I'm very skeptical of the technical challenges associated with this problem (business model and financing aside). The amount of delta-v required to perform maneuvers to repeatedly "dock" with different pieces of space junk, and then again to de-orbit is very high. You MIGHT be able to de-orbit on the order of magnitude of ~10 pieces of low-earth orbit debris per mission. Maybe. If you're really good. And low-earth orbit junk isn't the major issue since it will de-orbit naturally in a reasonable time-frame. Higher orbit junk is what really matters, and will require much more delta-v to reach, and then again to de-orbit after "docking".
Allow me to blindly speculate here: a space-junk company is going to take one of the two following paths:
1) Perform low-earth orbit missions to de-orbit a few pieces here and then there, use the good PR to drive funding (let's just assume they can make the finances work via getting governments to pay for it or something). It will technically work, but it will only deorbit pieces that would naturally decay anyways at a meaninglessly low-volume. But the PR will be good and regulatory capture will ensure their investors get paid. The real problem will remain.
2) Go after the really big pieces in higher orbits. These pieces tend to be well-tracked and aren't really a large problem, but all the same outcomes in option 1 will occur. Investors will get paid, and of course, the real problem won't be solved.
Maybe I'm being pessimistic, but I see space-junk removal companies largely relying on the general public's lack of knowledge on how orbits work to drive PR. Maybe Kerbal Space Program 2 will go viral enough to fix that problem? We can only hope
The most realistic solution for space junk deorbiting I've seen is the recently tested electromagnetic tether ("Terminator tape"). It is a passive solution that does not require an external spacecraft, and could be activated by a satellite operator when a satellite reaches the end of its lifespan. Perhaps, such system should be made mandatory, maybe even going as far as adding a dead man switch for its automatic activation in case the satellite becomes uncontrollable and stops responding to the commands from the Earth.
But even with this solution removing high orbit debris still remains a hard problem.
This would work great for defunct satellites, but does nothing to solve the bigger space-junk danger: random bits and pieces of things from stage separations and previous collisions that are difficult to track. Definitely a step in the right direction, but it won't solve the largest threat.
They shouldn't be difficult to track by an object in space with a laser I would think?
edit: curious why the downvotes? Would a device in space with a LIDAR type of device not be very well suited to tracking small objects that are difficult to identify with cameras from earth?
The problem with this kind of system is that it isn't retroactive; all space junk currently in space will remain in space even if the tether device is mandated. And it's unlikely it gets mandated and approved by all spacefaring governments anytime soon.
So the solution is to eject our atmosphere into space in order to eliminate space junk?
Space junk constantly increases over time, so more and more pulses are required to clear out the junk, so more and more of our atmosphere is ejected into space for this purpose.
There is absolutely no way that this could go wrong.
I dont think it matters in the timespan of our species probable use for this planet.
However. Don't let that stop you from donating to my just launching "venture NGO" to study the feasibility of protecting the earth's atmosphere by wrapping it in a big paper sack: which will sequester carbon, preserve our Precious Planetary Gasses, shade us from the Sun's evil ultraviolet rays and other harmful radiation, and vastly stimulate the economy. We expect to raise $2 billion to commence the first study sometime in 2084.
Unless you plan to live forever, it's not a problem for you or your great great great great great grandchildren either. GP was pointing out that neither the Moon not the Earth care about human life and will do just fine without us.
There are on the order of... 10s of thousands of intentional satellites.
There are millions of pieces of debris.
It's useful for preventing future debris from dead satellites perhaps, but doesn't address the large number of existing objects which are currently the problem.
My understanding of the issue is that the biggest problems are a few well known defunct satellites in mid altitude orbit. We have no control over them so if two collide we are in big trouble. That almost happened last year. I think someone can make a big difference by targeting those first.
A couple of ideas that come with little knowledge, so take it with a big grain of salt:
1. "Electromagnetic Missile" with trajectory who's apogee is just below the targeted space junk. Turn on the electromagnet when just below the space junk to drag down its trajectory slightly, or even down to a de-orbit trajectory. Obviously, this only works with satellites built with magnetic materials. It may just be my outsider's perspective, but non-orbital missiles seem much easier and cheaper than rockets that go into orbital trajectories. Handling the return of the missile is tricky, perhaps it can also self-detonate fairly high in the atmosphere.
2. Ion engines or space sails driven tugs for use in getting to the space junk. My understanding is ion engines have a really favorable specific impulse. An optional chemical engine could be used to quickly de-orbit the tug upon reaching the satellite. Another idea to speed up de-orbit without requiring the tug the whole way would be a spring that would "push" the junk once it reached it, throwing it into an orbit that would more quickly drop it into the atmosphere. Newton could be used to our advantage to also push the tug into a new orbit to reach the next junk satellite sooner.
Obviously, arm-chair rocket scientist here, so feasibility of the above ideas can probably quickly be dis-proven.
Indeed that does seem incredibly difficult, my imagination goes to a cloud of poly-bots, perhaps powered by surface-based laser(s) and solar, such that they could be made to gradually approach the target orbit, attach to the object, and any that attach could help the others by accelerating the debris towards them.. then hopefully once enough were on, you'd have enough control on the object to de-orbit it? (Total space/engineering layperson here, just thought it might be a way around some of the tricky parts?)
Can you use the junk's energy to power the cleaner? Imagine this: the cleaner has a big spring on the back of it. The spring is slowly compressed using solar power. The orbiter grabs a piece of junk, and then launches it backwards. The cleaner now has gained some of the energy from the junk, and the junk has lost energy.
Going after bigger pieces in higher orbit might not bring much of an immediate benefit, but it can reduce the amount of damage if such an object is hit and shattered into many pieces (Kessler effect comes to mind).
So it might still be very worthwhile in the long term.
Low orbit stuff gets naturally de-orbited after a few years/decades by stray air molecules from the Earth's atmosphere, so there's little point to manually cleaning it. Debris in higher orbits can take centuries or millennia to naturally de-orbit, so manual cleaning there makes more sense.
With my very basic understanding of orbital mechanics, higher orbits require more dV simply because it's further from Earth.
The more interesting bit is that subtle orbital adjustments require much less dV in higher orbits than in lower ones.
I like to think of it like pushing a barrel uphill: it takes more effort if the slope is steep, but then once it's up there, it's a lot easier to get the barrel moving downhill.
Anyways, the "de-orbit" cost follows the same rule of higher being more costly in dV, the big difference with an ascension being that the atmosphere slowing you down is what you want (aerobraking is the word, I think?). So the difference in dV between a high orbit and a low orbit descent isn't proportionate to that of the ascent, if that makes any sense.
Maybe instead of de-orbiting debris they could collect it into a small number of well-known locations. Instead of 10k pieces of space junk to avoid in a particular orbit you could just have one or two. Might have less demanding delta-v requirements that way.
not likely that they will have one craft that is used to deorbit multiple items. more likely there will be one craft with 100 micro/cub satellites in orbit. once junk identified, mother craft ejects micro sat, micro sat performs one single burn to rendevu with junk over a very long period of time. passively connects to it somehow, like magnets or or something, then once connected, then does a single. deorbit burn to change the trajectory of the junk to deorbit significantly faster than normal. sacrifice itself with the deorbit
I remember a idea to use lasers to burn up space debris. Would you be able to just launch somd kind of weapons platform to handle space debris rather than trying to attach and slow them down?
If you can ablate the leading surface (if the object is not spinning quickly, which honestly is unlikely) then the ejected plasma may push the perigee either into the atmosphere or at least to a higher-drag altitude.
Actually, this works even better at higher altitudes because orbital velocity is tied to altitude.
It takes less delta-V to put a 1000km-apogee object on a collision course with the atmosphere than it takes to put a 400km-apogee object on a collision course with the atmosphere.
I'm no expert, but is that really a consideration for modern launches? I'm not aware of any space agency that is currently limited in what they can do by orbital debris. Maybe it changes the launch windows, or they adjust an orbit by a few km. But are missions actually being canceled such that they would fund someone to make those missions possible again?
My analysis assumed funding would occur. Pathways 1) and 2) are on the table regardless of the funding. Easy access to funding does not in anyway preclude options 1 and 2
Highly plausible analysis. Hopefully Woz is above the PR stunts and has a real plan for addressing the future problem (it's not really a problem yet, but it will be).
Woz the last 40 years has launched one PR stunt after the other (although, to be fair, I believe he has also done a fair amount of good things quietly in the background in the same time).
Allow me to blindly speculate here: a space-junk company is going to take one of the two following paths:
1) Perform low-earth orbit missions to de-orbit a few pieces here and then there, use the good PR to drive funding (let's just assume they can make the finances work via getting governments to pay for it or something). It will technically work, but it will only deorbit pieces that would naturally decay anyways at a meaninglessly low-volume. But the PR will be good and regulatory capture will ensure their investors get paid. The real problem will remain.
2) Go after the really big pieces in higher orbits. These pieces tend to be well-tracked and aren't really a large problem, but all the same outcomes in option 1 will occur. Investors will get paid, and of course, the real problem won't be solved.
Maybe I'm being pessimistic, but I see space-junk removal companies largely relying on the general public's lack of knowledge on how orbits work to drive PR. Maybe Kerbal Space Program 2 will go viral enough to fix that problem? We can only hope