Spy Satellite's Destruction Might Be Visible
A Standard Missile-3 (SM-3) is launched from the Pearl Harbor-based Aegis cruiser, USS Lake Erie (CG 70) on November 6, 2007 enroute to an intercept as part of a Missile Defense Agency test. A similar missile will be used to shoot down a crippled spy satellite in coming weeks.
Credit: U.S. Navy.

Debris from the Department of Defense's planned shoot-down of a spy satellite may be visible to skywatchers in the northwestern United States and Canada, according to the U.S. Naval Observatory.

Although it's hard to predict what will happen if the rocket succeeds in impacting the satellite, there is a chance that observers will see broken-off pieces of the satellite reflecting sunlight or burning up as they fall through Earth's atmosphere. The window of opportunity for the attempt is open for the next 10 days or so, though bad weather and high seas make it unlikely the exercise will occur today.

"There is a possibility that if someone were to have clear skies in the Pacific Northwest or Canada, they might see some of the debris," said Geoff Chester, public affairs officer for the U.S. Naval Observatory in Washington, D.C. "We just don't know. If the debris does enter the atmosphere then it's actually quite possible to see it anywhere along the ground track of the satellite."

Because only two satellites have been shot down before, each under unique conditions, experts don't have much experience to go on in predicting what to expect.

"Depending on the size of the fragments, it's possible that you might be able to track some with the naked eye, some with binoculars," said Chester. "We just don't know. It's virtually impossible to predict exactly what it's going to look like. If the debris enters the atmosphere then you would see something that would be akin to a swarm of meteors."

In addition to favorable weather conditions, many factors have to go right for this sky show to appear.

"They have to hit it first," Chester told SPACE.com. "It depends entirely on how many pieces this thing winds up getting busted up into. It's quite possible you would see the debris entering the atmosphere anywhere along the ground track of the satellite."

The satellite's path will take it east from Hawaii to the northwestern U.S. and British Columbia, then over the whole of Canada, down across the Atlantic, over West Africa, and back over the south Atlantic.

The actual impact will not be visible to anyone, because it will occur over Hawaii during daylight, Chester said. Even if the Department of Defense does not attempt to shoot down the satellite tonight, all future attempts will also be during daylight over Hawaii.

If Hawaii were dark at the time of the impact, there would be a chance that observers would see a cloud of hydrazine gas created when the satellite's liquid fuel spewed into the vacuum of space.

"The hydrazine would probably form a bright expanding cloud that would move rapidly across the sky along or close to the original satellite ground track and slowly dissipate," Chester said. "But I don?t know for sure."

In any case, there would not be a bright explosion to see because the rocket sent to impact the satellite is only supposed to hit it, not explode upon impact.

SPACE.com contacted several large ground-based observatories, and none reported having plans to attempt observations.