Using Lasers and Water Guns To Clean Space Debris 267
WSJdpatton writes "The collision between two satellites last month has renewed interest in some ideas for cleaning up the cloud of debris circling the earth. Some of the plans being considered: Using aging rockets loaded with water to dislodge the debris from orbit so it will burn up in the atmosphere; junk-zapping lasers; and garbage-collecting rockets."
Ok, now serious, really (Score:2, Interesting)
Someone writes on slashdot days ago about the interesting idea of put a "shield" on space made with a plastic soft container, for example a large plastic bag. fills then with water, the water frozens and you get a good ice shield to put on path of debris. once the shield caugth the debris then can send back to Earth on a planned reentry or ejected to deep space
Water???? (Score:5, Interesting)
Not only would lofting water into space be a colossal waste of energy and water, it would only exacerbate the problem!
IMHO the only 'clean' way to deorbit debris is to add energy to the debris in the retrograde direction without using additional mass, which means photons. Laser pulses could do it either by radiation pressure directly (huge laser), or by pulses that ablate the debris slightly (creates tiny beads of additional debris).
Electron/proton beams would work as well, as would alpha particles, but they'd pose a risk to humans in space. In fact, using charged particles might induce a charge on the debris that would then help direct the debris toward it's doom (debris vector, Earth's magnetic field, right hand rule....whatever).
PlanetES (Score:5, Interesting)
I predicted this as a kid (Score:1, Interesting)
I remember back almost 20 years ago when I was a high school freshman, our english teacher gave us this paper.
Within a big rectangle, we could write or draw anything we wanted.
The papers were then going to be scanned and put into some condensed format... some kind of tape or disk I guess.
Then our scanned work was going to be flown to space. I don't recall why... or where. Probably just piggybacking on some satellite launch?
But I do remember that I was a smart ass... and drew a picture of Earth with huge clouds of satellites and garbage cans and garbage bags orbiting it. It was my little protest to sending our stupid drawings up to space.
Man I wish I could see that picture again. I'm getting all nostalgic just thinking about it.
Re:How do you pull with a push? (Score:3, Interesting)
Orbital mechanics work in strange ways. For example, in a circular orbit, you don't thrust up to go up, you thrust forward. Going down, you thrust backward.
In this case, your best bet will be to hit the forward side of the object. If that's not possible, then hitting the bottom of it (depending on where it is in the orbit) will also have an effect. I can't remember offhand what happens from in-plane radial delta-V application, but I think it's a combination of changing the eccentricity of the orbit without affecting the total energy, and changing the longitude of periapsis. Sorry, it's been a couple years since I took orbital mechanics...
Now if you get a space-based laser up, you get more freedom in how your burns are applied.
A NASA physicist response (Score:1, Interesting)
I just saw an email response of this story from a physicist at NASA that specializes in space debris. Their response was that throwing water into space would just cause more space debris as ice.
So, don't get too excited about the water idea.
Re:Ok, now serious, really (Score:4, Interesting)
Doesn't work. The impactors will just break loose pieces of the ice. There has been some thought put into using Aerogel, since it has density low enough to not explode when hit by something going very. fucking. fast.
Energy (Score:2, Interesting)
Re:Water is heavy (Score:5, Interesting)
True, most only really think of oil as being the next big thing to cause mass hysteria, but few realize that potable water is a dwindling resource in certain regions. Even the giant Ogallala [waterencyclopedia.com] aquifer in the central United States is showing increased rate of depletion (not to mention pollution).
There are a few [amazon.com] books [amazon.com] on the subject.
Something doesn't seem to add up (Score:4, Interesting)
Something doesn't seem to add up. They've already indicated that slight modifications to trajectories can deteriorate an orbit, so some portion of the space junk caused by collisions must fail to remain in orbit. But they also say that collisions cause more junk, which causes more collisions, as though this were a never-ending cycle of feedback.
It seems as though there must be a threshold somewhere where the introduction of further space junk removes from orbit, on average, an equal amount of debris as it introduces. The farther past this threshold, the more likely that introducing debris will remove more than is introduced. There must be a point of equilibrium.
Take the following exaggerated scenario, for example. Let's say that by chance or plan, there is debris in orbit within every cubic meter at stable altitudes. (I am not a physicist, but this seems highly improbable statistically.) The introduction of a meteoroid through this debris field would almost certainly cause a significant chain-reaction with many affected objects acquiring unstable orbits leading to failure.
Not-to-scale pictures aside, I doubt we're anywhere near such a threshold -- even if we are reaching a point where our ability to avoid debris is insufficient to mitigate the danger. But surely it would be at least interesting, if not practically useful, to know this "saturation" point.
Or perhaps this is already known, and I am just unaware.
Re:Water is heavy (Score:2, Interesting)
Re:Ok, now serious, really (Score:2, Interesting)
Wrong and wrong.
Clouds of water aren't meant to freeze solid and become some kind of ice wall. Rather a cloud of ice particles or even water vapor would collide with the debris and impart drag which will reduce the debris velocity, which will cause the debris to impact the atmosphere and burn up faster than it otherwise would. The water hastens what would happen eventually. Most of the water is also recycled in the process.
On Aerogel, you are completely wrong. Tiny particles from the sun or comets impacting a relatively larger Aerogel "tennis racket" works. But larger pieces of Aerogel are extremely fragile. The stuff shatters when dropped. Little fragments of it go bouncing off everywhere, immediately followed by a bunch of people in lab coats trying to recover all the bits because the stuff is so damn valuable.
SO put a suitably sized amount of Aerogel in orbit and hit it with even small pieces of debris and suddenly you have the same debris AND a huge cloud of Aerogel fragments.
I do not think we need to fill earth's orbit with people in lab coats trying to pick up billions of Aerogel fragments. It would look funny but not practical.
Re:Something doesn't seem to add up (Score:5, Interesting)
This is a good point. But as collisions become more and more frequent, I don't think they be able to maintain momentum. The energy from each collision is spread out among all the fragments produced, and also some is lost during the impact as heat and the energy required to separate the fragments from the larger original pieces.
Let's say that "first-generation" objects are on a stable orbit with sufficient momentum to maintain orbit. After impact, some of the resultant second-generation fragments will fail orbit quickly due to grossly incorrect trajectories, while others enter trajectories that will take longer to fail. Over the time it takes for these second-generation fragments to fail, they cause more impacts. More of these third-generation fragments are lost more quickly, and the remaining ones proceed to cause fourth-generation impacts, and so on. This is the general chain-reaction idea being posited.
One factor to consider is the fact that as these particles reach higher "generations", they are in more and more grossly failing trajectories due to either bad vectors or insufficient momentum. These trajectories intersect less and less with stable orbits, so the collisions are more and more likely to be with already-failing particles. This could only accelerate the orbit failure. Essentially, these particles should clean themselves up.
Again, I am no astrophysicist, but it seems that if chance supported easily-achieved orbits, then we would already be at saturation. The fact that we're not suggests that the "random collisions creating a permanent* cloud of debris" theory may not be self-supporting.
Of course, it may be that the time it takes for this debris field to fail is on a scale which is inconvenient to us. But to say that we'll eventually end up with a stable cloud of microscopic bits just doesn't add up.
Water should return QUICKLY. (Score:3, Interesting)
Actually, it is likely that a lot of the water will come back to earth. In a LARGE number of years.
Most of it will come back immediately. The water spray itself, aimed to transfer momentum to the debris in order to deorbit it, should itself be in an atmosphere-intersecting trajectory. The bulk will miss and end up in the atmosphere.
What gets blasted into steam will still be deep in the gravity well. Most of it will be perturbed into denser atmosphere in reasonably short order. (Remember: The atmosphere doesn't "end". It peters out gradually until it merges with the solar wind out at the magnetosphere shock front.) Some will be ionized and the hydrogen will tend to blow away, leaving hydroxyl radicals and monatomic oxyygen - much like what naturally happens in the upper atmosphere already.
You WILL see an increase in upper atmosphere water and noctilucent clouds. But we're probably not talking enough water to have any other significant environmental impact. (Better use deionized water, though. Any chlorine would be a real issue for the ozone. I'm normally a debunker of ozone-hole hand-wringing but this could be significant.)
As to "running out of water": Think of the size of the oceans. We're talking a VERY small drop from a VERY big bucket.
PURE water, please! (Score:3, Interesting)
Send up seawater.
Distill, reverse-osmosis, or otherwise purify it first.
I'm normally one to debunk hand-wringing about the ozone layer. But most of the sprayed water will miss the debris and impact the upper atmosphere immediately (while the rest comes down slowly over many years). If you use unpurified sea water you'll put a LOT of chlorine ions from sea salt into the ozone layer - near the equator where it's a big deal - and chlorine is the catalyst for the ozone->oxygen transition that got freon banned.
Re:PURE water, please! (Score:3, Interesting)
If you use unpurified sea water you'll put a LOT of chlorine ions from sea salt into the ozone layer - near the equator where it's a big deal - and chlorine is the catalyst for the ozone->oxygen transition that got freon banned.
Salt has chloride ions, which are way more stable than molecular chlorine. Therefore, oxidizing chloride to chlorine would require energy input.
I actually spotted a possible fault in my argument (oxygen might be able to oxidize the chloride) but I'm not gonna tell you what it is.
Ok, doing some chem gives you this:
4Cl- + 4H+ + O2(g) <--> 2Cl2(g) + 2 H2O potential: -1.49V
Meaning that reaction isn't spontaneous, so it won't happen. Not sure what role sunlight will play, but I suspect it only interacts with Cl2 molecules and not Cl- ions.