for National Geographic News
The U.S. Navy is gearing up to use modified anti-missile rockets to shoot down an ailing spy satellite late tonight or tomorrow, depending on weather conditions at the North Pacific launch site.
As the countdown approaches, observers are still split on whether the primary motivation for the move is to protect public safety or to test weapons technology under the watchful eyes of foreign powers such as China.
The satellite, known as USA 193, went unresponsive to commands shortly after its launch on December 14, 2006, and is in an uncontrolled decaying orbit, the U.S. Department of Defense announced on February 14.
(Explore an interactive atlas of orbital objects.)
Left on its own, the school bus-size orbiter would crash on Earth sometime later this month or early next month, the department said in a press release.
According to government computer models, about 56 percent of the 5,000-pound (2,268-kilogram) satellite would survive reentry and hit the Earth.
At a February 14 press conference, officials added that President George W. Bush had authorized the shoot-down to prevent the satellite from releasing a toxic gas from its fuel tank.
Many analysts and bloggers, however, have speculated that the danger from the gas is minor.
"OK, so hydrazine looks pretty toxic. But what would the chance have been of it smashing through your roof?" asks the science and technology blog Exploring our World.
The Navy's real goal, skeptics say, is to counter a similar exercise in China last year and prove that U.S. rockets designed to intercept nuclear missiles can be retrofitted to hit satellites.
Burning Lungs, Seizures
In January 2007 China intentionally shot down one of its own aging weather satellites using a modified ballistic missile.
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