A private space company has a radical new plan to bag an asteroid

Company has previously tested its technology on the International Space Station.

See full article...

 

[beb01]

The only thing worth extracting in space is hydrogen and oxygen, water -- rocket fuel.. Everything else will take an established industry to concentrate, refine and forge. If water is the only thing worth extracting it would make better sense to send the processing plant to the asteroid rather than bringing the asteroid to the plant. Water content of any asteroid would be 10% or much less of its mass and 10 tons is a lot easier to ship than 100 tons.

 

[Mous]

They move the asteroid closer to earth to do refining because it's cheaper than transporting all the refinery equipment to the asteroid belt. But what happens to the leftover crushed rock? Can't just toss it out because it'll add to the Kessler cascade. The cost to send it back to deep space could double the original price of recovery. Maybe shoot it into the atmosphere to burn up, but there's still a cost of energy to work whatever process they choose. I think this project will remain in development phase for the foreseeable future.

 

[khumak50]

How are you taking that 100t asteroid to the Moon surface? It's easier for the facility to be in orbit, outside of gravity wells that need a controlled descent.

Also, if your facility is designed to process iron based asteroids, you are only going to capture and move iron based asteroids, why would you move an ice based asteroid to a facility that can't handle that.

That's kind of my point. For it to be economically viable the material you're processing has to be valuable enough to entirely offset all of the fuel used both to escape Earth's atmosphere, and to transport the asteroid for processing, and to transport all of the stuff you need to build the processing facilities, and to actually build that facility, and to operate and maintain that facility.

Which raw materials are valuable enough to do that? Water, Iron, or any other fairly common element? Doubtful. Rare earth elements? Maybe? Personally I'm not sold on the idea of asteroid mining unless we find a way to get to orbit and transport the asteroids without rocket fuel. I think water potentially becomes more viable if you build a facility on a planet or a moon so you have essentially an unlimited amount to process with minimal transportation cost. Same goes for common elements like iron.

So using rockets to transport an iron or ice asteroid to be processed most likely does not make sense but if you can build a processing plant on the moon or Mars and get billions of tons of it without using rockets to transport the raw material then it might make more sense. Of course this assumes you have a reason to actually build something massive at the same location or in the case of water maybe use it as a refueling station.

So for instance if you could build processing plants that could build satellites on the Moon instead of Earth (from materials mined on the moon instead of Earth), building and launching those satellites from the Moon would be cheaper than building and launching them from Earth. But you'd have to build a lot of them to recover the cost of transporting enough materials to build all the mining and processing plants on the moon so it's still pretty questionable IMO.

I'm not sold on anything other than a small scale research outpost for orbit or the moon unless we get to where we don't need rockets anymore.

 

[NezumiRho]

Are you saying that the DRC is going to declare war on China because they are building more and more cobalt less batteries?

Not at all! It seems there is a gap between no longer needing Element X because it has been engineered out and no needing said element because they have their own, infinitely cheaper supply elsewhere.

 

[fenris_uy]

Not at all! It seems there is a gap between no longer needing Element X because it has been engineered out and no needing said element because they have their own, infinitely cheaper supply elsewhere.

The effect is the same, DRC not getting money from extracting cobalt.

 

[wisebabo]

I assume they chose L2 for energy reasons. It's cheaper to get from Earth to L2. It's easier to perform a low-thrust capture into L2. L1 would provide more solar power, being closer to the Sun, but it's functionally little more than a rounding error.


"Space is big" may be a bit overused, but in regards to space around the L1/L2 saddle points, space is really big. There's no worry about debris, and will not be for a long long long time, particularly because those are unstable, and uncontrolled debris will not remain there.


Megastructures suck, and they're just fundamentally unnecessary. There are bizarre structural resonance issues that arise when you try to build something that large, and that's assuming tidal forces don't get you first. You build a swarm of smaller shades, and have them collectively provide the degree of shading you want.


You can't sit at L1. It's unstable. You can minimize your propellant usage by flying a wide orbit around the L1 point, but then you won't be eclipsing the Earth.

Maybe you could device some scheme where you actually are a solar sail, and use that force to maintain heliocentric orbit further inward from L1.


As mentioned, it's unstable. All that dust would drift away anyway.

Thanks! As you see I don't know anything about orbital dynamics, happy to learn

 

[micktransit]

An off-axis pull is just as unstable as an off-axis push. Neither is passively stable. What matters is payload structural stability and sufficient TVC to align with its center of mass. For a loosely bound aggregate asteroid reefing the bag into tension is necessary for controllable handling regardless of thrust arrangement.

As long as the tow-rope(s) is fastened on the thrust axis of the tug, it will be stable.
Like a bag of rubble hanging from a hook, in gravity.

Steering could be tricky though, with that pendulum behind.

 

[micktransit]

Thanks! As you see I don't know anything about orbital dynamics, happy to learn

Orbital stuff is really complex. There are a lot of helpful people here in the comments who really know about it.
I can't follow it all, but it's sinking in gradually.

(Just don't ever mention "Kessler", or "dropping" things from orbit.)

 

[Derecho Imminent]

As long as the tow-rope(s) is fastened on the thrust axis of the tug, it will be stable.
Like a bag of rubble hanging from a hook, in gravity.

Steering could be tricky though, with that pendulum behind.

I think for it to be stable you must be assuming constant acceleration. Without that you dont have a pendulum. If there is pendulum action then when you stop accelerating it turns into two objects orbiting a center of mass.

 

[micktransit]

I think for it to be stable you must be assuming constant acceleration. Without that you dont have a pendulum. If there is pendulum action then when you stop accelerating it turns into two objects orbiting a center of mass.

You're right. It would need constant acceleration. I hadn't thought that far.
My Earth-bound instinct failed.
It could be a tiny thrust, though.

Maybe they'd cut it loose, once it's on course?

I also hadn't thought about how to slow down on arrival, but I could assume that they have?

 

[wagnerrp]

You're right. It would need constant acceleration. I hadn't thought that far.
My Earth-bound instinct failed.
It could be a tiny thrust, though.

It's a 100t asteroid. Even assuming modest ΔV to maneuver a NEA, chemical propulsion is going to be several tens of tons of propellant sent on an escape trajectory. This would almost certainly be electric, meaning tiny thrust sustained over a long period.

I also hadn't thought about how to slow down on arrival, but I could assume that they have?

You wouldn't. You would perform some sort of ballistic capture, so that there's no high thrust burns necessary, and then use the electric thruster to stabilize the orbit.

 

[NetMage]

Can't just toss it out because it'll add to the Kessler cascade.

I don’t think you understand where L2 is located. There is no possibility of a Kessler cascade.

 

[vanzandtj]

Sure, but then you need to accurately push against the center of mass of the asteroid, otherwise you’re gonna flip end over end or burn your RCS a lot preventing it.

So now you need to secure the asteroid in the bag in such a way that the center of mass of what’s now an impromptu part of your spacecraft aligns with your thrust vector.

Of course if you have a system that swivels your engines on the fly as a control loop narrows down until it found the center of mass through ever decreasing corrections..

That’d be the big upside of a tow; it’s passively stable.

I suggest securing three engines to the bag, with their lines of thrust straddling the center of mass, so you can steer by adjusting thrust on the engines.

Don't most small asteroids spin or tumble chaotically due to the YORP (sunlight) effect? Seems like bagging a rotating asteroid is going to be a problem.

So place the first engine where it will oppose the rotation. Fire it periodically when it also yields a delta V in the right direction. (A typical asteroid rotational period is six hours.) If the initial axis of rotation is not orthogonal to the desired delta V direction, the engine location and thrust direction can be chosen to adjust the axis in that direction, so the delta V contributions get gradually more efficient. While that's in progress, install the other two engines. Start them when the asteroid stops rotating.

 

[vanzandtj]

They move the asteroid closer to earth to do refining because it's cheaper than transporting all the refinery equipment to the asteroid belt. But what happens to the leftover crushed rock? Can't just toss it out because it'll add to the Kessler cascade. The cost to send it back to deep space could double the original price of recovery. Maybe shoot it into the atmosphere to burn up, but there's still a cost of energy to work whatever process they choose. I think this project will remain in development phase for the foreseeable future.

The refinery will be manned. For quite a while, the leftover rock can be added to the radiation shield. It can also be sent to EML1 to shield the lunar space elevator facilities there.

 

[vanzandtj]

One other thing, an idea I've had for a long time is, since these mini-roids (and some of their larger brothers) are spinning very fast (just under the breakup limit), why not use that rotational energy? Attach a cable to the bag around a little roid) or to a cable alll around a big one and extend it way out. Then using a (ok maybe complicated) system of "buckets" have them move some mass far from the center of gravity and, at the proper moment, release it. (these raids are made of loose rubble, right?). The roid's rotation will slow down a tiny bit and IT WILL MOVE IN THE OPPOSITE DIRECTION from the mass you've released. If you time the releases correctly, you might get some significant velocity. (Maybe not nearly enough to move it to L1 in a reasonable amount of time but, given enough warning, easily enough to get it off an earth collision trajectory).

You're describing the orbital siphon discussed by Andrea Viale, Colin McInnes, and Matteo Ceriotti, though they envision transporting parcels of rubble rather than redirecting the asteroid.

 

[Derecho Imminent]

I think it might be more efficient to mount thrusters on the bag itself instead of trying to tow it with a rope.

 

[aapis]

Why don't they do something of value instead?

 

[wagnerrp]

I think it might be more efficient to mount thrusters on the bag itself instead of trying to tow it with a rope.

If you're pushing the asteroid, then you need to stabilize the asteroid to give you something firm to actually push into. As has been argued, you can "just pull the bag tight", but now you need enough tensile strength in your bag to actually achieve that. If you're dragging it from the front, your bagging material only has to be as strong as your thruster.

 

[SpikeTheHobbitMage]

If you're pushing the asteroid, then you need to stabilize the asteroid to give you something firm to actually push into. As has been argued, you can "just pull the bag tight", but now you need enough tensile strength in your bag to actually achieve that. If you're dragging it from the front, your bagging material only has to be as strong as your thruster.

You only need enough strength to hold against thrust either way. The advantage of pulling is that it doesn't need pre-tensioning. A pull rope is problematic because it makes control difficult at best and cripples efficiency. Side-mounted thruster pods are probably the most practical solution.

 

[dsp0549]

I’ve seen this movie before. Literally. It’s called Moon Zero Two. If this mission doesn’t include a psychedelic jazz lounge on the moon and a 1960s vision of 2021, I’m going to be disappointed. Highly recommend the MST3K treatment of it for anyone who wants to see how 'bagging an asteroid' usually ends up.

 

[wagnerrp]

You only need enough strength to hold against thrust either way. The advantage of pulling is that it doesn't need pre-tensioning. A pull rope is problematic because it makes control difficult at best and cripples efficiency. Side-mounted thruster pods are probably the most practical solution.

Cripples? Because of cosine losses or impingement on the bag? The exhaust cone of an ion thruster in a vacuum is >100°, and a chemical thruster is >200°. There's probably no point in even trying to avoid impingement by angling the thrusters, thus no cosine losses. A 100t asteroid is only going to be several meters across, so with a tether several tens of meters long, you're going to have negligible shadowing. I would only see a potential concern over bag erosion.

 

[SpikeTheHobbitMage]

Cripples? Because of cosine losses or impingement on the bag? The exhaust cone of an ion thruster in a vacuum is >100°, and a chemical thruster is >200°. There's probably no point in even trying to avoid impingement by angling the thrusters, thus no cosine losses. A 100t asteroid is only going to be several meters across, so with a tether several tens of meters long, you're going to have negligible shadowing. I would only see a potential concern over bag erosion.

A tether that long is going to present control issues, particularly (lack of) oscillation damping, and maneuverability at delivery is going to be nil.

 

[wagnerrp]

A tether that long is going to present control issues, particularly (lack of) oscillation damping, and maneuverability at delivery is going to be nil.

The only "control issue" with the tether is that you'll have to run the entire mission under thrust, but with an electric thruster, that's not impractical. We're only talking single-digit newtons of thrust here so oscillations are not going to feed back into the propulsion system, and you can actively manage thrust to damp them anyway. Take out the slack on the tether and slowly load it up, just as you would every other time you're towing something. It's not like you're trying to yank a car out of a ditch. Maneuverability is poor, since you'll have to turn extremely slowly to avoid wrapping the tether, but that's only a factor at the beginning and end of the mission. At the end of the mission, you can have other systems in place to assist, with less of a penalty since they didn't have to carry their extra mass into deep space to capture the asteroid.

I'm assuming we're an extremely loosely bound collection of pebbles, since that's what missions to date have demonstrated. If you're pushing on the surface with the same few newtons of force, you'll just push through it and out the other side. Now you have a bag around everything, so instead you'll push yourself and the bag into the asteroid until there's enough tension on the bag to drag everything. The load will shift, and you will need to be able to adjust your thrust vector to compensate. When you do, the load will just shift again, and you'll forever be chasing equilibrium. Or you need some mechanism by which you can translate your thrusters (not just pivot them) to balance without changing the thrust vector. For a tug, it doesn't matter what the load is doing, it will always be applied through a single point.

 

[Wickwick]

The only "control issue" with the tether is that you'll have to run the entire mission under thrust, but with an electric thruster, that's not impractical. We're only talking single-digit newtons of thrust here so oscillations are not going to feed back into the propulsion system, and you can actively manage thrust to damp them anyway. Take out the slack on the tether and slowly load it up, just as you would every other time you're towing something. It's not like you're trying to yank a car out of a ditch. Maneuverability is poor, since you'll have to turn extremely slowly to avoid wrapping the tether, but that's only a factor at the beginning and end of the mission. At the end of the mission, you can have other systems in place to assist, with less of a penalty since they didn't have to carry their extra mass into deep space to capture the asteroid.

I'm assuming we're an extremely loosely bound collection of pebbles, since that's what missions to date have demonstrated. If you're pushing on the surface with the same few newtons of force, you'll just push through it and out the other side. Now you have a bag around everything, so instead you'll push yourself and the bag into the asteroid until there's enough tension on the bag to drag everything. The load will shift, and you will need to be able to adjust your thrust vector to compensate. When you do, the load will just shift again, and you'll forever be chasing equilibrium. Or you need some mechanism by which you can translate your thrusters (not just pivot them) to balance without changing the thrust vector. For a tug, it doesn't matter what the load is doing, it will always be applied through a single point.

Even towing a cable, you're going to have to actively damp oscillations. Sure, the tension force acts through a single point, but that point won't be literally at the center of mass of the towing vehicle. As such, any off-axis tension will act to turn your vehicle.

That's certainly a solvable problem, but it's not as inherently stable as towing something on the ground where the side-to-side motions can dampen through friction.

And obviously, you'd design your tug so that the hardpoint is as close to the CoM as you can make it.

 

[wagnerrp]

Even towing a cable, you're going to have to actively damp oscillations. Sure, the tension force acts through a single point, but that point won't be literally at the center of mass of the towing vehicle. As such, any off-axis tension will act to turn your vehicle.

That's certainly a solvable problem, but it's not as inherently stable as towing something on the ground where the side-to-side motions can dampen through friction.

And obviously, you'd design your tug so that the hardpoint is as close to the CoM as you can make it.

I'm not saying it's inherently stable, but it's predictable. Everything that matters to the dynamics of the system are parts you brought with you, and the rock is a dead load.

 

[DCMarchisotto]

This kind of silliness always amazes me...especially that people would think this is anything other than a half-thought out concept. The highest concentration of asteroids in our system is the belt...112 million miles (at best) away from us. How are they getting there, robotics teleoperated from Earth? Then returned to a L2 point, then what? How are they processed in open space? Who is doing that? We can't seem to get into space without 50 delays and this is going to be run as an ongoing concern? And tell me again that the US wouldn't try to use this as a weapon ala Rods from God.

 

[Klive Aleksaander]

This kind of silliness always amazes me...especially that people would think this is anything other than a half-thought out concept. The highest concentration of asteroids in our system is the belt...112 million miles (at best) away from us. How are they getting there, robotics teleoperated from Earth? Then returned to a L2 point, then what? How are they processed in open space? Who is doing that? We can't seem to get into space without 50 delays and this is going to be run as an ongoing concern? And tell me again that the US wouldn't try to use this as a weapon ala Rods from God.

Of course they won't be going to the belt, they will be after NEOs (Near Earth Object). And there are a LOT of them.

More info at NASA's CNEOS (Center for Near Earth Object Studies).

Edit: tweaked link to CNEOS site

 

[wagnerrp]

And tell me again that the US wouldn't try to use this as a weapon ala Rods from God.

A weapon that costs hundreds of millions of dollars to fire, takes years to reach its target, and burns up harmlessly in the atmosphere when it does? They won't.

 

[Wickwick]

I'm not saying it's inherently stable, but it's predictable. Everything that matters to the dynamics of the system are parts you brought with you, and the rock is a dead load.

Agreed. I just thought it was an interesting case where our terrestrial experience that oscillations damp would lead to a simpler system than it actually is. So long as the cable is relatively long (tens of meters), I expect the time scales for the oscillations will be rather long so it's certainly something manageable.

 

[real mikeb_60]

That's kind of my point. For it to be economically viable the material you're processing has to be valuable enough to entirely offset all of the fuel used both to escape Earth's atmosphere, and to transport the asteroid for processing, and to transport all of the stuff you need to build the processing facilities, and to actually build that facility, and to operate and maintain that facility.

Which raw materials are valuable enough to do that? Water, Iron, or any other fairly common element? Doubtful. Rare earth elements? Maybe? Personally I'm not sold on the idea of asteroid mining unless we find a way to get to orbit and transport the asteroids without rocket fuel. I think water potentially becomes more viable if you build a facility on a planet or a moon so you have essentially an unlimited amount to process with minimal transportation cost. Same goes for common elements like iron.

So using rockets to transport an iron or ice asteroid to be processed most likely does not make sense but if you can build a processing plant on the moon or Mars and get billions of tons of it without using rockets to transport the raw material then it might make more sense. Of course this assumes you have a reason to actually build something massive at the same location or in the case of water maybe use it as a refueling station.

So for instance if you could build processing plants that could build satellites on the Moon instead of Earth (from materials mined on the moon instead of Earth), building and launching those satellites from the Moon would be cheaper than building and launching them from Earth. But you'd have to build a lot of them to recover the cost of transporting enough materials to build all the mining and processing plants on the moon so it's still pretty questionable IMO.

I'm not sold on anything other than a small scale research outpost for orbit or the moon unless we get to where we don't need rockets anymore.

Why haul the raw materials halfway across the solar system? As with most industrial processes, you want to minimize transport expense for the raw (i.e. relatively low value per unit mass) material: crush, concentrate, make into intermediate form of some kind (metal ingots, etc.). Seems like it would be better to send the factory to the asteroid and only ship high-intermediate or final products to market. Yeah, I'm pretty sure I've seen scifi stories built around that...

 

[wagnerrp]

Why haul the raw materials halfway across the solar system? As with most industrial processes, you want to minimize transport expense for the raw (i.e. relatively low value per unit mass) material: crush, concentrate, make into intermediate form of some kind (metal ingots, etc.). Seems like it would be better to send the factory to the asteroid and only ship high-intermediate or final products to market. Yeah, I'm pretty sure I've seen scifi stories built around that...

To start with, we have don't know how to crush, concentrate, and refine an asteroid. First generation designs are always bad. It makes sense to drag an asteroid nearby to experiment on and explore that process. And then do it all over again, because another asteroid may have a different composition requiring completely different processes.

 

[Wickwick]

To start with, we have don't know how to crush, concentrate, and refine an asteroid. First generation designs are always bad. It makes sense to drag an asteroid nearby to experiment on and explore that process. And then do it all over again, because another asteroid may have a different composition requiring completely different processes.

I think it's important to help people realize the size of the asteroid under discussion. A 100 tonne rock is about a quarter of the load hauled by the largest strip-mining dump trucks. Heck, it's only half of the mass of one of those dump trucks unloaded.

 

[wagnerrp]

I think it's important to help people realize the size of the asteroid under discussion. A 100 tonne rock is about a quarter of the load hauled by the largest strip-mining dump trucks. Heck, it's only half of the mass of one of those dump trucks unloaded.

Put another way, that's an asteroid around 4-6m in diameter, or about the size of the Orion spacecraft.

 

[SpikeTheHobbitMage]

I'm not saying it's inherently stable, but it's predictable. Everything that matters to the dynamics of the system are parts you brought with you, and the rock is a dead load.

It's a chaotic system and while a single cable attached near the CoG of the tow vehicle reduces positive feedback it also reduces the tug's control arm. It isn't fully predictable either because plume impingement subjects the payload to randomized lateral impulses and a loose aggregate can shift unexpectedly as it compacts under load.

Agreed. I just thought it was an interesting case where our terrestrial experience that oscillations damp would lead to a simpler system than it actually is. So long as the cable is relatively long (tens of meters), I expect the time scales for the oscillations will be rather long so it's certainly something manageable.

It's still vulnerable to harmonic oscillations, and any twist response in the cable is going to cause problems because there is almost zero control on that axis.

A better system would use a triangular base at each end joined by six cables in a zig-zag pattern. That provides a semi-rigid structure for positive control while also eliminating the dangerous free swinging motion that a soft link allows. If the bases are aharmonic with the cables and each other then cable oscillations will interfere destructively, further reducing control load. The downside is off-center CoG but that can be mitigated by making the cables adjustable to fine tune payload orientation. That has the additional benefit of detuning the cables.

 

[Komarov]

It's a chaotic system and while a single cable attached near the CoG of the tow vehicle reduces positive feedback it also reduces the tug's control arm. It isn't fully predictable either because plume impingement subjects the payload to randomized lateral impulses and a loose aggregate can shift unexpectedly as it compacts under load.

Heh heh, chaotic systems are completely predictable, your randomised lateral impulses and unstable rubble are just imprecisions in the description of its initial state.

Now I should avail myself of the most convenient egress.

 

[Wickwick]

It's a chaotic system and while a single cable attached near the CoG of the tow vehicle reduces positive feedback it also reduces the tug's control arm. It isn't fully predictable either because plume impingement subjects the payload to randomized lateral impulses and a loose aggregate can shift unexpectedly as it compacts under load.

It's still vulnerable to harmonic oscillations, and any twist response in the cable is going to cause problems because there is almost zero control on that axis.

A better system would use a triangular base at each end joined by six cables in a zig-zag pattern. That provides a semi-rigid structure for positive control while also eliminating the dangerous free swinging motion that a soft link allows. If the bases are aharmonic with the cables and each other then cable oscillations will interfere destructively, further reducing control load. The downside is off-center CoG but that can be mitigated by making the cables adjustable to fine tune payload orientation. That has the additional benefit of detuning the cables.

Chaotic systems aren't necessarily uncontrollable. One simply needs to stay away from attractors.

However, I will add that it's not against the rules to have thrusters on and around the net. Your tether then has to be supplying propellant, but we're talking Newtons of force here. There's no reason the circumference of the net can't support that. And sure, the mass distribution can shift. That would certainly factor into the need for active control - but not the impossibility of the same.

 

[wagnerrp]

It's a chaotic system and while a single cable attached near the CoG of the tow vehicle reduces positive feedback it also reduces the tug's control arm.

That's the whole point. It reduces the control arm. Oscillations in the tether will not couple into a rotational moment in the tug. That's exactly what you want. I don't see how that's a bad thing.

It isn't fully predictable either because plume impingement subjects the payload to randomized lateral impulses and a loose aggregate can shift unexpectedly as it compacts under load.

Shifts in the load will only cause temporary oscillations in the tether, and that can be damped by modulating the thrusters. For impingement, only a small fraction of impacts will actually be deflected to produce lateral thrust, at a fraction of its original speed and force, and that's a small fraction of the total beam, of what's only going to be a few N total.

It's still vulnerable to harmonic oscillations, and any twist response in the cable is going to cause problems because there is almost zero control on that axis.

I haven't thought through a good solution for eliminating twist in the line. You've got me on that one.

 

[Wickwick]

I haven't thought through a good solution for eliminating twist in the line. You've got me on that one.

Is there any reason to believe that a single craft would be better than a distributed architecture? After all, the propellant mass is the dominant factor and it can be partitioned.

So my idea is to split the tug into three vehicles each tethered together with one third of the nominal thrust on each corner.

You can now spin-stabilize the entire thing (revolutions per hour probably).

 

[wagnerrp]

Is there any reason to believe that a single craft would be better than a distributed architecture? After all, the propellant mass is the dominant factor and it can be partitioned.

So my idea is to split the tug into three vehicles each tethered together with one third of the nominal thrust on each corner.

You can now spin-stabilize the entire thing (revolutions per hour probably).

Now there's three points of failure instead of just the one. With appropriate revolutions and tether length (2-3/rph, 20m), centrifugal force would be an order of magnitude more than the realistic thrust output, and the tugs would be splayed out to the sides of the asteroid instead of pulling from the front. That eliminates any impingement concerns, but means any damping of the tether would need to be done mechanically rather than through the thruster.

 

[SpikeTheHobbitMage]

Chaotic systems aren't necessarily uncontrollable. One simply needs to stay away from attractors.

However, I will add that it's not against the rules to have thrusters on and around the net. Your tether then has to be supplying propellant, but we're talking Newtons of force here. There's no reason the circumference of the net can't support that. And sure, the mass distribution can shift. That would certainly factor into the need for active control - but not the impossibility of the same.

Not impossible, no, but oscillation in a multiple pendulum system is notoriously difficult to control. The rigid structure from the tug's CoG to the attachment point acts as a pendulum, the tether acts as the second, and the payload as the third.

I tried to argue side-mounted thrusters earlier and got voted down. If it's allowed then there's no point using a tow tether at all: Either mount the thrusters on a rigid ring with the payload bag slung in the middle or use propulsion modules spaced around the bag. The latter needs tension lines to keep the modules in place but that should be lighter than a rigid ring.