Q: How to design a satellite for orbital debris collection ...

[freddo411]

There is widespread interest these days in mitigating orbital debris.   Let's define orbital debris here as bits that are trackable but not under any control, and presumed to be disposable.

Elon has hinted in a tweet that a satellite could be an effective debris collector:

https://twitter.com/elonmusk/status/1130060332200747008

Questions:

* Is it cost effective to launch a satellite costing the low single digit millions of dollars to collect orbital debris?
* Is there a design for capturing debris that will not produce other smaller debris?  Describe this....
* Describe the design of a cost effective debris sat.   Describe maneuvering capability?  How does it track and rendezvous with the debris

See also this thread:
https://forum.nasaspaceflight.com/index.php?topic=48286.0  (Starlink derived debris deorbiting)

[jstrotha0975]

I'll take a crack at it. I would build a satellite that deorbits larger space junk and not collect it. It would have SEP (Solar Electric Propulsion) and would gently nudge into the space junk and push it into the atmosphere to burn up. It would use Space junk tracking satellites and ground stations to position itself.

[SWGlassPit]

There are a number of challenges:

1. Rendezvous -- precision ephemeris data isn't always going to be available, particuarly when ephemerides can only come from external sources.  External ephemerides will get you "close", but the vehicle will have to do its own terminal guidance.

2. Contact -- whether by docking, harpoon, net, glue, whatever.  Derelict satellites and debris won't have active attitude management, and wresting control of a tumbling vehicle will prove difficult -- doing this without generating a large amount of additional debris doubly so.

3. Effecting disposal -- after rendezvous and attachment, there needs to be enough propellant to propel the target into a reentry or disposal orbit.  This is on the order of hundreds of meters per second, which, even with SEP, will require a substantial amount of propellant.  Furthermore, the mass properties of the target either need to be known a priori or figured out quickly, in order to ensure that attitude control can be maintained for the required maneuver to be performed correctly.

4. Reuse -- either these vehicles are going to be used on multiple targets, or they will "go down with the ship."  Both cases present challenges.  Single use vehicles are of questionable economic viability.  Reusable vehicles have to somehow recover from the disposal step and repeat the rendezvous, docking, and disposal again on another vehicle.  This makes for an enormous propellant budget.

5. Launch -- one of the biggest sources of debris is the launch vehicles themselves.  It will be a challenge to ensure that launching and deploying these "reaper" vehicles does not itself create more debris.

[jstrotha0975]

Yeah, I meant to add that the satellite itself would have it's own guidance systems along with using other satellites and ground stations.

[freddo411]

There are a number of challenges:

1. Rendezvous -- precision ephemeris data isn't always going to be available, particuarly when ephemerides can only come from external sources.  External ephemerides will get you "close", but the vehicle will have to do its own terminal guidance.

2. Contact -- whether by docking, harpoon, net, glue, whatever.  Derelict satellites and debris won't have active attitude management, and wresting control of a tumbling vehicle will prove difficult -- doing this without generating a large amount of additional debris doubly so.

3. Effecting disposal -- after rendezvous and attachment, there needs to be enough propellant to propel the target into a reentry or disposal orbit.  This is on the order of hundreds of meters per second, which, even with SEP, will require a substantial amount of propellant.  Furthermore, the mass properties of the target either need to be known a priori or figured out quickly, in order to ensure that attitude control can be maintained for the required maneuver to be performed correctly.

4. Reuse -- either these vehicles are going to be used on multiple targets, or they will "go down with the ship."  Both cases present challenges.  Single use vehicles are of questionable economic viability.  Reusable vehicles have to somehow recover from the disposal step and repeat the rendezvous, docking, and disposal again on another vehicle.  This makes for an enormous propellant budget.

5. Launch -- one of the biggest sources of debris is the launch vehicles themselves.  It will be a challenge to ensure that launching and deploying these "reaper" vehicles does not itself create more debris.

Really good points.    I don't think it makes much economic sense to launch debris removal sats unless that sat can remove  many different target pieces.     This implies great maneuvering ability which isn't practical in LEO unless you have a lot of debris in one particular inclination.

Perhaps a lightweight drag device (100 m^2 mylar) could be attached to effect disposal without requiring dV.

Your point 5 should be addressed by good design and operation of future stages.

[Eer]

#4 would benefit from on orbit tender ship for refills of fuel.

As for capture, I figure something more akin to a fish net than a balloon embrace makes sense, but the fuel and guidance to resist and slow a large tumbling piece would be quite a design challenge.

[Barley]

Make them cheap and light enough that you can launch dozens at a time.  This also means you don't need to go for extreme reliability in build and operations.  If one fails send another.  Or two if you also need to deorbit the failed deorbiter

[SWGlassPit]

Make them cheap and light enough that you can launch dozens at a time.  This also means you don't need to go for extreme reliability in build and operations.  If one fails send another.  Or two if you also need to deorbit the failed deorbiter

The problem here is that without the extreme reliability, you don't reduce debris, you increase it.

One errant "harvester" colliding with another vehicle could completely undo the results of hundreds of successful missions.

[Barley]

Make them cheap and light enough that you can launch dozens at a time.  This also means you don't need to go for extreme reliability in build and operations.  If one fails send another.  Or two if you also need to deorbit the failed deorbiter

The problem here is that without the extreme reliability, you don't reduce debris, you increase it.

One errant "harvester" colliding with another vehicle could completely undo the results of hundreds of successful missions.

The type of collision that makes things worse is a high speed one that produces lots of debris.  That's not likely to happen as a direct result of a failure.  By the time you're close enough to a rendezvous to have much chance of a non-random collision the relative speed is fairly low.

A high speed collision could happen as an indirect result of a failure, after a mission loses control and becomes space junk, but that's just a matter of numbers.  If you're over 50% successful you win the numbers game.  You should aim for a good deal better than 50% success, but that's a long way from extreme reliability.

[Lar]

There's a Starlink thread on this too. Crosslinking them would be helpful

(I did that)

[Comga]

There's a Starlink thread on this too. Crosslinking them would be helpful

(I did that)

But this is a much better place to discuss this, as few of the ideas there are unique to Starlink
The origin may have been a Tweet by Musk that it would be "simple" to have Starlink satellites collect debris.

With their 2 by 4 meter size and their possibly 2 by 5 meter solar panels, a constellation of 500 Starlink satellites may already present a cumulative cross-section of half a hectare.  If they can sense the impact of small debris they would generate a statistically significant sampling of the micro-debris population at their altitude.

And do keep in mind, professionals have spent decades discussing orbital debris populations, trends, mitigation, and elimination.  The value of members of the general public, like us, coming up with concepts, without regard to the literature, is small to negligible.  Better we should provide links to some of the existing knowledge on the subject like NASA's orbital debris program office.

Any successful ADR concept must be technologically feasible, economically affordable, and politically acceptable to the international community. In addition, debris removal activities should also be accomplished in a manner that does not unduly increase hazards to people and property on Earth from reentering debris.

The June 2010 National Space Policy for the United States of America directs NASA and the Department of Defense to “Pursue research and development of technologies and techniques… to mitigate and remove on-orbit debris…” However, it should be noted that, currently, no U.S. government entity has been assigned the task of removing existing on-orbit debris.

[SWGlassPit]

Make them cheap and light enough that you can launch dozens at a time.  This also means you don't need to go for extreme reliability in build and operations.  If one fails send another.  Or two if you also need to deorbit the failed deorbiter

The problem here is that without the extreme reliability, you don't reduce debris, you increase it.

One errant "harvester" colliding with another vehicle could completely undo the results of hundreds of successful missions.

The type of collision that makes things worse is a high speed one that produces lots of debris.  That's not likely to happen as a direct result of a failure.  By the time you're close enough to a rendezvous to have much chance of a non-random collision the relative speed is fairly low.

A high speed collision could happen as an indirect result of a failure, after a mission loses control and becomes space junk, but that's just a matter of numbers.  If you're over 50% successful you win the numbers game.  You should aim for a good deal better than 50% success, but that's a long way from extreme reliability.

The speed necessary to start shedding debris isn't that high.  Deployed satellites are designed for structural loads consistent with microgravity.  Relatively low speed collisions can start breaking off things like antennas, solar arrays, radiators, etc.  You also have plenty of stored energy sources like propellant and pressurant tanks that aren't necessarily designed for collisions with large objects.

[rakaydos]

While not a satellite,  I'm something of a fan of the "suborbital  dense gas cloud" approach. Use an Electron or New Shepard or something to send up a glorified weather balloon on an intercept-at-apogee trajectory, fill up the balloon with CO2 or something, and pop the balloon just before impact. Since the balloon's gasses has effectively no orbital velocity, they will "deorbit" themselves in minutes. But before they do, the debris that were intercepted will impart velocity on the cloud- not enough to become orbital, but enough to affect the debris own orbit. (hopefully enough to make the debris themselves suborbital)

[SWGlassPit]

While not a satellite,  I'm something of a fan of the "suborbital  dense gas cloud" approach. Use an Electron or New Shepard or something to send up a glorified weather balloon on an intercept-at-apogee trajectory, fill up the balloon with CO2 or something, and pop the balloon just before impact. Since the balloon's gasses has effectively no orbital velocity, they will "deorbit" themselves in minutes. But before they do, the debris that were intercepted will impart velocity on the cloud- not enough to become orbital, but enough to affect the debris own orbit. (hopefully enough to make the debris themselves suborbital)

Anything dense enough to deorbit a satellite from such a brief encounter will cause a fantastic amount of debris shedding.

The damage effects you see in the video below are due to impact with a "dense" gas cloud at speeds substantially slower than what you are describing here. 

[whitelancer64]

In 2011 a group of researchers at the Naval Research Laboratory (NRL) came up with the idea of launching a few tons of Tungsten dust into orbit, the intent being to increase drag at that orbital altitude. IIRC, because Tungsten is so dense, it would deorbit fairly rapidly, within a few years, even if it were dispersed at 1,100 km (the altitude at which small debris is most of a problem).

That paper is called "A Concept For Elimination Of Small Orbital Debris" if anyone wants to read about it.

A similar idea, but with launching (much cheaper) water, has also been suggested in the past.

[SWGlassPit]

Wouldn't dense material stay in orbit longer?  Higher ballistic coefficient and all?

That sounds like as bad an idea as the Westford Needles project was.

[daedalus1]

Wouldn't dense material stay in orbit longer?  Higher ballistic coefficient and all?

That sounds like as bad an idea as the Westford Needles project was.

Yes you are correct, the effects of drag are less on a more dense and lesser cross sectional area.
The only realistic solution is to make satellite owners responsible for deorbiting their satellite within a certain period of end of life. Even if communication is lost.

[whitelancer64]

Wouldn't dense material stay in orbit longer?  Higher ballistic coefficient and all?

That sounds like as bad an idea as the Westford Needles project was.

I'm not an expert in aerodynamics, so you may be best off reading their paper. It's available for free on arxiv. I've got the paper open and it says that the orbital lifetime of dust depends on its size and density and is heavily influenced by radiation pressure from the Sun. It estimates that if 60 micron dust were released at 1100 km it would deoribt in about 15 years. I'd guess that larger particles would be more prone to drag and would deorbit faster, while smaller particles would stay in orbit longer, though the paper does not specifically say that.

I got into a very long argument with someone else about that and yeah, the needle experiment suggests we should exercise great caution before trying something like this.

[whitelancer64]

Wouldn't dense material stay in orbit longer?  Higher ballistic coefficient and all?

That sounds like as bad an idea as the Westford Needles project was.

Yes you are correct, the effects of drag are less on a more dense and lesser cross sectional area.
The only realistic solution is to make satellite owners responsible for deorbiting their satellite within a certain period of end of life. Even if communication is lost.

Techincally this is off-topic for this thread anyway, since this wouldn't be used to deorbit satellites, but very small debris.

[jee_c2]

I've read some other topics about deorbiting sats. For bigger debris, like non working satellites, I can imagine something like this:
Initially: launch the deorbiter special sat, with many closed "sails".
1. Aproach the sat to be deorbited
2. Attach to the sat - this can be tricky, if it stumbles.
3. Attach the closed sail on it
4. Open the saiil (the sail can be an inflatable structure)
5 orienting the the attached sat
6. Aim next target, and then steal momentum from the other sat, by kicking away, so, slowing it down, fastening it' s deorbiting process.
Kicking: some mechanical way (springs- may be too weak), or some small bouncing particles, or small rocket like objects..