## Deorbiting space junk

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Rob Lister
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### Deorbiting space junk

Happened across this
Lockheed Martin seeks to clean up space junk
http://www.ft.com/cms/s/0/0644ee74-2cef ... z3BarrLjK4

The title says enough to get the gist without infringing on the copyright of an article that says a lot of nothing. Lockheed doesn't have a plan to rid us of space junk, but they did get a big chunk of change to track the junk. But only some junk. The easy junk. The junk the size of a grapefruit.

Which is good. Knowing where it is helps us avoid running into it.

But, they have no plan to rid us of it.

It doesn't take a grapefruit-sized piece of space junk to ruin a mission's day.

Consider: An astronaut on the space station takes a shit. That turd is then ejected into space. It retains the same orbital velocity (algebraically summed with the ejection velocity of a few feet per second) as the space station. And there it sits (relatively), just waiting for a passing vessel to run into it. Thus ends that vessel.

Look at a map of the space junk they can actually track ...

And multiply those dots by about 100 and you have a better picture of the real existing hazard.

Okay, but as of now it is still not really major hazard. It looks dire but the odds of running into something substantial are still pretty slim (though it does happen).

But we're only 50 or so years into this. What happens in a 100 more years? It WILL eventually be a big concern.

We need to
1) De-orbit what we orbit (if you orbit a pound you must de-orbit a pound).
2) Don't create debris; de-orbit your shit (literally and figuratively).
3) De-orbit the existing debris (and that is the tough part).

The problem is that the minimum energy required to de-orbit a pound of junk equals the energy expended in orbiting that pound of junk from the top of the atmosphere to wherever it is. The [relative] velocity must be reduced such that its orbit falls below the wisp zone (or, I suppose, increased such that it exits the system altogether).

Here's one plan I've seen, loosely described:
Consider a orbiting sheet of Kevlar 10 miles on a side travelling perpendicular to the earth's plane in X orbit in a direction opposite the earth's rotation (which is head-on to most debris). A piece of debris strikes the sheet and punches through. The velocity is thus reduced by some value, lowering its orbit. But so too is the orbit of the sheet (Newton, et al). Energy must be expended to keep it in its sweeping orbit.

Where does that energy come from?

As I think about it, maybe that isn't the biggest problem. It can start the sweep at a high orbit and by the time its orbit is reduced to re-entry velocities, it is swiss cheese, it's mission done, time to launch its replacement.

But how many Kevlar sheets do we need to make a dent? Better get bigger sheets.

It is a hard problem.

Get started now.

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### Re: Deorbiting space junk

There may be evidence of a Space Junk problem, but I do not believe it is man-made. . . .

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### Re: Deorbiting space junk

I once checked a patent translation for a device meant to deorbit space junk. Sometime within the last year I think. Iirc it was supposed to harpoon it. Slow it down just enough that gravity would do the rest of the work. It assumed something like a mostly intact defunct satellite, not a small grapefruit. Anyway, somebody over here is thinking about the problem too.
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DrMatt
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### Re: Deorbiting space junk

Last I heard, astronaut poop is deliberately ejected into a falling trajectory. After a couple orbits, it's supposed to vaporize on re-entry.
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Rob Lister
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### Re: Deorbiting space junk

That would be nice of them.

My wee-brain and calculator tells me they have to eject that turd at 290 fps (200 mph) to move it from 210Km to 60Km. I guess they have a turd cannon.

Anaxagoras
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### Re: Deorbiting space junk

Rob Lister wrote:That would be nice of them.

My wee-brain and calculator tells me they have to eject that turd at 290 fps (200 mph) to move it from 210Km to 60Km. I guess they have a turd cannon.
Are you accounting for gravity?

My understanding is that if the velocity is even slightly less than the velocity sufficient to keep it in a stable orbit, it will eventually fall out of orbit into the atmosphere.

Although 200 mph isn't inconceivable.
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DrMatt
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### Re: Deorbiting space junk

Angle is important too. Do it wrong and you've just got poop in an eccentric orbit.
Eccentric orbital poop. Sounds like a name for a band.
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### Re: Deorbiting space junk

DrMatt wrote:Angle is important too. Do it wrong and you've just got poop in an eccentric orbit.
Eccentric orbital poop. Sounds like a name for a band.
So would you just shoot it straight backwards, or backwards and down maybe?
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Rob Lister
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### Re: Deorbiting space junk

Just backward.

Looking at what I wrote above, my units were wrong. 210 miles, not Km. 60 miles, not Km.

... but when I think harder about it (which hurts a little) they don't really need to get down to 60 miles. 60 is where it would be 'captured' (velocity quickly reduced to zero). If it is just a bag of shit meant to burn up anywhere, 100 miles would do as well. It would just take longer to slow down. The ISS orbit is already so low that the station itself would probably fall in less than a decade if not routinely re-accelerated. Re: our long lost Skylab.

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### Re: Deorbiting space junk

There's the danger with the kevlar sheet plan that the junk isn't slowed enough to de-orbit but is broken into multiple smaller pieces of junk so making it more dangerous. Though I suppose the smaller pieces would in turn be impacted and slowed if the sheet is kept orbiting for long enough.

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### Re: Deorbiting space junk

The kevlar sheet thing of that size doesn't sound remotely realistic in the first place to me.

I agree that there ought to be a rule from now on that any new satellite has to have means to deorbit. That doesn't solve the problem of the junk that's already up there, but it's the logical first step and the lowest-hanging fruit. Let's at least stop adding to the problem.
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Rob Lister
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### Re: Deorbiting space junk

Anaxagoras wrote:The kevlar sheet thing of that size doesn't sound remotely realistic in the first place to me.

I agree that there ought to be a rule from now on that any new satellite has to have means to deorbit. That doesn't solve the problem of the junk that's already up there, but it's the logical first step and the lowest-hanging fruit. Let's at least stop adding to the problem.
It is hard to visualize.

Pretend they could make such a sheet, then orbit it at 25,000 miles.

It has an orbital period of 24 hours. So over the first 24 hours it sweeps out on 10 mile thick swath. Its velocity is actively reduced during that period by ~20fps, thus reducing it's altitude by 10 miles1 and the next closer 10 mile square swath could be swept in a tiny bit less than 24 hours, etc, until it finally finds the top of the atmosphere X years later, having swept out a single ring 10 miles thick.

Orbital period of the starting path at 25,000 miles is 24 hours.
Orbital period of the finishing path at 100 miles is path 1.5 hours

Find X.

Matt may be able to do that math, I can't. But if feels like a really long time. Feels like 3 to 4 years. And that's just one 10-mile wide ring. We need to tip that orbit by 10 miles and do it again, etc.

1 rule of thumb is 1 mile up/down for each 2fps increase/decrease for orbits less than 500 miles. Pretend the rule applies to higher orbits for simplicity

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### Re: Deorbiting space junk

The orbits of several satellites were disrupted when ed moved to Florida.
Such potential!

DrMatt
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### Re: Deorbiting space junk

Hey, I know, send up a big vacuum cleaner to clean it all up ... in the... er....vacuum of space.... never mind......
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### Re: Deorbiting space junk

Various schemes have been suggested over the years. Seems the problem is not big enough yet to make any solution cost-effective. While there is a lot of junk out there, remember that even orbital space is a huge place.

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### Re: Deorbiting space junk

Japan's troubled 'space junk' mission fails

An experimental Japanese mission to clear 'space junk' or rubbish from the Earth's orbit has ended in failure, officials said Monday, in an embarassment for Tokyo.

Over 100 million pieces of garbage are thought to be whizzing around the planet, including cast-off equipment from old satellites and bits of rocket, which experts say could pose risks for future space exploration.

Scientists at the Japan Aerospace Exploration Agency (JAXA) were trying to test an electrodynamic 'tether'—created with the help of a fishing net company—to slow down the orbiting rubbish and bring it into a lower orbit.

The hope was that the clutter—built up after more than five decades of human space exploration—would eventually enter the Earth's atmosphere and burn up harmlessly before it had a chance to crash into the planet.

The 700-metre (2,300-foot) long tether—made from thin wires of stainless steel and aluminium—was due to be extended out from a cargo ship launched in December carrying supplies for astronauts at the International Space Station.

Problems arose quickly, however, and technicians tried for days to remedy the situation but only had a one-week window to carry out the mission before the vessel reentered the Earth's atmosphere before dawn on Monday.

"We believe the tether did not get released", leading researcher Koichi Inoue told reporters.
https://phys.org/news/2017-02-japan-spa ... ssion.html

Let's try again times 1000

ed
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### Re: Deorbiting space junk

If we increased the mass of the earth gravitational attraction would increase thus scouring the space junk. Then all one would have to do is reduce the mass again.
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### Re: Deorbiting space junk

ed wrote:If we increased the mass of the earth gravitational attraction would increase thus scouring the space junk. Then all one would have to do is reduce the mass again.
Insofar as you are located in Florida which last I checked in on Earth, all we need to do is get you to increase the mass of your ass.

It'll be a cinch.
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### Re: Deorbiting space junk

ed wrote:If we increased the mass of the earth gravitational attraction would increase thus scouring the space junk. Then all one would have to do is reduce the mass again.
This might not work as although it would pull the orbiting junk lower, it would also compress the atmosphere so that the junk would need to get lower before encountering appreciable atmospheric drag.

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### Re: Deorbiting space junk

Solution: Increase the amount of gas in the atmosphere.
Any man writes a mission statement spends a night in the box.
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