Orbital debris removal concept -- Please poke holes in it...

In summary: The drag sheet would need to be at least 10 times larger than the LEO satellite to have any effect. Yes. Everything else at that height orbits at a similar speed, or it would not be part of the orbiting debris... correct?Yes.
  • #1
Flyboy
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I'm sure everyone here is aware of the hazards of orbital debris, and the difficulty of removing it. Lots of concepts have been proposed to help address it, but not many tests have been executed so far, mostly on larger debris like whole satellites. But what about the smaller stuff? Stuff that can't be easily grappled, or fitted with a drag sail, or (insert deorbit concept of choice here)? Sure, it's not as overtly hazardous, but as a cumulative threat, especially at higher orbits where atmospheric drag is minimal, it's nothing to disregard.

So, what about forcibly adding some localized drag? I wonder how effective it would be to put a large sheet of mylar or something similar in a sounding rocket, launch it into the orbital altitudes where such debris is a problem on a suborbital trajectory, and use it to slow down debris enough to accelerate the deorbit process, or even outright deorbit it? I know it's not the most economical option by any stretch of the imagination, but as a purely theoretical idea... how reasonable would it be?

Assume the following restrictions:
  • Launch window is when the drag sheet will pose no threat to any satellites or large debris at any point in flight.
  • Sheet can be reinforced with fibers of some sort to provide extra tear resistance.
  • Sheet is spin stabilized/extended by spinning up the payload section of the launcher before ejection of the sheet from the launcher. This also provides the pointing control to ensure it's oriented to provide maximum surface area to the oncoming debris.
  • For this initial consideration of the concept, destruction of the drag sheet and launcher upon reentry is to be considered total, with no debris surviving to the surface to cause littering.
 
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  • #2
The Mylar sheet will have many holes in it, but very little captured space debris.
Fragments of Mylar and shards of fibre will become part of the orbital debris field.
 
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  • #3
Baluncore said:
The Mylar sheet will have many holes in it, but very little captured space debris.
Well, he didn't mean "Please poke holes in it" that literally... :wink:
 
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  • #4
berkeman said:
Well, he didn't mean "Please poke holes in it" that literally... :wink:
Mike, you crack me up :smile:
 
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  • #5
Here's how you can evaluate your idea.

Orbital debris has velocities approximately XXXXX ft/sec.
Orbital debris velocity vectors are in what range of directions, in degrees relative to the equatorial plane?
Consider the velocity of, say, a 0.22 LR rifle bullet, one of the slowest and lightest bullets.
Will the sheet stop that rifle bullet? If you are not familiar with guns, ask around for somebody to help.
The Mylar sheet is on an ballistic path with a velocity and direction. What is the approximate velocity?
What percentage of debris will have velocity relative to the sheet less than the rifle bullet?
If the sheet could just barely stop the bullet, what percentage debris would be stopped vs punch through the sheet?
 
  • #6
One trap, for beginners in the art of catching particles with tethers, or in sheets, is the speed of sound in the material.

The velocity of the particle to be captured, will need to be less than the speed of a mechanical wave in the tether or the sheet. Fast particles cause local damage before the bulk of the material can become a momentum drogue, and so begin to slow the particle.
 
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  • #7
I think I should clarify this a bit. I'm not looking to  stop the debris. Trade some of that kinetic energy to either vaporizing a portion of the sheet, or transferring directly to the sheet, though I doubt there will be much transfer.

I'm looking to slow it down enough to accelerate the deorbit process. If I wanted to completely stop it, that would be a completely different approach.
 
  • #8
Baluncore said:
One trap, for beginners in the art of catching particles with tethers, or in sheets, is the speed of sound in the material.

The velocity of the particle to be captured, will need to be less than the speed of a mechanical wave in the tether or the sheet. Fast particles cause local damage before the bulk of the material can become a momentum drogue, and so begin to slow the particle.
I have no idea what you are trying to say. The sound speed of mylar is around 2 km/s. One will have issues catching well below this speed.
 
  • #9
Frabjous said:
I have no idea what you are trying to say. The sound speed of mylar is around 2 km/s. One will have issues catching well below this speed.
One will have issues at any speed. You need to explain what you mean by issues, and how you will select particles, and of what speed, for removal.

LEO satellites orbit at velocities of about 7 km/s. Everything else at that height orbits at a similar speed, or it would not be part of the orbiting debris problem.

It seems counter-intuitive, but as a lower orbit is encountered, the speed is increased, and the particle is in a thicker atmosphere, which accelerates both the orbital velocity and the rate of descent.

Since the orbital velocity is faster than the speed of sound in Mylar, only local damage will be done when the sheet is perforated. In order to decelerate a particle, there must be a loss of momentum. That requires the sheet material both have mass, and be travelling slower than the particle. But the thin Mylar sheet would have a low mass/area, so would make little difference to the momentum of a particle.

An orbiting Mylar sheet would encounter particles head-on at 14 km/sec, at a much greater rate, than particles orbiting in a similar direction. If the sheet was not in orbit, how could you keep it up there long enough to be of some use.

To avoid picking up too much thin atmosphere, the Mylar sheet would need to orbit edge-on. It would be perforated by particles in orthogonal orbits, having differential velocities of typically 10 km/sec. Many of those would be accelerated by the encounter.
 
  • #10
Flyboy said:
I'm not looking to  stop the debris.

I'm looking to slow it down enough to accelerate the deorbit process.
The theory is sound, and to be honest with that clarification it's already more thought through than many such ideas, but:
- It would work but only for small particles, which does not really pose any real threat - it's useless for anything bigger than sand (and alike).
- The efficiency is low. The ISS caught some of your clients during the years, but compared to the suspected number of small debris the cross section of the ISS could fish out only negligible amount.
 
  • #11
The number of particles in orbit has been measured/estimated as a function of size. This plot, from https://www.spaceacademy.net.au/watch/debris/gsd/gsd.htm, shows the magnitude of the orbital debris problem. You should be able to find newer information by searching Kessler syndrome or orbital debris.
Debris numbers.jpg


There is some good information on orbital impacts in Structural Failure, by Wierzbicki and Jones. This book was published in 1989, so the numbers are dated, but the impact information should still be good. It's available used from Amazon: https://www.amazon.com/dp/0471637335/?tag=pfamazon01-20.

This plot from that book shows the risk of impact. It also allows the calculation of the necessary size of a particle sweeping system.
Impact risk.jpg


Impacts at orbital velocities are not as simple as a tennis ball hitting the racket. Things get vaporized and fragmented. This figure from Wierzbicki and Jones shows what happens when a particle impacts a multilayer space station wall at orbital velocity.
Impact process.jpg
 
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  • #12
jrmichler said:
This plot from that book shows the risk of impact. It also allows the calculation of the necessary size of a particle sweeping system.
I think that's the key plot here. If we target 1 cm objects then we get an impact every ~3000 years for a 100 m2 area. A suborbital trajectory will have the sheet in the relevant altitude range for maybe an hour or 10-4 years. To intersect an average of 1 particle it needs an area of 3*109 m2, that's a diameter of ~50 km.

This is from 1990, we do have more debris today, but the required effort per particle is still absurd even if we assume every collision with the sheet will deorbit the debris object.
 
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