Thursday, February 12, 2009
Tech / Science Kapow!
Posted by Jonathan Golob on Thu, Feb 12, 2009 at 6:50 PM
A long-predicted space junk nightmare has finally occurred:
It happened some 490 miles above northern Siberia, at around noon Eastern time. Two communications satellites — one Russian, one American — cracked up in silent destruction. In the aftermath, military radars on the ground tracked large amounts of debris going into higher and lower orbits.
...
The American satellite was an Iridium, one of a constellation of 66 spacecraft. Liz DeCastro, corporate communications director of Iridium Satellite, based in Bethesda, Md., said that the satellite weighed about 1,200 pounds and that its body was more than 12 feet long, not including large solar arrays.In a statement, the company said that it had “lost an operational satellite” on Tuesday, apparently after it collided with “a nonoperational” Russian satellite.
....
Mr. Johnson said the United States military’s tracking radars had yet to determine the number of detectable fragments. “It’s going to take a while,” he said. “It’s very, very difficult to discriminate all those objects when they’re really close together. And so over the next couple of days we’ll have a much better understanding.”At a minimum, Mr. Johnson added, “I think we’re talking many, many dozens, if not hundreds.”
The debris could threaten the space station and its astronaut crew, he said.
Why is all that debris such a nightmare? Physics time!
The orbital velocity of a satellite at 490 miles (about 780 km) above the earth's surface is 7460 meters per second (m/s) or about seventeen thousand miles per hour. Let's say that 1,200 pound satellite broke up into fifty pieces, matching roughly what the radar showed. The average piece mass would be about 24 pounds, or 11 kg.
The kinetic energy of such a piece, moving at about 7500 m/s and weighing 11kg is governed by the formula:
ke = 1/2 m*v^2
ke = 1/2 (11kg)*(7500)^2 = 310 mega joules.
That's the same as about 86,000 kWH. That's about the same amount of energy needed to power five American houses for a year.
That's the same as about 86 kWh, or the same amount of energy as a 737-800 dropped from about 800 meters.
All that energy makes the satellite pieces act like really powerful projectiles randomly flying about in orbit, capable of puncturing or pulverizing almost anything else nearby—including the International Space Station.
Crap.
Updated: I used a really shitty Joule to kWh converter and got a wrong number. Eric from Boulder caught it before I did. Enjoy the corrected post, with an even creepier metaphor.
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1
I'm sorry, we Americans have no idea how much energy it takes to power our houses.
Can you translate it into how many pianos falling on my head that is, from 10 stories?
Or maybe how many anvils falling on Wile E. Coyote, from the top of the big canyon?
Thanks you.
Can you translate it into how many pianos falling on my head that is, from 10 stories?
Or maybe how many anvils falling on Wile E. Coyote, from the top of the big canyon?
Thanks you.
2
I'm guessing that the chances of any of those "many dozens" colliding with the space station (or, say, GW Bush) is pretty miniscule (though I don't have the formula handy to prove it).
3
Don't we have a space junk vacuum cleaner flying around out there somewhere?
Don't worry. The Chinese and we are getting pretty good at shooting down orbiting objects.
Don't worry. The Chinese and we are getting pretty good at shooting down orbiting objects.
4
The problem will be a chain reaction in which collisions produce debris that cause more collisions until... the earth is surrounded by a cloud of debris so thick that we will be essentially condemned to stay earthbound, unable to venture through beyond.
Talk about shitting your nest. I think I read about all this in a sci-fi book...
Talk about shitting your nest. I think I read about all this in a sci-fi book...
5
maninjapan:
You are correct, to an extent. And, indeed, it would be better if there were fewer, larger pieces rather than hundreds of 1kg or so chunks for that very reason.
The other complication is there is actually a fairly narrow orbital altitude into which we generally place satellites--above where the atmosphere provides significant drag but below where launch costs become prohibitive. So, this band from 490 miles to 200 or so is more crowded than you'd expect.
Then consider time. The odds of a collision with one of these objects at any given point in time is low. But, in the vacuum, they aren't going to slow down. Integrate those low odds over decades or centuries, and the odds of a collision are non-trivial.
You are correct, to an extent. And, indeed, it would be better if there were fewer, larger pieces rather than hundreds of 1kg or so chunks for that very reason.
The other complication is there is actually a fairly narrow orbital altitude into which we generally place satellites--above where the atmosphere provides significant drag but below where launch costs become prohibitive. So, this band from 490 miles to 200 or so is more crowded than you'd expect.
Then consider time. The odds of a collision with one of these objects at any given point in time is low. But, in the vacuum, they aren't going to slow down. Integrate those low odds over decades or centuries, and the odds of a collision are non-trivial.
7
THEY tell us that two satellites collided. THEY tell us debris will burn up as it enters Earth's atmosphere. THEY tell us there are no Aliens just waiting to invade while at the same time destroying our communications network in space. OH SURE okay, when do they land?
8
I'm betting it's not really satellite debris but actually small asteroids that are precursors to a larger asteroid the size of Texas that's headed straight for us and we only have 20 days left!!!
Somebody call Bruce Willis!
Somebody call Bruce Willis!
9
The aliens will land when the last analog tv signal stops and digital HD begins. That is their pre-determined landing signal.
10
"About 86,000 kwhr". Nah, nothing like that.
I think you picked up three extra zeros somewhere. But, sure, if one of those pieces were to hit the space station, it would not be surviveable.
I think you picked up three extra zeros somewhere. But, sure, if one of those pieces were to hit the space station, it would not be surviveable.
11
She was walking all alone
Down the street in the alley
Her name was sally
She never saw it
When she was hit by space junk
In new york miami beach
Heavy metal fell in cuba
Angola saudi arabia
On xmas eve said norad
A soviet sputnik hit africa
India venezuela (in texas
Kansas)
Its falling fast peru too
It keeps coming
And now Im mad about space junk
Im all burned out about space junk
Oooh walk & talk about space junk
It smashed my babys head
And now my sallys dead
Down the street in the alley
Her name was sally
She never saw it
When she was hit by space junk
In new york miami beach
Heavy metal fell in cuba
Angola saudi arabia
On xmas eve said norad
A soviet sputnik hit africa
India venezuela (in texas
Kansas)
Its falling fast peru too
It keeps coming
And now Im mad about space junk
Im all burned out about space junk
Oooh walk & talk about space junk
It smashed my babys head
And now my sallys dead
13
@5 - Assuming the satellites broke into 50 or more pieces, the pieces would be going in a variety of directions and, presumably, would have their velocity altered. It's also probably safe to assume that each satellite lost a tremendous amount of kinetic energy in the collision (hence breaking into pieces), and the remnants are probably now moving at a slower velocity. So, won't most of the pieces eventually fall from orbit and burn up in the atmosphere?
14
True @13, but ISS' orbital altitude ranges between 173 and 286 miles, so any fragments re-entering the atmosphere will have to pass through that altitude range on their way down.
The likelihood of ISS passing though their de-orbit track at the same time is, as @2 points out, statistically small, but not impossible. And of course the more fragments there are, the higher the odds of that actually occurring.
Looks like the boys & girls at Peterson are going to have their work cut out for them.
The likelihood of ISS passing though their de-orbit track at the same time is, as @2 points out, statistically small, but not impossible. And of course the more fragments there are, the higher the odds of that actually occurring.
Looks like the boys & girls at Peterson are going to have their work cut out for them.
16
@15:
The wiki entry for Iridium indicates there are spares on-orbit to maintain the minimum of 66 satellites required for full coverage, which presumably means they should have some limited maneuverability. But, I can't immediately dredge up any specs on the bird itself, and the available images don't show any obvious Verniers or other typical RCS thrusters, at least to my untrained eye.
The wiki entry for Iridium indicates there are spares on-orbit to maintain the minimum of 66 satellites required for full coverage, which presumably means they should have some limited maneuverability. But, I can't immediately dredge up any specs on the bird itself, and the available images don't show any obvious Verniers or other typical RCS thrusters, at least to my untrained eye.
18
I'm just shocked Iridium is still around. They were basically the bellwether of the dot-com bust.
20
#1 asks a good question. I even took a few college physics classes (got A's) and I have no clue what enough electricity to power five houses equals in falling anvils or pit bull bites or anything else slightly tangible.
21
Eric from Boulder: Good catch! It serves me right for using a crappy javascript joule to kWh converter. I redid the calculation by hand.
Sad duck and LuddAmerican: Enjoy my new metaphor, using the corrected value (or rather joules) and a 40,000 kg airplane dropping from 800 meters. ;p
Mahtli69: I had a lengthier post that also considered the collision itself. (Collisions are better analyzed using momentum... and yeah.)
I might do a follow-up post, but the fact that some of the pieces ended up in a higher orbit tells me it wasn't a head on collision, that would absorb much of the energy. It seemed more oblique, and thus most of the energy would remain as kinetic energy moving the pieces. But, who knows. I'd be making wild guesses as to mass of the Russian satellite, and their relative vectors before the collision if I wanted to do more precise calculations.
Comte: Thank you for the great comments.
Sad duck and LuddAmerican: Enjoy my new metaphor, using the corrected value (or rather joules) and a 40,000 kg airplane dropping from 800 meters. ;p
Mahtli69: I had a lengthier post that also considered the collision itself. (Collisions are better analyzed using momentum... and yeah.)
I might do a follow-up post, but the fact that some of the pieces ended up in a higher orbit tells me it wasn't a head on collision, that would absorb much of the energy. It seemed more oblique, and thus most of the energy would remain as kinetic energy moving the pieces. But, who knows. I'd be making wild guesses as to mass of the Russian satellite, and their relative vectors before the collision if I wanted to do more precise calculations.
Comte: Thank you for the great comments.
22
@16: Darling! Hee hee.
I was just wondering whether we took the Russian satellite out. Duh, I'm repeating the obvious. If so, maybe a message to the Chinese? I'll never know.
I was just wondering whether we took the Russian satellite out. Duh, I'm repeating the obvious. If so, maybe a message to the Chinese? I'll never know.
23
@21
I may not have the math skills to be a Rocket Scientist, but I've got most of the other bases fully covered.
@22:
Cosmos 2251, was deactivated over a decade ago, so there wouldn't have been much point in "taking it out", especially using a commercial sat. There's some speculation it might recently have developed an instability in its orbital track, but of course, the Russians aren't copping to anything.
There's a nice CGI representation of the collision up on YouTube already, including predicted debris trajectories, if anyone is interested.
I may not have the math skills to be a Rocket Scientist, but I've got most of the other bases fully covered.
@22:
Cosmos 2251, was deactivated over a decade ago, so there wouldn't have been much point in "taking it out", especially using a commercial sat. There's some speculation it might recently have developed an instability in its orbital track, but of course, the Russians aren't copping to anything.
There's a nice CGI representation of the collision up on YouTube already, including predicted debris trajectories, if anyone is interested.
24
Humans are such a sloppy bunch. When will we grow up enough to start thinking about cleaning up after ourselves automatically, before our messes try to kill us?
25
Alternately it could be thought of as a Bombardier Q400 dropped from ~1150 meters.
I'm going to hell.
I'm going to hell.
28
To give this a little perspective (maybe), using the range of ISS orbit altitude given by Comte in @14 above, the total volume of space available for the ISS is over 100 billion cubic kilometers. That is about 1/10th the total volume of the Earth, and more importantly, a large space to play in. Accordingly, it seems extremely unlikely that debris from this collision would hit the ISS.
It also illustrates the extreme unlikelihood of two satellites colliding. If one of those satellites had arrived at the collision point a couple of milliseconds earlier or later, they would've missed each other, and probably never have come that close to each other again.
That said, there are currently 8000 man-made objects being tracked. Also, the odds of a collision go way up if there are multiple objects on the same orbit inclination. For example, the Iridium satellites are on a polar orbit, so the odds of a collision with another object also on a polar orbit would go way up where they converge at the poles (and way down near the equator). Note: the Russian satellite was not on a polar orbit, so that doesn't apply in this case.
Jonathan - I like your metaphor, but giving a shout out to air resistance, it would be more accurate if that 737-800 were crumpled up into a ball before being dropped from 800m.
It also illustrates the extreme unlikelihood of two satellites colliding. If one of those satellites had arrived at the collision point a couple of milliseconds earlier or later, they would've missed each other, and probably never have come that close to each other again.
That said, there are currently 8000 man-made objects being tracked. Also, the odds of a collision go way up if there are multiple objects on the same orbit inclination. For example, the Iridium satellites are on a polar orbit, so the odds of a collision with another object also on a polar orbit would go way up where they converge at the poles (and way down near the equator). Note: the Russian satellite was not on a polar orbit, so that doesn't apply in this case.
Jonathan - I like your metaphor, but giving a shout out to air resistance, it would be more accurate if that 737-800 were crumpled up into a ball before being dropped from 800m.
29
So the USG has military satellite tracking radar, yet no one could predict that these two were going to collide? Seeing as how the Iridium satellites apparently can be moved around, then, it could have been avoided.
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