Friday, August 8, 2008

U.S. Navy Satellite Shoot -Down: The Inside Story

U.S. Satellite Shootdown: The Inside Story
By James Oberg
First Published August 2008

While assessing the hazards of hydrazine reentry from space, a journalist discovers the hazards of media commentary as well

Assessing technological risk is a thorny enough problem here on Earth, even with our experience and our intuition about familiar uncertainties, factors, and processes. But transport the problem into the unearthly venue of outer space, where human experience is limited, and sound assessment becomes astronomically more challenging.

A notable and illuminating case in point was the U.S. decision earlier this year to use a missile to knock out a derelict spy satellite, to head off the possibility of its splashing a half ton of toxic hydrazine fuel somewhere on Earth. That official explanation of the shootdown—and, it turns out, an entirely plausible and credible explanation—nonetheless met with a chorus of public criticism and skepticism. Coming as it did barely a year after China shot down one of its satellites with a missile, in what struck many observers as an obvious antisatellite weapon demonstration, the U.S. shootdown was widely, but I believe incorrectly, seen as a response to that event.

To be sure, the shootdown of the U.S. satellite was an impressive feat of technology. The Navy missile launched on 21 February 2008 achieved a head-on collision with the 2.3-metric-ton USA 193, dispersing the contents of the vehicle's propellant tank [see photo, “Hydrazine Bomb”] harmlessly in space.

To accomplish the intercept, military teams had to reprogram the guidance system of an antimissile missile designed to target much slower and lower missiles. That meant designing an intercept orbit that maximized the infrared brightness of the target and provided a ground track subsequent to the intercept that passed mostly over water or lightly populated regions for the first few hours. It also meant training the missile's onboard computer not only to home in on the rapidly approaching target outline but also to shift position at the last possible millisecond to hit a “sweet spot,” behind which the fuel tank was installed.

Read the full story by clicking on the link under the "Topical Links" heading at the upper right top of this page.

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