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Musk May Hold Competition for Tunneling Tech

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Elon Musk commented last week on the SpaceX-sponsored Hyperloop competition for engineering students, hinting that building tunnels for the technology is one of the trickiest pieces of the puzzle.

The 2019 competition was conducted in a mile-long test tube, with teams trying to reach the highest speed possible and safely bring themselves to a stop. Forty-two teams took part in this year’s contest, with the team from Technical University of Munich setting a record of 288 mph.

Musk said that next year’s competition will be held in a tube that’s over six miles long, with a curve instead of being in a straight line like the current test tube. But, eventually the plan is to build a longer Boring Company-dug tunnel.

“I don’t think we’ll have a long enough, straight enough underground tunnel a year from now but I think three years from now we definitely will,” Musk said at the competition. “So figure three years from now, we’ll at least have a couple miles.”

Musk said the company may enlist the help of students to solve the complicated task of tunneling.

“I think a tunneling thing would be pretty exciting,” Musk said. “Because as I just articulated the primary challenge is how do you tunnel effectively, especially how do you put in the reinforcing segments and get the dirt out effectively — it’s harder than it seems.”

Musk said a speed that is one-tenth that of walking – about a mile every three hours – would be a significant in his goal of building a network of underground transportation tunnels.

 
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Too bad the tunnel for the Super Conducting Super Collider in Texas couldn't be used. I believe 14 miles of the 52 mile circumference has been bored and abandoned. It may be flooded by now. The Austin Chalk is a great formation to bore through.
 
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I've been researching a land vehicle concept that takes advantage of a maneuver more commonly used in spacecraft propulsion-- the oberth maneuver, and an underground tunnel is the perfect environment for it.

I hope it can be built one day because it uses only sustainable fuel- namely a combination of gravitational potential energy, solar, and geothermal.

It requires an underground tunnel, magnetic levitation in a vacuum, like the hyperloop, but uses a different form of propulsion, and the tunnel has to be deep.

In essence it's a giant underground skateboard ramp, with an electric motor that pushes off a moving water tank instead of the ground to go faster than an airplane.

I’ve done some back of the napkin calculations to compare a Tesla Model S vs a land based oberth maneuver vehicle of the same mass & available energy. These are rough numbers just to give an ideal of the potential performance and compare with an automobile.

Long story short with it’s lithium battery pack partially charged up with 45kWh of energy, at roughly 70mph the 2250kg Tesla can do 135 miles in about 115.2 minutes (3mi/kWh). At 13.3 cents per kWh, it costs $5.98 for the energy. The ratio of kinetic energy to total kWH consumed with the Tesla on this trip is about 0.67%. (2250kg @ 70mph has 0.306kWh kinetic energy vs 45kWh consumed on the trip)

The land based oberth maneuver vehicle also weighs 2250kg and has 45kWh energy and follows a ramp (maglev in vacuum) which is 4.4km deep. It consists of a 1350kg passenger section (16.22kWh gravitational potential energy), 750kg water (9.01kWh gravitational potential energy), and a 150kg tank (1.8kWh gravitational potential energy) and 18.03kWh of electromechanical potential stored in capacitors in the track. The vehicle coasts down the ramp reaching about 294m/s at the bottom (657mph). The water tank is ahead of the passenger section on a long tether. On the flat section at the bottom of the ramp, the passenger section "reels in" then releases the tank with the 18.03kWh electromechanical potential, bringing the tank to a halt on the tracks (from conservation of momentum), transferring all its kinetic energy plus the mechanical impulse to the passenger section. After the mechanical impulse at the bottom of the ramp between the tank and passenger section, the 1350kg passenger section is traveling 1096mph, can go 135 miles in 7.38 minutes (about 15.6x faster). At $0.004/gallon the water costed $0.79 (less than 1/7th the energy cost). The ratio of kinetic energy to total kWH consumed with the land based oberth maneuver vehicle is about 100% (~99.3% more of the vehicle's potential energy was converted to kinetic energy).

After traveling up a second ramp back to the surface, the passenger section still has 28.8kWh of kinetic energy. The water is emptied from the tank at the bottom of the ramp and only the empty tank is lifted (the water is left to evaporate, and rock temp increases with depth). Factoring regen braking with 70% kinetic-to-kinetic efficiency at the destination, and using some of the recovered energy to recharge the capacitors, and some of the energy lift the empty tank, there is still a 0.36kWh excess of recovered from the regen above and beyond the energy used to push the vehicle at the ramp bottom. The excess energy comes from the lowered gravitational potential energy of the water left to evaporate at the bottom of the tunnel. It isn't perpetual motion because the vehicle requires gravitational potential energy to move itself forward, and geothermal and solar energy to lift the water out of the tunnel.

In summary the hypothetical land based oberth maneuver vehicle can theoretically go 15.6x faster, for less than 1/7th the energy cost, with the same amount of energy and mass as a Tesla Model S.

land-based-oberth-maneuver.jpg

oberth.jpg
 
(re-posted without images since I'm a new member and the first attempt didn't appear)

I've been researching a land vehicle concept that takes advantage of a maneuver more commonly used in spacecraft propulsion-- the oberth maneuver, and an underground tunnel is the perfect environment for it.

I hope it can be built one day because it uses only sustainable fuel- namely a combination of gravitational potential energy, solar, and geothermal.

It requires an underground tunnel, magnetic levitation in a vacuum, like the hyperloop, but uses a different form of propulsion, and the tunnel has to be deep.

In essence it's a giant underground skateboard ramp, with an electric motor that pushes off a moving water tank instead of the ground to go faster than an airplane.

I’ve done some back of the napkin calculations to compare a Tesla Model S vs a land based oberth maneuver vehicle of the same mass & available energy. These are rough numbers just to give an ideal of the potential performance and compare with an automobile.

Long story short with it’s lithium battery pack partially charged up with 45kWh of energy, at roughly 70mph the 2250kg Tesla can do 135 miles in about 115.2 minutes (3mi/kWh). At 13.3 cents per kWh, it costs $5.98 for the energy. The ratio of kinetic energy to total kWH consumed with the Tesla on this trip is about 0.67%. (2250kg @ 70mph has 0.306kWh kinetic energy vs 45kWh consumed on the trip)

The land based oberth maneuver vehicle also weighs 2250kg and has 45kWh energy and follows a ramp (maglev in vacuum) which is 4.4km deep. It consists of a 1350kg passenger section (16.22kWh gravitational potential energy), 750kg water (9.01kWh gravitational potential energy), and a 150kg tank (1.8kWh gravitational potential energy) and 18.03kWh of electromechanical potential stored in capacitors in the track. The vehicle coasts down the ramp reaching about 294m/s at the bottom (657mph). The water tank is ahead of the passenger section on a long tether. On the flat section at the bottom of the ramp, the passenger section "reels in" then releases the tank with the 18.03kWh electromechanical potential, bringing the tank to a halt on the tracks (from conservation of momentum), transferring all its kinetic energy plus the mechanical impulse to the passenger section. After the mechanical impulse at the bottom of the ramp between the tank and passenger section, the 1350kg passenger section is traveling 1096mph, can go 135 miles in 7.38 minutes (about 15.6x faster). At $0.004/gallon the water costed $0.79 (less than 1/7th the energy cost). The ratio of kinetic energy to total kWH consumed with the land based oberth maneuver vehicle is about 100% (~99.3% more of the vehicle's potential energy was converted to kinetic energy).

After traveling up a second ramp back to the surface, the passenger section still has 28.8kWh of kinetic energy. The water is emptied from the tank at the bottom of the ramp and only the empty tank is lifted (the water is left to evaporate, and rock temp increases with depth). Factoring regen braking with 70% kinetic-to-kinetic efficiency at the destination, and using some of the recovered energy to recharge the capacitors, and some of the energy lift the empty tank, there is still a 0.36kWh excess of recovered from the regen above and beyond the energy used to push the vehicle at the ramp bottom. The excess energy comes from the lowered gravitational potential energy of the water left to evaporate at the bottom of the tunnel. It isn't perpetual motion because the vehicle requires gravitational potential energy to move itself forward, and geothermal and solar energy to lift the water out of the tunnel.

In summary the hypothetical land based oberth maneuver vehicle can theoretically go 15.6x faster, for less than 1/7th the energy cost, with the same amount of energy and mass as a Tesla Model S.
 
Did I miss the part of your discussion where you calculated the g-force of this maneuver? If it is too great, you may be describing a project that could be suitable only for freight, not for humans.

I see now why you first attempted posting using graphics. I suggest bringing your post count up to speed quickly (Oberth maneuver probably not needed) so that you can do so. My first concern is the seeming large initial cost of creating a gravity well - that is, enhancing the z-axis relative to the x- & Y-axes - and how long it could take to recoup that expense.
 
Did I miss the part of your discussion where you calculated the g-force of this maneuver? If it is too great, you may be describing a project that could be suitable only for freight, not for humans.

My understanding so far is that limiting the slope of the ramp limits the negative g’s experienced by the passengers during the coast to the bottom while still giving the same kinetic energy at the bottom as long as the depth is the same.

Then using a longer tether limits the g-forces during the push at the bottom for a given energy transfer.

According to one source I found, at around 3-4km depth the rocks can be hot enough to turn water into steam, so I assume recouping the investment in the tunnel would depend on how lucrative it ends up being gaining access the geothermal energy source.