The Pentagon may try to shoot down failing spy satellite USA 193 on Wednesday, according to amateur sky watchers.

Ted Molczan, the dean of North American satellite spotters, who keeps an eye on the heavens from his Toronto apartment's balcony, on Monday posted on a satellite-observation Web site a "Notice to Airmen" issued earlier that day by the FAA's Honolulu Control Facility.

The notice, a standard advisory to commercial and private pilots, announces the closing of airspace over a large area of the Pacific southwest of Hawaii between 2:30 a.m. and 5:30 a.m. Thursday in Coordinated Universal Time (UTC).

That corresponds to between 4:30 p.m. and 7:30 p.m. Wednesday Hawaii-Aleutian Standard Time (HST), or between 9:30 p.m. Wednesday and 12:30 a.m. Thursday Eastern Standard Time.

FOX News' Adam Housley blogs about early shootdown window

Molczan, who predicted more than a year ago that USA 193 would re-enter Earth's atmosphere in early March 2008, calculates that the failing spy satellite will pass over the restricted area at about 3:30 a.m. UTC Thursday — 5:30 p.m. HST or 10:30 p.m. EST Wednesday, about an hour after the closure of the airspace goes into effect.

• Click here for the "NOTAM" Molczan posted to the Visual Satellite Observer's Home Page.

That's a mere 13 hours after space shuttle Atlantis is scheduled to land at Cape Canaveral. If Atlantis needs to land a day later, the satellite shootdown may also have to be pushed back.

Even better, as some bloggers quickly noticed, it's during a lunar eclipse over that section of the Pacific, making visual spotting of the satellite even easier. And it'll be just as the sun is setting, meaning that the satellite will be still be illuminated even as night falls.

• Click here for Ted Molczan's chart of the restricted airspace over the Pacific, and the satellite's trajectory over it (pdf).

Another Notice to Airmen posted Tuesday morning blocks out the same region of the Pacific 24 hours later, presumably for a second attempt at downing the satellite should the first try fail.

Navy officials told FOX News Tuesday that the "window of opportunity" will open as soon as Atlantis returns to Earth, which will likely be in the pre-dawn hours of Wednesday morning in Hawaii.

But the first attempt was likely to be Thursday, according to the officials, though they did not specify which time zone they were referring to.

The White House announced last week that the Navy would try to shoot down USA 193 using the Aegis missile cruiser USS Lake Erie, citing the health risks posed by the satellite's 1,000 pounds of frozen hydrazine fuel.

The Navy officials told FOX News the destroyer USS Decatur will also be armed with missiles and ready to take a shot as a backup to the Lake Erie.

The officials stressed that a definite time for the shootdown had not yet been set.

• Click here to visit FOXNews.com's Space Center.

USA 193, also known as NROL-21, is owned by the National Reconnaissance Office and lost power and radio communication soon after going into orbit on Dec. 14, 2006.

Very little of its hydrazine, normally used by satellite thrusters to counter orbital errors and decay, has been used, and experts think the spherical fuel tank would survive re-entry.

Hydrazine (N2H4) reacts violently with oxygen and would seriously burn the lungs of anyone who inhaled fumes from the cracked fuel tank.

However, 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.

Last week, Deputy National Security Adviser James Jeffrey discounted comparisons to the Chinese anti-satellite test.

"This is all about trying to reduce the danger to human beings," he said. "Specifically, there was enough of a risk for the president to be quite concerned about human life."

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.

The largest uncontrolled re-entry by a NASA spacecraft was Skylab, the 78-ton abandoned space station that fell from orbit in 1979. Its debris dropped harmlessly into the Indian Ocean and across a remote section of western Australia.

In 2000, NASA engineers successfully directed a safe de-orbit of the 17-ton Compton Gamma Ray Observatory, using rockets aboard the satellite to bring it down in a remote part of the Pacific Ocean.

In 2002, officials believe debris from a 7,000-pound science satellite smacked into the Earth's atmosphere and rained down over the Persian Gulf, a few thousand miles from where they first predicted it would plummet.

The Associated Press contributed to this report.