From Tesla to Hyperloop

[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.

[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..

[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 

[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.