Theoretical question about a new Energy and implications of using it

[mfb]

But your calcs are suggestive, is there a practical way to harness orbital energy?

To change the orbit you need to change the energy (that's fine) but also the angular momentum. A closer orbit of the Moon has a lower angular momentum. Total angular momentum is conserved. Where did the difference go?

Lowering the Moon's orbit to geostationary orbit would release 3.1*10²⁹ J by the way, a factor 10 more than calculated above. The factor 1/2 comes from the ratio of total energy to gravitational energy. Tides would be a massive problem until the orbit is locked to Earth's rotation.

@mc Kravitz: Please keep posts on topic here. Not sure what you mean by "radial ideas" (radical ideas?), but they might not be a good fit anywhere. Moderators/Mentors have a green "Mentor" badge, like the one you can see at the top of this post.

 

[mc Kravitz]

Lowering the Moon's orbit to geostationary orbit would release 3.1*10²⁹ J by the way, a factor 10 more than calculated above. The factor 1/2 comes from the ratio of total energy to gravitational energy. Tides would be a massive problem until the orbit is locked to Earth's rotation.

@mc Kravitz: Please keep posts on topic here. Not sure what you mean by "radial ideas" (radical ideas?), but they might not be a good fit anywhere. Moderators/Mentors have a green "Mentor" badge, like the one you can see at the top of this post.

Have you ever seen the vis viva equation? It calculates the total energy of an orbiting body. It is derived from the sum of potential (gravitational) energy and kinetic energy and yes it takes into account angular momentum. That is the formula I used in my calculations. Remember, the kinetic energy is always positive but the potential (gravitational as you call it) is negative except at infinity where it approaches zero. The total orbital energy is always negative. It is the difference in orbital energy that matters. And that is what I used in my calculation.
I now realize that I did make one mistake. I should have used the semi-major axis of the orbit rather than the phrase "distance from the earth". The semi-major axis is equal to the radius when the orbit is a perfect circle.

I once had a math teacher who was not the brightest bulb in the chandelier. Whenever questioned, she would respond with the statement "I'm the teacher, you're the student" . I managed to ace the course by doing what the teacher wanted and not what the books and common sense dictated. [Insult deleted from post by the Mentors]

 

[Melbourne Guy]

Lowering the Moon's orbit to geostationary orbit would release 3.1*1029 J by the way, a factor 10 more than calculated above.

Is this similar to using anti-matter for power, @mfb? You need to expend the same amount (probs more in practice) to create the anti-matter in the first place, before you can then annihilate it to use the energy. I'm thinking that from your "lowering the Moon". Seems like it's not going to happen by itself!

 

[berkeman]

I'm thinking that from your "lowering the Moon". Seems like it's not going to happen by itself!

If you tied a long rope around the Earth and ran it up to the Moon and tied it around the Moon, it would only take a little while to reel in the Moon, no?

 

[Melbourne Guy]

If you tied a long rope around the Earth and ran it up to the Moon and tied it around the Moon...

Since we're in the sci-fi forum, I'm gunna say, "Yes!"

 

[mfb]

Is this similar to using anti-matter for power, @mfb? You need to expend the same amount (probs more in practice) to create the anti-matter in the first place, before you can then annihilate it to use the energy. I'm thinking that from your "lowering the Moon". Seems like it's not going to happen by itself!

No. There is nothing to spend, it's energy gained from the gravitational attraction between Moon and Earth. You do have to get rid of angular momentum, however.

 

[DaveC426913]

No. There is nothing to spend, it's energy gained from the gravitational attraction between Moon and Earth. You do have to get rid of angular momentum, however.

I think what MG is asking is HOW you go about lowering the Moon so that the energy becomes available. Retro rockets or some such?

Oh! i got it. A huge magnet on the Moon and a motor on Earth. The moving magnet induces current in the motor, which provides power. The moon in turn experiences magnetic drag, causing it to fall closer.

Booyah!

 

[berkeman]

Dont you need to slow it down, maybe using rockets or some such?

Rope...

 

[DaveC426913]

Rope...

I am not sure of the details of the Moon lasso motor, but now that i worked out the electromagnetic generator, i can see the principle is sound. Any mechanism that constricts the moon's movement in its orbit can be hooked up to a generator.

 

[mc Kravitz]

I am not sure of the details of the Moon lasso motor, but now that i worked out the electromagnetic generator, i can see the principle is sound. Any mechanism that constricts the moon's movement in its orbit can be hooked up to a generator.

My thinking exactly. The amount of constriction can be miniscule in terms of the Earth moon system but provide a substantial amount of energy to the earth.
Anyone got any ideas on just how to safely get the energy to earth?

<Off-topic comment deleted: please place feedback in the dedicated feedback forum, not in the technical forums>

 

[DaveC426913]

<Response to off topic comments deleted>

Anyone got any ideas on just how to safely get the energy to earth?

I do. Post 37.

 

[mc Kravitz]

I do. Post 37.

That was my assumption in my initial post 20. Melbourne Guy clearly pointed out the danger of using that method in his response; post 21.
Anyway, thank you for agreeing with the original idea.
If we want "established physics" to join us in this quest, we'll need a safe and effective method to extract energy from the moon's orbit.

As a result of Melbourne guy's post, I started to consider a strong concentrated magnetic field that could be ferried closer to Earth where it could energize a generator without putting on a light show in every electrical distribution network on the planet.

I think this is a worthy topic even though PF will only allow it in a "fictional sense" and it deserves some debate.

I know the moderators here are honestly trying to protect the fragile minds of student and beginners but let's remember the words of Albert Einstein

"Creativity is intelligence having fun" Albert Einstein
"The measure of intelligence is the ability to change" Albert Einstein

I believe that future discoveries in physics will come from the young/young at heart physicists.

 

[berkeman]

I believe that future discoveries in physics will come from the young/young at heart physicists.

If this helps to motivate you to keep studying more science and working on contributions, that is a very good thing. Please do keep working your way up through the levels of school -- that's where you gain the understandings of mainstream science that help you to extend that knowledge.

 

[mc Kravitz]

I want to apologize to DaveC426913. If I offended him, it was not intentional. I received 4 warning points for "insulting a member". I assume it was my attempt to correct his understanding of orbital energy. I had just finished a college level class on orbital mechanics and I just assume that everyone on here would know the mechanics of it. It is clear to me now that that was an unfair assumption.
I did finish at the top of the class and I honestly believe that I understand the topic very well. I'm sure I could get a letter from the professor verifying that.
I would be more than willing to help anyone on this forum with orbital mechanics problems.
It was the material I learned in the class that made me think of the possibility of extracting energy from the moons orbit.
DaveC426913 did get the larger picture, as evidenced by his post (#37).
Melbourne Guy, to his credit pointed out the potential dangers of my original proposal and I quickly and apologetically agreed with his assessment. I did not intend to insult him either.
The fact that many people only think of the kinetic energy component of orbital energy is completely understandable, although incorrect.
If you extract kinetic energy from an orbiting body, it does "slow" it down at that point in the orbit, but what really happens is that the orbit is altered and becomes more elliptical. In this new elliptical orbit the body will actually have more kinetic energy as it approaches it's periapsis. At periapsis, the potential energy is lower ( a bigger negative number). Extracting kinetic energy at this point will lower the eccentricity again altering the orbit. The point is; if we are going to try to develop the mechanics of actually extracting orbital energy for the good of all mankind (which I feel confident can be done), we must fully understand orbital mechanics.
As I pointed out in an early post and DaveC426913 agreed in his post 37, magnetic field energy transfer seem the best option. But not disturbing our electrical grid must be a prime objective.
Since I am a no-body to mainstream physics at this point in my life, I choose to seek out help from imaginative young or young at heart people on forums. I apologize to the moderators of this forum if that offends you. But I must try! If I m incorrect I'll be the first to admit it, as evidenced by my reaction to Melbourne Guys insightful post.

 

[Melbourne Guy]

No. There is nothing to spend, it's energy gained from the gravitational attraction between Moon and Earth. You do have to get rid of angular momentum, however.

I'm struggling with "you do have to get rid of the angular momentum" aspect, @mfb. Possibly, @berkeman's lasso idea was tongue in cheek, but doesn't it take energy to 'reel the Moon in'? Given, angular momentum is is a conserved quantity, where do you 'get of it' to?

Melbourne Guy, to his credit pointed out the potential dangers of my original proposal and I quickly and apologetically agreed with his assessment. I did not intend to insult him either.

No fear, @mc Kravitz, I did not take anything you wrote as insulting, to me at least. I obviously can't talk for others. PF is generally a very respectful site, which is a credit to the efforts of the moderators and their clear rules, and I find it helpful, if reading a post gets my dander up, to walk away for a while before responding. Usually, that takes any heat out of my planned reply.

 

[mfb]

I'm struggling with "you do have to get rid of the angular momentum" aspect, @mfb. Possibly, @berkeman's lasso idea was tongue in cheek, but doesn't it take energy to 'reel the Moon in'? Given, angular momentum is is a conserved quantity, where do you 'get of it' to?

Well, as implied in post 31 I don't think it's practical, but leaving that aside:

Option A: Let's assume the universe only has Earth, Moon, and some space station far from Earth. You can launch something from Earth to pass behind the Moon in its orbital path. The object gains some kinetic energy and angular momentum, the Moon loses both. Catch that object at the space station, converting the kinetic energy into whatever you want. The space station gets some momentum away from Earth, that can be balanced by the gravitational attraction of Earth over time. The space station also gains some angular momentum, but it's far away so this doesn't correspond to a large angular velocity. Then drop the object so it falls back to Earth. Catching it there recovers the energy needed to launch the object.

Option B to use the Moon's energy: Install a mass driver on the Moon that shoots mass out at the "back", making them stationary relative to Earth. They fall down to Earth where you can extract their kinetic energy, gaining far more than you needed at the Moon. Over time a part of the mass of the Moon ends up on Earth while the Moon goes to a higher orbit. In a universe with only Earth and Moon you could end up with an arbitrarily small moon at an arbitrary distance (having a large angular momentum from being very far away), with the Sun raising the orbit will destabilize the Moon's orbit until it stops orbiting Earth.

 

[Melbourne Guy]

Install a mass driver on the Moon that shoots mass out at the "back", making them stationary relative to Earth. They fall down to Earth where you can extract their kinetic energy,

Shades of Heinlein's The Moon is a Harsh Mistress! But thanks, @mfb, Option A was clear enough for me to muddle through the concept.

 

[some bloke]

Two of the biggest issues I can see with the magnetic generation of energy are that a magnetic field from the moon could well cause electrical currents in everything, and that getting the huge magnets to the moon would be incredibly impractical.

I don't know the physics behind this so it's just supposition, but with the Earth already being a magnet, can we not flip it so that we build the coils on the unpopulated lunar surface (using the silicon which makes up 20% of the surface to make superconductors). Thus the movement of the moon through the Earth's magnetic field will generate power which can then be transferred to Earth via a laser or something. Bonus points for building solar panels on top of the coils!

All of this has gotten a little sideways on the OP's question, and on my suggestion (which was to somehow siphon off the gravity holding the Earth in orbit with the sun, not to slow an orbital body down!). Obviously we don't know enough about gravity to hypothesise a way to do this, but if it were modeled as magnets (and we assume a civilisation who can do this can manipulate gravitational fields like magnetic ones), then can you use the magnetic field to generate power and leave other things orbiting because of it drifting away?

 

[Lren Zvsm]

Toady we use energy sources like fossil fuels which in turn cause global warming, which is a slow process in which our planet changes its habitat to a hostile one for humans.

For a science fiction book idea I would like to know if there is a theoretical source of energy that using it would create a slow process that would change the habitat of a civilization living in the solar system / several solar systems (meaning using this source would slowly destroy or change somehow the solar system or the universe).

I don't know about energy sources, but one possible pollutant that could span the solar system might be self-replicating machines that were designed to build themselves into livable habitats for humans. These habitats might take the form of super tough "blisters," bubbles on the surfaces of moons or asteroids that contain oxygen, water, and enough organic material to form the basis of a hydroponic system of agriculture. (Yes, these latter features might require human help for assembly.)

But what if the self-replicating mechanisms become defective, and reproduce wherever the right combination of minerals exist--water, oxygen, and hydroponic media be damned? What if they start reproducing like cosmic cancer cells? We could destroy them, but could we ever destroy enough of them to stop their spread? What if their initial forms were small enough to "stow away" on manned or unmanned spacecraft ? Might they not displace existing colonies?

 

[Melbourne Guy]

What if they start reproducing like cosmic cancer cells?

It's the grey goo scenario, which Drexler first described in Engines of Destruction, and which has been used in many sci-fi stories, including, peripherally, in Reynolds' Revelation Space series and more recently, The Expanse series.

Fun idea, there are many ways you can go with grey goo, from a limited incursion that is heroically conquered, to an outright blight that can only be outrun and so fractures your civilization.