Author Topic: Kinetic Batteries... In Space!  (Read 1043 times)

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Offline DanDanDan

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Re: Kinetic Batteries... In Space!
« Reply #30 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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Offline gmalivuk

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Re: Kinetic Batteries... In Space!
« Reply #31 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.
The world is so exquisite with so much love and moral depth, that there is no reason to deceive ourselves with pretty stories for which there's little good evidence. Far better...is to look death in the eye and to be grateful every day for the brief but magnificent opportunity that life provides.

Offline DanDanDan

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Re: Kinetic Batteries... In Space!
« Reply #32 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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Offline arthwollipot

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Re: Kinetic Batteries... In Space!
« Reply #33 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.
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Offline DanDanDan

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Re: Kinetic Batteries... In Space!
« Reply #34 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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Offline daniel1948

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Re: Kinetic Batteries... In Space!
« Reply #35 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.
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Offline arthwollipot

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Re: Kinetic Batteries... In Space!
« Reply #36 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.
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Offline DanDanDan

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Re: Kinetic Batteries... In Space!
« Reply #37 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.

Offline Alex Simmons

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Re: Kinetic Batteries... In Space!
« Reply #38 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.

Offline daniel1948

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Re: Kinetic Batteries... In Space!
« Reply #39 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.
Daniel
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Offline gmalivuk

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Re: Kinetic Batteries... In Space!
« Reply #40 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.
The world is so exquisite with so much love and moral depth, that there is no reason to deceive ourselves with pretty stories for which there's little good evidence. Far better...is to look death in the eye and to be grateful every day for the brief but magnificent opportunity that life provides.

Offline DanDanDan

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Re: Kinetic Batteries... In Space!
« Reply #41 on: April 11, 2019, 05:37:12 PM »
BTW, plz plz plz correct my vocab

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