One of the growing concerns is the amount of small debris in LEO. The big stuff can be tracked and mostly avoided, but the small stuff is a more difficult proposition. A hundred gram shard at some LEO closing velocities can impart the kinetic energy of a main tank gun. It is not the new large satellites that are the problem as most of them have deorbit strategies built into their launch vehicle upper stages and their own end of life safeing plans. It is the thousands of much smaller units proposed by all and sundry that concerns some people.
With the quantity of LEO debris existing and tens of thousands of small satellites that may hit orbit in the next decade, the odds of collisions are higher than some people like. Each collision will create large quantities of smaller debris in unpredictable orbits that increase the odds of further collisions in an ever increasing cascade. I personally don’t know the odds of this happening or if it is a rational concern. There are some people that appear well informed that are seriously concerned about a Kessler syndrome that could make LEO uninhabitable by man or unarmored machine.
It would seem that there might be a market developing sometime in the next decade to remove small debris from LEO from simple self interest. Present and future LEO operators along with their insurance companies might decide that the time has come to address the problem. Deciding to address the problem does not necessarily mean that they will feel generous about the solutions. The tragedy of the commons will not disappear like the air and gravity in LEO.
The solution for cleaning out LEO will have to be economical, safe in terms of having near zero chance of making the problem worse, and work in a timely manner. It won’t happen if the proposed solutions are too expensive, risky, or take centuries to operate.
I suggest that a modest satellite could be launched into polar orbit to get a start on the task. It should have excellent detection equipment along with enough on board computing power to calculate intercept trajectories in real time of objects closing at up to 14 km/sec. After action tracking and calculation must be capable of checking the new orbit or deorbit of the target debris.
The mechanism I suggest is laser sails the size of kites that are steered to intercept by the on board laser. The south bound orbit would focus on debris on the northern leg of their orbit while on the north bound portion it would focus on the debris on the southern leg of their orbit. The zigzag of normal west to east orbits to the limits of their inclination would provide high closing velocities with impact resultant sub-orbital if done right.
In this cartoon, the cleaner is heading south with one of the kites in position to impact some debris heading north-east. The dotted line is the possible changed trajectory of the debris as it deorbits. The purple rectangle is a kite that has been used a few times.
The cleaner is heading south and a piece of debris is heading north east with a closing velocity of between 12 and 14 kilometers per second. The laser propelled and steered kite array is a hundred or so kilometers ahead of the cleaner and one of them is off to the side that the debris will pass through. The kite is laser propulsion steered into an intercept which costs the kite a bit of sail and the debris a bit of velocity. Each gram of sacrificial kite material impacts the debris chunk with the kinetic energy of several 50 caliber bullets. Depending on the amount of sacrificial kite mass, debris mass, and debris orbital velocity, a deorbit is likely. Failing that, the debris should have a much lower perigee that will speed up its’ orbital decay.
After the kite has been used several times it will look like Swiss cheese and is steered back aboard while other kites take its’ place. Two or more ventilated kites are mated together for another go in their turn. Repeat until there is nothing left of the stock of kites but tatters. Then the cleaner sat is either replenished or deorbited in its’ turn.
It has often been suggested that the debris should simply be targeted with a laser. The ablation of the larger debris would cause it to deorbit while the smaller ones would be vaporized. It seems to me that it would take a lot more laser and power to get that job done which would create a couple of other problems. One is that it would be far more expensive, and the other is that it would clearly be a space based weapon.
While it would still take a considerable amount of time to significantly reduce the debris field, a 50 kilometer track per orbit would be bandwidth limited rather than hardware limited. Several dozen or hundreds of pieces gone per day would add up over time. Off hand each gram of sacrificial kite could take down a hundred grams of debris. A ton of lost kite for a hundred tons of eliminated debris seems like it would be a good trade.
johnhare
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Can you get a proof of concept into a cubesat?
Possibly only one kite.
The test debris could be launched from a second cubesat or be real.
Britain pays for its light houses by charging ‘light dues’ on all ships that dock in British ports. The due is charged by the tonne of cargo.
https://www.gov.uk/government/speeches/light-dues-2017-to-2018
Debris dues could be charged on all launches. A small organisation with an international committee could collect the dues and pay the firms that clear the debris. Both the USA and Russia would have to be members.
If the original idea passes the giggle test, a cubesat would be an ideal test bed. Launched as a secondary from Vandenburg, it could deploy a kite and make multiple attempts on real debris to create data for proof of concept.
Closing velocities approaching 16 km/s would be expected to vaporize the portion of a light sail hitting a target. But how many targets would be broken up rather than just slowed? Also, what about minute debris too small to track?
The idea I keep coming back to is a satellite shaped somewhat like a large dumbbell. Electric charge would be split between the 2 ends, at least one end magnetically shielded to reduce pickup of charge from ambient plasma. The resulting electric field would pull (weakly) on passing conductors and dielectrics, throwing debris into other orbits. in LEO the new orbit would have a chance of a lower apogee, intersecting the atmosphere.
I don’t know about debris that would be broken up. That would be learned during some modeling and test missions. I think the ones that break up would also be slowed down as well, though that would need verification before much effort is spent on the system.
The minute debris too small to track by existing systems would require better detection on board, or it would be ignored as too small to do serious damage. Assuming some effort is to be spent cleaning up LEO, decisions would have to be made about minimum sizes to be addressed. It seems possible that the tiny ones could be hit directly with the laser instead of the kite impact. Milligram paint chips are in a different category from kilogram tank fragments.
I don’t see how your weak electric pull would work considering sub-millisecond time the debris would be in range of the field.
As I understand it, you wouldn’t want to simply shine a laser on a satellite because it might disintegrate randomly, or worse, explode due to residual propellants. For that same reason, you don’t want to smack it with any projectile.
I think it would be best to deploy inflatable micro-sats with a glue head. The glue head latches onto the satellite, the inflatable structure is deployed. It is reflective.
A laser shines on the inflatable structure and drags the orbit down over time.
Should be safe.
I was thinking more about the scads of small stuff out there than a complete satellite. For that I would think a deorbit tether might be more effective.
Thinking about this led me to find this (old expired) patent:
https://www.google.com/patents/US4033524
“There is disclosed a method of controlling, inter alia, earth orbiting satellites and vehicles by cold plasma injection control in the magnetosphere and thereby influencing the space medium through which the satellite travels. The injection of cold plasma changes the atmospheric drag on the satellite as it traverses the earth’s magnetosphere.”
I don’t think this would work in LEO, but at higher altitudes significant perturbations to the plasma in the magnetosphere could be possible with (perhaps surprisingly) small releases of gas.
So, similar to what Dr Greene and the Space Environment Research Centre are planning?
“I don’t see how your weak electric pull would work considering sub-millisecond time the debris would be in range of the field.”
I expect I’m thinking of a much larger scale electric dipole than you are.
PeterH,
If your dipole were to be sized at a kilometer and oriented correctly, it would have something less than a tenth of a second to operate on the debris at orbital closing velocities. I must be missing your intent.
Say you fired an ABM or boost assisted artillery shell along a trajectory which intersects directly in front of the orbital path of an LEO satellite. The satellite collides with the shell or the ABM. The ABM or boost assisted artillery shell would be traveling at much less than orbital speed when struck by the satellite. It would be as if the satellite hit a brick wall. Do the various satellite pieces loose velocity or gain velocity? If they loose enough velocity, wouldn’t the pieces fall from orbit?
If you could control all the pieces it would work. It might be a problem if you couldn’t and the break up caused the problem that was to be solved by shrapneling the satellite into scattered orbits. It might work if the shell deployed a blanket like catcher to absorb velocity from all the components at once, though it would be a white knuckle mission until it was proven .
You could eject a material like bb’s in front of the satellite’s flight path.
If you want a material interceptor to de-orbit a dead satellite, a puff of gas may be a good option to avoid more debris.
How much delta-v is needed to deorbit a LEO satellite?
For the puff of gas, a balloon might be used to control the expansion of the puff. A bit of gas unrestricted would go to vacuum very rapidly making timing a crucial mater.
I was using 100 m/s for the lower debris. It would take more with increased altitude with some calculations getting involved. My understanding is that 500 m/s at apogee would lower the perigee into the atmosphere for most debris of interest. Obviously not toward GEO.