Space Debris
Space Junk hits Earth Often, not People
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Navy to shoot down satellite Feb. 20: The Navy will attempt to shoot down a wayward U.S. spy satellite as it falls toward Earth. NBC's Jim Miklaszewski reports.

Odds of anyone being hurt from falling debris: 1 in a trillion
By Seth Borenstein
updated 12:52 p.m. PT, Wed., Feb. 20, 2008

WASHINGTON - Giant chunks of manmade space junk — like the dead satellite that the U.S. government is trying to shoot down — regularly fall to Earth. Yet no one has ever been reported hurt by them.

Chunks of debris weighing two tons or more from satellites and rocket parts fall uncontrolled every three weeks or so, according to an analysis by a Harvard University astronomer who tracks satellites and space debris.

And that's just based on the last three years. Go back a decade or so when countries didn't try to control these falling objects. Back then, two-ton chunks fell to Earth much more frequently said Jonathan McDowell, who runs Jonathan's Space Report, which tracks the world's space launches and satellites.

It's likely that 50 to 200 "large" pieces of manmade space debris return to Earth every year, according to the Center for Orbital and Reentry Debris Studies. Bill Ailor, the center's director, like those at NASA's Johnson Space Center, said he was asked by the government not to comment specifically on the current satellite re-entry issue.

In the past 40 years, about 12 million pounds of manmade space junk has survived re-entering Earth's atmosphere, according to the orbital debris center.

Yet experts in the field know of only one report of a person being hit by space debris. Lottie Williams of Tulsa, Okla., was struck on the shoulder in 1997 by a small piece of debris from a discarded piece of a Delta rocket. She was unhurt.

The reason space junk doesn't regularly hit people is simple: About 70 percent of the Earth is water.

And on average there are about 130 people per square mile of land on Earth, but people don't take up a lot of space. Far more than 99.9 percent of the land on Earth is not occupied by a person at a given time, according to rough calculations by researcher Alex de Sherbinin of Columbia University. 

There is no one place on Earth that is more prone to space junk than others. Where satellites fall depend on their particular orbit.

So the orbital debris center that studies the issue puts the odds of anyone being hurt by any piece of re-entering space junk at one in a trillion, saying you are far more likely to get hit by lightning.

Using Columbia University's population density maps, McDowell calculated that at the highest possible risk, there's a 1-in-10,000 chance that the dead satellite could hit a person. However, it's probably closer to one in a million, McDowell said.

That doesn't take into account toxic fumes from the ton of frozen and dangerous hydrazine rocket fuel, which is the reason Pentagon officials said they needed to shoot down the dead satellite. The Centers for Disease Control and Prevention put out a notice to local public health officials warning of the toxicity of the fuel.

McDowell is skeptical, however, given the odds.

"My gut reaction is that this is just completely bogus," McDowell said of the decision to shoot down the satellite based on a public health threat. He doesn't completely discount the danger of the rocket fuel, however.


U.S. issues notice on downing of satellite
A Delta II rocket lifts off in December, carrying a reconnaissance satellite that failed hours later.

WASHINGTON (CNN)  -- The U.S. Navy likely will make its first attempt to shoot down a faulty spy satellite Wednesday night.

A Delta II rocket lifts off in December, carrying a reconnaissance satellite that failed hours later.

The U.S. government issued a formal notice warning ships and planes to stay clear of a large area of the Pacific Ocean west of Hawaii.

The notice says the two- and-a-half hour window begins 2:30 a.m. Thursday Greenwich Mean Time, which is 9:30 p.m. Wednesday on the East Coast, and 4:30 p.m. Wednesday in Hawaii.

The timing is also after the U.S. space shuttle Atlantis is scheduled to be safely on the ground.

Pentagon officials caution that the notice reflects the first opportunity to take a shot at the satellite, but it's possible the attempt could be delayed until later. Watch Pentagon spokesman Jeff Morrell describe the launch window

"We have to make the notification, but it's possible the conditions won't be ideal, or that everything won't be ready," said a Pentagon official who asked not to be identified.

Pentagon officials says if the first attempt to hit the satellite fails, there may be time for a second attempt, but that would only come after an assessment that would be hours or even days after the first attempt.

Because the 5,000-pound satellite malfunctioned immediately after launch in December 2006, it has a full tank of fuel. It would likely survive re-entry and disperse potentially deadly fumes over an area the size of two football fields, officials have said.

The Navy plans to fire at the satellite as it enters Earth's atmosphere at an altitude of about 150 miles.

Officials want the missile to hit the edge of the atmosphere to ensure debris re-enters and burns up quickly.

The Missile Defense Agency estimated the cost of a sea-based attempted intercept at $40 million to $60 million.

Without any intervention, Pentagon officials have said they believe the satellite would come down on its own in early March.

The option of striking the satellite with a missile launched from an Aegis cruiser was decided upon by President Bush after consultation with several government and military officials and aerospace experts, said Deputy National Security Adviser James Jeffrey.

"If we miss, nothing changes," said NASA administrator Michael Griffin. "If we shoot and barely touch it, the satellite is just barely in orbit" and would still burn up somewhat in the atmosphere, he said.

"If we shoot and get a direct hit, that's a clean kill and we're in good shape," he added.


Navy Shoots Satellite
Defense Dept. photo by U.S. Navy

The USS Lake Erie launches a Standard Missile-3 at a non-functioning National Reconnaissance Office satellite as it traveled in space at more than 17,000 mph over the Pacific Ocean on Feb. 20, 2008.

Defense Dept. photo by U.S. Navy Petty Officer 2nd Class Michael Hight

Satellite Shoot Down

U.S. Navy Petty Officer 2nd Class Andrew Jackson activates a modified tactical Standard Missile-3 from the Combat Information Center of the USS Lake Erie as the ship operates in the Pacific Ocean on Feb. 20, 2008. The Aegis cruiser launched the missile at a non-functioning National Reconnaissance Office satellite as it traveled in space at more than 17,000 mph over the Pacific Ocean. The objective was to rupture the satellite's fuel tank to dissipate the approximately 1,000 pounds of hydrazine, a hazardous material which could pose a danger to people on Earth, before it entered into Earth's atmosphere. USS Decatur and USS Russell were also part of the task force.

Defense Dept. photo by U.S. Navy

President George W. Bush decided to bring down the satellite because of the likelihood that the satellite could release hydrazine fuel upon impact, possibly in populated areas.

Defense Dept. photo by U.S. Navy

A single modified tactical Standard Missile-3 launches from the U.S. Navy AEGIS cruiser USS Lake Erie, successfully impacting a non-functioning National Reconnaissance Office satellite approximately 247 kilometers (133 nautical miles) over the Pacific Ocean.

Department of Defense

Joint Chiefs Vice Chairman Gen. James Cartwright points to a video during news conference at the Pentagon, Thursday, Feb. 21, 2008, hours after a Navy missile scored a direct hit on the failing spacecraft.

Credit: Conceptual animation by Analytical Graphics Inc. & Applied Defense Solutions, Inc.

Computer simulation of the missile's impact with the satellite.

SOURCE: Scientific American

Was a Satellite Shootdown Necessary?
An SM-3 missile U.S. Navy / AP

By Jeffrey Kluger 
Wednesday, Feb. 20, 2008

It's a measure of how peacefully human beings have used space in the 50-plus years we've been traveling there that we're a whole lot better at putting things into orbit than we are at blowing them back out. That, of course, is a function of practice. Thousands of pieces of machinery have been lofted into space since the launch of Sputnik in 1957 and almost all of them have either tumbled back down on their own or simply remained in orbit.

This week, the Pentagon tried something different. On Wednesday evening, it announced that it successfully launched a sea-based missile and shot down a crippled satellite gliding 150 miles overhead, in a $60 million effort to blast it out of the sky before it could tumble home and hurt someone. It's been a neat little feat on the part of the military planners — but that doesn't mean they're telling the whole truth about why they bothered in the first place.

The clay pigeon in the military's cross hairs was an unnamed, 5,000-lb. spy satellite that was launched in 2006 and never quite got its purchase in space, suffering a malfunction almost immediately upon its arrival in orbit. Comparatively low-orbiting craft like this one tumble back to Earth faster than high-orbiting ones, as the upper wisps of the planet's atmosphere produce increasing amounts of drag, pulling the object lower and lower. This one was on a trajectory that would have caused it to begin its terminal plunge sometime in March, sending it on a fiery descent that should have entirely — or at least mostly — incinerated it.

So why make the effort at such a complicated bit of sharpshooting just to bag a target that was coming down anyway? The Pentagon says it's all about safety. Five thousand pounds of out-of-control satellite can do an awful lot of damage if it drops on the wrong spot. What's more, this particular satellite is carrying a 500-lb. tank of frozen hydrazine fuel — nasty stuff if you're unlucky enough to inhale it. Striking the ground at reentry speed, the gas could immediately disperse over a patch of ground as big as two football fields.

None of this, however, was likely to happen. For one thing, 70% of the Earth's surface is water. Even considering that the flight paths of most satellites are designed to carry them over as much land as possible, that's still a lot of uninhabited square mileage lying below. NASA acknowledges that 3,000 satellites and 6,000 pieces of space debris are currently circling the planet — a pretty huge swarm of potentially incoming rubbish to justify devoting so much attention to just one.

The hydrazine argument is similarly suspect. It's extremely hard for a spacecraft component to survive reentry even if you want it to. The scientific experiments carried aboard the Apollo lunar modules were powered by radioactive fuel, which was itself encased in heavy ceramic just to ensure that it would survive such an accident. Even then, there were white knuckles whenever one flew since the risk existed that an uncontrolled reentry would crack the cask and leak radiation. The hydrazine tank — a hollow vessel — is nowhere near as robust and is unlikely to make it through the heat and aerodynamic violence of the plunge that awaits it, meaning that it will spill its contents high in the atmosphere, where it will represent barely a breath of gas that will disperse harmlessly.

The more believable explanation for the duck hunt is that it's been an exercise in politics rather than safety. Washington was none too pleased in January of 2007 when China shot down one of its own weather satellites after it had outlived its usefulness, a bit of technological sword-rattling that proved it could target any other nation's orbiting hardware with equal ease. Beijing too made vague claims of worrying about the public weal, but Washington saw the act more as the political statement it probably was, and concluded — correctly — that American spy satellites are not quite as safe as they once were. An American shootdown would be one way to return the gesture. The timing is particularly suspicious since Russia and China issued a joint condemnation of the militarization of space only days before the Pentagon went public with its plans. While Beijing's sudden pacifism is hardly credible after it own exercise in cosmic skeet-shooting, neither is the Washington's insistence that there is no linkage between the two events.

Another possibility is that the Pentagon was indeed nervous about something aboard the satellite, but not the tank of fuel. Spy satellites are, by definition, made of secret hardware, and nothing so pleases one military power as the chance to seize and pick over the technology of another. Should American camera and communications components fall into the wrong hands, whatever tactical advantage was gained in developing them would be lost.

With success announced on Wednesday night, the Pentagon is hardly likely to change its explanation now. They say the mission to destroy the satellite been accomplished, and —for now—any questions that it's raised may be gone along with it.

SOURCE: Time Online

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