Within days, a Pearl Harbor-based Navy ship may be called upon to perform a first: try to shoot down a failing minivan-sized military satellite while it's still in space.

The cruiser USS Lake Erie is expected to fire one or more modified SM-3 missiles to punch a hole in the 5,000-pound spy satellite over the Pacific. Two other Navy ships will provide trajectory information and backup.

The window to accomplish the mission will open in three to four days, and remain open for about a week after that, officials said.

President Bush ordered the shoot-down attempt after security advisers said the craft's re-entry posed potential danger to civilian populations.

James Jeffrey, deputy national security adviser, said with descent, the satellite could release more than 1,000 pounds of hydrazine fuel. The fuel could spread across an area equal to two football fields.

The goal is to hit the satellite just before it enters earth's orbit so that the hydrazine tank explodes.

Hydrazine is similar to chlorine or ammonia and affects the lungs and breathing.