Bus sized UARS satellite crashing back to Earth Friday

[LEDAdd1ct]

The "Estimated human casualty risk (updated to 2011): ~ 1 in 3200" isn't indicating a 1 in 3200 chance of a particular individual casualty. It's indicating the chance of any individual casualty. That extends chances in your favor by a few billion.

Empath, could you please explain the statistic to me in simpler terms? I'm not an idiot, but I am having trouble grasping the distinction. :thanks:

 

[LEDninja]

... It belongs to the U.S. Government. ... For any geographically challenged members that puts the U.S. right in the target zone.

A U.S. satellite should return to the U.S.A. On its own if possible.

No fun looking for another country's satellite. I still remember the search for a Russian satellite powered by a nuclear reactor instead of solar panels. Never found the reactor BTW.

This satellite was decommissioned back in 2005-2006. Then brought to a lower orbit to avoid hitting other satellites. They should have brought it down all the way then. A powered reentry would have a much better chance of coming down where they wanted rather then somewhere on earth.

 

[DM51]

... could you please explain the [1 in 3200] statistic to me in simpler terms? I'm not an idiot, but I am having trouble grasping the distinction. :thanks:

It means the chance of a fragment hitting someone are 1 in 3200. As there are ~6,000,000,000 people in the world, the chance of it hitting you are about 1 in 20,000,000,000,000.

 

[Colorblinded]

This satellite was decommissioned back in 2005-2006. Then brought to a lower orbit to avoid hitting other satellites. They should have brought it down all the way then. A powered reentry would have a much better chance of coming down where they wanted rather then somewhere on earth.

It's possible they set it on a course to have it land in the US back then... maybe. I don't know how well they can predict the exact path of a powerless orbiting satellite that many years in to the future.

 

[DM51]

I don't know how well they can predict the exact path of a powerless orbiting satellite that many years in to the future.

They can't predict it with any accuracy, really - it's basically out of control. They'll get a better idea of where it's likely to fall as the time gets nearer. As almost 70% of the earth's surface is sea rather than land, the likelihood is it will fall into the sea.

 

[AnAppleSnail]

Knowing what little I do about satellite de-orbiting, I'll try to shed a bit of light here.

An orbit: Imagine a big cannon. If you shoot a cannonball fast, it will travel rather far. If you shoot it far enough, it will hit the ground over the horizon, since the ground will curve down below the shot's path. If you shoot fast enough, the cannonball's trajectory will not touch the ground for quite some time - possibly never.

The International space station is in orbit. If the Space Shuttle links up and pushes it along its orbit, its altitude will slowly increase as it speeds up. Slowing down an orbiting object will decrease its altitude, and slowing it enough will (crash)-land it on the Earth.

Most methods of de-orbiting require a lot of fuel. A satellite goes quite fast in its orbit, and to slow down enough to come down quickly uses more fuel than it has - so a quick de-orbit is out.

A slow de-orbit is harder to predict. The atmosphere attenuates to lower and lower densities, but temperature and solar fluctuations make it more or less dense at a satellite's orbital height. This increases or decreases the braking that will bring the satellite down. If you have a low orbit, it might circle the Earth once an hour. Uncertainty of as much as 15 minutes means that it would hit a quarter of the Earth from where you thought. Given +/-, that's half the Earth under fire.

Satellite wreckage is dangerous. The fuel (often hydrazine) is very toxic, and leaks from wreckage. Often that burned up on the way down. Other chemicals can be dangerous, and of course there are heavy pieces of metal falling out of the sky. Some solid-rocket motors weigh about 1 metric ton on impact.

There is a possible non-fuel-using de-orbit method that is faster and slightly more predictable than un-controlled de-orbiting. Paying out a conductive wire from an orbiting satellite low enough in the ionosphere will slow the satellite. The conductive wire travels through the Earth's magnetic field, producing a braking force. This only works in the ionosphere, because the return path for electrons is the ionosphere. It's rather like a bicycle dynamo. There have been attempts to mount a de-orbit tether reel on every satellite.


Summary: Satellite landings are hard to predict. Satellites do not make good hats, and wreckage should not be licked. De-orbiting satellites in a way that is easy to predict (that is, quickly) costs hundreds of thousands or millions of dollars worth of fuel in orbit. For slower methods (tether or uncontrolled) it is harder to estimate landing zones.

 

[Colorblinded]

They can't predict it with any accuracy, really - it's basically out of control. They'll get a better idea of where it's likely to fall as the time gets nearer. As almost 70% of the earth's surface is sea rather than land, the likelihood is it will fall into the sea.

Kind of my suspicion. Up to an extent you can make a prediction (not 5-6 years) but with so many variables it's basically just a guess that ultimately states: "well, it should probably land on our heads in late 2011."

 

[Steve K]

Knowing what little I do about satellite de-orbiting, I'll try to shed a bit of light here.
<..... a big snip.... >

Summary: Satellite landings are hard to predict. Satellites do not make good hats, and wreckage should not be licked. De-orbiting satellites in a way that is easy to predict (that is, quickly) costs hundreds of thousands or millions of dollars worth of fuel in orbit. For slower methods (tether or uncontrolled) it is harder to estimate landing zones.

that's an excellent summary! Any satellite in low earth orbit (which is most satellites) experiences a little bit of drag from the atmosphere that will eventually cause it to return to earth. The UARS was slowed down by a controlled burn in 2005 which put it in a lower orbit with thicker air, which caused it to return sooner than it would have otherwise. Still... it's taken 6 years to finally make it back home. With the odd shape and lousy aerodynamics that it has, it's anyone's guess where it'll eventually end up.

Steve K.

 

[Mattb]

Just googled and found this:

http://www.foxnews.com/scitech/2011...-nasas-falling-65-ton-satellite-in-real-time/

Quoting a portion of the article:

"The 20-year-old research satellite is expected to break into more than 100 pieces as it enters the atmosphere, most of it burning up. Twenty-six of the heaviest metal parts are expected to reach Earth, the biggest chunk weighing about 300 pounds (136 kilograms). The debris could be scattered over an area about 500 miles (800 kilometers) long."

300 pounds!!! :shakehead

 

[Steve K]

The NASA site for the satellite is here.

The report describing the 26 items that are expected to impact the earth is here.

The report has the info on the size, weight, material, etc. of each of the parts (see page 8). Oddly, it lists the batteries as being made of stainless steel, which only describes the shell of each cell. Each battery is about 100 pounds and rather dense, so if you see one coming your way, try to jump out of the way.

To me, the most interesting bit of data on page 8 is the "debris casualty area" for each of the chunks. Each of the batteries has a debris casualty area of 0.91 square meters, so they really have to hit you directly to hurt you (and it *will* hurt!). A big piece of the structure has a debris casualty area of 2.44 square meters, so it's going to be harder to jump out of the way. It's the 300 pound chunk, but it's just made out of aluminum, so it's not going to hurt quite as much as the batteries.
Good news, eh??

Steve K.

 

[LEDninja]

Oddly, it lists the batteries as being made of stainless steel, which only describes the shell of each cell. Each battery is about 100 pounds and rather dense, so if you see one coming your way, try to jump out of the way.

What flashlight will they fit?:naughty:

Each of the batteries has a debris casualty area of 0.91 square meters, so they really have to hit you directly to hurt you (and it *will* hurt!). A big piece of the structure has a debris casualty area of 2.44 square meters, so it's going to be harder to jump out of the way. It's the 300 pound chunk, but it's just made out of aluminum, so it's not going to hurt quite as much as the batteries.

If I got hit I'd be dead either way.

 

[Steve K]

What flashlight will they fit?:naughty:

I'll admit, it was vaguely tempting to think about how you could use one or two of the battery's cells. Each cell was rectangular and weighed a few pounds each. You can see the the photo of the power module here, and you can see the three batteries on the bottom half of the module. Each battery is made of 22 cells connected in series. Lots of energy in those batteries, and we basically handled them as if they were explosives. That was because if you ever dropped a wrench across the terminals or such, they would release all of their energy quite quickly.... this was called "rapid spontaneous disassembly".

The batteries were supplied by Gates in Florida, and were very, very carefully matched. They must have done a good job, because the batteries got (partially) charged and discharged every 90 minutes for about 15 years.

Steve K.

 

[LEDAdd1ct]

Thanks for the concise explanation, DM51.

If I remember correctly, the article said there was no fuel left, which is a good thing.

Hey, if it lands in my yard and makes some pretty craters, I'll offer a CPF discount of 50% to come and stare at it.

 

[matrixshaman]

"fairly solid evidence that these satellites contain nuclear material"???

Please, would you share that with us?

For what it's worth, I was part of the group at McDonnell Douglas that provided the Modular Power Subsystem, which takes power from the solar panel, charged up the nicad batteries in our module, and provided the battery power to the rest of the satellite. The three batteries, which each weigh about 100 pounds, are on the list of the 26 chunks that are expected to make it back to the surface of the earth.

I had the pleasure of transporting one of the MPS electronics modules (I think it was the Power Regulator Unit) to Kennedy Space Center and helped swap it out for the one in the MPS (don't recall why). Pretty neat, and was in the clean room with the UARS satellite itself.
You can get some tech details on the MPS module from our simple sales literature here and here.

I'm not sure why the gov't doesn't want people to keep any debris... maybe just to discourage people from traveling into the impact area prior to the event and getting injured? Besides, some of the stuff in the satellite is toxic. Certainly the cadmium in our nicads is toxic. The beryllium used in some of the satellite structure is toxic too, if it has oxidized. BeO is not uncommon in power semiconductors, and the packaging often contains warnings.

Anyway, don't listen to the conspiracy theories or other craziness out there. Just stay indoors, and put on a hard hat... just in case you win the 1 in a trillion lottery.

Steve K.

'Nuclear powered satellites' google search yields 320,000 hits
Here is just a few:

http://www.spacedaily.com/reports/Nuclear_Power_In_Space_999.html

Nuke powered satellite expected to hit Earth (old news - this already happened)
http://www.nytimes.com/1988/05/14/w...atellite-expected-to-hit-earth-in-summer.html

http://www.space.com/6322-nuclear-powered-soviet-satellite-acts.html

Russia to build Nuclear powered satellite to gobble up old satellites and space debris - this is what is needed but not sure about the nuke powered:
http://dvice.com/archives/2010/11/russia-to-build.php

But if you are saying you know the UARS has no nuclear power than that's good news.

 

[cdrake261]

It means the chance of a fragment hitting someone are 1 in 3200. As there are ~6,000,000,000 people in the world, the chance of it hitting you are about 1 in 20,000,000,000,000.

If I did math right, it's one in 187,500 chance world wide.

Or one in 90,625 chance of hitting one person in the USA

 

[beerwax]

i thought 'they' could predict reasonably accurately the band that the satelite will land in. f'n' miles either side of the orbit path. and they would have tried for an orbit path that didnt pass over washington new york bejing etc. look at a globe and you will seeyou can pick orbits that spend more time or less time over water and a water landing i would think would be the preferred option.

the debris casualty area - i wonder if that only applies to a hit to a human body or allowance has been made for events like hits to a car plane boat lpg gas tank.

anyway the correct way to calculate the odds for someone in the crash window is 32000 times the number of folks in the crash window, not the number of folks on the planet.

a couple of big chunks expected . is there an expected impact velocity for these chunks ?

 

[AnAppleSnail]

i thought 'they' could predict reasonably accurately the band that the satelite will land in. f'n' miles either side of the orbit path. and they would have tried for an orbit path that didnt pass over washington new york bejing etc. look at a globe and you will seeyou can pick orbits that spend more time or less time over water and a water landing i would think would be the preferred option.

the debris casualty area - i wonder if that only applies to a hit to a human body or allowance has been made for events like hits to a car plane boat lpg gas tank.

anyway the correct way to calculate the odds for someone in the crash window is 32000 times the number of folks in the crash window, not the number of folks on the planet.

a couple of big chunks expected . is there an expected impact velocity for these chunks ?

Changing orbits costs a lot of fuel, which is expensive to put in orbit. Also, as an atmosphere satellite, it has to study the atmosphere above cities. In other words, for this to do its mission the orbit must go over cities - and can't dodge them later. Because of unpredictable atmospheric effects, it's hard to accurately determine the time it will come down. Because of its great speed, an imprecision of 15 minutes could put it halfway around the world from your guess. Finally, unpredictable aerodynamic effects can move it further from its predicted impact point. A fast de-orbit to reduce these problems would cost hundreds of millions of dollars.

The expected impact velocity is complicated. You sure wouldn't want to be under it, but I wouldn't expect sonic booms and secondary splash craters.

 

[Ken_McE]

I'm not sure why the gov't doesn't want people to keep any debris... maybe just to discourage people from traveling into the impact area prior to the event and getting injured?

It's stuffed with some of the best remote sensing technology that existed as of 1990. They're probably afraid someone might take bits to the nearest Chinese embassy and walk away with fistfulls of cash. Save the Chinese (or whoever) billions in research costs, jump their technology up right next to ours.

 

[Imon]

'Nuclear powered satellites' google search yields 320,000 hits
Here is just a few:

http://www.spacedaily.com/reports/Nuclear_Power_In_Space_999.html

Nuke powered satellite expected to hit Earth (old news - this already happened)
http://www.nytimes.com/1988/05/14/w...atellite-expected-to-hit-earth-in-summer.html

http://www.space.com/6322-nuclear-powered-soviet-satellite-acts.html

Russia to build Nuclear powered satellite to gobble up old satellites and space debris - this is what is needed but not sure about the nuke powered:
http://dvice.com/archives/2010/11/russia-to-build.php

But if you are saying you know the UARS has no nuclear power than that's good news.

Being a little bit of a space nerd myself I remember being intrigued as a kid when I saw a diagram of the Voyager 2 and saw it had a "nuclear battery"

That's a bit misleading but it makes more sense to label it as a nuclear battery in a popular science book rather than a radioisotope thermoelectric generator (RTG). RTGs basically use the heat given off from decaying radioactive material to generate electricity and I doubt they are a fissile risk. RTGs have been around for many many decades and are typically used by satellites and probes that require power but have to make long trips where solar panels are impractical. In fact, I believe one of the Voyager probes are still working, although some of the instruments have been shut down.

 

[AnAppleSnail]

Being a little bit of a space nerd myself I remember being intrigued as a kid when I saw a diagram of the Voyager 2 and saw it had a "nuclear battery"

That's a bit misleading but it makes more sense to label it as a nuclear battery in a popular science book rather than a radioisotope thermoelectric generator (RTG). RTGs basically use the heat given off from decaying radioactive material to generate electricity and I doubt they are a fissile risk. RTGs have been around for many many decades and are typically used by satellites and probes that require power but have to make long trips where solar panels are impractical. In fact, I believe one of the Voyager probes are still working, although some of the instruments have been shut down.

I'm not an expert on the overall safety, but RTGs are specifically chosen for using relatively small masses of radioactive isotopes. Here is a 1997 report on the environmental impact of RTGs.

PDF clicky

I suggest starting with 4.1.1.1, but it's a lot of other data included.