Network News

X My Profile
View More Activity
The new Washington
Post Weather website
Jump to CWG's
Latest Full Forecast
Outside now? Radar, temps
and more: Weather Wall
Follow us on Twitter (@capitalweather) and become a fan on Facebook
Posted at 11:30 PM ET, 02/20/2008

If the Missile Misses

By Dan Stillman

A satellite's journey through the atmosphere

From the Pacific Ocean, a Navy ship is expected as early as tonight or tomorrow to shoot down, or at least attempt to do so, an out-of-control U.S. spy satellite that is falling toward Earth. Government officials say the satellite, primarily due to its tank containing 1,000 pounds of unused toxic fuel, could pose a safety threat if it is not intercepted.

Believe it or not, approximately 100 to 200 large manmade objects reenter the atmosphere each year, usually with little fanfare. These objects -- mostly satellites and related hardware -- encounter levels of the atmosphere quite different from what we're familiar with closer to the Earth's surface.

Most satellites orbit Earth at altitudes from 100 miles to more than 22,000 miles up, and zoom around the planet at speeds from about 7,000 mph to 17,000 mph.


Vertical profile of the atmosphere showing the altitude and temperature of different layers. Click image to enlarge. Courtesy National Weather Service.

As a dying satellite loses speed, it also loses altitude and drops through the exosphere, the outer edge of the Earth's atmosphere where the line between space and atmosphere is fuzzy at best. The top of this uppermost layer of the atmosphere is more than 6,000 miles above the ground. The density of molecules, mainly hydrogen and helium gas, is so low that the chance of them bumping into each other is very small. With few collisions to slow them down, some molecules gather enough speed to escape into space. Because of its low density, the exosphere has little effect on a falling satellite, and in fact some satellites orbit Earth within this layer.

Around 430 miles above the Earth's surface, a falling satellite would reach the top of the thermosphere. Temperatures decrease dramatically through the thermosphere, from a searing 3,000°F or so near the top of the layer to a frigid minus 150°F near the bottom. On the other hand, the density of the air increases with decreasing height, causing more and more friction between the atmosphere and satellite as it falls. The heat generated by the friction can begin to breakup, melt or vaporize the satellite, or lat least parts of it, as it reaches the lower end of the thermosphere.

The top of the mesosphere begins about 50 to 55 miles above the ground. After bottoming out at the bottom of the thermosphere, temperatures rise moving downward through the mesosphere, approaching 30°F by the bottom of the layer. But air density continues to increase with decreasing height. Any unprotected components of a falling satellite that make it through the thermosphere are unlikely to survive the increased friction of the mesosphere. It was in this layer that the space shuttle Columbia disintegrated while reentering the atmosphere in February 2003.

About 30 miles from the Earth's surface, temperatures begin to fall again. This marks the top of the stratosphere, which is probably best known for its "good ozone." Ozone gas occurs naturally in the stratosphere and absorbs harmful ultraviolet radiation from the sun, limiting the amount that reaches the ground. But manmade chemicals called chlorofluorocarbons (CFCs) have been conclusively linked to the "ozone hole," a large area of decreased ozone that appears annually over Antarctica from September through December. Although CFCs were banned in the late 1980s, recovery of the ozone hole has lagged due to the long lifetimes (more than 40 years) of CFCs in the atmosphere. Only satellite parts that are protected by specially designed heat shields have a legitimate chance of surviving into the stratosphere.

A final shift in temperature occurs around 5 to 10 miles above the ground. This is the top of the troposphere, the layer that contains the clouds we see, the weather we experience and the air we breathe. Temperatures in the troposphere increase with decreasing height, climbing from around minus 50°F to minus 100°F at the top to the temperatures we feel here at the surface. Ozone found in the troposphere is considered "bad ozone." It forms when pollution from vehicles, factories and other manmade sources interacts with sunlight, and too much of it can result in unhealthy air. Any satellite component that reaches the troposphere is likely to hit the ground at a relatively low speed, slowed by the increasing density of the air, but can still be a threat to people and property.

How much of a threat? According to the Center for Orbital and Reentry Debris Studies, more than 50 objects are believed to have survived reentry and hit the ground over the past 50 years. But in that time, only one person has reported being struck, and she was not injured. Overall, the odds of being hit and hurt by satellite debris is less than one in 1 trillion, far less than the one-in-1.4-million chance of someone in the United States being hit by lightning.

By Dan Stillman  | February 20, 2008; 11:30 PM ET
Categories:  Education, Science, Technology  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   Del.icio.us   StumbleUpon   Technorati   Google Buzz   Previous: Alert: Winter Storm Watch Issued
Next: Forecast: Brief Calm Before Next Storm

Comments

Thanks for posting this! I love this sort of stuff. I would PAY to watch that thing get hit and hurdle back to Earth. Heck, I would pay to watch the meteor that struck last night on the west coast in Oregon! If you haven't seen the video on the meteor in portland last night, look it up, it's awesome.

I also can't wait until tonight's lunar eclipse...provided the skies magically clear by 10PM.

How awesome has today been? Shuttle landing, satellite bashing, alberta clipper teasing us with snow, meteor (hits?) west coast, and the lunar eclipse. COOL!

Posted by: weatherdudeVA | February 20, 2008 7:52 PM | Report abuse

fyi, its "missile" not "missle" :)

Posted by: jtf | February 20, 2008 7:56 PM | Report abuse

Nice article, very informative. Good read.

Posted by: Period | February 20, 2008 7:57 PM | Report abuse

Hope you have fun with the snow. I bet there won't be much accumalation simply due to them being prepared; (LOL) if they weren't prepared you would probably get more snow then expected with 2-3"

Posted by: Heatblizzard | February 20, 2008 8:19 PM | Report abuse

Theodore Postol, a professor of science, technology and national security policy at MIT, a former science adviser to the Navy, cast considerable doubt tonight on the alleged threat from the hydrazine.

Posted by: Steve, Capital Weather Gang | February 20, 2008 8:58 PM | Report abuse

Here's a picture of the ongoing eclipse as seen a few minutes ago in NW DC.

Posted by: Ian, Capital Weather Gang | February 20, 2008 9:07 PM | Report abuse

Ian, having trouble accessing the picture through the link.I am looking forward to seeing your shots. I lost my camera recently, and it's killing me! Especially at moments like this :(

Posted by: Snowlover2! | February 20, 2008 9:16 PM | Report abuse

in recent news, away from the eclipse..i know im not supposed to. but the NAM is showing some nice cold rain for the dc area. not what i like to see, ugh

Posted by: thejesse2442 | February 20, 2008 9:28 PM | Report abuse

in recent news, away from the eclipse..i know im not supposed to. but the NAM is showing some nice cold rain for the dc area. not what i like to see, ugh

Posted by: thejesse2442 | February 20, 2008 9:28 PM | Report abuse

WOW! It's so...clear out!

The roads are iced over in Lake Ridge. At least mine is. The snow is beginning to blow around and make mini-drifts on things. Watch out for that, as it's supposed to get into the low 20s tonight.

The moon is awesome looking, as usual.

Posted by: weatherdudeVA | February 20, 2008 9:28 PM | Report abuse

It pretty much looks like a waxing moon. I get solar and lunar mixed up. As usual... oh well.

Posted by: Peter | February 20, 2008 9:29 PM | Report abuse

Peter: Just remember that solar is the less common one. The one that will fry your eyes out if you look at it without special glasses, lol.

Posted by: weatherdudeVA | February 20, 2008 9:47 PM | Report abuse

Gorgeous view of the lunar eclipse in now-crystal clear skies, right off my balcony!

Posted by: ~sg | February 20, 2008 9:58 PM | Report abuse

Woohoo..The clouds parted and the lunar eclipse is in full view!

Posted by: Sara in Oakton | February 20, 2008 10:01 PM | Report abuse

If a *solar* eclipse were to happen during the daytime, would it get really dark outside for like an hour? That'd be sweet.

Posted by: Peter | February 20, 2008 10:10 PM | Report abuse

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1007 PM EST WED FEB 20 2008

...WINTER STORM WATCH IN EFFECT FROM THURSDAY EVENING THROUGH
LATE FRIDAY NIGHT...

THE NATIONAL WEATHER SERVICE IN STERLING VIRGINIA HAS ISSUED A
WINTER STORM WATCH...WHICH IS IN EFFECT FROM THURSDAY EVENING
THROUGH LATE FRIDAY NIGHT.

LOW PRESSURE ACROSS THE GULF OF MEXICO WILL BEGIN SPREAD SNOW ACROSS
THE MID ATLANTIC REGION THURSDAY NIGHT. AS WARMER AIR ALOFT MOVES
INTO THE AREA ON FRIDAY...SNOW IS EXPECTED TO MIX WITH THEN CHANGE
TO SLEET AND FREEZING RAIN. THIS NEXT STORM COULD BE A HIGH
IMPACT EVENT...WITH THE POTENTIAL FOR SIGNIFICANT AMOUNTS OF SNOW
AND...OR ICE ACCUMULATIONS.

A WINTER STORM WATCH MEANS THERE IS A POTENTIAL FOR SIGNIFICANT
SNOW...SLEET...OR ICE ACCUMULATIONS THAT MAY IMPACT TRAVEL.
CONTINUE TO MONITOR THE LATEST FORECASTS.

$$

ROGOWSKI/PELOQUIN

Posted by: jtf | February 20, 2008 10:10 PM | Report abuse

Good Article, I love learning new things.
So what layer in the atmosphere do the cumulomimbus clouds form...or should expand to..Dont some of cumulonimbus clouds penetrate into high levels of the trophosphere in severe storms.

Posted by: StormChaser | February 20, 2008 10:13 PM | Report abuse

StormChaser: Cumulonimbus clouds form in the troposphere, but can have "overshooting tops" into the tropopause -- the layer between the troposphere and stratosphere...

Posted by: Jason, Capital Weather Gang | February 20, 2008 10:29 PM | Report abuse

Wow! Never knew that the top of the thermosphere was so hot. It goes to show how powerful the sun's light is when there's nothing to block it.

A sparkling blanket of snow, a lunar eclipse, my 17th birthday tomorrow... there's not much more to ask for!

Posted by: mcleaNed | February 20, 2008 10:41 PM | Report abuse

CNN reporting the satellite has been hit.

Posted by: Ian, Capital Weather Gang | February 20, 2008 10:48 PM | Report abuse

To Peter who was wondering about the daytime solar eclipse -- there was one in I want to say 1994, and IIRC it got noticeably dimmer outside but definitely not like nighttime. It was more along the lines of mid-twilight.

Posted by: Anonymous | February 21, 2008 11:01 AM | Report abuse

The EPA has been kept out of the loop on this one. Therefore, this has nothing to do with a fuel tank. This has something to do with weapons tests.

Posted by: Ken | February 21, 2008 1:23 PM | Report abuse

The comments to this entry are closed.

 
 
RSS Feed
Subscribe to The Post

© 2012 The Washington Post Company