WASHINGTON (CNN) -- The attempt by the U.S. Navy to use an anti-missile missile to shoot down a potentially hazardous satellite will cost between $40 million and $60 million, Pentagon officials told CNN on Friday.
A missile is launched from the Navy guided missile cruiser USS Shiloh during a 2006 test.
The missile alone costs almost $10 million, Lt. Gen. Carter Ham said at a Pentagon briefing. He declined to give an overall cost estimate.
"I think we're working with all the parties to [find] how much did it cost to modify the missiles, the fire control, that kind of business," he said.
Pentagon officials argue the effort is worth the expense because of the slim -- but real -- chance that the satellite's unused fuel, 1,000 pounds of toxic hydrazine, could land in a populated area.
Because the super-secret spy satellite malfunctioned immediately after launch in December 2006, its fuel tank is full, and it would probably survive re-entry and disperse harmful, even potentially deadly fumes over an area the size of two football fields.
The missile will carry no warhead; the objective is to break the satellite apart through the force of impact alone, defense officials said.
One Pentagon official -- who spoke on condition of anonymity because the planning for the operation remains classified -- told CNN that since early January, a Navy team, including 200 industry experts and scientists, has been working furiously to modify its sea-based Aegis missile defense system so it can shoot down a satellite in low orbit.
Among the challenges is modifying sensors designed to detect the heat from an incoming warhead so they can spot the much-cooler satellite, which has no heat source and is warmed only by the sun's rays.
In addition, the official says, a floating X-band radar has to be modified to track the satellite's trajectory, and the "fire-control" systems on the Navy ships also needed modification.
No attempt will be made to shoot down the satellite until after the U.S. space shuttle lands next Wednesday.
"The window will open when the shuttle is on the ground," Ham said.
Pentagon officials say three missiles have been modified for the mission, so in theory, the Navy may get three shots at the satellite, although only one at a time.
"They want the period of a day or two to assess the effect of the first missile ... to probably get an orbit or two, to get an understanding of what effect the first intercept had on the satellite before launching another interceptor," Ham said.
The Aegis cruiser USS Lake Erie was chosen for the mission. It's fully equipped with sea-based missile defense systems, has long been the Navy's primary ship for the sea-based missile defense program and has the technology needed for the operation, officials said.
It will be accompanied by two destroyers --- the USS Decatur and the USS Russell -- at an undisclosed location in the Pacific Ocean north of the equator. The Decatur will feed trajectory information to the Erie, and the Russell will back up the Decatur.
Defense officials say the ships' radars and software were modified to track targets much faster than the ballistic missiles they were designed to track.
A host of ground-based radars, telescopes and sea-based radars will help determine if the satellite was hit. The Air Force also will have a plane in the air that can detect the release of hydrazine gas.
The USNS Observation Island, a ship that uses telemetry to monitor objects in space, will collect information on the satellite both before and after the missile launch.
The Navy will use its $9.5 million Standard Missile 3 in the shoot-down. The combined speed of the missile and satellite at impact is expected to be about 22,000 miles per hour.
The government started thinking about how to approach the satellite problem in December. And on January 4, President Bush and various senior officials agreed to begin planning for the shoot-down.
On Tuesday, the president approved the plan.
CNN's Mike Mount contributed to this report
