> Note that downthread they've already moved the goalpost from "these pumps are technologically impossible" to "but they'll need a lot of them!"
I never said vacuum pumps are "technologically impossible". My original comment references the Space Power Facility [1] and categorises the vacuum problem as an engineering problem. A hard one, but engineering nonetheless.
The comment you link to [2] replies to someone claiming the original white paper calls for a 22:1 atmosphere:tube pressure ratio. I pointed out that the figure they're referencing, Figure 11, discusses the capsule and not the tube.
I'm skeptical about the economics of de-pressurising the tube, but that's an engineering problem and I've always held it as such. The materials problem is the thermal expansion of the top of the tube relative to the bottom.
>The comment you link to [2] replies to someone claiming the original white paper calls for a 22:1 atmosphere:tube pressure ratio. I pointed out that the figure they're referencing, Figure 11, discusses the capsule and not the tube.
I happen to be that someone. :) You were talking about state-of-the-art axial compressors (the GEnx-2B67), so I assumed you were talking about the axial compressor on the front of the pod. Mea culpa. But then you drew an analogy to the pressures in the SPS ("To get a sense of the engineering differences between 6:1 and 1,000:1..."), as if the Hyperloop people were trying to make a 1000:1 axial compressor. As I pointed out in my reply,[1] rotary vane compressors can easily maintain those pressures.
>The materials problem is the thermal expansion of the top of the tube relative to the bottom.
If that were really a problem, no pipelines of any kind could be built. Again thermal expansion joints are the solution, since with the abandonment of air-ski levitation the pod walls no longer have a requirement to be ultra-smooth. Tiny leakage on these joints is fine, since it will be made up for by the pumps located along the track.
> If that were really a problem, no pipelines of any kind could be built
The Trans-Alaska Pipeline system, which I believe is the largest at least in the United States, is 1.2m in diameter [1]. We're talking about a pipe almost 3 times wider that needs to hold itself against the atmosphere and keep capsules neatly contained.
Side note: long pipelines zig-zag to allow for thermal expansion and contraction [2]. You can't do that with the Hyperloop. (Bridges handle this with various ingenious methods, most of which will work for the Hyperloop's longitudinal expansion.)
> thermal expansion joints are the solution
Scaling pipe expansion joints where they maintain the near vacuum and deal with the structural stress of a capsule whizzing by will be difficult. By "difficult" I mean these are problems NASA (for the ISS) and Schlumberger (for pipes) have been grappling with for years and with billions of dollars in R&D.
> The materials problem is the thermal expansion of the top of the tube relative to the bottom.
What exactly is the problem here? Is it because the top of the tube is exposed to direct sunlight? I thought it was supposed to be covered in solar panels anyway. Is it still a materials science problem if the tubes are shaded, because providing a structure that shades something with expansion from direct sunlight exposure seems quite a bit easier than to do so while trying to keep vacuum to a particular level.
I never said vacuum pumps are "technologically impossible". My original comment references the Space Power Facility [1] and categorises the vacuum problem as an engineering problem. A hard one, but engineering nonetheless.
The comment you link to [2] replies to someone claiming the original white paper calls for a 22:1 atmosphere:tube pressure ratio. I pointed out that the figure they're referencing, Figure 11, discusses the capsule and not the tube.
I'm skeptical about the economics of de-pressurising the tube, but that's an engineering problem and I've always held it as such. The materials problem is the thermal expansion of the top of the tube relative to the bottom.
[1] https://en.m.wikipedia.org/wiki/Space_Power_Facility
[2] https://news.ycombinator.com/item?id=15459820