Also, the big stuff (many of which are rocket stages with some fuel left in them) sometimes explodes: http://www.newscientist.com/article/dn10979

If we can deorbit even one *before* it explodes, we can cut the number of space debris by hundreds or thousands.

Quite easily. Well, moderately easily...most normal GPS receivers would work in space except they have an arbitrary limit of 60,000ft and Mach 1 (?? not sure of the exact speed off the top of my head) that keep them from being turned into guidance systems for ballistic missiles. GPS is already routinely used for spacecraft navigation, you just need a more expensive receiver without the imposed limit.

If this were air, you'd be completely correct. However, in the vacuum of space and with a very light balloon (we're talking on the order of 10lbs for a football-field size one) there isn't much of a moment arm. The force due to drag would probably be measured in ounces and then you have just the weight of the actual structure. Generally when satellites attitude control systems fail, they don't immediately start spinning like crazy, probably just a few degrees per minute.

Only if it has substantial mass. If it is a low mass device, than the drag on it will make it parallel (behind) the satellite.

I think the ribbon would just end up moving to being in a line behind the satellite along the path it just came from in orbit...think of how a ribbon follows behind a car...in its slipstream. Anyway, being behind the satellite doesn't really help increase drag, so it wouldn't help bring it down quicker.

That's all fine and good if you have great attitude (direction) control of your spacecraft. If you lose your gyros or something during the lifetime of the spacecraft, then you wouldn't be able to control an Ikaros like sail. Having a spherical balloon that doesn't care about direction and can inflate with minimal mechanical effort seems a lot more reliable.

Many satellites change their orbit...because of the speeds they are moving, distances covered, etc. even a small change in orbit can mean that a day or two later you're in a completely different part of the world than where you would have been, had you not done anything. The space station does this all the time, they routinely move 100mi or more over the course of a day or so to avoid space debris. Other, smaller, satellites do this too, however there are also many that don't have engines on them and can't really move themselves.

They should have a competition....launch a bunch of micro-satellites...one with a sail like surrey's, one with a balloon like this article, one with a small rocket, and one with nothing special on it....then the first one to burn up wins!

Actually most spacecraft (including "secret" government satellites) are tracked by both governments and private entities. Since the last collision the US Air Force has actually started expanding their capability for this even more. They are very open to working with other parties to solve space debris issues and avoid collisions with their satellites or between other satellites.

The most important part is to get a system working for future spacecraft (and rocket stages) that are going up. Once that is solved, then we can go and work on the stuff that is already up there.

I think that this balloon could be attached to a lot of space junk with a (very small) robotic space craft of its own. That robotic craft could use gps and cameras to rendezvous with the debris, then some type of manipulator arm could grab onto the debris. Since the force applied by this balloon would be *VERY* small (but applied over a long period of time - months) the bond between the two spacecraft wouldn't have to be very strong.

Yeah, the simpler the system, the better. Unfortunately parachutes and solar sails require the spacecraft to control what direction they are pointing in...that's why I like balloons for it, because they are spheres and work the same from every direction.

This mass of a giant balloon could actually be incredibly small...on the order of 10lbs. This would almost certainly be lighter than the amount of propellant needed to deorbit. The down side is that with propellant you could be down in a matter of days, the large balloon could still take months.

The other nice part about a balloon is that its roughly spherical...so you don't have to worry about what direction the spacecraft is pointing. This isn't a problem for spacecraft that already have guidance/engines for them...just add more propellant, but some spacecraft don't have guidance/engines so you'd have to add a lot more than just propellant.

Also they have developed materials that, once inflated in the vacuum of space, can hold their shape without any internal pressure.