8 ms·

But that's at a pressure of 100Pa (1/1000 atm). How much power does it take to maintain a vacuum of 1/1000atm in a tube hundreds of miles long? It seems this

by acadien 13y ago

But that's at a pressure of 100Pa (1/1000 atm). How much power does it take to maintain a vacuum of 1/1000atm in a tube hundreds of miles long? It seems this point is skipped over in the whitepaper, so perhaps its negligible. Edit: yes I was referring to the power to sustain a vacuum in a leaky system, of course no power is required to maintain a vacuum in a perfectly sealed system :)

btgeekboy 13y ago
I think that's handled by the rooftop solar cells.
- rozap 13y ago
  Right, but that power is coming from somewhere, which costs something. Not a deal breaker, but saying "only 134hp" is sort of missing the point.
ansible 13y ago
How much power does it take to maintain a vacuum of 1/1000atm in a tube hundreds of miles long? It doesn't require any power, if there are no leaks. The power required will be determined by the amount of leakage that is considered tolerable to the system.
- nawitus 13y ago
  There'll certainly be leaks, it's another question how much.
- hristov 13y ago
  But there will be leaks. He himself said there would be leaks and he would use commercial pumps to continuously keep the vacuum.
- HCIdivision17 13y ago
  Regular mechanical pumps can haul gas to pressures of a hPa. Any lower, and you're looking at something like turbomolecular pumps. (And efficiency may call for a second stage of specialized mechanical pumps.) But in my experience, small mechanical leaks are usually of the order of a hPa or so, meaning no high vacuum tech will be needed. Just a fleet of giant blowers and mechanical pumps. (I worked on a wide area sputtering machine for a few years with a few hundred HP of mechanical backing pumps for about a hundred foot long chamber with a 10 sq foot average cross section (order of magnitude error for anonymity ;)) The machine would haul down to 10 or 1 hPa with leaks you could _hear_. So yeah, it could work practically, especially if it's a welded system and not a giant mess of bolts and o-rings.
HCIdivision17 13y ago
To me, a 1/1000 atmosphere vacuum system IS a really leaky machine :) Anecdotally, the machine I used to work on would gleefully chew on that for hours idling while we scrambled to find the hiss on the system. It made an awesome sound when it ground into the atmospheric pressure on initial pumpdown, but at about 1/100 atmo it got bored (mere minutes), and without additional high speed stages the mechanical pumps would backwash at 1/10000 atmo (though it would take a while to get from 1 hPa to 0.1 hPa, many multiples of the time it to to get from 100 hPa to 1 hPa). Edit: fixed units (0.001hPa is still leaky for base pressures but a completely different thing from 0.001atm).
- Balgair 13y ago
  I used to work with a system of about 1m^3, 2 little mechanical pumps would get you to 10E-6 atm or so. A turbo pump got you down to 10E-9 or there abouts. The door on the thing was about 2.5 feet in diameter, with a big ol' O-ring that would get twisted and tangled all the time (we broke it once, gorilla glue worked just fine to fix it). I also second the great sound they made. It was like 2 very angry horses going 'Brahbrahbrahbrahbrahrbah...' getting quieter all the time. If the system will be welded together that'll reduce the leaks quite a bit and the maintenance too, which I think will be the biggest problem. It's not making it work, it's keeping the thing working that will eat up the costs. Eventually, as the thing ages, you'll have bigger and bigger leaks. Figuring out how to deal with that will be a moon-shot on it's own.
  - shabble 13y ago
    I imagine you might be able to locate flaws with a custom capsule along the lines of a pipeline pig[1]. It would be exceptionally hard to actually fix it from the inside whilst travelling, so you either need to do it from the outside (which requires site access and elevation gear), or bypass/shut down the tube and fix internally. [1] https://en.wikipedia.org/wiki/Pigging#Intelligent_pigging https://en.wikipedia.org/wiki/Pigging#Intelligent_pigging
    - HCIdivision17 13y ago
vidarh 13y ago
Sections 4.2 and 4.5. It estimates the cost of vacuum pumps for the tube and stations at $260 million. I haven't seen if they've broken out costs to maintain the pumps, but it specifically also mentions compensating for minor leaks with higher pump capacity to be able to continue operating and fixing smaller leaks as part of routine maintenance.

by acadien 13y ago

btgeekboy 13y ago

I think that's handled by the rooftop solar cells.

rozap 13y ago
Right, but that power is coming from somewhere, which costs something. Not a deal breaker, but saying "only 134hp" is sort of missing the point.

ansible 13y ago

How much power does it take to maintain a vacuum of 1/1000atm in a tube hundreds of miles long? It doesn't require any power, if there are no leaks. The power required will be determined by the amount of leakage that is considered tolerable to the system.

nawitus 13y ago
There'll certainly be leaks, it's another question how much.
hristov 13y ago
But there will be leaks. He himself said there would be leaks and he would use commercial pumps to continuously keep the vacuum.
HCIdivision17 13y ago
Regular mechanical pumps can haul gas to pressures of a hPa. Any lower, and you're looking at something like turbomolecular pumps. (And efficiency may call for a second stage of specialized mechanical pumps.) But in my experience, small mechanical leaks are usually of the order of a hPa or so, meaning no high vacuum tech will be needed. Just a fleet of giant blowers and mechanical pumps. (I worked on a wide area sputtering machine for a few years with a few hundred HP of mechanical backing pumps for about a hundred foot long chamber with a 10 sq foot average cross section (order of magnitude error for anonymity ;)) The machine would haul down to 10 or 1 hPa with leaks you could _hear_. So yeah, it could work practically, especially if it's a welded system and not a giant mess of bolts and o-rings.

HCIdivision17 13y ago

To me, a 1/1000 atmosphere vacuum system IS a really leaky machine :) Anecdotally, the machine I used to work on would gleefully chew on that for hours idling while we scrambled to find the hiss on the system. It made an awesome sound when it ground into the atmospheric pressure on initial pumpdown, but at about 1/100 atmo it got bored (mere minutes), and without additional high speed stages the mechanical pumps would backwash at 1/10000 atmo (though it would take a while to get from 1 hPa to 0.1 hPa, many multiples of the time it to to get from 100 hPa to 1 hPa). Edit: fixed units (0.001hPa is still leaky for base pressures but a completely different thing from 0.001atm).

Balgair 13y ago
I used to work with a system of about 1m^3, 2 little mechanical pumps would get you to 10E-6 atm or so. A turbo pump got you down to 10E-9 or there abouts. The door on the thing was about 2.5 feet in diameter, with a big ol' O-ring that would get twisted and tangled all the time (we broke it once, gorilla glue worked just fine to fix it). I also second the great sound they made. It was like 2 very angry horses going 'Brahbrahbrahbrahbrahrbah...' getting quieter all the time. If the system will be welded together that'll reduce the leaks quite a bit and the maintenance too, which I think will be the biggest problem. It's not making it work, it's keeping the thing working that will eat up the costs. Eventually, as the thing ages, you'll have bigger and bigger leaks. Figuring out how to deal with that will be a moon-shot on it's own.
- shabble 13y ago
  I imagine you might be able to locate flaws with a custom capsule along the lines of a pipeline pig[1]. It would be exceptionally hard to actually fix it from the inside whilst travelling, so you either need to do it from the outside (which requires site access and elevation gear), or bypass/shut down the tube and fix internally. [1] https://en.wikipedia.org/wiki/Pigging#Intelligent_pigging https://en.wikipedia.org/wiki/Pigging#Intelligent_pigging
  - HCIdivision17 13y ago

vidarh 13y ago

Sections 4.2 and 4.5. It estimates the cost of vacuum pumps for the tube and stations at $260 million. I haven't seen if they've broken out costs to maintain the pumps, but it specifically also mentions compensating for minor leaks with higher pump capacity to be able to continue operating and fixing smaller leaks as part of routine maintenance.