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General Discussions => Skepticism / Science Talk => Topic started by: DanDanDan on April 08, 2019, 10:23:01 PM

Title: Kinetic Batteries... In Space!
Post by: DanDanDan on April 08, 2019, 10:23:01 PM
In a sense, each piece of garbage in orbit can be thought of as a kinetic battery. So what am I missing here? Why not think of that energy as an asset instead of purely as a liability? Mine it, so to speak.

Is it just not feasible to take the momentum of a piece of space junk and transfer to a satellite? Or use the energy for any of the other million purposes that I'm not imaginative enough to dream up.

No way am I the first to have considered this, because I ain't no rocket scientician. File drawer effect, maybe?

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Title: Re: Kinetic Batteries... In Space!
Post by: CarbShark on April 08, 2019, 11:27:13 PM
The fact that you can think of them that way doesn’t mean it’s going to
be practical to use their kinetic energy.

They are in orbit and that’s not a convenient place to store energy. To retrieve all those bits of pieces would take a lot of energy to match orbits and speeds, and then there would be the energy required to get that fuel into orbit.

All of the ideas for getting rid of space junk I’ve seen have involved a way to send it down into the atmosphere. Not retrieving it. Even the pieces that may have some use.


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Title: Re: Kinetic Batteries... In Space!
Post by: brilligtove on April 08, 2019, 11:55:18 PM
If we could set up a satellite with some sort of electromagnetic braking system that worked at those speeds, maybe you could set up something that could do regenerative-braking style power generation by catching scrap?

Seems like a really difficult and inefficient approach compared to zapping crap with lasers from a higher orbit, sending it down the gravity well.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 09, 2019, 03:24:40 AM
This is why I'm thinking of the situation as a sort of mining problem. It's a resource that hard to get at, but a resource none the less.
Title: Re: Kinetic Batteries... In Space!
Post by: 2397 on April 09, 2019, 04:33:56 AM
With orbiting garbage, we have to either accelerate or decelerate it to move it away from or down to Earth. Both require an input of energy.

I don't know what the composition of it all is, but it's probably far too fragmented to be worth gathering it up vs. mining an asteroid.
Title: Re: Kinetic Batteries... In Space!
Post by: daniel1948 on April 09, 2019, 09:58:03 AM
With orbiting garbage, we have to either accelerate or decelerate it to move it away from or down to Earth. Both require an input of energy.

I don't know what the composition of it all is, but it's probably far too fragmented to be worth gathering it up vs. mining an asteroid.

I think this is the crux: It's too far away and too fragmented.

There are energy sources that are just too intense to capture because we cannot build anything that can withstand it. Thermonuclear energy is one example: Up to now we have been unable to build a vessel that can contain it because it's too hot for our materials. Each bit of orbiting debris has such high energy that anything it strikes will be seriously damaged. Add to that the fact that it is so spread out that it would require a huge collector. Then there's the problem of getting that energy somewhere it can be used. A collector would have to be in orbit, so how do you get the energy anywhere useful? Note that this stuff is so diffuse that existing satellites are rarely struck by it.

And finally, with solar coming down in price, retrieving energy from orbiting debris will never compete in cost effectiveness. The cost of building a space debris energy collector would be vastly more than building a solar collector farm or a wind farm.

Here's a thought experiment: Imagine there actually were a perpetual-motion machine that produced energy absolutely free, but it cost a million dollars to build a machine with a constant output of one watt. Would you buy one? Residential solar seems to range from about three to four dollars per watt, depending on your location, and industrial-scale solar is even cheaper. Your orbiting-debris energy collector, like this imaginary perpetual motion machine, is just not cost effective.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 09, 2019, 01:02:01 PM
Add ultralight ferromagnetic foam. Maybe.

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Title: Re: Kinetic Batteries... In Space!
Post by: gmalivuk on April 09, 2019, 01:40:17 PM
This is why I'm thinking of the situation as a sort of mining problem. It's a resource that hard to get at, but a resource none the less.
If it uses more energy than you can get, then it's not really a resource.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 09, 2019, 02:15:04 PM
This is why I'm thinking of the situation as a sort of mining problem. It's a resource that hard to get at, but a resource none the less.
If it uses more energy than you can get, then it's not really a resource.
Good point. Still have to do something with it tho.

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Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 09, 2019, 02:16:26 PM
No doubt that these sort of plans are out there, I'm just wondering if they've been made public.

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Title: Re: Kinetic Batteries... In Space!
Post by: CarbShark on April 09, 2019, 02:43:08 PM
No doubt that these sort of plans are out there, I'm just wondering if they've been made public.

I seriously doubt it. There are plans, however, to send dangerous space junk into the atmosphere. (When I say "plans" that doesn't mean they are intending to do it, but if the they decide to do it, they at least have a plan.)

There's also the issue of ownership.  Space junk is actually owned by whomever put it into orbit. It would literally be illegal (in violation of treaties) to collect space junk.

Nudging it into the atmosphere is ok, though.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 09, 2019, 03:06:20 PM
BTW, all of this dovetails with the discussion on the pod about firing lasers or particle beams around black holes.

IMO, it would be a massive waste to not recycle that energy by turning it into a sort of conveyor belt.

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Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 09, 2019, 03:06:54 PM
Patent dibs!

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Title: Re: Kinetic Batteries... In Space!
Post by: gmalivuk on April 09, 2019, 04:25:26 PM
This is why I'm thinking of the situation as a sort of mining problem. It's a resource that hard to get at, but a resource none the less.
If it uses more energy than you can get, then it's not really a resource.
Good point. Still have to do something with it tho.
Yeah, the best option would be to bleed that energy into the atmosphere by deorbiting all the junk so it doesn't hit actually important things.
Title: Re: Kinetic Batteries... In Space!
Post by: gmalivuk on April 09, 2019, 04:33:54 PM
This site (https://space.stackexchange.com/questions/88/what-is-the-total-mass-sent-into-orbit-over-all-history) has an estimate of about 13,000 tonnes launched into space as of the end of 2017. Let's grossly overestimate the amount of secret military launches or whatever and round it up to 100 million kg. Let's further imagine that it's all traveling at escape velocity instead of slow enough to orbit in approximately a circle.

This gross overestimate of the total kinetic energy ever sent into orbit comes out to 1.7 TWh.

That may seem like a lot, but it's less than 0.1% of the electrical energy the US uses each year.
Title: Re: Kinetic Batteries... In Space!
Post by: brilligtove on April 09, 2019, 04:35:48 PM
This site (https://space.stackexchange.com/questions/88/what-is-the-total-mass-sent-into-orbit-over-all-history) has an estimate of about 13,000 tonnes launched into space as of the end of 2017. Let's grossly overestimate the amount of secret military launches or whatever and round it up to 100 million kg. Let's further imagine that it's all traveling at escape velocity instead of slow enough to orbit in approximately a circle.

This gross overestimate of the total kinetic energy ever sent into orbit comes out to 1.7 TWh.

That may seem like a lot, but it's less than 0.1% of the electrical energy the US uses each year.

...Kyle? Is that you?
Because Science!
Title: Re: Kinetic Batteries... In Space!
Post by: CarbShark on April 09, 2019, 05:34:25 PM
This site (https://space.stackexchange.com/questions/88/what-is-the-total-mass-sent-into-orbit-over-all-history) has an estimate of about 13,000 tonnes launched into space as of the end of 2017. Let's grossly overestimate the amount of secret military launches or whatever and round it up to 100 million kg. Let's further imagine that it's all traveling at escape velocity instead of slow enough to orbit in approximately a circle.

This gross overestimate of the total kinetic energy ever sent into orbit comes out to 1.7 TWh.

That may seem like a lot, but it's less than 0.1% of the electrical energy the US uses each year.

Exactly. Plus, if you were able to collect it, you'd then how to figure out how to easily use it. But, you're also in an environment (space) where you have a virtually unlimited source of energy (the sun). A bigger challenge in orbit is protecting yourself from energy rather than being able to generate enough.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 09, 2019, 05:52:40 PM
This site (https://space.stackexchange.com/questions/88/what-is-the-total-mass-sent-into-orbit-over-all-history) has an estimate of about 13,000 tonnes launched into space as of the end of 2017. Let's grossly overestimate the amount of secret military launches or whatever and round it up to 100 million kg. Let's further imagine that it's all traveling at escape velocity instead of slow enough to orbit in approximately a circle.

This gross overestimate of the total kinetic energy ever sent into orbit comes out to 1.7 TWh.

That may seem like a lot, but it's less than 0.1% of the electrical energy the US uses each year.
First off thanks! Good stuff, good times. I effin love thought experiments.

Second, what's the current cost of a human-generated watt in orbit, I'm now wondering.

The thing is, another and maybe better name for these could be gravity batteries, which are far more efficient than solar.

Lastly, given how clever scientists can be, I'm guessing that some would jump at the chance to do something other than chuck the stuff in the garbage.

Even trash has value, is my central point.

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Title: Re: Kinetic Batteries... In Space!
Post by: Alex Simmons on April 09, 2019, 07:19:04 PM
Even trash has value, is my central point.

It's often a negative value.
Title: Re: Kinetic Batteries... In Space!
Post by: daniel1948 on April 09, 2019, 08:07:32 PM
BTW, all of this dovetails with the discussion on the pod about firing lasers or particle beams around black holes.

That is about as realistic as a sky hook to an orbiting satellite. It's a mathematical curiosity with no real application at all.

The thing is, another and maybe better name for these could be gravity batteries, which are far more efficient than solar.

No. There is no relation at all. Solar is a means of gathering energy. A battery is a means of storing energy. The relative efficiencies is totally irrelevant to any consideration. Further, the theoretical efficiency of a gravity battery tells you nothing about the cost of "mining" a resource that's so spread out that it will require more energy to obtain the debris than the energy contained in the debris. If it requires a thousand joules to gather one joule, your system is useless.

Clearing junk out of orbit is another issue, which is serious, and will be very expensive to do and will consume orders of magnitude more energy than could possibly be harvested from it. Note that to recover energy from a gravity battery, the weight has to operate some sort of generator as it falls. That means attaching it to a cable that is pulled by the weight. In the case of de-orbiting space junk, there's no generator to attach that cable to.
Title: Re: Kinetic Batteries... In Space!
Post by: arthwollipot on April 09, 2019, 09:13:15 PM
There's also the issue of ownership.  Space junk is actually owned by whomever put it into orbit. It would literally be illegal (in violation of treaties) to collect space junk.

Nudging it into the atmosphere is ok, though.

Isn't there something still on the books about maritime salvage? Perhaps some agreement based on that can still be made.
Title: Re: Kinetic Batteries... In Space!
Post by: CarbShark on April 09, 2019, 09:22:33 PM
There's also the issue of ownership.  Space junk is actually owned by whomever put it into orbit. It would literally be illegal (in violation of treaties) to collect space junk.

Nudging it into the atmosphere is ok, though.

Isn't there something still on the books about maritime salvage? Perhaps some agreement based on that can still be made.

I don’t think they’ll renegotiate in order mine space junk for kinetic energy.

And I believe you are free to send derelict debris into the atmosphere if it poses a danger. 


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Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 10, 2019, 12:46:32 AM
That is about as realistic as a sky hook to an orbiting satellite. It's a mathematical curiosity with no real application at all.

Turns out that Texas A&M is already on this idea. As I thought, it's not new. https://www.space.com/20024-space-junk-removal-sling-sat.html

"The spacecraft would harness the momentum exchanged during both of these actions to cruise over to the next piece of space junk on its list, minimizing fuel use and extending its operational life to the point that such a mission might be practical."

Quote
No. There is no relation at all. Solar is a means of gathering energy. A battery is a means of storing energy.

On that point, you're correct. I completely botched what I was trying to say. I meant that converting solar energy is far less efficient than converting kinetic energy. Gravity batteries are currently being built that are charged with solar.

As for what I was also trying to suggest, intentionally putting some kind of object or system of objects in orbit to later be used as a fuel saving conveyance, like a conveyor belt, I'm optimistic. Comparing it to the Halo Drive would be ore accurate if a gravity assist is part of the equation.

On whether or not objects in orbit can withstand debris strikes, here's this. https://en.wikipedia.org/wiki/Whipple_shield
Title: Re: Kinetic Batteries... In Space!
Post by: gmalivuk on April 10, 2019, 08:18:54 AM
Launching an object to orbit in order to harvest its energy later is a horrifically inefficient way of doing things, even if you could magically obtain 100% of its kinetic and potential energy after that.

All of the energy spent to lift propellant that's ejected later, and all the energy spent to get through air resistance, and all the energy spent just fighting gravity, are gone forever. The final payload accounts for only a tiny fraction of the energy cost to send it to space in the first place.

Using it to conserve fuel in a craft already in space is one thing. After all there definitely is some energy there and any of that you could harvest would translate into energy savings for whatever harvested it. But comparing it to a battery shows just how many orders of magnitude you're missing here.
Title: Re: Kinetic Batteries... In Space!
Post by: daniel1948 on April 10, 2019, 08:30:06 AM
... I meant that converting solar energy is far less efficient than converting kinetic energy. Gravity batteries are currently being built that are charged with solar.

As for what I was also trying to suggest, intentionally putting some kind of object or system of objects in orbit to later be used as a fuel saving conveyance, like a conveyor belt, I'm optimistic. ...

But a "gravity battery" has physical connection to the weight to allow it to be raised when you have power, and lowered when you need power. There's no need to go extremely high, and the higher you try to go, the more expensive the mechanism becomes. Rather than looking at theoretical efficiency, you have to look at cost per kWh of energy obtained or stored. Gravity is practical when you have sloping terrain. Otherwise it is cost prohibitive. A "conveyor belt" to space, if it were even possible to build, which it's not, would be astronomically expensive (pun intended).

If you had solar panels that were only 5% efficient but cost $1/kWh obtained, and a gravity "battery" that was 99% efficient but cost $1,000 per kWh stored, the solar panels would be the only possible choice. (Except of course that production of energy and storage of energy are entirely different things. You cannot compare solar panels to gravity batteries. You need to compare your gravity battery to chemical batteries or other energy storage methods. For example, your space battery to a conventional Earth-based gravity battery, which would be much cheaper.) Physical efficiency is only relevant as it affects cost. Cost is the bottom line.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 10, 2019, 08:51:07 AM


But comparing it to a battery shows just how many orders of magnitude you're missing here.

Could you be more specific? Not being snarky, I just get the feeling that I'm doing a horrible job of explaining the picture I'm trying to paint with words.

I'm using the battery comparison only, and I do mean only, because it's hypothetically possible to harness energy from virtually anything with potential energy. That's the name of the game with thought experiments: hypothesis.

When I was talking about putting things in orbit, I was picturing the use of garbage which we are already putting up and will continue to put up. Otherwise, the source of such materials would have to be the moon, meteors, asteroids, etc, given how strong the gravity on Earth is.

Isn't that the whole point of setting up a moon base before going to Mars? Shipping stuff around  in space is vastly more cost effective when that stuff is sourced in low or micro gravity.

This isn't the solar freaking highways situation. I'm proposing we produce research now, and hopefully a product later. I am not not not saying that we're ready for construction.

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Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 10, 2019, 10:02:26 AM
But a "gravity battery" has physical connection to the weight
No, the battery is the weight itself. The suspended, moving mass "contains" the potential energy is the battery. Anything locked to the part that goes up and down is also part of the battery. Anything that stays stationary relative to the source of gravity, which is the closest thing to being a true source, is something else. For example, if the weight is connected to an electrical generator, which is on the ground, the electrical generator is not part of the battery. That I think we agree on.

BTW, don't forget that, technically, there is no such thing as an original source of energy. The first law of thermodynamics states that the total amount of energy in a closed system cannot be created nor destroyed (though it can be changed from one form to another). Source: http://www.physicscentral.com/experiment/askaphysicist/physics-answer.cfm?uid=20120221015143

Even the Big Bang was a conversion of something to something. There are hypotheses out there that something can come from nothing and not immediately disappear, but we haven't thrown out the first law of thermodynamics yet .

Thermodynamics specifies that all energy in a closed system is recycled energy. That's what I'm saying can, is, and will be done. Recycling through conversion.
Quote
Gravity is practical when you have sloping terrain. Otherwise it is cost prohibitive.
Incorrect. In fact, that exact type of battery that you are saying doesn't work was discussed on the show. https://www.youtube.com/watch?v=mmrwdTGZxGk Steve himself once pointed out that, paraphrasing here, simply raising stuff straight up is a phenomenal way to store energy.

Perhaps the confusion here comes from the idea that we should use masses sourced on Earth. Unless we're talking about stuff that is going to be raised up and thrown away anyway, you're correct, it's cost prohibitive. We will use stuff already in space, such as materials from asteroids and moons.
Quote
You cannot compare solar panels to gravity batteries.
Yes I can, and I'll do it again to demonstrate where I'm coming from. And keep in mind that thermodynamics specifies that everything is basically something converted to something, which was converted from something, etc. 

You're saying that one is a converter and the other is a container. I'm saying that both are potentially both, and such processes are already being used. If you disagree with that, you're disagreeing with physicists, not me.

Take for example light coming from the sun toward us, and a meteor that's flying at us. Both things have potential energy, and as we speak, humans are harnessing such energy. I can point you to more explanatory sources if you'd like.

Everything I'm talking about has been done before, either in the same way that I'm describing, or in different forms. Such technologies will be used all the time in the coming space economy. It's inevitable.
Title: Re: Kinetic Batteries... In Space!
Post by: Billzbub on April 10, 2019, 12:48:18 PM
Okay, consider this.  Let's say we want to de-orbit the space junk as our primary mission.  However, since we have to spend the energy to somehow de-orbit it, we might as well harness some of it's energy while we are there.  For example, we could send up a satellite that shoots a harpoon at space junk as it passes by that attaches a drag wire to the junk.  The wire generates a current as the junk travels through earth's magnetic field, and that generation of energy slows the junk in it's orbit just enough to eventually de-orbit it.  This is converting kinetic energy into electricity through the use of the earth's magnetic field.  If that energy is then used by some mini ion drive encased in the harpoon mechanism to further de-orbit the junk, then we could accelerate the effort to clean up our local space by such harvesting of kinetic energy.
Title: Re: Kinetic Batteries... In Space!
Post by: daniel1948 on April 10, 2019, 01:14:44 PM
@DanDanDan:

The concrete block battery was discussed as being much less practical and much less cost-effective than other means of storing energy. And note, please, that the blocks are raised or lowered on cables connected to the motor/generator which supplies the energy to raise them and recovers the energy when it's time to release it.

On thermodynamics: the universe is a closed system, but the Earth is not. The Earth receives energy from a thermonuclear power station we call the sun, located at a convenient distance. This is irrelevant to your idea of harnessing energy from space junk.

Specifically, how do you propose to capture the gravitational and/or kinetic energy of the space junk? Any method of recovering either involves connecting the moving and/or raised mass to something that captures the energy by slowing or lowering the object. Regenerative braking on an electric car works because the generator in the car (which is also its motor) applies drag to the wheels. Your cement-block tower recovers energy via a cable that is connected to a generator that applies drag to the weight as it falls. What are you going to attach to the space junk to apply the drag that can be converted into useful energy?

You are correct in saying that all energy has to come from some other form of energy. In the case of solar, the sun is converting mass into photons and conveniently sending some of them our way. A solar panel catches them and converts them to electricity. In the case of a battery, unless it's a one-use battery, which is wasteful of resources, you need a source of energy to charge it.

It's true that we've expended the energy to put all that space junk up there. But it's so spread out that recapturing that energy would be massively cost-prohibitive. Also note (thermodynamics again here) that you cannot get more energy out than you put in: all the energy contained in all the space junk is only a fraction of the energy in the fuel used to put it up there. If you could recover all that energy, you could probably power one large U.S. city for about a minute. At a cost of many trillions of dollars in infrastructure.

The space battery is just not a cost-effective method of either storing or recovering energy. And there's actually no practical way to recover it. Pointing out that it has both kinetic energy and gravitational potential energy does not get you any closer to an actual mechanism for recovering it.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 10, 2019, 02:05:14 PM
@daniel1948
Yep, something is getting lost in translation between us. Not sure what else I can say, other than my conclusion at this point.

I was a bit confused by their flip flopping on it, but as of episode 716 @1:09:00, they are back to praising concrete-tower batteries.

Of course their opinion doesn't matter as much as the evidence, which if you have followed the links, is there. Engineers are on board, scientists are on board, investors are on board, that's good enough for me.

The separate and original question has been answered: Yes, this method is being researched, and yes, it's being researched because objects in orbit contain usable potential energy and we have the tech to use it. In time, I'm betting that this will be a more commonly used method.

Space garbage, your days are numbered!

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Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 10, 2019, 02:05:53 PM
Okay, consider this.  Let's say we want to de-orbit the space junk as our primary mission.  However, since we have to spend the energy to somehow de-orbit it, we might as well harness some of it's energy while we are there.  For example, we could send up a satellite that shoots a harpoon at space junk as it passes by that attaches a drag wire to the junk.  The wire generates a current as the junk travels through earth's magnetic field, and that generation of energy slows the junk in it's orbit just enough to eventually de-orbit it.  This is converting kinetic energy into electricity through the use of the earth's magnetic field.  If that energy is then used by some mini ion drive encased in the harpoon mechanism to further de-orbit the junk, then we could accelerate the effort to clean up our local space by such harvesting of kinetic energy.
I noticed that they're researching that too! Awesome idea.

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Title: Re: Kinetic Batteries... In Space!
Post by: gmalivuk on April 10, 2019, 02:36:59 PM
Point of clarification: the energy-saving methods that have been mentioned are not using any of the (relatively insignificant) potential energy orbiting things have, but rather the kinetic energy. Relative to the surface, about 96% of the energy of anything in low orbit is kinetic.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 10, 2019, 02:43:09 PM


Point of clarification: the energy-saving methods that have been mentioned are not using any of the (relatively insignificant) potential energy orbiting things have, but rather the kinetic energy. Relative to the surface, about 96% of the energy of anything in low orbit is kinetic.

Thanks! This is why I love getting into these conversations. It smooths out my knowledge base.

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Title: Re: Kinetic Batteries... In Space!
Post by: arthwollipot on April 10, 2019, 09:29:52 PM
Launching an object to orbit in order to harvest its energy later is a horrifically inefficient way of doing things, even if you could magically obtain 100% of its kinetic and potential energy after that.

That's not what's being proposed. The stuff is already up there - it was launched for other reasons. We might as well see if we can get some energy from it on its way down. No-one's saying we should launch stuff just so we can harvest the energy of bringing it back down again.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 10, 2019, 09:36:34 PM
Launching an object to orbit in order to harvest its energy later is a horrifically inefficient way of doing things, even if you could magically obtain 100% of its kinetic and potential energy after that.

That's not what's being proposed. The stuff is already up there - it was launched for other reasons. We might as well see if we can get some energy from it on its way down. No-one's saying we should launch stuff just so we can harvest the energy of bringing it back down again.
Amen

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Title: Re: Kinetic Batteries... In Space!
Post by: daniel1948 on April 10, 2019, 09:37:32 PM
Launching an object to orbit in order to harvest its energy later is a horrifically inefficient way of doing things, even if you could magically obtain 100% of its kinetic and potential energy after that.

That's not what's being proposed. The stuff is already up there - it was launched for other reasons. We might as well see if we can get some energy from it on its way down. No-one's saying we should launch stuff just so we can harvest the energy of bringing it back down again.

DanDanDan suggested a "conveyor belt": putting stuff into orbit as version of a gravity battery.
Title: Re: Kinetic Batteries... In Space!
Post by: arthwollipot on April 10, 2019, 10:00:42 PM
DanDanDan suggested a "conveyor belt": putting stuff into orbit as version of a gravity battery.

You're right - I had missed that.

As for what I was also trying to suggest, intentionally putting some kind of object or system of objects in orbit to later be used as a fuel saving conveyance, like a conveyor belt, I'm optimistic. Comparing it to the Halo Drive would be ore accurate if a gravity assist is part of the equation.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 10, 2019, 10:36:02 PM
Launching an object to orbit in order to harvest its energy later is a horrifically inefficient way of doing things, even if you could magically obtain 100% of its kinetic and potential energy after that.

That's not what's being proposed. The stuff is already up there - it was launched for other reasons. We might as well see if we can get some energy from it on its way down. No-one's saying we should launch stuff just so we can harvest the energy of bringing it back down again.

DanDanDan suggested a "conveyor belt": putting stuff into orbit as version of a gravity battery.

Yep. That's where I screwed up my explanation. I definitely never meant to say that we should launch stuff from Earth just to bring them back down to Earth.

We do use the gravity of other planets, moons, etc for gravity assists to slingshot satellites and such around, which I imagine to be like driving a car down a moving conveyor belt in order for it to take an extra long jump at the end.

So in effect, the planets are the "batteries" which our satellites steal energy from. Such a conveyor belt made from man-made objects is one thing that I was hypothesizing about. We're nowhere near that, but it's fun to imagine how to get the idea to work, like with the Halo Drive.
Title: Re: Kinetic Batteries... In Space!
Post by: Alex Simmons on April 11, 2019, 12:39:03 AM
I suggest taking up an undergrad physics class.

The mass of the Earth for instance, is 5.972 × 10²⁴ kg. It is travelling in orbit around the sun at 30,000m.s⁻¹.

That gives it a kinetic energy to draw from of:
0.5 x 5.972 × 10²⁴ x 30000² = 2.6874x10³³ joules.

A 100kg piece of space junk orbiting the Earth at 8,000m.s⁻¹ gives it a KE of:
0.5 x 100 x 8000² = 3,200,000,000 joules

That's nearly 24 orders of magnitude difference when considering assist manoeuvres via a transfer of KE.
Title: Re: Kinetic Batteries... In Space!
Post by: daniel1948 on April 11, 2019, 07:19:53 AM
And using gravity assist to add or subtract kinetic energy from a space probe is an entirely different matter than harvesting energy from orbiting debris for use back here on Earth. The practicality of one does not imply practicality of the other.
Title: Re: Kinetic Batteries... In Space!
Post by: gmalivuk on April 11, 2019, 08:23:06 AM
Yeah in particular, gravity assists make use of, y'know, gravity. Acceleration is much more efficient, in terms of kinetic energy, when you're already going fast. At 60km/s (such as you might get by diving towards Jupiter) an additional 1 m/s adds as much kinetic energy as accelerating from rest to 346m/s.

For orbiting debris, that effect is irrelevant. If you can catch something at perigee that has a really high apogee, you could in theory tether it to get a boost that would add a little energy to your own craft. If it's in a mostly circular orbit, all you can do is change the direction of your own orbit. If that's something you need to do frequently, then great, you can save some fuel this way. For anything else that's pretty much useless.

Thus, the proposal to save some fuel in a satellite designed to deorbit space junk might be feasible, but this will never be the way to go to the Moon.
Title: Re: Kinetic Batteries... In Space!
Post by: DanDanDan on April 11, 2019, 05:37:12 PM
BTW, plz plz plz correct my vocab

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