Space Things

[Dadhawk]

Originally Posted by Irace86.2.0

He said the larger command module allows for more life support systems for much more time, and it allowed them to test the systems more, but there are other reasons, as it allows for four astronauts instead of three and more redundancies, more time on the ground for experiments, and better comfort too

I mistyped command module, when I meant service module, have now corrected.

So really what I was trying to say is that I get why the made the command module larger, but that doesn't explain why the service module couldn't have grown equally, particularly given there is no LEM and the rocket is more powerful than a Saturn V.

[ZDan]

Originally Posted by Irace86.2.0

I don't know if you are confused or I am, but just so we are clear, the Hyperloop isn't a giant air hockey surface with air coming up from the walls of the tube.

Yeah, I know. The point remains the same. Long train, being supported on air bearings, with air scavenged from limited frontal area, in a low-pressure environment. it's just a stupid idea which none of the hyperloop peeps have tried to develop. Because it is a dumb idea that won't work.

The saying goes, would you rather be in a submarine or in a boat during a tsunami? An underground train in a tunnel surrounded by solid rock, especially one that is pinned to the sides of the tube, is much sturdier than a train moving on the surface on tracks or that's elevated.

In an earthquake, the "solid rock" you seem to think is immovable, MOVES. And your puny "low pressure" tubes will move with the moving earth. It is absurd to think that tubes underground should somehow be immune from this as aircraft are immune from tidal waves. It's even worse down here, any seismic movement is by god going to wreck any man-made structures.

As the RAND article mentions, this would be a massive task, but the economics would pay out over a ground/elevated train, and the benefits over commercial air travel would be clear. Why hasn't it been done?

Because it's a fecking dumb idea that won't work.

[Spuds]

Hyperloop: I've done some quick math, and I haven't done this in years so I could be wrong. Assuming something the size of a 737-700 cabin that weighs half as much as the empty plane, and with no losses to drag/friction/heat/etc, the object would need to be moving at a bit over 1000mph at standard temperature and pressure (sea level, 0°C) to convert enough dynamic pressure into downward static pressure to achieve lift.

Again, 0 factor of safety. 0 losses. 0 payload. Sea level pressure. The math gets way worse when you add reality into the process.

PS, that's about Mach 1.3. Good luck with shockwaves.

Edit, something seems fishy, I will look back into this tonight.

[Spuds]

I have a minute to list assumptions:

Object is a cylinder
5m diameter
30m length
20,000kg mass
G=10m/s^2

Atmosphere is assumed Earth at STP
273K Temperature
101kpa Pressure
1.2kg/m^3 air density
340m/s speed of sound

Let's assume all moving air from the front of the object is redirected to a series of perpendicular holes along the bottom half of the object, increasing the static pressure against a near wall. We will ignore the classic form of Bernoulli's equations because that would just reduce the pressure around the outside of the object and be counterproductive. Probably not the easiest way to do it, but welcome to my head.

Total pressure of the inlet (TPI) is equal to total pressure of the perpendicular outlet (TPO). Losses and compressible flow properties are ignored. Atmospheric pressure is also ignored in this configuration.

TPI = TPO

1.2*(v^2)/2 + 0 = 0 + 20,000*10/(5*30)

v = 47m/s which is ~ 100mph

I was indeed off by a 10 factor somewhere. However, that's 100mph against a sealed wall, with no airflow going out. The second a crack forms is a different regime with different assumptions.

I'll be back...

[Irace86.2.0]

Originally Posted by Dadhawk

I mistyped command module, when I meant service module, have now corrected.

So really what I was trying to say is that I get why the made the command module larger, but that doesn't explain why the service module couldn't have grown equally, particularly given there is no LEM and the rocket is more powerful than a Saturn V.

Your guess is as good as mine. Maybe safety for a larger margin for error. Hard to know.

[Irace86.2.0]

Originally Posted by ZDan

Yeah, I know. The point remains the same. Long train, being supported on air bearings, with air scavenged from limited frontal area, in a low-pressure environment. it's just a stupid idea which none of the hyperloop peeps have tried to develop. Because it is a dumb idea that won't work.

In an earthquake, the "solid rock" you seem to think is immovable, MOVES. And your puny "low pressure" tubes will move with the moving earth. It is absurd to think that tubes underground should somehow be immune from this as aircraft are immune from tidal waves. It's even worse down here, any seismic movement is by god going to wreck any man-made structures.

Because it's a fecking dumb idea that won't work.

It is an interesting design choice to run a large “hypothetical” mouth on this Virgin Hyperloop pod. Maybe they will add a turbine in the front for reduced drag or for air bearings. Who knows?

Meanwhile, there a few different projects using vacuum tubes. The RAND article says achieving 0.5 bar with air pumps would not be a challenge. The loading doc could extend out like airplanes do and create an air tight junction to board.

How much PSI is needed for lift, and how much is available using a turbine at say 1000 mph. The theoretical limit proposed by RAND and others is multiples of Mach speeds. Maybe Spuds will figure this out, but lots of money is pouring into these projects worldwide, so I don’t think we can dismiss the idea of a low pressure tube concept so frivolously. Knowing China, the will likely do it first.

BTW, there are tunnels under oceans. Subways and underground tunnels do far better than massive structures swaying above ground. There is little mass and a lot of structural support with few things to toss about. Unless it is directly on a fault line that shears, it should be fine. Underground tunnels would be much better than above ground for simplicity, safety, permitting, and so on.



https://innovationorigins.com/en/hyp...-in-operation/

https://www.scmp.com/news/china/scie...land-transport

[Spuds]

Originally Posted by Irace86.2.0

It is an interesting design choice to run a large “hypothetical” mouth on this Virgin Hyperloop pod. Maybe they will add a turbine in the front for reduced drag or for air bearings. Who knows?

Meanwhile, there a few different projects using vacuum tubes. The RAND article says achieving 0.5 bar with air pumps would not be a challenge. The loading doc could extend out like airplanes do and create an air tight junction to board.

How much PSI is needed for lift, and how much is available using a turbine at say 1000 mph. The theoretical limit proposed by RAND and others is multiples of Mach speeds. Maybe Spuds will figure this out, but lots of money is pouring into these projects worldwide, so I don’t think we can dismiss the idea of a low pressure tube concept so frivolously. Knowing China, the will likely do it first.

BTW, there are tunnels under oceans. Subways and underground tunnels do far better than massive structures swaying above ground. There is little mass and a lot of structural support with few things to toss about. Unless it is directly on a fault line that shears, it should be fine. Underground tunnels would be much better than above ground for simplicity, safety, permitting, and so on.



https://innovationorigins.com/en/hyp...-in-operation/

https://www.scmp.com/news/china/scie...land-transport

Wait, are you talking about a vacuum tube using pressure differential to push/pull a vehicle on rails or using ram air to lift a vehicle drawn through the tube by magnets?

[bcj]

Where would one dispose of the tailings from a 5meter x 1000kilometer hole in the ground?

[Irace86.2.0]

Originally Posted by Spuds

Wait, are you talking about a vacuum tube using pressure differential to push/pull a vehicle on rails or using ram air to lift a vehicle drawn through the tube by magnets?

The proposal is below, but different companies are using different techniques for propulsion. The basic idea is to use a low pressure environment with a fan on the front of the pod to divert the air resistance from the front of the pod to the rear and to compress it to create an air bearing on the feet.

I feel like I am the only one here that has actually seen this document. Seems like the critics have only watched interviews and read news headlines and not this document below because all I have heard is the most exaggerated or basic explanations for this concept (a la ThunderF00t et al). Yes, he is not the origin of this idea like the critics like to remind everyone, but this document seems specific enough, even though it is simple enough, that it seems like a creation from him and his team. I mean, I read the RAND document, which is also sighted in the document below, and this setup seems very much like a Tesla product with induction motors, batteries, solar, etc.

https://www.tesla.com/sites/default/...loop-alpha.pdf

[Irace86.2.0]

Originally Posted by bcj

Where would one dispose of the tailings from a 5meter x 1000kilometer hole in the ground?

Anywhere. It isn't a lot. We have a lot of empty space for piles of dirt.

5 meter hole is pi x 2.5^2 x 1000 x 1000 = roughly 20 million cubic meters. Sounds like a lot until you realize that it is equivalent to 0.02 cubic kilometers, which is a square 0.27 km x 0.27 km x 0.27 km, or it is equivalent to 5 trillion US gallons, and then for reference, Lake Tahoe has an average of 35 trillion gallons in it, so you could build seven tunnels and dump it all in Lake Tahoe, and from the perspective of looking down on the whole country, you might not notice a dot went from blue to brown.

[ZDan]

Yeah, Virgin Hyperloops is just streaming along, eh?

Honestly, I've given it no more than 15 minutes of consideration to decide it is a stupid idea that is going nowhere. Others have invested years and 100s of millions of dollars to get us where?

I'm open to being surprised but so far I will stand by my for-free initial assessment. It is a dumb idea that won't work.

[Irace86.2.0]

Originally Posted by ZDan

Yeah, Virgin Hyperloops is just streaming along, eh?

Honestly, I've given it no more than 15 minutes of consideration to decide it is a stupid idea that is going nowhere. Others have invested years and 100s of millions of dollars to get us where?

I'm open to being surprised but so far I will stand by my for-free initial assessment. It is a dumb idea that won't work.

So you are admitting that before you spent all this time criticizing the concept of a hyper loop, you had only considered it for 15 minutes before deciding it was a stupid idea, and that you have never even read up on any of these proposals below? Interesting...for an aerospace engineer.

https://www.tesla.com/sites/default/...loop-alpha.pdf
https://www.rand.org/content/dam/ran...2008/P4874.pdf
http://et3.nl/images/upload/file/ET3...posal013au.pdf

I would be shocked if China or Dubai doesn't have a low-friction, low-pressure, tubed train under construction in the next five to ten years. Dubai is wanting to do an underwater train to India, and they want to do a train from Dubai to Abu Dhabi, with talks of both potentially being hyper-loop-style trains.

https://interestingengineering.com/t...t-train-mumbai

[Irace86.2.0]

@Spuds

"Also, the MagLev doesn't need a power supply to keep levitating. It will keep levitating as long as the speed is over 150km/h (93mph). So when it slows down, the tires will drop down, and the carriage will land as normal."

That statement is pretty interesting because the train clearly takes aerodynamics seriously with the shape of that nose, which seems like it would force the train's nose down, and yet such a heavy train is able to achieve lift at just shy of 100 mph. The Hyperloop proposal says up to 60% of the air would just pass through the fan system out the back, generating a little thrust, but ultimately it would only take a smaller percentage to generate lift, and considering the maglev train, even in a low-pressure tube, that seems reasonable.

[ZDan]

Originally Posted by Irace86.2.0

So you are admitting that before you spent all this time criticizing the concept of a hyper loop, you had only considered it for 15 minutes before deciding it was a stupid idea, and that you have never even read up on any of these proposals below? Interesting...for an aerospace engineer.

If anyone wants to pay me for my time I would be happy to investigate further.

Difficult to take your first link seriously, complaining about high speed rail plans but offering up magic dust as a superior alternative. Yeah, well, whaddya got? Nothing...

VHST concept from 1972 is cute. But geez, you'd think if it was workable we would have something by now?

OK, let's see what China and/or Dubai come up with.

Do I think it would be cool? Yeah. Do I think it's any kind of practical solution to moving humans around? No, I do not. Prove me wrong, children, prove me wrong!