Shortly after the launch of Sputnik, in the cold war era escalation of space technology, a giant aluminized mylar balloon was launched as a satellite. This was the "Echo" satellite, designed to be used as a low tech, passive low-Earth orbital relay for terrestrial telecommunications. You've seen pictures of this satellite on places like www.weirdspot.com and elsewhere for ages: Please Register or Log in to view the hidden image! Echo was BIG. but in LEO, only a few pounds of gas were sufficient to inflate it to its full diameter (30.5 m for Echo 1, 41 m for Echo 2). Which got me thinking: How practical would it be to require all future launches of space hardware to take along a small instrument package that included balloon satellites like the Echo, designed to be deployed ABOVE the debris field, and make use of a half-silvered "solar sail" to maneuver the thing so that it re-enters the atmosphere at a descent rate slow enough to allow it to capture other bits of orbiting debris and bring them back into re-entry along with it? In this manner, the cost of cleaning up the orbiting junk yard would be borne in part by those still launching satellites. Incendiary devices designed to assure that the balloons mostly incinerate upon reentry would obviously go a long way toward making such countermeasures a safe and effective means for clearing out the space lanes. The rather large re-entry profile of these devices would hopefully assure that each new launch would clear out more debris than was initially generated in the act of sending them off into space. According to the latest IEEE Spectrum (February, 2015), we are fast approaching the "Kessler Syndrome", which means that we may be unable to safely launch new spacecraft without them being damaged or knocked off course by collisions with a band of space debris still orbiting Earth from over 50 years of space conveyance. Any better ideas?
For deorbiting satellites - likely practical, although systems like the Terminator Tether might be easier/cheaper. For capturing other bits of debris - the engineering required to a) maneuver a small satellite to intersect the orbit of some other debris, b) survive the impact without generating a lot MORE space debris and c) continue to a controlled deorbit is formidable. You might be better off designing specific microsatellites to do this, then require that people launching satellites take a few along on each launch.
Great suggestions. I would additionally propose the launch of a few small test satellites to assess the feasibility / efficacy of capturing a few select chunks in the early simulation stages of the program. If a somewhat denser satellite is needed for effective capture of larger debris, expanding foam may be used instead of a gas propellant. This idea would somewhat mitigate the solar sail part of the idea, the intention of which is to make use of solar energy in order to de-orbit debris. This is possibly the greenest part of the scheme. Large reflective balloons deployed right now might also be a means of mitigating global warming, although this effect would stop when either we 1) cleared out all of the debris, or 2) were unable to launch any more, due to economics, program glitches, or the possibility of making the situation worse in ways not yet foreseen. I haven't seen any better proposals, and the temporary light pollution added to night sky would, after most of the junk was removed, be minimal. The light show would be a real boon to the UFO conspiracy industry, which I'm sure would support this.
What about a electromagnetic satellite that would use the sun to energize it to collect all particles or debris then deorbit and burn up with those debris attached?
You mean by reflecting light back to Earth and thus reducing the need for fossil fuels for lighting? There was a program to do that in Russia decades ago but it was never flown.
More likely, the debris field would damage the systems of an "electromagnetic" satellite (just break a wire and it's no longer electromagnetic) and you'd have another really solid, fast moving and hard-to-track piece of space junk. I'd say it was like catching bullets, only these bullets all have insane muzzle velocities needed to continue to orbit. A major advantage of something like the Echo was its utter simplicity. All this thing would really need to do is slow down the orbital speed of debris so that it orbits lower and eventually re-enters the atmosphere, at which point it vaporizes and ceases to be something expensive to track and/or mitigate.
No, not like that, or like beaming microwave energy at Earth to power communication networks, which was also once proposed. I mean, using sunlight for a maneuvering sail to increase the likelihood that the orbiting balloon will collide with debris with sufficient force to cause it to re-enter, like hitting a bullet with another bullet moving in the opposite direction. They needn't stop each other precisely; only slow each other down so that both will re-enter. The size is also a critical mission parameter. It needs to be big enough to catch debris. but small enough and guided enough so that it does not interfere with the continued strategically significant operation of swarms of GPS satellites currently in LEO.
Well when the electromagnetic satellite is made there won't be any loose wires and the speed of it will match the speed of existing debris. There could be a TV camera and propulsion jets to maneuver it with for better control.
You aren't getting the picture. Such a craft would run out of hydrazine long before it brought down any real tonnage of space debris. Simpler, in this case, is better.
Problem there is then you end up with hundreds of small bullet bits (or hundreds of pieces of mylar and spacecraft. Some may re-enter; some may not - and you end up with more debris than you started with.
The really great thing about mylar is, shear strength is about 20 kg/mm^2, which is incredible!. It's also extremely light. I doubt that a tiny shard of shredded mylar traveling at orbital velocity would be able to penetrate a space suit (made of the same material, by the way! The optional foam fill would make it even better in every way.
The problem is that energy goes up by the square of the velocity difference. A .44 magnum round, fired on the ground, will hit you with an energy of around 1200 joules; a 100 _microgram_ piece of mylar traveling at orbital speed will hit you with twice that energy.
I'm not saying there isn't materials science work to be done here. Don't forget, the projectile also has some atmosphere and perhaps foam to get through. But the other dynamic in play is the velocity profile of the projectiles. Remember that the object of this mission, and many identical ones following it, is simply to slow them enough to de-orbit. For the entire balloon, this will have already been accomplished when it enters the debris field. Shards of its mylar and things that hit it, along with most of the balloon should eventually re-enter, assuming they don't absorb large additional amounts of projectile energies. Anyway, would you rather be pelted by bits of balloon, or bowling balls? It may take several missions / balloons to bring bigger projectiles down. This is just an orbital sooting gallery with Mylar ducks I'm proposing. A perfect peaceful project for the talents of a sniper.
Definitely the bits of balloons. But now imagine you are the controller for the ISS. Would you rather have the station try to dodge a bowling ball, or dodge 200 bits of balloon, any one of which could destroy it? That's one of the reason you have to be VERY careful trying to deorbit things through collisions. If you deorbit 90% of a satellite, but 10% of it remains in orbit in two pieces, you've just made your problem worse, not better. Indeed, collisions are one of the biggest problems with debris right now - not collisions with the ISS or spacecraft, but collisions between junk. A collision can turn 2 pieces of deadly junk into 100. And with over half a million pieces of space junk orbiting right now (and with that number going up all the time) it is not a trivial problem.
With that mindset, I guarantee, nothing will ever be done. I don't think it will be practical to de-orbit them using only compressed air or something heavier that will easily vaporize, like a water or a dry ice-filled balloon. In fact, I'd be pretty surprised if this was not the means for inflating the Echo series satellites. If we can make practical run-flat tires (and we can), I don't really see a problem with this approach. Can you foresee any problems with an orbiting wind? I'd go for the 90% de-orbit, if that's in terms of total mass. Smaller, high speed projectiles can be easily handled by other means. Most commercially significant chunks of space debris are not in polar orbits nor even LEO. The economics of spaceflight has for over 50 years been dictated by sending everything up as near to the Earth's equator as you can get, launched West to East to take maximal advantage of the Earth's direction of rotation. The orbits are inclined, typically from 2 to 5 degrees with respect to the equatorial plane, to take advantage of the Comsat maneuver, the company for whom I worked for 22 years built on Arthur C. Clarke's vision of a network of geostationary communication satellites. Orbits of those kinds of satellite debris are the ones we should be most worried about in terms of the Kessler syndrome, and for which the balloon satellite shooting gallery should be an easy fix. On the other hand, waiting until the Earth has an orbiting ring of junk as wide and thick as the rings of Saturn is one way to make a space platform from which to tether a space elevator, another of Clarke's visions. It may take a while for enough spacecraft to break up in order to accomplish this, but launching new satellites or even more vital space missions to try and save this rock will become uneconomical long before then.
Oh, I think there's plenty you can do - you just have to be careful not to make the problem worse with well-intentioned efforts to make them better. Rapid dispersal, unintentional de-orbit of commissioned satellites. I disagree. The big problems, right now, are not the intact upper stages orbiting the Earth in an inclined orbit; they are easily seen by radar and their orbits are easily predicted. The big problems are the bolt-sized bits in (for example) polar orbits - more than enough energy to destroy a spacewalking astronaut (or even the ISS if it hit at the right angle) but hard to see on radar and hard to predict due to their high drag to inertia ratio. NASA has stated that the greatest risk to space vehicles are from these difficult-to-track smaller objects. In fact the Shuttle windows have been replaced several times due to collisions with paint chips; far smaller than fragments of a balloon would be. Keep in mind that what people consider "solid" rings are actually about 3% material; the rest is empty space. (And long before that you'd hit the Kessler limit, and anything not in a perfectly equatorial orbit would be pulverized.)
Great answers to a touchy problem. I was really very unsatisfied with the treatment I read in the Feb 2015 issue of IEEE Spectrum, and also previous ones, which was what inspired me to start this thread. This was much better already, and it's still on the first page.
Ok, so let's put aside the balloon satellite idea for a while. How about ideas to paint or otherwise coat the smallest, fastest moving bits with something that would make them easier to track? I've worked with things like ground penetrating radar. You wind up with processing shorter wavelengths that can only resolve stationary corner reflectors down to about 1/3 of a wavelength, and higher power cannot be used because microwave emissions are regulated so as to not interfere with terrestrial communications. That leaves you with optical tracking of projectiles, which was tried for Star Wars during the Reagan years with only limited success. So this technology would need to be shared with other countries or else you would be violating their airspace.
