The U.S. Navy geared up Wednesday for its first try at shooting down failed spy satellite USA 193 from three ships bobbing west of Hawaii.

As soon as space shuttle Atlantis landed in Florida, a Defense Department official declared open season on wayward surveillance birds.

"We're now into the window," he told a Pentagon press conference minutes after the shuttle landed at 9:07 a.m.

Rough seas in the northern Pacific may push the attempt back to Thursday, but conditions appeared to be improving throughout Wednesday.

Other factors, including the orientation of the satellite in its polar orbit, could influence a decision on the timing of the shootdown effort, added the official, who asked not to be named.

A final decision would be made by Defense Secretary Robert Gates.

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The plan is for the Aegis missile cruiser USS Lake Erie to shoot a modified "kill vehicle" at the satellite as it streaks overhead at about 5:30 p.m. Hawaiian time (10:30 p.m. EST).

If either of the Lake Erie's two missiles aren't ready to go, the destroyer USS Decatur will launch its one backup missile.

The Navy ships will have a window of only a few seconds to, in effect, hit a bullet with a bullet.

The destroyer USS Russell will also be on the scene, but will not prepare to launch any missiles.

The weather forecast for Honolulu, just east of the huge swath of Pacific airspace the FAA had blocked out for late Wednesday afternoon and evening, called for partly cloudy skies with scattered showers and 10-mph winds in the evening.

The FAA has restricted the airspace from 4:30 p.m. to 7:30 p.m. Hawaiian time Wednesday, and then again on Thursday and Friday.

A lunar eclipse will begin in Hawaii at about 5 p.m., aiding visibility. Sunset will be at about 6:30 p.m.

The plan is to hit USA 193, also knows as NROL-21, with a heat-seeking Aegis missile fired from the Lake Erie.

The missile's heat-seeking capabilities may not be of much use, since the satellite's been dead for over a year and won't be generating any heat of its own until it re-enters the atmosphere.

But the targeting computers on the Lake Erie and the Decatur have been adjusted to compensate for the new target.

The intercepting missile will carry no warhead; it's meant to break up the satellite by sheer force.

The Aegis system was originally designed to work against ballistic missiles re-entering the atmosphere.

The Pentagon official said Wednesday morning that the window of opportunity would remain open until Feb. 29. The Defense Department expects the satellite to re-enter the atmosphere in early March.

President Bush approved the satellite shootdown last week out of concern that toxic fuel on board the satellite could crash to earth and injure humans.

USA 193 carries about 1,000 pounds of hydrazine fuel, meant to power orbital-adjustment thrusters, in a reinforced spherical tank.

Since the spy bird went dead soon after it entered orbit on Dec. 14, 2006, very little of its fuel was used.

What's left is frozen solid, only increasing the chances the heavy metal ball will survive the heat of re-entry.

Hydrazine could seriously burn the lungs of anyone who happened to inhale the fumes from a cracked fuel tank.

Officials will know nearly immediately whether the missile has hit the satellite, but it will take a day or two to know whether it the fuel tank has been destroyed, officials said.

Independent space experts downplay the health risks, noting that falling satellites have never injured anyone.

"We are worried about something showing up on e-Bay," GlobalSecurity.org director John Pike told the Associated Press last week, pointing out that some sophisticated surveillance technology could survive re-entry.

"The Chinese and the Russians spend an enormous amount of time trying to steal American technology," Pike said. "To have our most sophisticated radar intelligence satellite — have big pieces of it fall into their hands — would not be our preferred outcome."

The Russians are angry about the planned shootdown, contending it constitutes an unauthorized test of an anti-satellite weapon.

China startled the world in January 2007 by using a ballistic missile to destroy one of its old weather satellites in orbit, drastically worsening the problem of space debris, which poses a hazard to other satellites and humans in orbit.

The USSR and U.S. abandoned their own anti-satellite-weapon programs in the mid-1980s.

Because USA 193 is already so low, the risks of the planned shootdown creating more space debris are minimal. Most of the pieces would burn up Earth's atmosphere.

In the past 50 years, about 17,000 man-made objects have re-entered the Earth's atmosphere.

FOXNews.com's Paul Wagenseil and The Associated Press contributed to this report.