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."
Laser Broom (Score:3, Informative)
To be clear, they are not talking about blowin' up space junk with lasers. The laser will instead slow down small pieces of space debris so that their orbits deteriorate. (Blowing things up is the domain of the other Project Orion [wikipedia.org].)
This mechanism is called a laser broom, and there is a short entry [wikipedia.org] about it on Wikipedia. I can't seem to find a more detailed, technical description of how this process works.
Re:Water.... (Score:4, Informative)
I thought that number sounded a bit high as a gallon only weighs about 7 pounds, but sure enough, a cubic foot of water DOES weigh around 60 lbs. 62.42796 pounds [fourmilab.ch] to be exact. And a gallon is actually just over 8 pounds.
Re:Huh? (Score:5, Informative)
Since space is a "near" vacuum wouldn't the water flash to steam instantly and be useless?
The enthalpy of vaporization for water is very large. On exposure to vacuum, immediately the water will begin to boil. This will very rapidly cool the water so that most of it ends up freezing (the enthalpy of fusion is comparatively much lower). Not only does this make mathematical sense, but it's witnessed daily on vacuum lines in labs.
Re:Water???? (Score:4, Informative)
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).
You do know that electrons/protons/alpha particles have mass, right?
Re:Space Quest (Score:4, Informative)
Unfortunately, most of the folks on here are probably too young to get the reference [dosspot.com], so, here's some text from the original boxes:
Project Orion "Laser Broom" is best option (Score:3, Informative)
The proposed Orion space debris laser fits nicely with our recent problems of creating so much debris in LEO. It would be a single pulsed laser on an equatorial mountaintop capable of ridding LEO of hazards in 4 years.
With the recent collisions this is becoming imperative. We need to have a clean LEO environment or we aren't going to do much in space.
http://www.spacefuture.com/archive/orions_laser_hunting_space_debris.shtml
http://adsabs.harvard.edu/abs/1997SPIE.3092..728P
http://en.wikipedia.org/wiki/Laser_broom
http://cat.inist.fr/?aModele=afficheN&cpsidt=3109525
Water makes a great shield inside a space station but is a dumb idea for "collecting" debris.
Re:Well, armchair rocket science here... (Score:2, Informative)
Zapping: This isn't what you think. The idea is to ablate one side of the debris so it de-orbits, rather than making it into smaller pieces.
Collecting: Probably not easy.
Adding atmosphere: interesting point about de-orbiting bad things, but the de-orbiting is going to happen anyway if these things are in a low enough orbit to be a debris problem. Adding density to space will just accelerate the deorbit.
Re:Water.... (Score:3, Informative)
The main problem with imperial units (apart from the aforementioned different standards in different parts of the world) is that there are so many units for a single measurement. Length can be measured in inches, in feet, in yards, in furlongs, in fathoms, in rods, in chains, in miles, and who knows how many others. Volume is even worse. Not only do you have teaspoons, tablespoons, ounces, cups, pints, quarts, gallons, etc. but there is the whole pantheon of cubic length units: cubic inches, cubic feet, etc. A pound of gold weighs less than a pound of feathers because precious metals and gems are weighed in troy units and common items like feathers are measured in avoirdupois units.
To further add to the confusion, each unit is a different fraction of the others. 12inches to the foot. 3 feet to the yard. 16 ounces to the pound. 2000 pounds to the ton. And to top of all that confusion lies the convention that you need to need to use at least two units for each measurement: Joe is 5ft9in tall. He weighs 177lbs, 14 oz.
Heaven help you if you want to calculate anything.
Re:Something doesn't seem to add up (Score:3, Informative)
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.
Yes, but we are far from that point, and unprotected spacecraft will start turning into swiss cheese long before.
Re:Something doesn't seem to add up (Score:5, Informative)
Your imagined point of equilibrium is the point where there's nothing but space garbage, and if you shoot up more there'll be more garbage even though some of it falls back. I'm sure you remember Newton's law of conservation of momentum, now apply it to two oribiting satellites on almost similar trajectories crashing into each other, breaking into many pieces. Basicly, they'd become a spray of junk, some going up, some down, some faster, some slower. They'll spread out as if you fired a shotgun, catching up to some satellites while slowing down covering a greater and greater area to collide with others which will again behave the same way. It doesn't matter if 90 of 100 bits fall to earth if they take out >1,1 satellite each on average. It'll just escalate exponentially like a nuke going off, leaving a fine layer of bullets all over the stable orbit.