# I Space Trash

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1. Dec 17, 2017

### Rednecknav

How much energy needs to be be expended to throw a non operating satellite (or other space trash) out of orbit (L4 or L5) or L2 into deeper space.... thus minimizing space debris in earth orbit.

I could only find formulas for getting an object INTO orbit....

Background of question: we were discussing space debris and the seemingly endless number of monitored pieces of debris in various orbits around earth. Discussion gravitated towards;

1. Collect trash, and reuse... compact it, melt it, build stuff.... I don’t know....
2. Collect trash, compact it and throw (send) it to deeper space out of orbit.

I’m trying to figure a way to collect it.... also want to know how to dispose of it.

2. Dec 17, 2017

### JRMichler

Google is your friend on this. Try search term satellite deorbit for ideas that are being currently considered. Also compare the delta V needed to move to a graveyard orbit vs deorbit vs send to deep space.

3. Dec 17, 2017

### Staff: Mentor

You can calculate this for yourself from energy considerations. What is the total energy of the satellite (kinetic plus potential) in its current position? What is its potential energy at infinity? The difference is a lower bound on the amount of energy that must be expended to send it away from the earth.

4. Dec 18, 2017

### Staff: Mentor

Interesting problem. Here's one of the links from that search:

http://www.esa.int/Our_Activities/Space_Engineering_Technology/Clean_Space/How_to_catch_a_satellite

I only skimmed the articles briefly, but is anybody looking at using a counter-orbit approach to deorbiting space junk? Kind of like a sweeper net of sorts. I understand that the delta-v energy is very high, but maybe some tough netting material would survive for a few hours -- enough to sweep a portion of an orbital path before the total velocity of the net and swept objects was low enough to cause the whole thing to deorbit.

Come to think of it, the impact with the netting material may be enough to slow the junk enough that the "net" wouldn't actually need to capture it. Just the impact of the counter-orbiting netting would be enough to cause the pieces of junk to deorbit...

5. Dec 18, 2017

### JRMichler

You need to catch space junk before you deorbit it. The deorbit satellite can either match velocity with the piece of junk, or try to snag it as it passes. Orbital velocity in low earth orbit is 25,000 feet per second, so the closing velocity could be as high as 50,000 feet per second in opposed orbits. Same direction orbits with a ten degree inclination difference will have the closing velocity over 4,000 feet per second. The closing velocity is the challenge.

A lead bullet hitting a thick cold rolled steel plate at 1,000 feet per second will splash without damaging the plate. A lead bullet hitting a two inch thick steel plate at 2,000 feet per second will leave a crater the size of your finger tip. And I calculated once that the kinetic energy of an object at 10,000 feet per second is equal to the energy of an equal mass of high explosive.

Practical realities pretty much require that the deorbit satellite match orbits with each piece of space junk, then grab it, then deorbit it.

6. Dec 20, 2017

### stefan r

Anytime I ask a question like this I look at the maps or charts on project rho. (warning, that link has a lot of science fiction and is intended for science fiction writers) As far as I know the delta-v maps are accurate.

Earth-moon lagrange 1 and 2 are listed at 140 m/s to earth escape. EML 4 and EML 5 are 430 m/s.

The Kessler effect applies to the solar system too. It will take much more mass to get there. It is still space trash.

The statement might be true but not really a good answer. Satellites can escape from earth using a gravity assist from the moon. The trash would be acquiring energy (and momentum) from the moon's orbital energy. There is not much trash in orbit around L2 (yet?). I suspect the plan involves Luna in some way.

The alternative, deorbit, is easiest if you shift from circular orbit to elliptical. If the ellipse grazes the atmosphere the satellite will slow down and eventually burn. Calculating the total energy to stop a satellite would give you a much larger number.

7. Dec 20, 2017

### Staff: Mentor

By far the most space junk is in low Earth orbit, where deorbiting it just needs velocity changes of something like 100 m/s, while letting it escape from Earth needs about 4000 m/s. Guess which one is easier.

For objects in geostationary orbit both approaches would need more than 1000 m/s, so they are typically moved to a graveyard orbit only - away from the active satellites but still in an Earth orbit.
High velocity impacts are the best method to split up junk to create even more and smaller objects, that makes everything worse. At these speeds it doesn't matter if you have a flexible net or a collection of steel rods, the result is the same.
The volume of the inner solar system exceeds the volume of low Earth orbit by a factor of 1014.

8. Dec 20, 2017

### Staff: Mentor

... and my understanding was that for LEO, Earth's drag is sufficient to de-orbit obsolete satellites in a reasonable amount of time. We just need to reduce our rate of pollution below the rate that Earth cleans it up for us. The caveat being that break-ups are waaay worse than rogue/dead satellites because they are like shotguns to blast other satellites and smaller particles experience less drag and are therefore longer-lived. I vaguely recall a doomed Russian or Chinese satellite a few years ago that created such a major debris problem.

9. Dec 20, 2017

### Bigjoemonger

In 2009 Iridium 33 and Cosmos 2251 crashed into each other at about 26000 mph. Created 1000 pieces larger than 10 cm and many more smaller pieces. About half of the debris is still in orbit today.

10. Dec 20, 2017

### Staff: Mentor

Only in the very low orbits. Things 1000 km up (where most of the debris is) will stay there for much longer than a human lifetime, and even at 500 km orbital decay takes a long time. Hubble has an average height of 539 km today, in September 2016 it was at 545 km - just about 5km/year decay.

11. Dec 23, 2017

### stefan r

The volume of the Atlantic ocean is 3 x 1017 m3 A trash barge usually displaces less than 3 x 103 tons.

12. Dec 23, 2017

### phinds

I don't get what your point is.

13. Dec 24, 2017

### Staff: Mentor

A trash barge somewhere in the Atlantic ocean is not a threat to ships in the Atlantic. And this comparison would need LEO to be fully blocked by trash. Which is completely unrealistic.

14. Dec 28, 2017

### Chronos

IIRC it is called the escape velocity. Note that the escape velocity of the sun [> 40 km/sec exceeds the escape velocity of earth [ > 11 km/sec]. So it is possible for space junk to leave earth orbit, yet still collide with earth. depending on its solar orbital trajectory.

15. Dec 31, 2017

### Rednecknav

Thanks for the reply. Great sources of information for calculations.

16. Dec 31, 2017

### Rednecknav

Thank you all for your responses so far. I’m enjoying the discussion thus far and look forward to more.