From Tesla to Hyperloop

[Jim200]

Elon has created quite a stir, and a lot of design problems, some of which will be solved in the prototype he plans to build. His idea of welded tubes is probably unworkable. I would favor flanged tubes bolted together with an appropriate gasket. This would allow quick construction and easy tube replacement if required. Placing an escape/maintenance door would also be easy. Thermal expansion is a big problem which is going to require expansion joints. However, a simple expansion joint will cause excessive leakage from the aeroski suspension and thus a splined joint with an elastomer or other design will be required. But you are still going to have to reduce the volume expansion and resulting pressure perturbation which could affect capsule stability. The axial compressor driven by an electric motor should have a long life as compared to a two stage axial compressor in a modern turbofan which are driven by hot exhaust gasses. However redundancy is a good idea here, as is with other components such the air tank. Swissmetro have studied evacuated tube transport for a long time and much info is online or in technical papers. Their plan was two 5 meter underground tunnels with 200 to 400 person capsules travelling at 300 mph using maglev. A pressure of about 1 psi was considered safe and achievable with standard vacuum pumps. Aerodynamics and the blocking factor were to be studied on an 800 ft, one tenth scale prototype called Histar, but I have not seen any results. Their capsule did not use an axial compressor even though aerodynamic friction is greater due to the higher pressure. Unfortunately, the Swiss government cut funding in 2009. // I suspect that Elon's capsule will use doors similar to those on aircraft. His idea for solar panels on the tubes is good idea near acceleration points, but is too expensive in other areas. Two solar farms connected to the grid would cost about one fourth as much. Another big problem is the transition from 0.147 psi tube pressure to atmospheric and vice versa at the terminals. This could be done by switching to parallel lines of pressurization/depressurization chambers. As you prepare to leave, you lower the pressure to that of the tube, check capsule parameters and go. The next incoming capsule should enter that same chamber and be allowed to rise to atmospheric pressure and the people can exit on an up escalator. A far out idea is to use a plasma window, but I don't know how well that works. There are a lot of problems to be solved, but little by little, solutions can be found.

[Phoebe Vet]

"I am looking for a lot of men who have an infinite capacity to not know what  can't be done."

Henry Ford 

[carnej1]

oltmannd

chrisjmiller

I've read the PDF, but can't find any reference to this problem: the compressor is a single point of failure.  The compressor is needed to:

1. enable the (barely) subsonic speeds by preventing a pressure wave building in front of the 'pod';
2. provide suspension through the air pads; and
3. provide air for the passengers.

There's a battery powerful enough to last the entire journey, so electrical power supply failure isn't a problem, but what if there were a mechanical failure? It seems to me the pod would rapidly decelerate to a halt (pressure build up in front and friction below) - I don't know if this would be rapid enough to cause injury, but it sounds unpleasant. Also the oxygen masks would be needed as there's no longer an air supply.

In addition, all the following pods would need to stop.  There's a reference to an 'emergency mechanical braking system' (4.5.3), though it isn't explained. It seems to suggest that pods could trundle to their destination on wheels, but that could take several hours, couldn't it?

Compressors are simple mechanically and well understood (jet engines), but they still fail occasionally.  If failure rates were comparable with passenger jets (a bit harsh, the environment is more benign than that), I estimate about one a month for the 'fleet' of pods.

Have I missed something? (I hope so, I like the concept.)

The paper just fleshes out the bare bones of the central technology, lots of details and "what-ifs" are considered without any fleshing out.  

For this particular problem, I can think of a few of approaches.  You could split the compressor load between two batteries and compressors, so if one fails, you can maintain your air suspension while the aero drag slows you down.  You could have some stored compressed gas to maintain suspension while the aero drag slows you down.  You could have some relatively low friction pads that would be sacrificed during an emergency stop.

I suspect the cost to build this thing won't be 1/10th the cost of HSR once you figure out and engineer all the details.

I'd also be much happier if the tubes were transparent.  Perhaps they could be extruded Lexan with the solar panels embedded?

Some other questions:

How do you deal with the need to repair/replace a tube pylon/support or tube section?  Does any failure put the whole thing out of commission?

Ditto for any leaks?  What's the cost of keeping the partial vacuum up when there are more than a few trivial leaks?

How do you deal with thermal expansion/contraction?  Expansion joints?  Do force compression/tension?  Normal pipeline tricks don't apply here.

 Transparent tubes like in the movie "Logan's Run"?

 I doubt current materials are strong enough for this application. Maybe when materials technology can produce clear diamonoid tubing but neither you nor I will be around then..

[oltmannd]

chrisjmiller

I've read the PDF, but can't find any reference to this problem: the compressor is a single point of failure.  The compressor is needed to:

1. enable the (barely) subsonic speeds by preventing a pressure wave building in front of the 'pod';
2. provide suspension through the air pads; and
3. provide air for the passengers.

There's a battery powerful enough to last the entire journey, so electrical power supply failure isn't a problem, but what if there were a mechanical failure? It seems to me the pod would rapidly decelerate to a halt (pressure build up in front and friction below) - I don't know if this would be rapid enough to cause injury, but it sounds unpleasant. Also the oxygen masks would be needed as there's no longer an air supply.

In addition, all the following pods would need to stop.  There's a reference to an 'emergency mechanical braking system' (4.5.3), though it isn't explained. It seems to suggest that pods could trundle to their destination on wheels, but that could take several hours, couldn't it?

Compressors are simple mechanically and well understood (jet engines), but they still fail occasionally.  If failure rates were comparable with passenger jets (a bit harsh, the environment is more benign than that), I estimate about one a month for the 'fleet' of pods.

Have I missed something? (I hope so, I like the concept.)

The paper just fleshes out the bare bones of the central technology, lots of details and "what-ifs" are considered without any fleshing out.  

For this particular problem, I can think of a few of approaches.  You could split the compressor load between two batteries and compressors, so if one fails, you can maintain your air suspension while the aero drag slows you down.  You could have some stored compressed gas to maintain suspension while the aero drag slows you down.  You could have some relatively low friction pads that would be sacrificed during an emergency stop.

I suspect the cost to build this thing won't be 1/10th the cost of HSR once you figure out and engineer all the details.

I'd also be much happier if the tubes were transparent.  Perhaps they could be extruded Lexan with the solar panels embedded?

Some other questions:

How do you deal with the need to repair/replace a tube pylon/support or tube section?  Does any failure put the whole thing out of commission?

Ditto for any leaks?  What's the cost of keeping the partial vacuum up when there are more than a few trivial leaks?

How do you deal with thermal expansion/contraction?  Expansion joints?  Do force compression/tension?  Normal pipeline tricks don't apply here.

[chrisjmiller]

I've read the PDF, but can't find any reference to this problem: the compressor is a single point of failure.  The compressor is needed to:

1. enable the (barely) subsonic speeds by preventing a pressure wave building in front of the 'pod';
2. provide suspension through the air pads; and
3. provide air for the passengers.

There's a battery powerful enough to last the entire journey, so electrical power supply failure isn't a problem, but what if there were a mechanical failure? It seems to me the pod would rapidly decelerate to a halt (pressure build up in front and friction below) - I don't know if this would be rapid enough to cause injury, but it sounds unpleasant. Also the oxygen masks would be needed as there's no longer an air supply.

In addition, all the following pods would need to stop.  There's a reference to an 'emergency mechanical braking system' (4.5.3), though it isn't explained. It seems to suggest that pods could trundle to their destination on wheels, but that could take several hours, couldn't it?

Compressors are simple mechanically and well understood (jet engines), but they still fail occasionally.  If failure rates were comparable with passenger jets (a bit harsh, the environment is more benign than that), I estimate about one a month for the 'fleet' of pods.

Have I missed something? (I hope so, I like the concept.)

[carnej1]

john_edwards

After  every lawyer in America is dead this possibly has a chance, science not withstanding.  We will all be NIMBYs when they want your house, your town, your city because a support is need right there as it has the tube needs to be in a straight line.  I'd be willing to bet the approval process to move power lines, national parks, lakes, and who knows what will take a century at least.  And how noisy will it be on the outside as it whizzes by at 600+mph?

Good point about Nimby's but if such a thing were built why would you think it would be loud?

It's a sealed tube with much of the air pumped out and the vehicle generates very little friction so I don't see what would cause excessive noise..

[oltmannd]

BaltACD

john_edwards

After  every lawyer in America is dead this possibly has a chance, science not withstanding.  We will all be NIMBYs when they want your house, your town, your city because a support is need right there as it has the tube needs to be in a straight line.  I'd be willing to bet the approval process to move power lines, national parks, lakes, and who knows what will take a century at least.  And how noisy will it be on the outside as it whizzes by at 600+mph?

His presentation identified Interstate rights of ways as being where initial construction should be - that being the case, I don't know how well the concept would mesh with the turns that exist on the Interstates.  70 MPH and 700 MPH are worlds apart.

There's quite a bit in the paper about alignment.  The worst problem is the southern end approach to the LA basin. 

[Schuylkill and Susquehanna]

PETITNJ

There is a slight error in your calculations.  The acceleration due to gravity is 9.8 meters per second squared, or 32 feet per second squared.  It's easy to get them mixed up - I've done it a few times.

10 feet per second^2 is roughly 0.3 gravities, which is not that bad, really.  A quick acceleration onto a highway in a car will give you and acceleration of more than 0.3 G.

Based on 0.3 G, the total acceleration experienced by the rider would be about 1.1 G.  (1 G down, 0.3 G back, use the Pythagorean Theorem.)

This is a really great idea, but likely nothing will come of it because of problems getting permits, buying land, governmental restrictions, and funding.  Too bad.  Maybe in 50 years we will have something like this.  This is definitely and idea ahead of its time.

S&S

[petitnj]

For a "back of the envelop" calculation of the acceleration needed we propose:

Accelerating for 1/2 the trip (15 minutes = 1000 seconds to make life easy)

Distance to accelerate 1000 miles (5,000,000 feet again to make life easy)

d = 1/2 a t^2 so the acceleration needed is a = 2 d / t^2  = 10,000,000 feet/ (1,000 * 1,000) sec^2

a = 10 ft/sec^2 which is equal to gravity. Not a problem to accelerate faster than this and reach a cruising speed faster. 

[BaltACD]

john_edwards

After  every lawyer in America is dead this possibly has a chance, science not withstanding.  We will all be NIMBYs when they want your house, your town, your city because a support is need right there as it has the tube needs to be in a straight line.  I'd be willing to bet the approval process to move power lines, national parks, lakes, and who knows what will take a century at least.  And how noisy will it be on the outside as it whizzes by at 600+mph?

His presentation identified Interstate rights of ways as being where initial construction should be - that being the case, I don't know how well the concept would mesh with the turns that exist on the Interstates.  70 MPH and 700 MPH are worlds apart.

[oltmannd]

You can read the whole paper here: http://www.teslamotors.com/sites/default/files/blog_images/hyperloop-alpha.pdf

[Phoebe Vet]

Deggesty

As Larry (Tree) remarked almost a month ago, there is the problem of acceleration and deceleration that seems to be ignored in the promotion of this means of transit. I saw nothing of it in the account in this morning's paper.

You regularly sit in your automobile as you accelerate from near 0 to 60 or 70 mph entering the highway.  Is that uncomfortable?  It takes you about a quarter of a mile.  If that same rate of acceleration is maintained for 4 more miles you are at his promised speed.

This argument is a red herring.

[oltmannd]

Jim200

Elon said that it is a Concorde and railgun and with an air hockey table. That suggests to me that it is a Mach 2 aircraft mounted on a railgun with an air cushion and launched in a hyperloop, high altitude ballistic loop, to the target city. It could land conventionally like the space shuttle, or even better, align with the target city's railgun and recharge the railgun's supercapacitors.

Not close.  Read the guy's paper that came out today.

[oltmannd]

john_edwards

After  every lawyer in America is dead this possibly has a chance, science not withstanding.  We will all be NIMBYs when they want your house, your town, your city because a support is need right there as it has the tube needs to be in a straight line.  I'd be willing to bet the approval process to move power lines, national parks, lakes, and who knows what will take a century at least.  And how noisy will it be on the outside as it whizzes by at 600+mph?

Doesn't have to be dead straight.  The alignment of I-5 is mostly good enough.  Noise is a good question, but since tube is partially evacuated and no direct contact from vehicle to tube, it might not be very noisy.

[oltmannd]

overall

Some of you were talking about decelaration above. I have a question; just how do you get it stopped exactly?

Two ways.  You can use the linear induction motor in reverse.  Or, there is an emergency friction brake of some sort.  Either way, you don't want to do more than about 0.1G for regular service braking.

[john_edwards]

After  every lawyer in America is dead this possibly has a chance, science not withstanding.  We will all be NIMBYs when they want your house, your town, your city because a support is need right there as it has the tube needs to be in a straight line.  I'd be willing to bet the approval process to move power lines, national parks, lakes, and who knows what will take a century at least.  And how noisy will it be on the outside as it whizzes by at 600+mph?

[oltmannd]

It used a linear induction motor to get things moving with occasional mid-route boosts.  Lots of roller coasters do this.  Nothing weird or new about it.  Acceleration can be as gentle as needed.  Actually, gentle is easier - lower power requirement.

It uses suspension like an air bearing. Nothing weird or new here, either.  Just bigger.

It uses a suspended tube for a guideway.  This is new.  It needs the guideway to be partially evacuated.  This is really new.  It uses a compressor on the front end to "suck" in the air in front of the train and push it out the back through the air suspension, so the thing essentially coasts with little friction between induction motor boosts.  

The suspended tube guideway is designed for easy alignment and to be earthquake tolerant.

There are a gazillion details where the devil can pop up.  He's thought through a bunch of them but has "wave the hands" kinds of answers.  Fair enough.  This isn't a complete design - just a concept/feasibility study at this point.

It's pretty wild....but not crazy.  I think I'd rather spend the day and drive than climb aboard.....but that's what people said when RRs first appeared, too.

[overall]

Some of you were talking about decelaration above. I have a question; just how do you get it stopped exactly?

[BaltACD]

carnej1

Deggesty

As Larry (Tree) remarked almost a month ago, there is the problem of acceleration and deceleration that seems to be ignored in the promotion of this means of transit. I saw nothing of it in the account in this morning's paper.

The design Musk is promoting has a top speed of around 750 MPH which is barely transonic (MACH 1), the G-load would not require "Space Shuttle harnesses" for the passengers....

 As far as some hypothetical far future 3,000 MPH "transatlantic tubetrain", it would have to be designed with long acceleration/deceleration phases, it could not launch out of the station like a horizontal Saturn V rocket..

 Regardless,  the technological and financial obstacles that must be overcome for any such system to be built are so huge that we may as well be debating Starship designs...

While I realize 'passengers' would not accept it, Top Fuel and Funny Car drag racing cars routinely accelerate from 0 to in excess of 300 MPH in less than 1000 feet and under 5 seconds.  (because of the speeds being reached by these top class cars - the competitive track has been reduced from 1320 feet {1/4 mile} to 1000 feet several years ago).  Needless to say, such acceleration would not be conducive to breaking out one's personal electronics and accesing Wi-Fi.

[vsmith]

I believe what this will be most successful at is separating investors from their money.

[carnej1]

Deggesty

As Larry (Tree) remarked almost a month ago, there is the problem of acceleration and deceleration that seems to be ignored in the promotion of this means of transit. I saw nothing of it in the account in this morning's paper.

The design Musk is promoting has a top speed of around 750 MPH which is barely transonic (MACH 1), the G-load would not require "Space Shuttle harnesses" for the passengers....

 As far as some hypothetical far future 3,000 MPH "transatlantic tubetrain", it would have to be designed with long acceleration/deceleration phases, it could not launch out of the station like a horizontal Saturn V rocket..

 Regardless,  the technological and financial obstacles that must be overcome for any such system to be built are so huge that we may as well be debating Starship designs...

[Murphy Siding]

     Wouldn't it be more economical, and only slightly less of a technical reach, to just use Doc Brown's machine from Back to the Future?

[Deggesty]

As Larry (Tree) remarked almost a month ago, there is the problem of acceleration and deceleration that seems to be ignored in the promotion of this means of transit. I saw nothing of it in the account in this morning's paper.

[Phoebe Vet]

This country was built by dreamers, and every one of them was mocked by people who said it couldn't be done.

 

“People who say it cannot be done should not interrupt those who are doing it.” 

    ―     George Bernard Shaw

[Ulrich]

CSSHEGEWISCH

Elon Musk strikes me as a dreamer who is enamored of "Gee Whiz" technology and thinks that human progress occurs only when that technology is developed, whether there is a demand for it or not.  He has opined that human progress slipped when the Concorde was retired from commercial airline service and a replacement supersonic airliner had not been developed.

 

They said the same about the Wright Brothers and their various contemporaries who so very foolishly proposed to fly people through the air at hundreds if not thousands of feet above the ground. Imagine that, and from two high school dropouts who owned a bicycle repair shop.  If anything, Musk may be slightly ahead of his time. This will happen, IMHO.

[CSSHEGEWISCH]

Elon Musk strikes me as a dreamer who is enamored of "Gee Whiz" technology and thinks that human progress occurs only when that technology is developed, whether there is a demand for it or not.  He has opined that human progress slipped when the Concorde was retired from commercial airline service and a replacement supersonic airliner had not been developed.

[jclass]

Loopie Doopie Doopie Doop...Doop Doop Dee Doop.

http://www.businessweek.com/articles/2013-08-12/revealed-elon-musk-explains-the-hyperloop

[Jim200]

Elon said that it is a Concorde and railgun and with an air hockey table. That suggests to me that it is a Mach 2 aircraft mounted on a railgun with an air cushion and launched in a hyperloop, high altitude ballistic loop, to the target city. It could land conventionally like the space shuttle, or even better, align with the target city's railgun and recharge the railgun's supercapacitors.

[carnej1]

tree68

carnej1

Methinks that actually raising enough private investor money to build anything like this is the biggest issue...

I don't disagree - but even if the money was there, one has to get past the idea of needing space-shuttle type restraints on both ends of the trip.

From what I've read about the various "tube train" hyper high- speed proposals the acceleration/decelleration phases are supposed to take place over a long distance and period of time so the G forces acting on passengers would supposedly not be excessive. Of course, that may pose some difficulty if there is a high volume of traffic in the tube you are traveling in, a "rear ender" would be ugly, to say the least...