Deorbiting by using the momentum of debris.

[jee_c2]

I haven't seen deorbiting methods yet, which use the momentum, the moving energy of the debris itself for the repeated process.

My idea is to make a bigge r - could be refuelable - space craft, which is using electric propukion (VASIMR could be nice), and is equipped by a longer railgun, or similar device(*), which can generate linear moving energy from electric energy.

The deorbiting would look like:
1. Approach debris  (ie non functioning sat /like StarLink or similar/
2. Capture it somehow, there are many proposals for that
3. Accelerate it with the help of the railgun* mostly backwards, but also calculating the orbit change necessary for the next target. This will put the debris sat to an orbit, which leads it to denser layers, and so the objective is accomplished. If more is needed, some sort of cross section grower can be attached to the debris, so that fasten the work of the atmospheres top layers.
4. Repeat

Solar panels should gather energy for the next action. Some sort of reusable energy storage is needed to store the energy. And this is not so easy - ie batteries can be too heavy. But since it is a multi mission orbit sweeper, that also could be an option.

Also an engineering challange is the "shooting"  of the sat. How to grab it, where the rail should be, how long? Positioning is critical, so center of mass also relative to the gun. And so on.

[Pete]

There is no posible way the cleanup ship will get more delta-v from expelling the debris, than would be consumed by the mass and complexity of the equipment needed to handle such forces. Current engineering will leave an energy/efficiency gap of *several* magnitudes between them. We haven't managed to make this work with small, carefully-machined uniform masses. Debris will be in wildly varying shapes, sizes and materials.

Also:
VASIMR propulsion and Solar power are incompatible, also by magnitudes. It can be very efficient, yes, but requires HUGE power input, or HUGE patience for maneuvers. More patience than anything on Earth orbit will have.

Cool idea, but it runs headlong into engineering capability at our current ability.

[laszlo]

There is no possible way the cleanup ship will get more delta-v from expelling the debris, than would be consumed by the mass and complexity of the equipment needed to handle such forces. Current engineering will leave an energy/efficiency gap of *several* magnitudes between them. We haven't managed to make this work with small, carefully-machined uniform masses. Debris will be in wildly varying shapes, sizes and materials.
...
Cool idea, but it runs headlong into engineering capability at our current ability.

(emphasis mine)

While I totally agree that this won't work at our current level of tech and that the comments about VASIMIR are spot on, I would like to remind folks that the rocket equation "proved" many years ago that the extra mass and complexity of equipment needed to recover boosters would never make economic sense.

This is actually a form of ISRU, recycling available ambient mass into usable reaction mass. All that it needs is for someone to decide that it's worth doing the research, designing engines that can work with this reaction mass, spacecraft that can "mine" the raw materials and equipment to process it into a usable form.

I'm not saying that it's trivial, just that it's not so far out of line with designing advanced methane engines that can use feed stock collected on another planet that is processed into the required fuel.  Remember how weird that sounded years ago?

This is one of those ideas that is scientifically possible and technologically not feasible - at the moment. When the perceived need becomes great enough, someone will develop the enabling tech and everyone else will wish they'd thought of it

My main concern is what happens to the reaction mass.  I'm not sure if the expelled particles can safely whiz around on their new vectors without becoming collision problems themselves unless they've been reduced to molecular dimensions. It could also be that it would make more sense to have separate specialized spacecraft for each function, rather than a Swiss Army knife version to do it all.

[edzieba]

Remember that this does not give you any 'free' propulsion. You need to use on-board deltaV to match velocities with the target debris to start with, and once you have done that you need to expend additional energy to modify the delta-V of both the debris and your 'catcher' craft (and this will be a combination of the deltaV added to the debris and the deltaV added to the catcher). It changes what mechanism you can use for propulsion (e.g. linear EM accelerator; attach a tether, spin up, then detach in opposing vectors; mechanically compress a spring between objects then release to impart opposing impulses; etc) but TANSTAAFL.

[jee_c2]

There is no posible way the cleanup ship will get more delta-v from expelling the debris, than would be consumed by the mass and complexity of the equipment needed to handle such forces. Current engineering will leave an energy/efficiency gap of *several* magnitudes between them. We haven't managed to make this work with small, carefully-machined uniform masses. Debris will be in wildly varying shapes, sizes and materials.

May be, I'm not sure. Perhaps the gained deltaV is negligible. In that case, we have to reconsider the whole approach, since deorbiting could be achieved by other ways as well.
Varying shapes? Sure. Question is if we can simplify that into a single cable, which is connecting the target sat to our accelerator pair of rails. That makes the case simpler, and a bit more difficult the same time (the cable itself, positioning, aiming)

Also:
VASIMR propulsion and Solar power are incompatible, also by magnitudes. It can be very efficient, yes, but requires HUGE power input, or HUGE patience for maneuvers. More patience than anything on Earth orbit will have.

VASIMR was only an example, propulsion can be some traditional rocket engine, with refueling option.

Thanks for your thoughts on it!

[jee_c2]

This is actually a form of ISRU, recycling available ambient mass into usable reaction mass.

Exactly, good insight! And  even a bit more, using not only the mass, but also the velocity of it, achieving useful acceleration for the spacecraft, and deorbit the target craft. (I thought the target sat should be accelerated as a whole.)

My main concern is what happens to the reaction mass.  I'm not sure if the expelled particles can safely whiz around on their new vectors without becoming collision problems themselves unless they've been reduced to molecular dimensions. It could also be that it would make more sense to have separate specialized spacecraft for each function, rather than a Swiss Army knife version to do it all.

The deorbiting shot (of the whole debris in one piece) could be planned (time, direction, also deltaV), assuring it won't cause any more problems. It should burn in the atmosphere.

I also agree with the "not yet developed, but it could be" (it is possible) thought.

[jee_c2]

Remember that this does not give you any 'free' propulsion. You need to use on-board deltaV to match velocities with the target debris to start with, and once you have done that you need to expend additional energy to modify the delta-V of both the debris and your 'catcher' craft (and this will be a combination of the deltaV added to the debris and the deltaV added to the catcher). It changes what mechanism you can use for propulsion (e.g. linear EM accelerator; attach a tether, spin up, then detach in opposing vectors; mechanically compress a spring between objects then release to impart opposing impulses; etc) but TANSTAAFL.

Shortly: yes, you are right.
I also thought about the other methods you lined up.

BTW: is it possible to spin up two tethered spacecraft without using rocket propulsion (thrusters)? And that without spinning the one putting the energy into the process? (This free falling, zero G mechanics is funny sometimes.) Without rocketry the sum of the impulse, spin will not vary for the whole system.
It may work, right?

[edzieba]

BTW: is it possible to spin up two tethered spacecraft without using rocket propulsion (thrusters)?

Only by spinning an internal device (reaction wheel) up in the opposite direction. If you include the reaction wheel as a part of your two=spacecraft system, then no*.

And that without spinning the one putting the energy into the process? (This free falling, zero G mechanics is funny sometimes.) Without rocketry the sum of the impulse, spin will not vary for the whole system.
It may work, right?

No free lunches, you cant spin up without inputting momentum.


* barring mechanisms like the YORP effect which act over very long periods with very low forces.

[meberbs]

BTW: is it possible to spin up two tethered spacecraft without using rocket propulsion (thrusters)?

Only by spinning an internal device (reaction wheel) up in the opposite direction. If you include the reaction wheel as a part of your two=spacecraft system, then no*.

And that without spinning the one putting the energy into the process? (This free falling, zero G mechanics is funny sometimes.) Without rocketry the sum of the impulse, spin will not vary for the whole system.
It may work, right?

No free lunches, you cant spin up without inputting momentum.


* barring mechanisms like the YORP effect which act over very long periods with very low forces.

Actually, it is common for satellites to use torque rods (basically electromagnets) to exchange angular momentum with the Earth through the magnetic field. This can be used in combination with gyros or reaction wheels to desaturate them if they accumulate too much angular momentum. This can happen for example if a spacecraft is shaped such that atmospheric drag tends to torque it in one direction.

https://en.wikipedia.org/wiki/Magnetorquer

[freddo411]

I haven't seen deorbiting methods yet, which use the momentum, the moving energy of the debris itself for the repeated process.

My idea is to make a bigge r - could be refuelable - space craft, which is using electric propukion (VASIMR could be nice), and is equipped by a longer railgun, or similar device(*), which can generate linear moving energy from electric energy.

The deorbiting would look like:
1. Approach debris  (ie non functioning sat /like StarLink or similar/
2. Capture it somehow, there are many proposals for that
3. Accelerate it with the help of the railgun* mostly backwards, but also calculating the orbit change necessary for the next target. This will put the debris sat to an orbit, which leads it to denser layers, and so the objective is accomplished. If more is needed, some sort of cross section grower can be attached to the debris, so that fasten the work of the atmospheres top layers.
4. Repeat

Solar panels should gather energy for the next action. Some sort of reusable energy storage is needed to store the energy. And this is not so easy - ie batteries can be too heavy. But since it is a multi mission orbit sweeper, that also could be an option.

Also an engineering challange is the "shooting"  of the sat. How to grab it, where the rail should be, how long? Positioning is critical, so center of mass also relative to the gun. And so on.

Actually, this is one of the least crazy orbiting debris cleaning ideas around.    It's extremely fuel-expensive to perform any kind of debris collection and disposal, so you very likely need to use tricks like this.

So, I don't think it is very practical to capture a piece of debris and then accelerate it using a rail gun because your rail gun won't be very long, and thus you won't impart much momentum.

On the other hand, you could use the debris momentum in another way.   Attach a tether, and unspool it slowly.   Your garbage collector goes up, and the debris goes down.   This orbital maneuver has already been proven out in actual space missions.    https://en.wikipedia.org/wiki/Space_tether#Momentum_exchange_tethers,_rotating

[Nomadd]

 People might be underestimating railguns. Check out some of the specs for navy research.
 Besides, they can just use one of the Psyche based ore guns in a few years.

[jee_c2]

So, I don't think it is very practical to capture a piece of debris and then accelerate it using a rail gun because your rail gun won't be very long, and thus you won't impart much momentum.

Actually, I thought a longer rail, which could be assembled in an automated way in orbit (sequential, gradual assembling), after the launch.

On the other hand, you could use the debris momentum in another way.   Attach a tether, and unspool it slowly.   Your garbage collector goes up, and the debris goes down.   This orbital maneuver has already been proven out in actual space missions.    https://en.wikipedia.org/wiki/Space_tether#Momentum_exchange_tethers,_rotating

That is a good idea! How much momentum can be transferred this way? Probably depending on the tether length, right? The main objective is to deorbit the debris (sat). For that, it's orbit has to be changed enough to enter denser regions. If this method could achieve this, it is probably way simpler, than a rail gun (or similar, electromagnetic accelerating method/device).
As I see, the tether connected sweeper and target body system have to be rotating. For that, some propulsion is needed, I think. Is it so, or can an electric tether help with starting the rotation?

[jee_c2]

...
  Besides, they can just use one of the Psyche based ore guns in a few years.

You mean plasma rail gun?
I could not find "Psyche based ore guns" on the net.

[edzieba]

BTW: is it possible to spin up two tethered spacecraft without using rocket propulsion (thrusters)?

Only by spinning an internal device (reaction wheel) up in the opposite direction. If you include the reaction wheel as a part of your two=spacecraft system, then no*.

And that without spinning the one putting the energy into the process? (This free falling, zero G mechanics is funny sometimes.) Without rocketry the sum of the impulse, spin will not vary for the whole system.
It may work, right?

No free lunches, you cant spin up without inputting momentum.


* barring mechanisms like the YORP effect which act over very long periods with very low forces.

Actually, it is common for satellites to use torque rods (basically electromagnets) to exchange angular momentum with the Earth through the magnetic field. This can be used in combination with gyros or reaction wheels to desaturate them if they accumulate too much angular momentum. This can happen for example if a spacecraft is shaped such that atmospheric drag tends to torque it in one direction.

https://en.wikipedia.org/wiki/Magnetorquer

You're right, I completely forgot about magnetotorquers. Though as you said, they're usually used for desaturating your actual pointing mechanism, and IIRC are only used as the primary pointing mechanism for extremely small satellites where you are volume and mass constrained (e.g cubesats) where the very low slew rates are an acceptable alternative to no control.

People might be underestimating railguns. Check out some of the specs for navy research.
 Besides, they can just use one of the Psyche based ore guns in a few years.

The downside to the navy railguns is the building sitting around them to power the shot (and pre-accelerate the projectile to prevent it welding to the rails), and the power grid they're connected to power the building. Plus the whole needing to mill the debris down into a nice armature that doesn't rip your railgun apart after a shot or two (a not insubstantial problem for railguns).



Using a momentum exchange tether is attractive, but still has some implementation issues.
A nonrotating tether would end up being extremely long to perform appreciable momentum exchange with such small masses, and still requires a manoeuvre to match the 'catcher' craft to the debris (and with the mas of that long tether, you might as well carry a few tens to hundreds of single-use de-orbit solid rockets plus some glue).
A rotating tether on a lower elliptic orbit that intersects the debris orbit minimises energy expenditure of the 'catcher' (indeed, the less energy the catcher has the more effective the momentum exchange). The down side is that intersection of a few km/s velocity difference: even if you spin up a tether so the tip speed matches the debris speed for a 0-0 intercept, as soon as you latch onto it you now have to deal with the momentum difference in your combined system. The more manageable you make that momentum difference, the less benefit you gain the from the whole setup in the first place.

[john smith 19]

Actually, I thought a longer rail, which could be assembled in an automated way in orbit (sequential, gradual assembling), after the launch.

TBH I think this is a solution looking for a problem.

Roughly speaking anything above 10cm in size can be tracked by ground radar. It's orbit is known and in principle avoidable.

That leaves a huge number of items below that size that cannot be tracked but have more than sufficient KE to do substantial damage if they hit something (or someone) with enough relative velocity to them. LEO orbital velocity is about 7900m/s A rifle bullet is about 680m/s.

So you're going to fire your rail gun at this object to slow it down quite a lot and speed up your vehicle a bit to the point the debris is below orbital velocity (the Shuttle used its OMS engines to reduce speed by about 100m/s, but then it came in at an AoA of between 45 and 70 degrees to maximize surface area)

What happens to the pellets? Can you guarantee they will stay with the debris and enter with it? Or do you expect them to ricochet off? You have now created more  debris than you have disposed of. It's also non trackable being very small.

VASIMIR needs huge power levels. A small VASIMIR test needs the entire output of the ISS (about 200Kw) to operate.  Ion drives of various architectures are available OTS and operate in the Kw range. A substantial system could be built around using all the slots of a secondary payload adapter, if you can solve how to deploy the magnetic gun barrel (rail or coil)

Once again the real issue with space debris is all the "dark" matter that's far too small to see (like paint fragments that penetrated one of the three panes of a Shuttle window) but not too small to damage (or potentially kill)

The small stuff's dispersion is unknown (although if it's like the radar tracked objects it's very widespread) and you (literally) never see it coming. Finding a way to solve that problem (and getting people to pay for it) would substantially lower the risks of launching things into space and of them being damaged once in space.

[Twark_Main]

This reminds me of the Sling-Sat proposal from a while back. https://www.space.com/amp/20024-space-junk-removal-sling-sat.html

A proposed space-junk removal system would hop from one piece of debris to the next without burning much fuel, potentially making a de-clutter mission economically feasible with current technologiy.

The TAMU Space Sweeper with Sling-Sat, or 4S for short, would harness the momentum imparted by capturing and ejecting one object to slingshot on to the next chunk of space junk, its developers say.

...

The most technically and politically sound idea is a simple rendezvous mission, during which a clean-up craft would travel to and de-orbit debris objects one at a time, Missel said. But such a mission would burn loads of fuel to get between widely spaced targets, making it “fatally plagued by inefficiency,” he added.

The 4S system, which Missel and Mortari are developing, aims to correct this fatal flaw. It would snare debris at the end of a spinning satellite, then fling the object down to burn up in Earth's atmosphere.

The spacecraft would harness the momentum exchanged during both of these actions to cruise over to the next piece of space junk on its list, minimizing fuel use and extending its operational life to the point that such a mission might be practical.

I found the bold part interesting. If it can use the same acceleration hardware to capture debris then it reduces fuel use further (less propellant needed to rendezvous), roughly doubling the supply of "free" momentum available to jump from object to object. This gives the trajectory planners additional degrees of freedom, because it can capture and release in two different directions and at two different parts of the orbit (eg waiting so that the debris is launched retrograde at apogee).

The associated PhD dissertation has further details. https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/149391/MISSEL-DISSERTATION-2013.pdf?sequence=1&isAllowed=y

And just as a bonus, here's another, newer proposal that uses a tether instead of two rigid pantograph arms. Unlike the Sling-Sat proposal, this would require ~zero propellant for rendezvous. However the author points out that this means the satellite's altitude will keep raising with each removal. https://www.researchgate.net/profile/Zachary_Asher/publication/327387888_Space_Debris_Field_Removal_Using_Tether_Momentum_Exchange_-_Presentation/data/5b8bf35c299bf1d5a73922b1/Space-Debris-Field-Removal-Using-Tether-Momentum-Exchange-Presentation.pdf

[BeamRider]

A notional concept:
1. Debris Disposer (DD) sat uses solar-array-powered electric motor to compress a spring-loaded "catch-kick" plate.
2. DD sat uses solar-sail +/- acceleration to approximate intercept orbit to targeted debris.
3. Conventional thrusters are used to make final approach to debris.
4  Debris touches catch-kick plate, triggering a release catch, kicking debris into lower-energy orbit and eventual re-entry.
5. Go to step 1 and repeat.

This concept uses a solar sail to do gradual orbital adjustments to re-target to next debris after pushing off previous debris. Final approach would have to use conventional consumable-fuel thrusters to be practical.  The main problem would be balancing the need for a DD/Sail with a mass adequate to accelerate the debris, against low enough mass DD/Sail required to make solar sailing work. Each kick might also prang the sail!

[john smith 19]

A notional concept:

This concept uses a solar sail to do gradual orbital adjustments to re-target to next debris after pushing off previous debris. Final approach would have to use conventional consumable-fuel thrusters to be practical.  The main problem would be balancing the need for a DD/Sail with a mass adequate to accelerate the debris, against low enough mass DD/Sail required to make solar sailing work. Each kick might also prang the sail!

That addresses a key point with most of these concepts. They are only good for a few pieces of debris before they run out of fuel, hence my suggestion about using ion thrusters

Since you have control of the approach to the debris object the logical approach would be to allow time to fold up the solar sail so its it's able to handle the shock load when the compressed spring is released. An alternative would be to build the sail capable of resisting the load but I suspect that would make it too heavy.

BTW this principle of using a compressed spring was used in a British WWII anti tank weapon called the PIAT AKA  a "recoiless mortar"

[Nomadd]

...
  Besides, they can just use one of the Psyche based ore guns in a few years.

You mean plasma rail gun?
I could not find "Psyche based ore guns" on the net.

That's because I just invented the term
 Reference to mining metal on the Psyche asteroid.

[edzieba]

A notional concept:

This concept uses a solar sail to do gradual orbital adjustments to re-target to next debris after pushing off previous debris. Final approach would have to use conventional consumable-fuel thrusters to be practical.  The main problem would be balancing the need for a DD/Sail with a mass adequate to accelerate the debris, against low enough mass DD/Sail required to make solar sailing work. Each kick might also prang the sail!

That addresses a key point with most of these concepts. They are only good for a few pieces of debris before they run out of fuel, hence my suggestion about using ion thrusters

Since you have control of the approach to the debris object the logical approach would be to allow time to fold up the solar sail so its it's able to handle the shock load when the compressed spring is released. An alternative would be to build the sail capable of resisting the load but I suspect that would make it too heavy.

BTW this principle of using a compressed spring was used in a British WWII anti tank weapon called the PIAT AKA  a "recoiless mortar"

Problem: the target debris object cannot fold its sails. Kicking it with a spring-mounted plate is basically taking a large sledgehammer to it. The best hope is that all the debris fragments you generate will receive some of that impulse and move into lower orbits to decay, but in general you have now created a large spreading debris cloud.