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.
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