Satellite Shoot Down: How It Will Work

The U.S. Navy could shoot down an errant spy satellite as early as Wednesday night. Now a new computer model shows what might happen.

The spy satellite USA-193, also known as NROL-21, was launched aboard a Delta II rocket on Dec. 14, 2006 from Vandenberg Air Force Base in California. Shortly after the satellite reached orbit, ground controllers lost contact with it. Though the satellite's objective is secret, many believe it is probably a high-resolution radar satellite intended to produce images for the National Reconnaissance Office.

On Feb. 14, senior U.S. government officials at a Pentagon press briefing described a Defense Department plan to try and shoot down the defunct satellite, after becoming convinced that the spacecraft's toxic hydrazine fuel posed an unacceptable risk to people on the ground. The attempted strike could come Wednesday evening.

With this press information, computer modelers Bob Hall and Tim Carrico at Analytical Graphics, Inc. (AGI) put together a computer-generated simulation of the missile-satellite collision. The model shows a hypothetical deployment of U.S Navy ships in the Northern Pacific Ocean and the firing of a Standard Missile 3 at the failed satellite.

Information the modelers do know:

• The satellite has a mass of about 5,015 pounds (2,275 kilograms).
• The missile would be fired from a ship in the North Pacific Ocean.
• The interception would occur at an altitude of about 149 miles (240 kilometers).
• The satellite and missile would close on one another at a velocity of about 22,783 mph (36,667 kph).

If left alone, the satellite is expected to re-enter Earth?s atmosphere some time between the end of February and early March. About 2,500 pounds (1,134 kilograms) of satellite material would survive re-entry (the rest would burn up), including 1,000 pounds (453 kilograms) of hydrazine, according to a statement from the U.S. Department of Defense.

The collision between the fired missile and the satellite would not only break the massive hunk of metal into pieces but would also speed up its tumble through Earth's atmosphere.

"If you want to bring something down, you slow it down. You apply a force on it which results in it being slowed down and decrease in its orbit," Carrico told SPACE.com. "Right at that point where they want to engage [the satellite] is at the edge of the atmosphere, so you're bringing it down faster."

The plan comes on the heels of the intentional destruction last year of China's Fengyun-1C weather satellite, which produced a flurry of concern over the hostile-or-not nature of the firing as well as a serious load of shrapnel littering Earth orbit. That debris is still in space, frustrating mission managers and satellite operators forced to dodge the potentially debilitating bits.

USA-193 is already on its way toward Earth and the interception will take place at a much lower altitude than that of the China satellite, presumably meaning that whatever happens, there will not be a fresh load of small junk sent into perpetual orbit.

If more details were made public, the model results could change depending on several factors, including the location of the ships and when the missile is fired.

"How the missile hits the satellite will affect how quickly the debris re-enters and what the velocity is between the objects and how they hit," Hall said. "Are they attempting to get most of the debris to come down in the Pacific almost immediately? Or ... over the course of two or three revolutions, is most of it going to start to fall out? If we had different information about the engagement we could re-run our model.

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