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Discussion Starter #1
I previously posted a vehicle concept based on an oberth maneuver, but I wondered if anyone from the original discussion ( A Gravity-Electric Hybrid & Thoughts on a "Land Based Oberth Maneuver?" ) agrees this idea may be a bit more practical than the original concept? The original concept, based on an oberth maneuver had both the vehicle and water tank descending a ramp, then an impulse would be applied between the vehicle and the tank to stop the tank thereby via conservation of momentum transferring the tank's kinetic energy to the vehicle before the vehicle followed a second ramp to the surface to continue on it's journey. The scheme was perhaps impractical due to the necessity of the vehicle descending into a tunnel. I propose a new concept with the same energetic efficiency, that negates the need for the vehicle to descend into a tunnel and negates the need for passengers to experience negative and positive G-forces, and likely reduces the overall infrastructure cost.
Summary:

The maglev car first accelerates horizontally in vacuum from gravity alone pulling a water tank down a gravitational well. The well curves 90 degrees to a horizontal section and when the falling tank reaches the horizontal section the vehicle applies a mechanical impulse to the tether sufficient to stop the tank, which transfers 100% of the mechanical impulse plus the kinetic energy of the tank to the vehicle via the tether. In some cases, depending on the masses of the vehicle and tank, at 70% kinetic to kinetic conversion efficiency via regen braking at the destination, more energy can be recovered from the vehicle than is used in the mechanical impulse, the balance of energy derived from the lowered gravitational potential energy of the water tank. Below certain depths, geothermal heat is sufficient to convert the water to steam, enabling power production via a turbine as the water rises back to the surface as steam. In essence the system combines transportation, hydroelectric and geothermal power production with potential improvements in efficiency and reduction in pollution over current systems by reducing the number of energy conversion steps, using renewable energy sources and providing new sources of untapped energy. A novel aspect of this "revised" land based maneuver vehicle is it isn't necessary for the vehicle to descend into a gravitational well, only the reaction mass, leading to reduced comparative infrastructure costs and increased passenger comfort compared to a "land based oberth maneuver". The new concept vehicle initially travels slower than the original concept because it takes less impulse to stop the tank and therefore the tank gravitational potential energy + impulse energy is less for the same tank mass and tunnel depth, but if the same total impulse is used, and the remaining impulse is used against the ground instead of the tether after the tank stops, then the same final vehicle velocity and energy efficiency at the surface is obtained because in both cases the tank's entire gravitational potential energy is efficiently transferred to the vehicle.

(Not to scale)


Original concept which required the vehicle to descend the tunnel as well:



In other words as long as the reaction mass drops into the well (whether the vehicle enters the well or not), and the same total impulse is used (entirely on the cable with the original vehicle or combination cable/ground with the revised vehicle), the final vehicle kinetic energy and velocity at the surface is the same.

The revised vehicle is more practical since the passengers don't need to experience negative and positive G forces, there doesn't need to be 2 separate ramps to depth, and the same ramp can be used to accelerate the vehicle in any direction.

Again, only the empty tank is lifted... the water is heated with geothermal in a sealed underground chamber (like a pressure cooker) where it is then run through a turbine and steam pipe to the surface, enabling power generation both as the water tank descends (powering the vehicle) and ascends (as geothermal steam).

Assuming 70% recovery of the vehicle's kinetic energy at the destination via regen braking and minimal transit losses via maglev in vacuum, more energy is potentially recoverable from the vehicle than was used for the mechanical impulse (on account of the lowered gravitational potential energy of the tank), and more energy still is recovered from the water turning to geothermal steam and running through a turbine on its way back to the surface.

In essence the concept both provides land transportation at airplane-like speeds and generates pollution free electricity, theoretically reducing fuel costs to $0 during normal use.

So far I've been able to calculate how much energy the vehicle receives from lowering the tank, but I haven't yet worked out how much energy can be extracted by heating a given mass of water to ~170C and running it through a turbine on the surface. We get the tank's total GPE transferred to vehicle from the tank mass kg * 9.8m/s^2 * height meters = Joules GPE. Any idea how to calculate the energy harvest from, say, 1000kg water heated to 170C with the generated steam run through a turbine?

PS regarding the necessity of vacuum conditions I was thinking if the vehicle never leaves the tunnel but only connects to an airlock for loading passengers and goods then there shouldn't be any additional energy costs to maintain the vacuum.
 

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The question is, how many pages will it take for you to realise this idea is just as impractical?
 

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Discussion Starter #3
I though that it may (?) be significantly more practical because:

1) The same tunnel can accelerate the vehicle in any direction
2) The tunnel can be narrower (lower cost)
3) The tunnel doesn't require the vehicle to transit through it (lower cost)
4) The tunnel doesn't need 2 separate ramps to the surface (lower cost)
5) The passengers don't experience any unpleasant G forces
 

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Why not just use the geothermal energy to generate oodles of power to drive the 'train' and anything else you want?
Be way simpler.
It might be a bit less efficient but the source is free and pretty near unlimited, so ...
 

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Discussion Starter #5
The main benefit I see over using pure geothermal to electric (other than added efficiency as you mentioned) is power density. The falling water I believe has high power density. If you want to accelerate the mass of 300,000kg (10 shipping containers) to 600mph you need about 3000kWh which if done over 30 seconds requires 360 megawatts for 30 seconds if my math is right. If you use the water to do much of the accelerating instead, it functions as a high power battery, so you could get away with much lower instantaneous geothermal power requirements and "re-elevate" the water much more slowly requiring less geothermal power (but same total energy), and therefore a potentially smaller plant. Also there's the efficiency loss with pure geothermal as you mentioned and you aren't harnessing the water's surface gravitational potential energy with conventional geothermal. Since such a system gives airplane like speeds without an airport size land footprint, it could give remote locations increased property values on account of quick access to major city centers and the job markets therein. If we compare the cost of digging the tunnel to building an airport I imagine the cost of such a system could be competitive for longer trips over say over 100km.
 

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Since such a system gives airplane like speeds without an airport size land footprint
Er, how do you figure that?
The land footprint (and cost to build) of 100km of overground vacuum tube would be far bigger than any airport, never mind the cost of the tunnel for the water truck, which alone would be horrendous.
And an airport is far more flexible in where to and how it can supply transport. This would be absolutely fixed A to B - no other options.
It's a financial black hole.
 

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I'm wondering if the concept is likely to change from MEATASTABLE to unstable and in the process eliminate the cargo?
 

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Discussion Starter #8
Er, how do you figure that?
The land footprint (and cost to build) of 100km of overground vacuum tube would be far bigger than any airport, never mind the cost of the tunnel for the water truck, which alone would be horrendous.
I'm saying the footprint could be much smaller than an airport size piece of land within the town's limits. Likely no bigger than a 1 lane road between the 2 destinations. I'm comparing to a "conventional" hyperloop- The system would potentially have lower power requirements. One could potentially forgo electricity entirely just letting the tank drop and the water turn to steam from down below. You'd only have to lift the empty tank which could likely be done with a counterweight. Then you wouldn't need to build an expensive electrical geothermal plant - just a vent for the steam- so potentially powered entirely by falling water and steam rising, though it would be slower and less efficient without the electrical component it would probably be cheaper.

One could make a worthless piece of land hundreds of miles from a major city highly valuable for residential development by connecting it with quick access to a major metropolitan center.
 

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Surely a wonderful idea, Metastable. There are a few bits I dont understand, but that is most likely down to my lack of knowledge in the areas of physics you are discussing. Are there any books I should read to better understand the concepts?
 

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Discussion Starter #10 (Edited)
Surely a wonderful idea, Metastable. There are a few bits I dont understand, but that is most likely down to my lack of knowledge in the areas of physics you are discussing. Are there any books I should read to better understand the concepts?
It's a hard problem conceptually but the simple explanation is this.... suppose in a vacuum you roll 2 marbles down a ramp and then push them apart with twice the energy one of them has (kinetic) at the bottom, one will stop and when the other reaches the top of a second ramp it will have all the kinetic energy of the other marble plus the total energy of the push (more than 100% of the energy of the push is transferred to the 2nd marble, a result of conservation of "momentum"). 66.6% of the final energy of the 2nd marble comes from the push and 33.3% comes from the kinetic energy of the other marble that stopped (total energy is conserved). If you can collect 70% of the 2nd marble's energy at the end you now have more energy than you used to push, the balance is derived from the "gravitational potential energy" the 1st marble originally had which is lowered because it is stopped at a lower height.

This is the closest thing I can find to a published paper on the topic:
 

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It's a hard problem conceptually but the simple explanation is this.... suppose in a vacuum you roll 2 marbles down a ramp and then push them apart with twice the energy one of them has (kinetic) at the bottom, one will stop and when the other reaches the top of a second ramp it will have all the kinetic energy of the other marble plus the total energy of the push (more than 100% of the energy of the push is transferred to the 2nd marble, a result of conservation of "momentum"). 66.6% of the final energy of the 2nd marble comes from the push and 33.3% comes from the kinetic energy of the other marble that stopped (total energy is conserved). If you can collect 70% of the 2nd marble's energy at the end you now have more energy than you used to push, the balance is derived from the "gravitational potential energy" the 1st marble originally had which is lowered because it is stopped at a lower height.

This is the closest thing I can find to a published paper on the topic:
Well that cleared that up.
 

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An alternative to the OPs concept is simply to exploit time/space wormholes: might be a bit mucky though🤪
 

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An alternative to the OPs concept is simply to exploit time/space wormholes: might be a bit mucky though🤪
Well this is all happening in a vacuum, and the energy is free, so there’s no reason why the passengers can’t be accelerated to say 95% the speed of light.

Only slight drawback is to the observers on Earth the journey would appear to take thousands of years. But you can’t have everything.
 

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Discussion Starter #14 (Edited)
Well it isn’t free energy.

If you check a kinetic energy calculator, if we have (2) 100kg ice skaters traveling together at 1m/s, they each have 50 joules kinetic energy.

If one pushes the other from behind with 100 joules, via conservation of momentum one loses 1m/s, the other gains 1 m/s.

The 100kg ice skater traveling 2m/s has 200 joules kinetic energy which is all the kinetic energy both skaters originally had, plus the 100 joule push.

KE = 1/2MV^2

If the skater that is still moving had gained their original 50 joules going down a ramp, they will lose 50 joules going up an identical ramp, leaving them with 150 joules kinetic energy which is the energy of the push, plus the kinetic energy of the other skater that stopped (66.6% of the energy from the push, and 33.3% of the energy from the lowered gravitational energy of the other skater.) More than 100% of the energy of the push transfers to the 2nd skater.
 

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Discussion Starter #16
It’s an oberth maneuver which certainly isn’t perpetual motion- it takes the gravitational potential energy of the water tank to move the vehicle forward, and geothermal energy to lift the water back out- no free lunch.

See below:


ABSTRACT
The role of work and mechanical energy in classical relativity has been a subject of renewed interest in this publication.1–4 Here we present a problem that illustrates the relationship between impulse and kinetic energy for a rocket-powered object that can also change its gravitational potential energy. The same introductory physics principles lead to a remarkable result when applied to the mechanics of spaceflight—the Oberth effect—whereby a small impulse can cause a large change in a rocket’s orbital energy without violating any conservation laws”

 

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All this extra tunneling for the gravitational energy battery is expensive work, and the moving parts will be subject to wear and tear. Maintenance & replacement of kit way below ground us going to be expensive and unpleasant. Far better to simplify this task. Ditch the extra tunnel stuff. Just have the minimum tunnel from A to B. Maglev, rails, vacuum filled or not as you wish. Use conventional maglev drive or electric motors, take your power from the grid, and treat the grid as your battery using it to regen slow your trains. Or synchronise one train arriving with one leaving, and cut out the middleman. Just like London Underground.

In a few years time, renewable energy will be relatively a lot cheaper than now. What don't you Iike about it?
 

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All this extra tunneling for the gravitational energy battery is expensive work, and the moving parts will be subject to wear and tear. Maintenance & replacement of kit way below ground us going to be expensive and unpleasant. Far better to simplify this task. Ditch the extra tunnel stuff. Just have the minimum tunnel from A to B. Maglev, rails, vacuum filled or not as you wish. Use conventional maglev drive or electric motors, take your power from the grid, and treat the grid as your battery using it to regen slow your trains. Or synchronise one train arriving with one leaving, and cut out the middleman. Just like London Underground.

In a few years time, renewable energy will be relatively a lot cheaper than now. What don't you Iike about it?
Yeah but good for interplanetary travel😁
 

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Essentially this is just another Hyperloop concept but with its energy source coming from its own power plant in the form of a complicated, expensive, and untried gravity/thermal process. I tend to agree with @HandyAndy that driving the transport module by existing maglev makes more sense.

If the system operator really wants to be self-sufficient in energy then a more practicable method would be to use the concept of a deep 'well' to access high thermal load to generate power that can be fed back to the grid to cancel any cost involved by driving the maglev.

By all means create a neutral cost system using the grid as a battery replenished by your own power plant. And if that happens to be new tech from deep heat then a second plant would be easy to install and to sell a lot of excess power as another profit centre.
 

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Discussion Starter #20 (Edited)
All this extra tunneling for the gravitational energy battery is expensive work, and the moving parts will be subject to wear and tear.
I should note somewhat similar tunnels are already presently built to obtain fossil energy- we call it “fracking”.




Eliminating the electrical grid from the equation reduces energy conversion steps and therefore improves energy efficiency which reduces costs over time as well as reduces the peak power load requirements for a given acceleration compared to a “conventional” hyperloop.
 
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