A senior U.S. military official says high waves in the Pacific, west of Hawaii, Wednesday will likely prevent a first attempt to use a specially modified ship-based missile to shoot down a falling U.S. satellite. VOA's Al Pessin reports from the Pentagon.

The senior official, who spoke to reporters on condition of anonymity, says he and others involved in the process want conditions to be as close to ideal as possible when they launch the interceptor missile. He says that is not expected to be true today, the beginning of an 11-day period during which the Navy could make as many as three attempts to shoot down the satellite.

The official says with so many days to work with, officials will not approve a launch that involves significant risk of failure during these opening days. He says the path of the satellite will provide only one ideal opportunity per day for a shoot-down, in large part because officials want to ensure that as much of the debris as possible re-enters the atmosphere over the ocean, rather than over populated areas. He says "well over 50 percent" of the debris is expected to fall within 4.5 hours after an intercept, and most of it is expected to burn up before it hits the water or the ground.

The official says crews and commanders will be on 24-hour alert until the mission is completed or the time runs out, but they would prefer to make their attempts during daylight in order to be able to maximize the use of optical sensors, as well as radar, to detect the results.

The most important part of the satellite is its tank of hydrazine fuel. Fumes from the fuel can cause respiratory problems and even cancer. A U.S. Navy official has said the missile guidance system can aim the interceptor warhead specifically at the relatively small tank on the school-bus sized satellite, even though the closing speed of the satellite and the warhead will be more than 30,000 kilometers per hour. Hydrazine tanks are made of very hard metal, and a similar one survived the destruction of the Space Shuttle Columbia as it re-entered the atmosphere five years ago.

Pentagon spokesman Bryan Whitman summarized the plan.

"We are going to maximize our opportunities to, one, destroy the tank in outer space, and, two, to bring the debris down in a way in which it mitigates risk to humans," he said.

Officials say U.S. Defense Secretary Robert Gates will make the final decision on whether to launch an interceptor missile, authority that usually rests with the captain of the ship involved. Whitman says the secretary wants to hear the details of each day's conditions, and recommendations from two senior generals.

He also repeated the U.S. rejection of charges from some countries that this is a test of a new U.S. anti-satellite weapon.

"We have been as transparent about that as we possibly can be," he said. "This is about reducing risk to human life on earth."

Officials explain that the three missiles prepared for this operation have been specially modified from their usual configuration, aimed at defending the United States against incoming ballistic missiles. They say there is no plan for an anti-satellite capability beyond this mission.

The United States sharply criticized China for shooting down one of its satellites just over a year ago. But U.S. officials say the two incidents are not comparable because China was specifically testing an anti-satellite weapon and because the malfunctioning U.S. satellite is in a much lower orbit than working satellites use.