# Send up a satellite to zap space junk if you want Earth's orbit to be clean, say boffins

A group of scientists have proposed a new method to clear up space junk using a satellite that shoots out powerful beams of plasma. Researchers from the Tohoku University, Japan, and The Australian National University, think that potential debris disasters might be averted by sending up a cleaning probe. The satellite works by …

1. #### Orbital cleaning

Here, I thought that has already been done (so to speak):

1. #### I'll see your Spaceballs

and raise you Quark. (No not that one.)

2. #### It all seems a bit far fetched, to me

I've three objections to this idea.

1. As far as I'm aware, applying a force to an obect in orbit, merely changes the orbit of that object. It does not "knock it out of orbit" A satellite launch comprises two burns, The first to get it to the right height, and the second to impart the required velocity that it has to have to orbit at that height.

2. Applying the force by a plasma jet has to apply that force exactly at the objects centre of mass, wherever that might be, or all it will impart is a spin. Given that the object is bound to be asymmetrical, finding the centre of mass might be a tad difficult.

3. The de-orbiter is essentially linked to the object, and without extra expenditure of fuel and mass will simply follow the object down to a matching fate

1. #### Re: It all seems a bit far fetched, to me

Indeed. The idea as I understand it is to slow the debris down so it falls into a lower orbit, more affected by the outer borders of atmosphere.

To do so you'd need to put your plasma throwing satellite on the same orbit as the debris, a couple of meters in front of it. Then you start blowing your plasma at the debris, and as a result it slows down, thus falling back and down into a lower orbit. So, to keep slowing it down your plasma throwing satellite will have to follow it for a short while, slowing down by the same amount, which means it will descend into lower orbits too. If you don't want it to go plunging into the atmosphere too, you'll need to use some kind of booster to make it climb back up so it can go search for some other debris to kill.

Not impossible, but sounds definitely fiddly and very fuel intensive.

1. #### Re: It all seems a bit far fetched, to me

"So, to keep slowing it down your plasma throwing satellite will have to follow it for a short while"

The article suggests the impulse being applied for less than half a minute. Given that the device uses a balancing plasma beam suggests that the designers don't see a need to follow the target over this period of time.

1. #### Re: Re: It all seems a bit far fetched, to me

The article states 1800 seconds, so half an hour, not half a minute.

Agree with a later commentator that the physics seems a bit off

2. #### Re: It all seems a bit far fetched, to me

> The article suggests the impulse being applied for less than half a minute

Well, there is some vagueness in the description, but I read "1,800 seconds" as being 30 minutes during which the cleaning satellite will have to blow plasma onto the victim. Which would mean the cleaning satellite will have to follow its prey for at least half an hour, through what (should be) a rapid deceleration and radical change of orbit. I might be wrong though.

3. #### Re: It all seems a bit far fetched, to me

"The article suggests the impulse being applied for less than half a minute."

Funny, I read that as 1800 seconds.

1. #### Re: 1800 seconds.

Performance =/= requirement.

1800 seconds for 5 months of decaying orbit. So I assume 900 seconds for 12 months or more, 60 seconds for 5 years or so (probably not a linear scale due to differences in atmospheric density etc, but you get the idea).

In fact, most debris *is* already on a decaying orbit... it's just not decaying fast enough!

Or as the posts below note: "Reading the original article (always advisable before calling the authors idiots) reveals that the figure of 1800 seconds is in fact the specific impulse of the thruster not any actual time."

So Stop being idiots, and read, listen and learn before spouting off how clever you are!

4. #### Re: It all seems a bit far fetched, to me

The article suggests the impulse being applied for less than half a minute. Given that the device uses a balancing plasma beam suggests that the designers don't see a need to follow the target over this period of time.

@Doctor Syntax - think about it, both cleaning satellite and junk will be moving at high speed. So for anything more than a very short burst/shot, the cleaning satellite would need to follow the junk, in fact given the aiming problem, it would need to predict the course of the junk and effectively lead the junk down.

Given the size of much of the junk, it might be better to drift net stuff - either having your net run slightly faster than the junk or marginally slower. Obviously, with a carefully chosen orbit the net will automatically take the collected junk down, to be burnt up in the atmosphere.

2. #### Re: It all seems a bit far fetched, to me

Actually, for low earth orbits, almost any change of velocity (increase or decrease) will cause the orbit to intersect the atmosphere.

I would suggest launching a retrograde orbit satellite with a big can of compressed gas and let it out. The drag of the gas cloud would deorbit any small objects until the gas cloud dispersed. One could use several puffs of gas for multiple objects. I haven't done the calculations though.

1. #### Re: It all seems a bit far fetched, to me

The contents of how many Olympic swimming pools would it take per satellite?

Although, to put a damper on the idea, there are a lot of scientists who'd be real pissed at you putting water vapour clouds _above_ the atmosphere and destroying their 'viewing' in infrared and millimillimeter wavelengths.

1. #### Re: It all seems a bit far fetched, to me

The contents of how many Olympic swimming pools would it take per satellite?

A number that would take up an area roughly the size of Wales.

1. #### Re: It all seems a bit far fetched, to me

The contents of how many Olympic swimming pools would it take per satellite?

A number that would take up an area roughly the size of Wales.

====

Couldn't we just launch Wales ? :oP

what ever strikes it isn't going to make that much impact, and may well improve the vista :o)

2. #### Re: It all seems a bit far fetched, to me

So, if they sent up a thingie to p*ss on the unwanted object, you're suggesting they'd p*ss off everybody?

Maybe they should launch a mini olympic sized swimming pool. People probably p*ss in them all the time.

Thanks, mine's the smelly waterproof wetsuit on the end peg

2. #### Re: It all seems a bit far fetched, to me

I would suggest a very large ball of Blu Tak, also launched in a retrograde orbit.

1. #### Blu-Tak

I think a giant slice of buttered toast would be better - everything will stick to that, then just de-orbot the toast..... And if it burns up on re-entry - it'll be toast...

1. #### Re: Blu-Tak

JPL scientists proposed the giant buttered toast technique in the late 1980s. Unfortunately the project was abandoned after further research at NASA showed that the butter would inevitably rotate towards the earth, instead of the direction of the debris.

2. #### Re: Blu-Tak

I think a giant slice of buttered toast would be better - everything will stick to that, then just de-orbot the toast..... And if it burns up on re-entry - it'll be toast...

Just ensure there are no cats within the old satellite, or the thing will just spin in situ for ever!

2. #### Re: It all seems a bit far fetched, to me

How about a ginormous ball of sticky ballistics gel equivalent going in polar orbit. that way the orbit won't decay so quickly. kinetic energy remains the same after colliding, and "live" satellites can be steered out of its path. Anything NOT live gets to be part of the thing. launch it at an altitude that collides with most of the space junk.

it's as good as any other idea, and doesn't require propulsion, just enough time to stick to everything [like using tape on a suit to get the cat hair off]

3. #### Re: It all seems a bit far fetched, to me

Similar thoughts crossed my mind.

For this to work as described would surely call for military-grade precision beaming. Could that be a clue as to anyone's motivation?

4. #### Re: It all seems a bit far fetched, to me

>1. As far as I'm aware, applying a force to an obect in orbit, merely changes the orbit of that object. It does not "knock it out of orbit" A satellite launch comprises two burns, The first to get it to the right height, and the second to impart the required velocity that it has to have to orbit at that height.

So, by your own words, taking velocity back out must surely preclude it from orbiting at that height.

Bear in mind that taking velocity out of a circular orbit (One which is equal in altitude at all points) does not result in a circular orbit, it lowers the point on the opposite side of the current position.

>3. The de-orbiter is essentially linked to the object, and without extra expenditure of fuel and mass will simply follow the object down to a matching fate

It is in no way linked to the object being de-orbited, how did you get that idea?

It imparts deceleration to the object, so it lowers one side of it's orbit until it intersects the atmo.

The craft doing the imparting has beams firing both ways, so it does not alter it's own orbit.

5. #### Re: It all seems a bit far fetched, to me

I've three objections to this idea.

1. As far as I'm aware, applying a force to an obect in orbit, merely changes the orbit of that object. It does not "knock it out of orbit" A satellite launch comprises two burns, The first to get it to the right height, and the second to impart the required velocity that it has to have to orbit at that height.

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Not exactly. The first burn is usually to establish the satellite in orbit, and if the first burn hasn't already done this, the second burn is to change the eccentricity of the orbit. The process you describe would be energetically inefficient.

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2. Applying the force by a plasma jet has to apply that force exactly at the objects centre of mass, wherever that might be, or all it will impart is a spin. Given that the object is bound to be asymmetrical, finding the centre of mass might be a tad difficult.

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Not correct. Given that the plasma jet does not deliver all its force at a single point, it would be very difficult (probably impossible) to avoid a deorbiting vector in the acceleration of the target. Depending on the distribution of the force, and the mass, there may also be a rotational force, but you don't care about that. All you have to do is slow down the satellite enough that it will enter a region of increased atmospheric drag in some portion of its orbit... which will tend to become more eccentric, with a lower perigee.

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3. The de-orbiter is essentially linked to the object, and without extra expenditure of fuel and mass will simply follow the object down to a matching fate

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I presume that is the reason for a high efficiency plasma thruster setup - the deorbit satellite will be maneuvering a lot, including slowing down and speeding up as it deals with targets and moves on. An interesting question is whether it can be refuelled by linking with a fuel tanker, which would substantially increase its operational life.

6. #### Re: It all seems a bit far fetched, to me

It's a shame these researchers are rocket scientists and not internet commentators otherwise they'd have spotted all these potential flaws in their plan ages ago.

3. #### Centrifugal force?

Let's apply Newtonian physics,

Newtons 1st law - The satellite is moving in a straight line with just gravity pulling it into orbit due to the altitude & velocity being nicely balanced.

Newtons 2nd law - The Plasma beam is an outside force changing the velocity.

Newtons 3rd law - gravity is also pulling earth towards the satellite.

Centrifugal force would sort of prevent all the floaty fun astronauts get up to.

Having said that, the basic principle of using balanced beams to hold satellite A in place while knocking satellite B out of orbit works, and satellite A has the ability to change it's own orbit at will, it could also be easily refuelled. A good name for this would be a hunter-killer satellite to get budget funding.

1. #### Re: Centrifugal force?

>Having said that, the basic principle of using balanced beams to hold satellite A in place while knocking satellite B out of orbit works

It works better by having the hunter-killer satellite in a slightly higher orbit than the junk as then the beam would be working with gravity to hasten the junk's descent.

4. #### Centrifugal force

Centrifugal force, space borne weaponry, hmmm.... I sense a white cat being stroked.

https://xkcd.com/123/

1. #### Re: Centrifugal force

There is an entirely new propulsion system that is based on the redirection of the reaction of centrifugal force. It is called a Centrifugal Propeller. It will be capable of launching from Earth and returning, 5 or 6 times in a single day. This will make the clean-up of near space, a simple matter. The Centrifugal Propeller will put all rocket and jet engine manufacturers out of business. It will continually accelerate in space so there will be gravity in the spacecraft while accelerating. At the halfway point of the journey you will simply turn the spacecraft around and re-engage the Centrifugal Propeller, and you will have gravity in your spacecraft again. It will mean a trip to Mars will be little more than a day-trip, and people will be leaving for day-shifts mining on the moon and return home for supper on the same day. There is a working proof-of-concept prototype.

1. #### Re: Centrifugal force

Centrifugal Force? .... an engineering phantom. There is no such thing. An object undergoing circular motion will be subject to a centripetal acceleration. The "force" outwards is a reaction to the circular motion.

[Takes off her pedant hat before she feels it necessary to refute the assertion "It surrounds us and penetrates us; it binds the universe together"]

1. #### Re: Centrifugal force

Centrifugal force is quite correct - although often misunderstood...

It is what happens when you solve newtonian mechanics in a rotating frame of reference.

If you solve in a static frame the centrifugal force won't appear, but you will have a pile of other things to consider (like very high lateral velocity), and the diagram becomes much more complex.

An orbit can be easily viewed in a rotating frame of reference (just assume the earth is a perfect sphere, so you don't mind it slipping backwards).

2. #### Re: Centrifugal force

"There is no such thing"

1. #### Re: Centrifugal force

"There is no such thing"

Wrong.

If it's just inertia viewed from a certain frame of reference, then it isn't a separate thing, is it? Why call it something different when it isn't?

1. #### Re: Centrifugal force

Why call a web page with writing on it an article, or a piece of paper with writing a letter?

Why have male and female instead of having "Humans with parts that go inside another, and humans with parts designed to take other humans parts inside them?"

Its the definition of a term to define a common situation, in this case an apparent force, which allows for succinct communication.

5. #### Song Title - Missed Headline

"Sweeping Satellite"

1. #### Re: Song Title - Missed Headline

Yes - as sung by Barry Kripke!

6. #### Enemy junk

Interesting that someone thinks they have a better chance of funding if they present the 1-tonne enemy satellite as "junk".

Somebody should tell them that the most dangerous space junk is the 99.99% - the millions of tiny and invisible pieces, not the handful of monsters you can see coming and avoid.

1. #### Re: Enemy junk

"Somebody should tell them that the most dangerous space junk is the 99.99% - the millions of tiny and invisible pieces, not the handful of monsters you can see coming and avoid."

It's both. A big dead satellite crashing into another object creates a storm of little bitty pieces. They tell two friends and they tell two friends until there is a fine mist of high velocity particles and no more satellite weather photos on the evening news.

Using high energy light is easy than trying to capture junk in orbit, but it's power intensive and it will take a lot of computing power to figure slow deceleration orbits so the clean up doesn't just cause more collisions. The power required might take something as large or larger than ISS to collect and store enough solar power to accomplish much cleaning.

7. #### Idiots

"The team has calculated that in order to send a one to two tonne object to reach the Earth’s atmosphere in about 80 to 150 days would require a thruster performance of 60 milliNewtons for 1,800 seconds."

Has it? Has it really? This team of boffins has calculated an impulse of 10J (0.006 x 1800) is enough to deorbit a two tonne satellite? A delta v of 5mm per second (divide the impulse by the mass) on its 9.4km/sec orbit speed will knock it out of orbit?

Am I the only person with an intuitive enough understanding of GCSE physics, that I didn't just glaze over when those numbers were mentioned, but actually had a mental 'this is bullshit' warning go off? You're all a bunch of fucking innumerate idiots. This is exactly like a newspaper breathlessly reporting that a farmer has grown a 10 trillion tonne turnip the size of Wales as truth, and not even bothering to clarify or have any 'these numbers aren't reasonable' warnings go off.

1. #### Re: Idiots

"A delta v of 5mm per second (divide the impulse by the mass) on its 9.4km/sec orbit speed will knock it out of orbit?"

Seems highly doubtful to me. But:

* How much delta-V is required to adjust a typical satellite in LEO into a more eccentric one that will naturally decay at a more acceptable rate due to increased aerobraking?

* How much delta-V is required to avoid an impending collision between two dead satellites in LEO? (overly simplistic question here, we also need to know how reliably and how far into the future we can predict the orbits of the two dead satellites, and how quickly we can get the "zapping" satellite launched and on station).

Those questions aside: if 10J isn't enough, then take the XKCD what-if approach and build a zapper that can do 100 J (repeat as necessary, or until the physics become silly).

2. #### Re: Idiots

"Am I the only person with an intuitive enough understanding of GCSE physics, that I didn't just glaze over when those numbers were mentioned, but actually had a mental 'this is bullshit' warning go off? "

You missed that all you need to do is get the orbit elliptical enough to start dragging in the upper atmosphere.

1. #### Re: Idiots

"You missed that all you need to do is get the orbit elliptical enough to start dragging in the upper atmosphere."

What, and you think a delta v of 5 cm/s, while it zips around at 9.4km/s is enough to do that?

I haven't missed anything, and I repeat my assertion. You're an idiot with zero intuition about what these numbers, what half an hour of a 60mN force on a two tonne mass moving at 9.4 km/sec actually *means* to it. Answer. Fuck all.

1. #### @Aquilus

47 posts since 2007.

Just got out of jail?

2. #### Re: Idiots

"You're an idiot with zero intuition about what these numbers, what half an hour of a 60mN force on a two tonne mass moving at 9.4 km/sec actually *means* to it. Answer. Fuck all."

Whatever makes you think they're going to be using this to being down 2 tonne objects?

A 2 tonne mass is easy to latch onto and bring down with other means. More to the point it's also easy to SEE, calculate trajectory on and AVOID.

The problematic shit is all 10cm or smaller and impossible to latch onto - which is where getting into the same orbit as the debris cloud, parking in front the leading edge and using a balanced ion thruster comes into its own - effectively firehosing the crud into the gutter (atmosphere)

Of course the laser broom solution is probably more practical in all cases, even with atmospheric blooming taken into account.

3. #### Re: Idiots

First, your numbers are out by an order of magnitude. 60mN is 0.06 not 0.006. (Innumerate?) So the product is 108.

Secondly, you don't get to energy by multiplying force and time. The equation you want is Newton's second law, F=Δp/Δt, which we can rewrite as Δp = FΔt to show that a force applied over a period of time gives a change in momentum. Dividing this figure by the mass will calculate the change in velocity, but because you were out by an order of magnitude, it's actually 54cm/s.

Now we can calculate the change in kinetic energy of the satellite: it will be ½m(v+Δv)² - ½mv² which is mvΔv + ½mΔv² . (This should look familiar as it's the Galilean equation for acceleration multiplied by mass. We could have gone that route directly using the "F=ma" form of the second law, but we've got a deltaV so we'll stick with this.)

We'll use your velocity of 9.4E3m/s. And as Δv is tiny we'll discard the Δv² squared term and call the change in energy mvΔv. Which is `2E3 * 9.4E3 * 0.054 = ~1MJ (~50kW)` This figure is a bit high because, I think, you've used the launch velocity not the orbital velocity. But it's the right ballpark. This energy is big because most of the transferred megajoule comes from the kinetic energy the plasma particles have from already being in orbit.

Anyway, detailed analysis suggest the impulse supplied will be enough to get an object in 1000km orbit down to 300km orbit, where the atmosphere will do the rest. There's an in-depth analysis here.

So, on the new numeric GCSE grading system, I reckon I'd give you -1.

1. #### Re: Idiots

@Brewster's Angle Grinder:

...

Blimey, you're clever!

Sorry, that was all just like rocket science to me....

2. #### Re: Idiots

@Brewster's Angle Grinder

I don't understand what you're doing with your energy calculation but 0.06 m/s is a tiny delta V. One article I looked at suggests a delta V of around 200m/s is required to put a satellite in geosynchronous orbit into a Hohmann transfer orbit that would intersect the atmosphere.

1. #### Re: Idiots

most satellites are NOT geosynchronous - that is the super high value real-estate/parking spot directly in front of the shops, that is roughly 3 times further out than most satellites bother with.

Sure it is high value and limited in quantity? - which would make it a prime candidate for clean up, but again, easy to disrupt.

Pushing something from geosynchronous will either drop it into a faster lower orbit (difficult), a slower higher orbit.. or a most likely an eccentric orbit which will eventually graze atmosphere and produce extremely expensive fireworks. Which is the desired outcome.

Lower orbits are easier to get to, but will decay more easily as well - and its always easier to push something in the direction it wants to go.

Something the article stated was that the process could take up to 150 days - almost half a year before atmospheric contact, They arent talking about something that will kick satellites out of the sky immediately.

Damn kids these days, always expecting instant gratification....

2. #### Re: Idiots

"One article I looked at suggests a delta V of around 200m/s is required to put a satellite in geosynchronous orbit into a Hohmann transfer orbit that would intersect the atmosphere."

99% of the junk is not at GEO, it's at LEO, with most of the remaining fraction at SEO

1. #### Re: Idiots

That may be technically true but objects in LEO require constant reboosting to stay in orbit. Spack Junk in LEO doesn't remain a problem for long. (Not that it matter since we're talking about something like a 50% difference in orbital and the error in my figure is greater than that.)

3. #### Re: Idiots

"Dividing this figure by the mass will calculate the change in velocity, but because you were out by an order of magnitude, it's actually 54cm/s."

108 / 2000 = 0.054 m/s = 5.4 cm/s

You're out by an order of magnitude.

4. #### Re: Idiots

Reading the original article (always advisable before calling the authors idiots) reveals that the figure of 1800 seconds is in fact the specific impulse of the thruster not any actual time. Half an hour would, in fact, be a surprisingly low figure. Typically these sort of drives have to be operated for many hours to give any sort of useful delta V.

5. #### Re: Idiots

You're all a bunch of fucking innumerate idiots.

Sorry, you're soooo wrong there.. I may be an idiot, but I'm relatively innumerate, and since I became single, I've not been doing much fucking.

1/10 - Must try harder.

6. #### Re: Idiots

"Am I the only person with an intuitive enough understanding of GCSE physics... You're all a bunch of fucking innumerate idiots."

Or perhaps we took Orbital Mechanics while doing Physics at University and understand that your GCSE Physics is bullshit, you should ask for a refund. Oh you might want to get a refund on your GCSE Maths too because 60 milli Newtons is 0.06.

8. A plasma beam requires both energy and material. The energy can be replenished from solar panels but the material will be exhausted. An alternative would be a laser pointed at the junk which then provides the material itself by evaporation. Of course the manoeuvring fuel will get exhausted anyway.

1. "An alternative would be a laser pointed at the junk which then provides the material itself by evaporation."

And can operate from the ground. Lookup "Laser broom" to see various proposals.

9. #### It isn't the big objects

It isn't the big objects that are the problem - they are *relatively* few in number and easy to track. It's the small objects that cannot be tracked, huge in number, and moving at 17,000 mph. Even an object like a paint chip can put a hole in a space craft or satellite - eradicating them will be the problem.

1. #### Re: It isn't the big objects

@fishman >>>Even an object like a paint chip can put a hole in a space craft or satellite<<<

Yes, if its going in near the same direction, a tiny piece of junk orbiting the other way is a 35,000mph smack in the face and you're into plasma physics the hard way.

To quote the late great Douglas Adams, 'Space is big, really big', and so are all the numbers involved in moving around in it. my rough maths give the volume of LEO space from 150 -> 1,150 miles altitude as well north of 250 billion cubic miles, thats a lot of sweeping up to do.

10. #### Consider:

I haven't done these calculations so what I'm about to post is pure speculation. (I'd like to see the real numbers:) If the entire "surface area" of all the orbital planes of all the "debris" (and even all the "non-debris") that is currently in orbit around the Earth, including Ed White's glove and a tool or two that got lost, was reduced to the two-dimensional surface area of Earth itself, the average distance between two pieces of debris (even paint chips) would be 170 miles (or something.) In other words, hitting one of these pieces of junk -on purpose- would be well-nigh impossible. Hitting one by accident would be something like an act of God. And remember, simply because everything is going 17,000 mph doesn't mean that the collision velocity is anything like that. The collision velocity might be miles-per-hour, not thousands of miles per hour.

The artists' images of a cluttered earth-orbit with stuff bouncing off other stuff is just nonsense, the area out there being just so huge. Plus, now, by international law, every item placed into near Earth (up to geo-sync) orbit, must have an end-of-life plan that assures either destruction or "no-factor" removal. Accidents and failures of self-removal mechanisms won't cause an urgent problem for, maybe, centuries. My sense is that there is something else to this. Like a military something else. Huh?

1. #### Re: Consider:

"Hitting one by accident would be something like an act of God"

And yet, after a few years on-orbit, the average set of solar panels look like the good ole' boys have been out with their shotguns and got bored.

End of life plans and cleanup for stuff launched NOW are all the norm, but the vast majority of junk in orbit was left there prior to the mid 1970s. It was when some expended 1960s-era boosters exploded on-orbit in the early 1970s that people started closer paying attention to bits falling off on the way up, bits falling off once on-orbit and the longevity of unecessary bits left behind on the way.

Skylab's booster gave NASA's engineers some sleepless nights when they worked out it might land on Spain - it finally came down about 18 months after the launch - over water as it happened - but they realised they had to start reliabily ensuring that things that didn't need to stay up came down quickly and that the "down" was unlikely to land on Sally from the Valley in the Alley.

1. #### Re: Consider:

>And yet, after a few years on-orbit, the average set of solar panels look like the good ole' boys have been out with their shotguns and got bored.

Given all the meteor showers, passing comets and their tails, I wonder whether part of the problem is that we assume space to be a clean vacuum and not a rather dirty place with lots of small particles whizzing by on their various trajectories.

1. #### Re: Consider:

Solar panels don't exactly look like shot-gun target practice, but they do look pretty messy. Almost ENTIRELY caused by rocks and dust coming in from someplace OTHER than up from Earth.

2. #### Re: Consider:

" If the entire "surface area" of all the orbital planes"

I believe that the vast majority of all the junk is concentrated into a very few orbital lanes, which also happen to be those which the majority of satellites and spacecraft are jaunting about in. Hence the demonstrated reality that these collisions do occur.

Your logic is along the lines of dividing the size of all the worlds ships by the size of all the worlds oceans and then confidently asserting that for two ships to hit each other is near-impossible. Which is obvious nonsense.

1. #### Re: Consider:

Two ships RARELY hit each other at sea--even in shipping lanes. They hit each other in harbors and other "choke points." Earth orbits are not "choke points." They are more like "at sea." Plus, the surface of the ocean is one-dimensional, while earth orbit is absolutely not.

3. #### Re: Consider:

" Hitting one by accident would be something like an act of God."

Yeah.

But God's kind of an arsehole sometimes..

11. #### Timeline

For the tinfoil hat theories (envisioning a military purpose) the linked article references this as a technique to de-orbit the junk satellite on a time scale of ~25 years. This is NOT a plan to burn once and drop into the atmosphere on the next orbit or so.

12. #### Factor of two

Maybe not what you'd think from my title. I don't see a need to have the other (maybe unwanted by whatever else it might strike) beam here. Or in fact the need to apply enough energy in one go to de-orbit your target. So what if action-reaction pushes your garbage deorbiter away? Use that to move it to another orbit (it will anyway) to put a little of the right action on some other target (no shortage of those), repeat as necessary. Eventually you get them all...or your buddy sats do, obviously you'd use more than one. Last I checked we have computers and stuff to handle ballistic calculations, and predict what might be the best path through a complex set of maneuvers. And even humans on the ground to check their work, and in fact also run computers on the ground so as to save the money required in launching them. No need for those to be in space themselves. Just sensors and some kind of beam - laser ablation of plasma. Given a choice, this old engineer would have both.

13. #### Cant space lasers do this?

Just wondering.

1. #### Re: Cant space lasers do this?

Only when attached to sharks...

2. #### Re: Cant space lasers do this?

Just wondering.

Yes, in theory. However given that they generally have to work by heating the material surface of the object to be de-orbited until some of it heats up and is ejected and though this providing a small opposite reacion. There are risks to this, becaues it could produce more debris, although admittetly hopefully in a very unstable orbit. However the downside is that without using an excessively powerful laser the beam because the object is almost certainly going to be rotating that applying enough energy in a certain spot for a long enough period of time is going to be very hard. Lasers can be used to provide motion through just the act of the photons hitting the object (external force), and this would be a more reliable and predictable method, however this is a very small effect compared to that of effectively turning the object into it's own fuel.

The plasma plan as listed here works through also being an external force and therefore not relying on the precise targetting required to turn the object itself into propellant and with luck shouldn't produce more debris - or at least should have a considerably lower risk of generating more debris. It will also be able to apply more external force in a shorter period of time compared to just a laser.

14. #### Space 1999

What we really need are a few nuclear bombs in synchronous orbit being detonated, err, synchronously. That'll produce a compression wave that'll push all the low mass debris downwards towards the Earth and so cause it to be snagged by the upper atmosphere.

Or it'll blow the Moon out of orbit. One way or the other it should be a pretty spectacular sight.

1. #### Re: "Blow the moon out of orbit"

While I understand the reference. The problem is, as a human, we can construct sentences that seem reasonable, but are entirely impossible.

15. #### Proud to be British

Isn't this all so wonderfully Wallace & Gromit?

Japan proposes a hugely expensive, complex plasma beam technology that will require control systems not yet invented to make it work, here in Blighty our boffins propose sending up a big net.

A question for true rocket scientists: Why are Japanese scientists proposing to slow the debris down, rather than using the plasma beam to add an earthbound vector to the space junk. I'd have though that more energy would be needed to materially slow fast moving debris than to give it a light punt in a downward direction?

1. #### Re: Proud to be British

Whilst not a rocket scientist, I have played Kerbal Space Programme enough to know that the most efficient way of deorbiting something is to apply retrograde force to that object - thus lowering its orbit on the opposite side to where the forces is applied. Force applied radially in will change the shape of the orbit, but not affect the orbital velocity - so whilst possible to send it down that way it will require a lot more force.

1. #### Re: Proud to be British

I have played Kerbal Space Programme enough to know that the most efficient way of deorbiting something is to apply retrograde force to that object

Really? I have also dabbled in KSP, and for me the most efficient (and shockingly rapid) method for deorbiting something is to launch it.

Mine is the flight jacket with the dogeared copy of "Haynes Saturn V Owner's Manual" in the pocket.

2. #### Re: Proud to be British

I'd have though that more energy would be needed to materially slow fast moving debris than to give it a light punt in a downward direction?

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Not really. That would change the shape of the orbit, but probably add energy - which corresponds to a higer orbit, not a lower one. Orbital mechanics is not one of those intuitively obvious areas for most people.

3. #### Re: Proud to be British

IANARS but my understanding is that orbital distance is determined by a combination of the mass of the object and the speed of object. Speed up and it moves out, slow down it moves in. It has nothing to do with where you place the object. So if you simply push an object towards the earth without reducing its speed, as soon as you stop exterting force on it the object will natually move back into its original orbit.

In order to work by pushing downwards, you'd need to push it and hold it at a low enough orbit to burn up and I asusme that would take a lot longer and be far less effiencient.

1. #### Re: Proud to be British

few things..

Mass doesnt affect required orbital velocity - that is purely dependant on how deep in the well you are.

It DOES affect how hard it is to reach or maintain that velocity.

Lower orbiting objects need to travel faster, as they are under the influence of more gravity. If they dont have enough velocity, they will fail to clear the curvature of the earth and fireworks will ensue. Too much velocity and they will head away from the planet - initially into a more elliptical orbit but with enough speed you get to escape velocity.

The same rules apply for further orbits except the required velocities are lower - as the effect of the planets gravity is lower.

You can use Einsteins warped table for visualization, the steeper the curvature the faster you need to move to avoid falling into the center.

Disclaimer.. While I am a user of satellite based technology, my understanding of orbital mechanics is primarily from reading Science Fiction,. Larry Niven in particular but with a nod to Arthur C Clarke

16. #### Just

Ask the Lizard People to turn up Earth's gravity for a while, sucking all the LEO objects back to de-orbit.

And what a boon for Weight Watchers.

17. #### Space GUARD, not Space FORCE

Donald Trump wants a "Space Force", but that's the wrong name. We don't need a "Space Force" modeled after the Air Force; we need a Space GUARD, modeled after the US Coast Guard. Search and rescue, because there's nothing like that up there now. Maintenance and repair of navigational aids such as satellites, much as the Coast Guard maintains buoys. Removal of "hazards to navigation", and there we are; collect all the space junk and broken satellites, and bring it back to the Space Guard space station.

Let's face it, ANY sort of mass that's already in orbit is very valuable. Use it to build new satellites and space stations.

Can't be done NOW, of course, but I think this would be a valuable goal.

1. #### Re: Planetes

Anime based on this concept calle Planetes. Basically they are the orbital bin collectors. :)

Not too bad a story, with the exception of the last 2 or so episodes that goes all out crazy space battles/conspiracy/sci-fi.

18. #### Quote include twice

I think that if the debris removal can be performed by a single high-power propulsion system, it will be of significant use for future space activity, but I'm not sure where I read that.

19. #### If they can build it, someone will weaponize it.

Can imagine, if this can be made to work, it would be quite useful for knocking enemy sats out of their correct orbit.

1. #### Re: If they can build it, someone will weaponize it.

A load of plasma hitting the satellite from a few metres will probably do terminal damage to the satellite anyway. They're well shielded, but not that well shielded - particularly the solar panels.

1. #### Re: If they can build it, someone will weaponize it.

Which would create more space debris. Not the best of ideas. Better to nudge them into a decaying orbit.

20. UK goes old tech with a net, Japan goes hightech with plasma guns and you wonder why our tech industry is not a true world leader, all the brains and funding goes overseas !

1. #### yes but

ours is in space already for testing.

sometimes simple is better - I mean, it's not rocket science is it? or maybe it is ;)

21. Shades of the anime series Planetes and the manga its based on.

22. I've seen things you people wouldn't believe: attack ships on fire off the shoulder of Orion. I've watched C-beams glitter in the dark near the Tannhäuser Gate. Space junk deorbited by plasma satellite. Member states gracefully leaving the EU.

Time to die.

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