned that a North Korean long-range rocket launch — expected between tomorrow and Wednesday — will be on an azimuth that puts Hawai'i on the tail end of a possible failure.

Defense Secretary Robert Gates, meanwhile, said the only scenario under which the United States "might" try to shoot down such a rocket is "if we had an aberrant missile — one that was headed for Hawai'i."

So how worried should Hawai'i be that some sub-orbital North Korean space junk may fall out of the sky?

"It's a big ocean. The percentages are not great that it's going to hit in Hawai'i," said Riki Ellison, chairman of the Washington D.C.-based Missile Defense Advocacy Alliance.

But there is that slim possibility, he believes.

Ellison said U.S. missile defense experts do not believe North Korea has the technology to put into space what it claims is a communications satellite, "so it's going to fall short, if they get there, and falling short is going to be going down towards Hawai'i."

America's top military officer, Adm. Mike Mullen, last week said the North Korean rocket — a three-stage Taepodong-2 — doesn't have the range to get to the West Coast, but it could reach Hawai'i.

"In some cases, yes, they could probably get down to Hawai'i," Mullen told CNN.

Even though the Pentagon believes the launch is a mask for the development of an intercontinental ballistic missile, U.S. discussion of defensive measures has been restrained.

"I can't discuss specific alert status or our capability," said Maj. Tracey Lewis, a spokeswoman for U.S. Pacific Command at Camp Smith. North Korea said shooting down a communications satellite would be considered an act of war.

CLOSE MONITORING

The news agency Reuters, citing defense officials, said the rocket — being readied for launch — appeared to have a bulb-shaped nose consistent with a satellite payload.

Military officials have hinted that a phalanx of ships, satellites and radars will be closely monitoring a launch, and that ground-based interceptor missiles in Alaska or California will be ready to attempt to shoot down a missile threatening Hawai'i.

Their reliability remains in question, though.

"If we felt the North Koreans were going to shoot a ballistic missile at us today, I am comfortable that we would have an effective system that would meet that need," Air Force Gen. Victor "Gene" Renuart, head of U.S. Northern Command and North American Aerospace Defense Command, said at a recent congressional hearing.

Ellison, with the Missile Defense Advocacy Alliance, said an ideal orbital launch from North Korea overflies Japan and heads east toward the Pacific. The nonprofit alliance supports a U.S. missile shield.

"North Korea has declared two 'clear zones' on either side of Japan for the first and second rocket stages accounting for the (booster stages) falling from their rocket or missile launch," Ellison said. "The North Korea trajectory following that flight path would terminate close to Hawai'i if the rocket failed to achieve orbit or was a long-range ballistic missile."

The only other North Korean test of a Taepodong-2 was in 2006. The missile failed 42 seconds into flight, but Ellison said telemetry monitoring showed it saved Hawai'i from another potential close call.

"I've heard it would have gotten very close to Hawai'i," Ellison said.

DEFENSE OPTIONS

U.S. and Japanese destroyers with Aegis ballistic missile tracking and/or shoot-down capability — which could intercept a North Korean missile in boost phase — are positioned near Japan to monitor the launch.

There are six ships at Pearl Harbor outfitted with ballistic missile defense capability: the cruisers Lake Erie and Port Royal, and destroyers Russell, Paul Hamilton, O'Kane and Hopper.

But Ellison said those ships would not be suitable for the defense of a high-flying North Korean rocket heading toward Hawai'i.

The cruiser Lake Erie was able to shoot down a malfunctioning U.S. spy satellite in space in February 2008, but with modified software, a modified SM-3 missile, a lot of planning and exact coordinates.

The ships are designed for short- and intermediate-range ballistic missile intercepts, Ellison said.

"They cannot pick up that kind of speed and that kind of direction and dynamics," he said of an incoming long-range North Korean missile.

An Army missile defense system called Terminal High Altitude Area Defense, also for short- and medium-range ballistic missile defense, is being tested on Kaua'i, but is still in development, Ellison said.

Ellison said one important tracking asset that hasn't been deployed ahead of the expected North Korean launch is the giant Sea-Based X-Band Radar, which remains docked at Ford Island for repairs.

Ellison said he is at a loss as to why the powerful radar hasn't pulled out of port.

"There's only really two reasons. No. 1, there is no chance that there is a threat at all that it (the North Korean rocket) could hit Hawai'i, and they are banking on that," Ellison said. "No. 2, which is what I think it is, is that they think this will be seen as a provocative act."