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SpaceX: “Close, but no cigar. This time”

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Re: SpaceX: “Close, but no cigar. This time”

#211

Post by schiffern »

schiffern wrote: post #205
sillysaurus3 wrote: post #160

Earlier quoted context omitted.

Sure, let's go over it together. Tlb is many things, but "rarely wrong" is probably near the top of the list. He certainly read those sections before making that comment, so there must be something here which made him as an engineering expert say that it doesn't properly address thermal expansion. I'll try to run an emulator of tlb's mind, but mine is far less sharp. The tube will be supported by pillars which constr…

> Is that really feasible, especially given that different points along the route could have temperature differences? Temperature differences would tend to cancel out, no? If one section is warmer than average and one section is colder, the overall change would be smaller. > the tube becoming bigger in the circular direction, like a bigger "O" Yep, by about 2 mm. No problem there. > But again, where precisely does 0.…

Can't reply to sillysaurus3 directly (https://news.ycombinator.com/item?id=8902595), so I'm replying here:

You make a great point! I didn't quite grok it before.

>Can that expansion really be pushed 175 miles north and 175 miles south simultaneously?

>Surely at some point the weight of the tube overcomes the steel's desire to expand, so the result would be the tube either scrunching up like an accordion or going in the lateral direction.

Agreed. I have a feeling some sort of active control (basically just motorized rollers) will be needed every couple of miles to prevent "sun kinks". I haven't done the math on that though. It might be sufficient that a large hollow tube shape is much more resistant to buckling than a rail shape.

"Sun kinks": http://www.climatecentral.org/news/climate-change-warp-railr...

Re: SpaceX: “Close, but no cigar. This time”

#212

Post by jacquesm »

kragen wrote: post #197
jacquesm wrote: post #59

Earlier quoted context omitted.

Hard to make any of those work across intercontinental differences. Drones, cruise missiles and small robot helicopters need to be launched from a location relatively close to the target.

Drones have been launched intercontinentally, although with a significant failure rate, since last millennium: https://en.wikipedia.org/wiki/AAI_Corporation_Aerosonde

600 km/L, that's very impressive fuel economy.

Re: SpaceX: “Close, but no cigar. This time”

#213

Post by jacquesm »

sillysaurus3 wrote: post #177
jacquesm wrote: post #169

Earlier quoted context omitted.

You are obviously not used to dealing with thermal expansion in other designs, but this has been done time and again before so from an engineering point of view this is mostly a solved problem and not a 'big deal'. For instance, you could have periodic sleeves that can slide over one another so you don't end up with the expansion on the final endpoints accumulated, the trajectory could be adjusted to allow for transl…

I realize I'm probably an idiot, but I do try to learn from my idiocy. Thanks for helping me learn. But I'm having trouble understanding how your reply takes everything into account, such as the fact that the hyperloop moves pods, not liquid. Pipelines for liquid are certainly a solved problem, but a pipeline of pods is new. Btw, in railroads (that other long distance transportation method) the expansion is dealt wit…

You could simply slide one tube into the next and leave the 'gap' between the tubes sit inside the sliding portion. That way you could have ridiculously close clearance to the tube except for that tiny bit (a few cm) every hundred meters or so. Just anchor one end of each tube and let the other slide freely.

Re: SpaceX: “Close, but no cigar. This time”

#214

Post by mikeyouse »

returnofdjedi wrote: post #31
moskie wrote: post #25

Earlier quoted context omitted.

Oh, you're asking if the video is slowed down/sped up. Ok. At first, I thought you were asking if we were watching it in realtime.... and seeing rocket after rocket blow up on this barge.

Cool.If would be great to know how musk distributes his time between Tesla And Spacex.

From here: http://www.businessinsider.com/elon-musk-day-in-the-life-of-...

> Musk splits his time between his two companies. He's at SpaceX's LA-based headquarters on Monday and Thursday, then he heads to Tesla (in the Bay Area) on Tuesday and Wednesday. On Friday he splits time between both. Tesla Design has offices in the same office park as SpaceX.

He lives in LA, so the schedule makes sense in that he flies LA -> SF Tuesday AM and then SF -> LA Thursday night.

Re: SpaceX: “Close, but no cigar. This time”

#215

Post by nemothekid »

murtza wrote: post #184
goshx wrote: post #26

Could someone please explain the "no cigar"?

I am working on a project to define phrases in English like "close, but no cigar". Here's the page for this phrase: http://jargonism.com/words/437 I would be interested to hear feedback from HN on what would be useful on the word page, in addition to a definition and an example?

Why do I need to sign up and confirm a newsletter to view the site?

Re: SpaceX: “Close, but no cigar. This time”

#216

Post by sillysaurus3 »

schiffern wrote: post #211
schiffern wrote: post #205

Earlier quoted context omitted.

> Is that really feasible, especially given that different points along the route could have temperature differences? Temperature differences would tend to cancel out, no? If one section is warmer than average and one section is colder, the overall change would be smaller. > the tube becoming bigger in the circular direction, like a bigger "O" Yep, by about 2 mm. No problem there. > But again, where precisely does 0.…

Can't reply to sillysaurus3 directly ( https://news.ycombinator.com/item?id=8902595 ), so I'm replying here: You make a great point! I didn't quite grok it before. > Can that expansion really be pushed 175 miles north and 175 miles south simultaneously? > Surely at some point the weight of the tube overcomes the steel's desire to expand, so the result would be the tube either scrunching up like an accordion or going…

The trick is to click on "link" next to the comment and then write a reply. I try not to reveal that or to use it during a heated debate, since the reason the "reply" link is hidden is to discourage flamewars, but it's obviously not intended to hamper tech talk. And I wish HN had a private messaging system so that I could've mentioned that in private.

For a sense of scale, 60 mph travels one mile in 60 seconds, or 0.016 miles per second. Hyperloop goes 760 mph, which is 0.211 miles per second. (Jeez, that's fast.) So it only takes about 10 seconds for the car to traverse 2 miles, or in other words to traverse whatever effect such a motorized roller would have on the path of the vehicle. Like, if the roller causes the track to move "outwards," for example toward the ocean, by a little bit, then the pod is going to move "a little bit toward the ocean and then back" in 10 seconds.

That seems like it might be reasonable. But I suppose the question is whether a 7,700 lb pod travelling at 760 mph can tolerate, say, a 2-meter deviation in its trajectory in 10 seconds. Meaning, one meter toward the ocean, and then one meter back towards its original course. Can the pod bank against the walls by a displacement of 0.2m per second? If you hold out your arms to the length of a meter, 0.2m is pretty small, but it's not too small. And the pod would be going sideways by that amount per second.

1-meter deviation due to thermal expansion is extreme. 0.25m per mile might be a more realistic deviation. So that would be a 1-meter deviation total: 0.5m toward the ocean, then 0.5m back, which would still mean the pod needs to scrape against the inner wall by 0.1m per second.

I wonder what the limits on the banking are...

Re: SpaceX: “Close, but no cigar. This time”

#217

Post by dredmorbius »

chobo wrote: post #200
dredmorbius wrote: post #185

Earlier quoted context omitted.

Any good references on BEIC and its army?

How did the power and economic reach of pre-modern organizations like the British East India Company compare to modern megacorporations? -- http://www.reddit.com/r/AskHistorians/comments/17mvv1/how_di...

Nice. I tried asking a similar question on corporate violence a ways back and got moderated out.

Re: SpaceX: “Close, but no cigar. This time”

#218

Post by sillysaurus3 »

jacquesm wrote: post #213
sillysaurus3 wrote: post #177

Earlier quoted context omitted.

I realize I'm probably an idiot, but I do try to learn from my idiocy. Thanks for helping me learn. But I'm having trouble understanding how your reply takes everything into account, such as the fact that the hyperloop moves pods, not liquid. Pipelines for liquid are certainly a solved problem, but a pipeline of pods is new. Btw, in railroads (that other long distance transportation method) the expansion is dealt wit…

You could simply slide one tube into the next and leave the 'gap' between the tubes sit inside the sliding portion. That way you could have ridiculously close clearance to the tube except for that tiny bit (a few cm) every hundred meters or so. Just anchor one end of each tube and let the other slide freely.

Each pod weighs 7,700 lb and is traveling at 760 mph. Are you sure a few-centimeter speedbump isn't a big deal? I don't know how to calculate whether or not it would be, but I'm interested in knowing why you feel it won't cause problems.

Remember, the pod comes into direct contact with the wall while banking, so it's going to take the full force of any few-centimeter bump.

Re: SpaceX: “Close, but no cigar. This time”

#219

Post by wickedlogic »

What is the weight on the rocket? It seems like towers with something like cable lasso's would help with the final descent stabilizing by securing the top of the rocket, or weighted arms/blocks that box in the rocket during final. So it never has to 'land', just hover.

Re: SpaceX: “Close, but no cigar. This time”

#220

Post by jonalmeida »

duskwuff wrote: post #161
jonalmeida wrote: post #101

Can someone explain what the rocket was trying to do? Was it trying to correct itself to land vertically thrusters-first? I also don't understand how it got in that particular trajectory either from this vine.

Here's a video of the desired behavior, more or less: https://www.youtube.com/watch?v=NoxiK7K28PU The video's a few years old, so the hardware's changed a bit since then, but I think you'll get the idea. :)

Thanks, I remember watching this along time ago. I was under the impression they had landing the rocket all figured out after this :)
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