Orbital Debris Cleanup - how to?

[Eer]

Ran across this from Les Johnson posted at Baen Publishing web site:

http://www.baen.com/Living_Without_Satellites.asp

It seems like this should be the subject of an X-prize or something.  There's a growing need for dedicated, autonomous or semi-autonomous solar-sail navigating space debris tugs that would individually (if the target is small enough) or in concert (fleet action) rendezvous with debris fragments and either decelerate them so they re-enter, or accelerate them so they raise their orbits out of harm's way (well above geosynchronous orbit).  Solar sails are not the only possible motive force - tethers using Earth's magnetic fields could also lend a hand.

Reusable, retaskable, long duration systems.  Perhaps larger craft would be regular customers of orbiting fuel depots.

There didn't appear to be a thread already discussing how to ultimately clean up orbital debris, so I started this, here.  Moderators, feel free to move/merge/delete as appropriate.

[floss]

A rock in LEO would clean most of the lower orbits pretty well but no country would allow it .(gravity tractor)

Another larger rock outside GEO would drag the dead satellites out of GEO .

[nadreck]

Problem breaks down into several parts:

GEO (dead easy, a couple of big, ion engine equipped, tenders rounds up dead bodies and sticks them tethered together (they become a single target) in a temporary (several years) graveyard orbit a few hundred klicks further out until it is worth dragging the whole lot of them about 5 times further out with the last of the fuel on that tender. Eventually someone picks them up for scrap metal when there is an industry that might support using where it was cheaper than raw material. At this time I estimate that there is probably between 1,000 and 3,000 tons of non operational satellites in GEO.

Multi plane constellations in MEO and high LEO, should be required to have deorbit capability on each new bird launched, or a tender on each plane to do the same. Existing ones would be more practical to deal with with an ION engine equipped tender since you could remove all the birds from a given plane with one tender then deorbit the tender and its collection of satellites.

Individual birds and uncontrolled spare parts, boosters etc in MEO and mid to high LEO, plus ones in highly eliptical oribits are a bigger problem and definitely there should be provision for future craft to make sure all parts can de-orbit successfully on their own.  Craft to deal with these would have to have a huge ΔV budget to make any inroads into the collected waste that exist.

Low LEO, well, in future there probably should be some way of managing new birds, but the good news is that they will all eventually re-enter on their own. 

Things like experimental micro, nano and pico sats should, except in special cases, be in future kept in virtual corrals with a tender that takes out ones that have no control or lose control and wander outside the control area.

All of this of course is my opinion on how things should be done.

[OlegSerov]

My logic is:

- So we have a lot of space junk that orbits the Earth.
- A lot of space objects de-orbit themselves due to atmospheric drag.
- Let's create an artificial atmosphere to de-orbit this junk.
- Just deliver a 10mT of helium up to the orbit (in other direction of a space junk) and disperse it.
- It must create an atmospheric drag within hi-volumes of space.
- How much drag it will create, I do not know how to calculate this stuff.
- Upgraded idea: disperse some organic stuff that decay within couple of days due to UV-light. It will provide much more denser cloud.

Positive things:
- It's much cheaper than lasers or unmanned vehicles.
- It covers a lot of volume by one lunch.

Negative things:
- It will de orbit active satellites, but because of higher mass/front area ratio, the effect will be less than on smaller objects.

So, Is it viable?
 

[Lee Jay]

Good idea.  But you don't need 10mt, you need more like a few hundred billion mt, and since it will disperse into space immediately, you'll need that every minute or so.

[OlegSerov]

Good idea.  But you don't need 10mt, you need more like a few hundred billion mt, and since it will disperse into space immediately, you'll need that every minute or so.

Can you prove it mathematically? It sounds cool, just like my idea, but without calculations it does not make sense.

[OlegSerov]

Good idea.  But you don't need 10mt, you need more like a few hundred billion mt, and since it will disperse into space immediately, you'll need that every minute or so.

Can you prove it mathematically? It sounds cool, just like my idea, but without calculations it does not make sense.

Just for the sake of argument. Image 10mT steel plate orbiting other way with delta v about 14km/s. Will it stop space junk? yes. Then image that it has 100 tin foil layers separated with 1mm. Will it stop it? Yes. Now image 1000000000 layers. Will it stop it? yes.

[mikelepage]

Welcome to the forum!

Good try, but there a quite a few problems with this.

1) you wouldn't use Helium because a) very expensive and b) very light so you wouldn't create as much drag as you might with a heavier gas.

2) You know space is big... right?  This is back of the envelope calculation so may be wrong:  Say you go for the worst region of debris at 600-1000km, that gives a volume of 2.4 x 10^20 cubic metres.  Your 10 mT of Helium works out to 0.25 Mmol or 1.5 x 10^29 Helium atoms.  That gives you a roughly 5*10^8 (half a billion) atoms per cubic metre of Helium, which might sound like a lot, until you find out that the density of atmosphere at 600km is already approx 0.1ng/cubic metre = 1.5 x 10^22 atoms per cubic metre.  So you're increasing the already existing atmospheric drag by 0.00000000000004%.

You need more gas to make this work...

3) ...of course then it's un-targeted - you take down your functional satellites as well as the space debris.  The US military may have a problem with this.

4) depending on what other agents you include, you may end up just generating more debris.

Whatever the solution is... it has to be targeted.  That much we know.

[ChrisWilson68]

Good idea.  But you don't need 10mt, you need more like a few hundred billion mt, and since it will disperse into space immediately, you'll need that every minute or so.

Can you prove it mathematically? It sounds cool, just like my idea, but without calculations it does not make sense.

Just for the sake of argument. Image 10mT steel plate orbiting other way with delta v about 14km/s. Will it stop space junk? yes. Then image that it has 100 tin foil layers separated with 1mm. Will it stop it? Yes. Now image 1000000000 layers. Will it stop it? yes.

The steel plate will stay together.  A cloud of gas will rapidly expand to be very, very, very diffuse -- so diffuse that it won't cause much drag.

[OlegSerov]

until you find out that the density of atmosphere at 600km is already approx

Where did you get that data?

[mikelepage]

until you find out that the density of atmosphere at 600km is already approx

Where did you get that data?

from here:
https://books.google.com.au/books?id=HSffDG356TkC&pg=PA16&lpg=PA16&dq=atmospheric+density+at+600km
&source=bl&ots=CZydyEasWV&sig=sbxAy9MWGahJt18e4a7R_iQCVtM&hl=en&sa=X&redir_esc=y#v=onepage&q=
atmospheric%20density%20at%20600km&f=false

[OlegSerov]

2) You know space is big... right?  This is back of the envelope calculation so may be wrong:  Say you go for the worst region of debris at 600-1000km, that gives a volume of 2.4 x 10^20 cubic metres.  Your 10 mT of Helium works out to 0.25 Mmol or 1.5 x 10^29 Helium atoms.  That gives you a roughly 5*10^8 (half a billion) atoms per cubic metre of Helium, which might sound like a lot, until you find out that the density of atmosphere at 600km is already approx 0.1ng/cubic metre = 1.5 x 10^22 atoms per cubic metre.  So you're increasing the already existing atmospheric drag by 0.00000000000004%.

I think you're wrong here, that is why:

Let's calculate the weight of atmosphere in volume shaped like torus with center radius of 7000km and tube radius 1km.

1. Volume: Torus volume formula: 2*pi^2*tube radius^2*center redius = 2 * pi * pi * 1km * 1km * 7000km  =~ 1.382 * 10^14 m3

2. Atmospheric density at 600km - http://www.wolframalpha.com/input/?i=Atmospheric+density+at+600km
1.1 * 10^-13 kg/m^3, your chart gives 10^-2ng/m3 ... 10^-14  kg/m3...

3. So we have the mass:  1.382 * 10^14 m^3 * 1.1 * 10^-13kg/m^3 = 1.382 * 10 ^ 1 * 1.1 kg =~ 13 kg of air.

4. Compare weight: 10mT = 10 ^ 4 kg vs 13 kg... 1:760

5. Now lets compare impulses:
Orbital speed at 600km:    7.56  km/s    ... 7.56 * 10^3 m/s

a) Atmosphere vs trash (atmosphere is static, which is probably not true)
mv^2/2 ... 13 * (7.56 * 10^3) ^ 2 / 2 =~ 3.715 * 10^8 J

b) Gas cloud at reverse orbit:

10000kg * (2 * 7.56 * 10^3) ^ 2 / 2 = 1.43 * 10^12 J


6. So kinetic energy is different, a vs b is 1:3849...

7. Orbit decay for debris: http://www.nasa.gov/news/debris_faq_prt.htm "Debris left in orbits below 370 miles (600 km) normally fall back to Earth within several years."

8. "Several years" just turned into several months thanks to only one Dragon launch.

Military still is not happy about that

 

[mikelepage]

Well okay, but launching into a reverse orbit has a large payload cost - not sure if a F9 is capable of launching 10 tons into that orbit, and by confining your calculations to a torus of radius 1km you're effectively doing a whole falcon launch to target an individual piece of space debris: by brownian motion (and with effectively zero air pressure) the gas will disperse beyond your 1km tube in approximately 3 seconds (speed of sound is ~333m/s)

[mikelepage]

And anyway, there's actually a lot of useful materials/electronics in the so-called "space junk" and de-orbiting them is less desirable than having some kind of way to target and harvest them.  There are lot of otherwise fully functional satellites, that have just run out of battery/propellent, or have one fried circuit board.   At $10,000/kg to get it into orbit in the first place, it would be better if we can figure out an efficient way to recycle all the material that's up there.

[KelvinZero]

Well okay, but launching into a reverse orbit has a large payload cost - not sure if a F9 is capable of launching 10 tons into that orbit, and by confining your calculations to a torus of radius 1km you're effectively doing a whole falcon launch to target an individual piece of space debris: by brownian motion (and with effectively zero air pressure) the gas will disperse beyond your 1km tube in approximately 3 seconds (speed of sound is ~333m/s)

Variations of this idea have been posted a few times. I had this idea myself.

In my scheme the material came from station keeping propellant fired with double your orbital speed to put it into a retrograde orbit. Obviously this stationkeeping propellant has to be something that is not itself a problem, or at least must be the lesser of two evils.

Certainly it will spread out, but the millions of targets are also spread out. That is why nets and hunting them down is not reasonable. I don't know whether it can be a gas or not. As far as I can see the only problem with a gas is that sunlight can knock it out of orbit. Otherwise it would just keep its momentum like any other satellite.

It is just a matter of statistics. For simplicity of argument, assume each satellite uses its its own mass in station keeping propellant over its life. Given that only a fraction of satellite mass will become dispersed dangerous fragments, there will be far MORE mass of the counter rotating material than of problem fragments.

Now just consider one dangerous fragment. The effect of the counterrotating gas must be small, but also the chance of this ONE particular fragment hitting a satellite is very VERY small... So the question is, on average, what mass of counterrotating material will this one fragment encounter before it encounters a satellite or station?

* You might start by saying "the mass of satelites and counterrotating material is equal, so if it hits a 1 ton satellite it has probably already encountered 1 ton of counterrotating material (..which would have slowed a nut or bolt out of orbit LONG ago)
* Then you could also observe you are also far more likely to encounter counter rotating material than things moving in roughly the same velocity as yourself, as is the case if you fell of a satellite in a commonplace orbit.
* Then you could also observe that due to the larger surface area/mass ratio of smaller objects, that  a cloud has the largest surface area to mass that you can achieve, so this biases you towards hitting it over discrete large objects.

..and also this gas will have more effect on small fragments with high surface area to mass than on large object that we might wish to keep in orbit, or could consider deorbiting by more directed means.

[mikelepage]

Well okay, but launching into a reverse orbit has a large payload cost - not sure if a F9 is capable of launching 10 tons into that orbit, and by confining your calculations to a torus of radius 1km you're effectively doing a whole falcon launch to target an individual piece of space debris: by brownian motion (and with effectively zero air pressure) the gas will disperse beyond your 1km tube in approximately 3 seconds (speed of sound is ~333m/s)

Variations of this idea have been posted a few times. I had this idea myself.

In my scheme the material came from station keeping propellant fired with double your orbital speed to put it into a retrograde orbit. Obviously this stationkeeping propellant has to be something that is not itself a problem, or at least must be the lesser of two evils.

Certainly it will spread out, but the millions of targets are also spread out. That is why nets and hunting them down is not reasonable. I don't know whether it can be a gas or not. As far as I can see the only problem with a gas is that sunlight can knock it out of orbit. Otherwise it would just keep its momentum like any other satellite.
<snip>
..and also this gas will have more effect on small fragments with high surface area to mass than on large object that we might wish to keep in orbit, or could consider deorbiting by more directed means.

Ooh that's interesting, I never though of dual-purposing station-keeping thrust before.  But why go to the effort of trying to emit the gas at double-orbital speed? especially if you're just going to run into it half an orbit later (I guess that's a good reason to use gas since it will disperse).

Here's a thought for how to reduce that small fragment space junk:

What if your entire craft was basically one big nitrogen gas thruster, initially placed in at some low-inclination LEO.  You use SEP to rendezvous with each bit of junk - specifically you make sure the craft gets to the rendezvous point just moments before the junk, and then you release a relatively dense cloud of gas directly into the path of the junk.  This propels your craft forward, allowing it to work its way upwards through the altitudes, and also slows the junk down to (closer to) deorbit velocity.

EDIT: should clarify that I don't see the SEP having all that much to do, every bit of space junk has to pass through the equatorial plane at some stage - it might just need some kind of advanced radar in order to be able to get much closer to colliding at multiple km/s, without actually colliding.

[OlegSerov]

Looks like we have a plan.

Most dangerous space junk is small pieces. It also the most major group of space junk. Big pieces you can track/predict, it much harder to predict/avoid small pieces.

Gas as a way to de-orbit these kind of junk is the most efficient way.

I wonder, is it possible to get funding for research purposes for this project?

[spacenut]

What about an orbiting powerful laser to just pinpoint the bad ones and burn them.  More efficient, as gas can affect good satellites. 

[OlegSerov]

What about an orbiting powerful laser to just pinpoint the bad ones and burn them.  More efficient, as gas can affect good satellites.

Nice way to test satellite destroyer. AFAIK They need a 747 plane to have chance to destroy ICBM with a laser. I think it's not feasible at this moment. You can try to prove otherwise.

[Stan-1967]

This still won't work.  It is a flawed assumption to model whatever gas you lift to that altitude as a torus.  It will not remain a torus for any significant amount of time, certainly not even long enough for a single orbit needed to disperse the gas, indeed I do not think you can even explain how to make a torus in the first place.     Is the thruster emitting this gas going to operate/expell it for the +60 minute orbital period at altitude?   What will the orbital height be after thrusting for 60 minutes?   Unless your gas is an insignificant portion of the mass of the vehicle, you will be in a very different orbit due to the DV of the cold gas thruster.

 The gas will rapidly disperse into a spherical shell in the top of the atmosphere.   The gas will first disperse because it will flow according to the pressure gradient, which will be more or less equivalent in the orbital plane at whatever altitude you propose to release it. 

Furthermore, each gas particle will disperse with not only the velocity you impart from launching or expelling it from your thrusters, but also the thermal energy imparted by it's temperature.   Once in the space environment, the gas in only constrained from expanding off into space by the earths gravity.   As long as the velocity of each gas molecule is not greater than earth escape velocity, it will simply keep moving in its path until it collides with another gas molecule, and the dynamics of that collision will disperse the gas even more.  The gas will rapidly shed it's thermal energy by radiating heat into space until it is equilibrium with the local space environment.