space junk

came across a nat geo story today on the subject of space debris, more commonly referred to as space junk, and the warnings coming out of nasa about its accumulation. i’ve been fascinated by the idea of space junk since first reading about it a few years ago. the fact that there are thousands of human-made doohickies whipping around in low earth orbit, forming what amounts to a “junkosphere,” is wild. since the size of this debris cloud grows by an average of 4% every year it also happens to pose real dangers for humanity’s future space initiatives, be they scientific, commercial, or military.

the first question you might ask if you’d never heard of space junk is “well, what the hell did we leave up there? and how much of whatever it is could we actually have left behind in 40 years?”  well…

space junk is mainly comprised of: derelict spacecraft and upper stages of launch vehicles, carriers for multiple payloads, debris intentionally released during spacecraft separation from its launch vehicle or during mission operations. a principle source for this debris are Satellite explosions, especially old upper stages left in orbit with stored energy sources, e.g., residual propellants and high pressure fluids, constitute the largest component of cataloged orbital debris, and tiny flecks of paint released by thermal stress or small particle impacts.

as for how much of it there actual is: approximately 11,000 objects larger than 10 cm are known to exist. the estimated population of particles between 1 and 10 cm in diameter is greater than 100,000. the number of particles smaller than 1 cm probably exceeds tens of millions.

the speeds and force at work are crazy-

quote: In low earth orbit the average relative velocity at impact is 10 km/sec (21,600 mph). At this velocity, even small particles contain significant amounts of kinetic energy and momentum. an aluminum sphere 1.3 mm in diameter has damage potential similar to that of a .22-caliber long rifle bullet. an aluminum sphere 1 cm in diameter is comparable to a 400-lb safe traveling at 60 mph. A fragment 10 cm long is roughly comparable to 25 sticks of dynamite.

for instance:




this 4-mm-diameter crater on the windshield of the space shuttle orbiter was made by a fleck of white paint approximately 0.2 mm in diameter.




these 2 mm impact holes were each made by dust grains.




this image shows the results of a lab test impact between a 1.2cm sphere of aluminum traveling at approximately 6.8 km per sec and a block of aluminum 18 cm thick. this test simulates what can happen when a small bit of space hits a spacecraft. in such an impact, the pressure and temperature can exceed those found at the centre of the earth (greater than 365 GPa and more than 6,000 K.)

now keep in mind these are bits of debris measuring in the millimeters. imagine these impacts on larger scales. for example, here are some pieces of debris which reentered the earths atmosphere.








don’t think the shuttle or ruttan’s space ship 1 or any of the thousands of satellites up there right now would handle a collision with one of these junk chunks too well. can you say “totaled?”

jerry bell had a fascinating piece on the subject in space daily a while back which included this, on the threat of space junk to the international space station:

So how soon can we expect an actual hull breach on the ISS? The National Academy of Sciences addressed this in a 1997 report. They calculated that over the ten years that the fully assembled ISS would operate there was a 19% chance of a penetrating hit on one of the pressurized modules!

a penetration would probably kill or seriously injure any astronauts in the punctured module, due to the shock wave and shower of high-speed fragments. Even if the surviving crewmen managed to seal off the punctured section, it would be depressurized and useless. If the damaged module were in the middle of the ISS, some crewmen might find themselves in an isolated section with no access to the ISS “lifeboat”, condemned to a lingering death from CO2 poisoning like many submarine crewmen who have been in similar situations. It is hard to imagine how the US Congress and the public would continue to support the manned space program after this kind of disaster, on top of Challenger and Columbia.

indeed.

a recent study showed that, even if humans were to never launch another spacecraft, the amount of debris in low orbit around earth will remain steady through 2055, after which it will increase. and of course, with any luck, we will be be launching more spacecraft as time goes on and technology improves. so all in all having a huge,ever growing, junk cloud encircling the planet might put a damper on our space tourism dreams. isn’t it just like us? the planet itself is already cluttered with junk, so now we are cluttering up the space around it as well. i wonder if one day earth will have its own rings, like saturn, only made of old crap? “they will know us by the trail of our junk!”

one thing which has captured my imagination about this debris cloud is the computer modeled visualizations of it. to actually see the planet with a million little specs of crap floating around it… it’s wild. (you can easily imagine each spec represented is a broken toaster, or old rusty car, or a diaper with a highly dangerous payload.)

here’s a recent comp. modeled example-






one thing which i’ve always wanted to see was a projection of each of these objects’ individual orbits laid over one another. unfortunately i’ve never been able to find one. so…

i decided to create a computer model myself. it took 8 months, feeding in huge amounts of data, and slowly rendering the whole mess into a high res image. the initial results were surprising-






as i ran my simulation forward to forecast what we could expect to see as these debris trends mounted and multiplied the results became downright scary! if ever there was an image shocking enough to shake things up and really impress upon people the horrifying threat our planet faces in years to come i believe this is it!!




as you can see things are worse than we thought.

anyhow, all joking aside there are many interesting sites out there focussed on space junk. if your interest is peaked check out:

cords the center for orbital and reentry debris studies. (don’t miss the animation on the front page.)

the nasa orbital debris program office

here is a page dedicated to one particular piece of space junk, a helium tank from the Russian Salyut 7-Cosmos 1686 (Kosmos 1686) spacecraft assembly.

and lastly here is an activity  you can do at home which illustrates “the penetrating power of a projectile with little mass but with high velocity.”

hope you enjoyed.