Sorry for sounding like such a fanboy, but during my 40 years on this earth, I have never been more impressed with a human being.
The guy is pushing the envelope on perhaps the most difficult engineering/technological endeavor ever attempted by a private company - and he's making it look cool and futuristic.
As if that wasn't enough, he's doing this in two different industries simultaneously.
I'm not saying he can do no wrong, but I'm just flabbergasted that there are still so many armchair critics and naysayers when it comes to Elon Musk.
> I'm not saying he can do no wrong, but I'm just flabbergasted that there are still so many armchair critics and naysayers when it comes to Elon Musk.
That's why you're a fanboy. Nobody is perfect, and Elon Musk likes to make fun of the competition quite publicly when they have an issue, while ignoring his project's own failures.
It is hard to even discuss the man on HN as anything that could even be taken as critical gets downmoded or flagged. Just look at yesterday's hyperloop discussions, nobody could say anything critical without being very actively attacked. By the way make sure "show dead" is turned on to see the full discussion.
Honestly his track record is very impressive indeed. His aspirations are also impressive. However his fans are insufferable as is HN's general attitude about the man. When someone is treated as if they're beyond reproach and their ideas are also, you're just asking to get led down the garden path.
The hyperhoop concept in particular is pretty bad, and the white paper leaves more questions than it does answers. The cost is too high and the value too low Vs. normal high speed trains (e.g. Japan). Plus there are massive safety issues surrounding it (as you can see from the thread yesterday, that were largely just ignored and downmodded).
Overall I'll be happy when people start acting rationally around the guy again. Currently I feel like I at a One Direction concert surrounding by a bunch of screaming teenage girls (on HN in particular).
PS - I wouldn't dream of criticising this rocket failure. Rockets are hard, the last 80 years have proven that again and again.
And his comment on their rocket being the butt of a joke, using engines literally made in the 1960s and stored in Siberia were true. It is upsetting, but still not as surprising that they suffered catastrophic failure having such an adversion to new tech.
> And his comment on their rocket being the butt of a joke, using engines literally made in the 1960s and stored in Siberia were true.
That was quite misleading on Elon's side. Engines were manufactured in 1970's (I believe in 1973-1974) after quite an extensive RND program - actualy, remake of similar engines, NK-15, which weren't nearly as good. NK-33 engines were tested as perhaps no others of theirs caliber - with tests like throwing metal chips (nuts?) into pumps, or running uninterrupted for ~4 hours (!) . Technical capabilities are also quite formidable - ok, Merlin-D has better thrust-to-weight, but worse Isp, and that's with the hindsight of ~40 years. Throttleable... relatively modest pressure by today's standards... And they were stored in Volga region, which is firmly Europe.
So, Musk's comment - intentionally or not - painted OSC's decision in less-than-objective color. Well, Elon is known for exagerrating... and sometimes quite grossly. We'll know the scale.
The odyssey of the reclaimed NK-33's is intriguing as hell, but I can only imagine that everyone involved in their resurrection knew the odds of failure would be higher than with modern engines. Soviet metallurgy in the 1970's likely didn't have the consistency and precision we have today. So while the NK-33 was (is) a remarkably advanced design, it was likely pushing the limits of the materials of its time and place–even before sitting in storage in uncontrolled conditions for decades.
Odds of failure would perhaps be higher, given all the rest equal. Which is not - Soviet rocket engine school was at its golden age at the time, there were a lot of people both academically educated and who participated in large scale experiments with engines. Granted, today's capabilities allow us to surpass the level of sophistication achieved during the space race. However, we still need to try hard enough - and we know the support from governments is not as great.
Limits of materials were pushed indeed. Some safety margins for materials were claimed as under 1.0 - i.e., 0.97 - that is, materials were pushed further than their limits. The idea was that since the engine is used once, we can use it in the manner that greatly reduces the life of the engine - and nobody would care, since a stage will be done with in a few short minutes. A lot of things were done quite unconventionally - remember SR-71, for example, or oxygen-rich pre-burners which were considered rather impossible.
NK-33 remains unsurpassed even today by many criteria. Now it includes even the ability to work after 40 years of shelf line - which probably left the trace on engines reliability.
The chamber pressure (and therefore Isp) are both dialed back for the sake of reusability. They're stated multiple times that they're not running those engines anywhere near their physical limits.
It's certainly good that SpaceX uses many ways to test hardware, including those approaches successfully used before. During development of F-1 some interesting debugging techniques were invented, some could be well applied in SpaceX.
Gas generator cycle in general doesn't allow reaching effective Isp as high as closed loop cycle. On the other hand, smaller pressure reduces stress and generally considered safer. NK-15 were single use engines, but NK-33 and most other modern engines are all reusable.
One example of his being polite doesn't mean he doesn't also make fun of competition publicly. Look at the interview where the interviewer asks him about a competitor's electric car (BMW I think) and he just laughs for a not-insignificant amount of time followed by something like "have you seen the thing?"
The "have you seen their car?" comment was from an interview with Bloomberg regarding BYD, not BMW.
He laughed when asked about BMW during the Q2 2013 conference call, but it was a chuckle followed by serious comments. It was only when the questioner began nervously laughing that he laughed for a significant time.
Compilation video containing both events (unfortunately with music, but I don't care enough to track down the individual sources): https://www.youtube.com/watch?v=8Gt6CAswSOY
So, the big criticism here is that… he's too forthright about competitor's products? I'm actually quite ok with that.
His theatrics aside, he wants to make electric cars viable and take us to mars. Even if he ultimately fails, if he makes everyone else rise up to compete with him, we as humanity win.
Sometimes -- and I'd argue often -- leadership consists more of both 1) getting out of the way of and 2) enabling those who Want To Get Shit Done.
I find the fanboiism somewhat tedious (I don't find the top comment of this thread all that insightful), but I do admire Musk for seeming to hit a number of remarkable goals. That said, I find Tesla and Solar City more impressive/promising than SpaceX (technical challenges and accomplishments notwithstanding) or the Hyperloop (ultimately an idea that's been rightfully junked in the past).
Given the history of US industry of doing just the opposite -- stalling and preventing needed innovation -- if I had to pick a single attribute of his that I find most encouraging it's his leadership in that regard.
He may not ever get to Mars, but he's doing something far more important, which is to drastically reduce the cost of putting things into LEO. If he can get it low enough a whole list of things pencil out that weren't economically feasible in the past, like space-based solar power generation.
Without SpaceX it's likely the business would have muddled along without putting any effort into reducing costs for decades.
Yes. The biggest achievement of SpaceX so far was economical and organizational. Musk cleverly employs latest - which are considered common sense in other industries - approaches to the industry known for its conservatism. That gives them - eventually - proverbial kick in the sensitive parts, making them care more.
To be fair, the BMW electric car is the ugliest car BMW has ever made. It looks like they accidentally welded two different models together in the middle. They deserve to be made fun of for that disaster.
Well, Elon Musk said talking about hyperloop was like shooting his own foot. It was a premature idea.
But the interesting part is some(more than some) people are actually trying trying to come up with a real world implementations of hyperloop and so far their verdict is 'it's doable' and they are working on it. And these people are engineers from reputed companies around the world.
I don't particularly like the concept of fan boy either, but like you said, this man has impressive track records. And that's absolutely brilliant.
The thing that intrigues me is in the new innovations he had in his rocket, and why NASA didn't have it before SpaceX.
It seems to me Musk was attempting to get the people who should be pushing bold new ideas to do so. The Hyperloop idea might have been premature but it certainly engaged people in discussing radical new ideas rather than discussing minor tweaks to an existing concept. That general thought is imbued in the culture of the companies he is involved with.
"Premature idea" is probably better phrased as "not feasible on technical grounds." Even tlb said it has huge problems. The steel expands in summer due to heat. Where does it go? Roads can expand using those interlocking teeth things, but hyperloop has to remain a closed system.
There was a 1970s proposal for an underground tunneled very-high-speed transport quite similar to the hyperloop. Partially-evacuated tubes, relatively small vehicles. Cost and other considerations torpedoed it.
Look up R.M. Salter at RAND:
"The Very High Speed Transit System" (August, 1972)
"Trans-Planetary Subway Systems -- A Burgeoning Capability" (February, 1978)
> The steel expands in summer due to heat. Where does it go? Roads can expand using those interlocking teeth things, but hyperloop has to remain a closed system.
Feel free to disagree with whether or not the approach outlined is feasible, but this is specifically covered in the whitepaper. See page 5, section "Earthquakes and expansion joints" as well as page 28, section 4.2.3 "Pylons and tunnels".
He doesn't properly address thermal expansion of the entire system. A long straight steel tube from SF to LA will expand a total of 300 meters over a 40C temperature change. Where does it go?
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 constrain the tube in the vertical
direction but allow longitudinal slip for thermal expansion as well as dampened
lateral slip to reduce the risk posed by earthquakes. In addition, the pillar to
tube connection nominal position will be adjustable vertically and laterally to
ensure proper alignment despite possible ground settling. These minimally
constrained pillars to tube joints will also allow a smoother ride. Specially
designed slip joints at stations will be able to take any tube length variance
due to thermal expansion. This is an ideal location for the thermal expansion
joints as the speed is much lower nearby the stations. It thus allows the tube to
be smooth and welded along the high speed gliding middle section.
This seems like the key sentence:
Specially designed slip joints at stations will be able to take any tube length variance
due to thermal expansion.
and the plan is for the tube to expand due to heat, and the expansion will be absorbed at the two stations at the end.
Is that really feasible, especially given that different points along the route could have temperature differences? I drove along Highway 1 and saw how incredibly different the weather can get, and while that's south of where the route is planned, it's easy to imagine that part of the tube could be roasting in direct sunlight while the other is cooled by rain. Something like 90 degrees F at one part vs 70F at another part. That's a difference of 32.22C to 21.11C, or a total temperature difference of 11.11C.
The route from SF to LA is about 350 miles. If a tube of that length expands 300 meters, then we can divide 300 meters by 350 miles to get the total expansion over a single mile. So a variation of 40C would give an expansion of 0.85 meters within a single mile.
Since the variation in that scenario would be ~11C, multiplying the expansion by 11C/40C equals an expansion of 0.235 meters.
So I suppose the question is: Is it feasible for those things the tube is resting on to absorb a quarter meter of expansion without that expansion being pushed all the way up to the station? It's the temperature differential along the route that seems to matter, not necessarily the difference from summer to winter.
... it seems like an expansion of 0.25 meters might be a big deal.
But I don't know what I'm talking about. Is all of that about right so far?
I'd also be curious whether the thermal expansion results in the tube becoming bigger in the circular direction, like a bigger "O", or if it expands parallel to the tube, like becoming a longer tube. Or even both.
It seems like the plan addresses this with the first part of that paragraph:
The tube will be supported by pillars which constrain the tube in the vertical
direction but allow longitudinal slip for thermal expansion as well as dampened
lateral slip to reduce the risk posed by earthquakes. In addition, the pillar to
tube connection nominal position will be adjustable vertically and laterally to
ensure proper alignment despite possible ground settling.
But again, where precisely does 0.25m of steel go? I'm having trouble visualizing how the pillars could "allow for 0.25m of longitudinal slip over 1 mile."
I realize that a temperature variation of about 10C over 1 mile is a little extreme, but we should examine how the system handles extreme situations.
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 translation of some end-to-end expansion into a sideways expansion (much like what you see in long runs of heating tubing where they throw in the occasional U or loop to make sure the tubing stays put on the longer stretches) and so on.
There are a lot of really hard technical challenges involved in the hyper loop concept, I'm not sure why you'd focus on the thermal expansion as the major one, it's trivial in comparison to some of the others.
Btw, in railroads (that other long distance transportation method) the expansion is dealt with by putting a small gap between two adjacent rails. That's obviously not possible with the hyper loop as it is currently envisioned but I think that the answer is in there: don't allow the differences to accumulate over long stretches. We already have plenty of long pipelines, this one is just a big bigger in circumference.
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 with by putting a small gap between two adjacent rails. That's obviously not possible with the hyper loop as it is currently envisioned but I think that the answer is in there: don't allow the differences to accumulate over long stretches.
If that's the case, then why does the plan assume each station on the endpoints is going to absorb most of the thermal expansion? Or am I misreading? They specifically say "the stations are the ideal points to absorb thermal expansion," and the stations are on the end, so it sounds like they're aiming for a long sleeveless steel tube.
Also, I was basing my criticism on Hyperloop Alpha. Obviously, their design can change in the future. But, as presented, what gives you the impression that sleeves could be incorporated into their design without causing problems for the pods?
I can visualize sleeves which expand into each other, and if they overlap into the direction of travel, so that the edges are pointing away from the pods rather than toward the pods, maybe that wouldn't cause any problems.
The Hyperloop travel journey will feel very smooth since the capsule will be
guided directly on the inner surface of the tube via the use of air bearings and
suspension; this also prevents the need for costly tracks. The capsule will bank
off the walls and include a control system for smooth returns to nominal
capsule location from banking as well. Some specific sections of the tube will
incorporate the stationary motor element (stator) which will locally guide and
accelerate (or decelerate) the capsule. More details are available for the
propulsion system in section 4.3. Between linear motor stations, the capsule
will glide with little drag via air bearings.
Sleeves would cause an edge to sort of "protrude outwards" into the path of the pod, wouldn't they? So it'd basically be a small speedbump. Again, the edge is pointed in the direction of travel, so that would basically be like the second half of a speedbump, basically a small "drop". Except since the pod is moving at 760mph, even a small drop can result in quite a lot of force, and can cause wear on the pod itself, couldn't it? And it might feel a little jarring to the passenger.
If the interior needs to remain smooth, what sort of design could fulfill that requirement? (Maybe that's a big "if", but if the pod is going to bank off the walls, then it sounds like that's the case.)
EDIT: Also, as someone else pointed out, pipelines that need to be straight might be a new concept. Many pipelines seem to use "U" bends, which can't be incorporated into hyperloop for obvious reasons: http://demonstrations.wolfram.com/PipelineExpansionLoop/
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.
FWIW, Musk makes no mention of expansion joints in the tube, only at the ends. He's also stated elsewhere (sorry, no source) that you'll probably need to run a polishing robot through the tube to get it microscopically smooth. That doesn't sound like a surfacing requirement that would tolerate gaps.
If you care to, check out the conversation that sillysaurus3 and I had down-thread. I would love to have someone experienced in MechE glance at my napkin math!
TL;DR it looks like simply pushing all the slack to the end stations is actually feasible, and it's easier to deal with there since the cars aren't moving very fast.
It might be, but if you did want to use expansion joints to alleviate some or all of the problem you most likely could.
There are other alternatives too, such as allowing the tubing to move sideways a bit in a long curve. That would change the overall shape of the trajectory but the air cushion they talk about could take care of that.
If they do end up using expansion joints they could actually use the fact that some air might leak in to purposefully increase local air density to use that as an impromptu air bearing.
Anyway, there is plenty of challenging engineering in hyper loop, but the least interesting part is how to make a long metal tube, either in one piece or out of segments.
And of course even more challenging than the engineering will be the economics and the paper tigers.
Right-of-way issues, liability. America loves its paperwork and setting up a new very large chunk of unproven infrastructure is going to be a total headache from a paper point of view.
Hyperloop has all the drawbacks of high speed rail and has unproven tech on top of that. It'll be a legal feeding frenzy.
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.
> Are you sure a few-centimeter speedbump isn't a big deal?
Depends on lots of things, such as the angle of incidence of the pod relative to the direction of the wall of the tube.
> 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.
I don't know how to calculate rockets landing on barges either, but SpaceX seems to be able to pull it off. There is nothing in the realm of engineering that says you can't make a bunch of tubes sliding over each other relative to the direction of travel for some vehicle to travel within that tube as long as you respect a couple of basics. One simply solution would be something like this:
seg2----- --seg1
----- ----------
0000000
Where the '0' are the elements of the pod in contact with the wall (I would assume they're using rollers there, anything solid would wear out the wall in no time at all).
That way there is no speedbump at all... It's not as if you're going to do right angle turns at the joint of two segments.
Anyway, I really think you're chasing a ghost here, the problems with hyperloop are not basic engineering.
That solution is interesting, but does it account for the fact that the tube curves all throughout its route? Some parts need to be curvy, some need to be straight. Are you sure that expansion can be coaxed into a curve shape rather than linear? How?
Also, curves still result in a speedbump with that solution. The pod will be traveling directly toward the gap just below "seg2" if it's banking against the wall. You could make the edge a sharp edge, like a sword's edge, but that doesn't help because due to expansion that edge will still protrude out into the path of the pod.
I know it seems like it shouldn't be a hard problem, but it's looking like one. Remember, 300 meters of expansion over 350 miles is 0.85m of expansion per mile. Hold out your arms to the length of a meter and picture how much steel that is. That's what your proposed joints need to deal with: 0.05cm of expansion per meter. So if you have your joints every 20 meters, that's still a 1cm gap, which means a speedbump around curves. Wouldn't that make curves very unpleasant for the passenger and the pod? And you can't have them every meter without increasing the engineering complexity and weakening the structural integrity, right? Yet whatever solution they come up with would need to be placed less than every 20 meters, otherwise they'll get a 1cm gap.
I have a feeling that no matter how many times I'm going to answer your 'but this is impossible' with showing you how in fact it is possible you're not going to concede that in fact it probably is possible nor are you going to stop so in the interest of conserving bandwidth I'll bow out of the conversation here with this final bit.
The solution for the above is that you need to take into account the radius of curvature and you're clearly not doing that. The inside of that tube needs to be relatively smooth in the direction of travel, not perpendicular to it. You could also interleave to two segments if you wanted it to be even smoother.
So no, this is not a hard problem in spite of your continued insistence that it is because you can't solve it.
If you don't have time, fine. If you don't want to talk, fine. But I have some strong words which, out of respect for HN's guidelines, I won't say. Being dismissive of a newbie's concerns while killing their interest in the field isn't great, especially after they've put hard work into giving you a clear-cut example of the technical reasons why something looks hard to them.
And I still don't understand how your solution wouldn't leak air into the hyperloop unless the steel sleeves were pressing very firmly into each other. Like the inner sleeve forcefully pressing into the outer sleeve.
I have no idea why you refuse to admit this is at the very least a nuanced problem.
> If you don't have time, fine. If you don't want to talk, fine.
I'm not on your payroll and you're stuck in a groove.
> But I have some strong words which, out of respect for HN's guidelines, I won't say.
Feel free, I'm not made of sugar. But you're arguing from a position that makes no sense to me, you're apparently entirely ignorant of the basics of mechanical engineering and you're going to tell the likes of Elon Musk and his band of merry engineers what they can or can not do. They just came within a hair of planting a friggin' rocket on a barge from space. Do you really believe they couldn't get a bunch of tubes to slide inside each other without overshooting their air intake budget? That's mostly a factor of 'how big are the pumps' and 'how many such sliding spots do we need' (a few hundred would do just fine) and how much room there is for additional seals (plenty).
> And I still don't understand how your solution wouldn't leak air into the hyperloop unless the steel sleeves were pressing very firmly into each other. Like the inner sleeve forcefully pressing into the outer sleeve.
No, you don't need that you can use regular seals for that, just like we do on high pressure air connections, fun fact, they work better when the difference is higher, go figure.
> I have no idea why you refuse to admit this is at the very least a nuanced problem.
Because it is a nuanced problem for you, but not for anybody that has the wherewithal to be hired on the engineering parts of a project like this. Just like my little brother would find assembly language a 'nuanced problem' and I find it relatively easy. It all depends on whether or not you're doing this (mechanical engineering) on a daily basis or whether you want to be back-seat driving nay sayer. Once you've decided on the latter any solution will be inadequate.
I don't know if you're having a bad day or have gotten into a strange mindset, but I just never expected this level of "personally insulting" out of Jacques Mattheij, especially against someone who freely admitted at the very top of the thread that I'm an idiot who is arguing from a position of ignorance. So I'll go try to find someone else to geek out with an interested newbie. Like, say, someone who finds engineering enjoyable.
You're not being insulted, you merely are trying to argue about things that you admit that you have no clue about and you persist in doing so regardless of the effort made to show you that you are wrong. So either stop arguing (I do know a thing or two about mechanical engineering) or start researching what I gave you above as the bits and pieces of the solution.
To have an enjoyable conversation with an interested colleague, rather than someone whose tone is "shut up and listen to your elders." Besides, having a crotchety back-and-forth makes for boring reading, and we should be respectful of the community.
Thanks for the pieces you've provided so far. I'll bring up my objections elsewhere. Hopefully anyone who's been having my same concerns will be able to do the same.
You argue that something is impossible but at the same time you outline your ignorance. The normal position for being ignorant is to study the subject, not to argue that something is impossible.
It's like saying a moonshot never happened because you couldn't do it yourself. There are lots of things that each of us individually can not do, but collectively we can do amazingly complex things. The specialization required takes time and effort. If you're unwilling to put in the time and/or make the effort then you should not take up positions that tell those that did make that effort what they should not be able to do according to you.
If mechanical engineering interests you then maybe you should go and study the subject rather than to take up strong positions like these and to be rigid in your inability to shift on those positions.
> I'll bring up my objections elsewhere. Hopefully anyone who's been having my same concerns will be able to do the same.
Basically that says that you want to argue, not learn and that you'll only take what agrees with your viewpoint.
>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 0.25m of steel go?
It slides all the way to the station. There trains are moving slowly, so they could add rails to the "expansion section" between the tube and the airlock. The stationary rails slide along the inside of the tube (no seal needed). Wherever the tube ends, the pod is already on the rails!
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.
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.
Ahh, thanks for the tip, and the wonderful discussion!
I agree, that would not work. I was suggesting that motorized rollers move the track longitudinally instead of sideways. Essentially they would take up the slack and actively push it to the end stations, counteracting the friction from the passive rollers. You could use thermometers and position sensors to model the stress on the tube.
That's an interesting idea, but are you sure that thermal expansion imparts enough force against 175 miles of steel in order to push it all the way to the station? 175 miles of steel would be incredibly heavy. It seems like the heating/cooling might even cause the steel to weaken enough such that, rather than rolling the tube towards the station, it would start to scrunch like an accordion. But I wish a structural physicist would step in with some calculations to prove whether or not 175 miles of steel on rollers could be pushed by thermal expansion without compromising hyperloop's structural stability.
Maybe we could ask /r/askscience?
EDIT: After re-reading your comment, I think you're saying the rollers would actually provide the force necessary to move 175 miles of steel, rather than letting the expansion passively push it. But those rollers would have to grip onto something in order to do that. They wouldn't be rollers so much as tank treads.
Hmm... Do you think that might work? Could 175 electric motors working in unison provide enough force to tank treads that bite into the concrete pillar below, and into the steel tube above, in order to successfully shift 175 miles of steel? And the system has to have temperature sensors every mile, and those sensors must not ever report incorrect readings or else the whole tube breaks. And those motors must never break down or run out of power...
I'm sounding pessimistic, but honestly I have no idea whether that would work.
EDIT 2: Ah, I think I've figured out why it can't work. It's not a straight tube. It bends all along the route. http://i.imgur.com/3TavjCY.png
So motorized rollers would actually need to bend the tube in order to successfully transmit the thermal expansion. In other words, when a piece of steel tubing is initially created, it's bent with a certain curvature. But if rollers are to transmit the expansion all the way to the station, the exact location of where the steel is bent needs to be dynamically defined at runtime, rather than statically assigned at compile time. Did I phrase that very clearly? It would help to be in-person, or maybe I could draw a picture if needed.
It doesn't seem like rollers could dynamically bend the steel all along the 175 mile track in order to carry the expansion.
>are you sure that thermal expansion imparts enough force against 175 miles of steel in order to push it all the way to the station?
Nope. That's why you may need to push it! :)
Assume the rollers have the Crr of a passenger train wheel (0.0020). If each section weighs 193 tonnes (23 mm thick by 2.23m diameter by 100' by 8 g/cm³), then each roller will provide ~400 N of friction. Over 175 miles (worst case) that works out to 3.56 meganewtons of resistance to motion.
For a thin-walled cylinder, buckling stress is modeled using the large deflection approximation[1] as:
σ_x = 0.238 Et/r
Where σ_x is the bucling pressure, E is the material's Young's modulus, t is the wall thickness, and r is the radius. Plugging in 190 GPa, 20 mm, and 1.125 m yields…
58 meganewtons, or about 16 times as strong as the predicted frictional force
I guess they may not need active control after all!
But what about curves? Won't it result in a lot of sideways force? Needs more calculations…
Sweet calculations! Thanks! Check out my above comment again, since I was apparently writing out an "EDIT 2" while you were doing these awesome calculations.
Basically, what do you think about the fact that it's not a long, straight tube? The rollers would need to dynamically bend the steel tube in order to carry the expansion all the way to the station, wouldn't they? Is that possible?
Even if there aren't any rollers, the tube still needs to re-bend itself somehow. But how? That would mean steel curves near the endpoints would move a whopping 150 meters in total. So it seems like part of the tube manufactured as a curve in summer would need to become a straight length of pipe by winter.
Heh, I love that we thought of two different but related problems simultaneously!
First yours, since it's much cooler. The minimum curve radius is 3.67 km, or a length difference of 18 mm between the left and right side over the length of one pylon.
Assuming that all sections start as straight tubes, how much sideways force would that apply on the pylon? For that we need to calculate the "flexural stiffness"[1], which for a hollow cylinder is given as:
EI = E pi/4 (D⁴ - d⁴)
Where E is Young's modulus, and D and d are the outer and inner diameter.
Therefore the bending moment[2] M is:
M = EIκ = E pi/4 (D⁴ - d⁴)κ
Where κ is the curvature, equal to 1/r.
Finally, muddling through the equations on the bending moment article (and treating the tube as a 200' beam with a load in the center) yields:
f = M / (100')²/(200') [not sure about this one]
A whopping 300 tonnes•f of lateral force on the pylons! Probably doable, but it means if your tubes are constructed straight your pylons are going to be buttressed at a ~60° angle. Also, note that this only applies to the slip distance (~150m, or three pylons), since the tube sections well within the curve will never move enough to be in a non-curved section of track, so they can be built curved from the beginning.
Also you can vary the curvature smoothly[3], which can substantially reduce the forces involved. For example, if you eased into the curve over 30 pylons and it only moved by 3, the sideways force would be reduced by 10x (since the curvature is always "about right"). Further calculations here are left as an exercise to the interested reader. :D
As for my own objection… Even on the sharpest turns successive pylons will only vary from straight line by 0.15°, so the lateral forces caused by expansion and contraction shouldn't exceed 9 tonnes force. Piddly by comparison.
Do you have an email address we could continue this at? I'm going to need a little while to get back into a happy mindset after a rather unfavorable exchange upthread. I'm really looking forward to picking your brain though. Thanks for chatting with me.
forgive my amateur and completely unscientific postulation here, but is it possible that this conversation is moot seeing as normal train tracks do not have to extend at normal train stations, despite the rails being steel and continuous?
Rail lines have more curves which can take up that slack, and the positional tolerances are much more forgiving. Because of its high speed operation the hyperloop is both incredibly straight and incredibly sensitive to kinking.
That makes total sense, but I don't think it would work. The expansion doesn't really cancel out. Imagine heating 1 mile of hyperloop by 11C, but only 1 mile. The result is 0.25m more steel that has to go somewhere.
Can that expansion really be pushed 175 miles north and 175 miles south simultaneously?
I'm not going to say that's impossible, because I'd imagine someone having similar objections to, say, the invention of A/C current. "Can pushing electrons back and forth really propagate thousands of miles?"
But if you visualize the implications of that, it's intuitively difficult to believe the expansion can be transmitted to the endpoints across the entire length of a solid steel tube 175 miles away. That would move an incredible amount of mass. 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.
(Jacques said sleeves could be the solution so that thermal expansion can't accumulate, but it seems like sleeves would introduce problems for the pod, possibly severe ones. When a pod travels over a sleeve, it would feel like a jolt, if I'm understanding his idea of "sleeves" correctly.)
I'm so happy someone is actually engaging with the comment and tossing ideas around with me though.
How about hedging your statement to "not CURRENTLY feasible using TODAY'S materials and structural concepts (trusses, etc)". Space flight and industrial production of fertilizer were both considered impossibilities when first proposed.
Sure, I'll reduce it to "Unless people make an advancement in structural materials similar to the invention of steel itself, which is to say 'fundamentally world-changing,' hyperloop is nothing more than an inspirational pipe dream, similar to world peace." (EDIT: This comment may actually get called out in the future once Hyperloop is fully deployed, as an example of some idiot's words. So it's probably more than a little dumb of me to have said this. In my defense, it's based on Hyperloop Alpha, as it's presented in the whitepaper. Their design could change radically before deployment.)
If you're planning on building a closed loop out of steel, and there's nowhere for the steel to go when it expands in summer, the plan may need some rethinking.
But it would need to be very strong lining in order to prevent any leaks between the segments. And any kind of a leak would need to be detectable and would shut down the hyperloop until it's resolved.
Between the wildly optimistic cost projections and the fundamental engineering difficulties, I'm much more inclined to call it a pipe dream than a perhaps-future-possibility.
It's a "reduced-pressure tube." A leak is still a big deal, isn't it?
Regardless, the core structural engineering is the focus of the criticism, not whether it might leak. Also, since Space X's whole point is to compete on cost savings, it was a little strange to hear cost projections that were so optimistic.
The entire purpose of the design is explicitly to keep the tolerance for leaks at a level where, to quote the whitepaper "standard commercial pumps could easily overcome an air leak and the transport pods could handle variable air density"
Section 4.5.4 otherwise covers this, and does point out that for large leaks, braking would be required, but smaller leaks are intended to be dealt with as part of regular maintenance, with no indication that it'd need to affect operations.
> Regardless, the core structural engineering is the focus of the criticism, not whether it might leak.
That may be so, but most of the criticism I've seen of it appears to just ignore large sections of the whitepaper.
EDIT: For example, with respect to handling expansion/contraction, consider that the world has gas and oil pipelines that has to deal with far worse conditions without leaks.
Because the hyperloop cars are discrete (as opposed to the continuous flow in a pipeline), I'd expect them to cause a lot of stress on the pipeline walls if they had to run around the bends in an expansion loop.
Humans have been engineering expansion joints for various types of continuous structures for well over a hundred years, including sealed pipelines.
The new design requirements and constraints posed by the Hyper Loop concept just increase the complexity of the problem. Certain engineers love this kind of challenge.
of course a profound technical concept will provoke questions regarding its technical feasibility.
so what is your point? that it's impossible? that it shouldn't be attempted? that it's not a problem worth working through?
"naysaying" doesn't mean "saying no". "naysaying" is the inability to see a little further into the future based on the knowledge we have today.
> "The steel expands in summer due to heat. Where does it go?"
a cliche example but- i'd love to be the anachronistic fly on the wall listening to all the "where will the hot metal go???" people talking to the Wright brothers.
Amen. It's also kind of insulting how much HN has bought into this "Great Man" theory of engineering and development. Sure, Elon Musk is a smart guy and seems to be a good leader who sets bold goals, but the real geniuses that make SpaceX possible are the brilliant engineers working there--who you've never heard of.
Watching the way HN reacts to SpaceX, in contrast to say, NASA, or the ESA makes me think those organizations should hire a charismatic frontman, too.
Edit: For example, see my sibling comment: "The thing that intrigues me is in the new innovations he had in his rocket, and why NASA didn't have it before SpaceX." (emphasis mine)
The question is, without Musk, would all of those amazing engineers have spontaneously ordered themselves into a company to build a rocket that will eventually take humanity to mars?
Musk's function isn't to design the rockets, it's to believe so totally in the idea, to commit so much of his own time and money to it, to overflow with passion, that a generation of engineers are willing to follow him down a path to either greatness or ruin. History is littered with failed rocket startups.
You have to be a little bit crazy to believe you're going to do that kind of stuff. Hell, even the smallest startups face impossible odds for success.
NASA could have a charismatic front man. I'd nominate Neil deGrasse Tyson. But here's the problem: NASA is ultimately run by Congress and the executive branch, not Neil deGrasse Tyson. Ultimately, his words would mean nothing because he can't back them up.
Musk, when he says he's going to build a Raptor engine, has the authority to make it happen.
> Watching the way HN reacts to SpaceX, in contrast to say, NASA, or the ESA makes me think those organizations should hire a charismatic frontman, too.
Well, yes, I think they should. People are drawing the completely wrong lessons from Jobs/Apple. "There's too much worship!" well, duh. Jobs inspired people, and that inspiration led to extremely dedicated fans.
Jobs made use of that in the tech sector, but where we really need it is in sectors which are highly affected by the good will of humans.
Charity. Science. Care of the planet. The development of the human race. Very-long-term thinking. All these need charismatic frontmen, people who inspire others to think about their own future and the future of others.
> Watching the way HN reacts to SpaceX, in contrast to say, NASA, or the ESA makes me think those organizations should hire a charismatic frontman, too.
Absolutely, yes. Hell, look at what Chris Hadfield did for the CSA.
There is a big difference here:
Previously, NASA basically received what they requested in the contract specifications. The Atlas V was what the USAF specified in the EELV contract.
The SpaceX Falcon 9/Dragon was designed by SpaceX, driven by Elon Musk's requirements. The part where the design matched what NASA wanted for the COTS program was a happy coincidence, but NASA were not driving the original design specifications.
Of course, the F9/Dragon was adapted to NASA standards, and is also an effective satellite launch vehicle.
I am not familiar with the hyperloop concept so maybe I am wrong but I never understood the "cost is too high" argument. Is this not almost always the case on every technology breakthrough? Things like gene mapping and 3D printing comes to mind - someone had to started doing it at prohibitive costs so we can evolve the tech and get the prices down.
> Is this not almost always the case on every technology breakthrough?
In the case of the hyperloop the technology isn't too bad. We can likely build it without developing too much. Most of the technological problems are already largely solved in aircraft design.
In this case it is more a "this cost literally too many resources" problem. High speed rail is fairly simple, you clear land (expensive), flatten it, even it out, and then lay metal tracks with wooden/concrete sleepers.
With the hyperloop you're literally building a tunnel that has to withstand weather including extremes, withstand negative pressure internally without crushing, transfer the weight/internal/external forces down to pillars, and yet still you're left with the "clear land" problem as nobody wants to live under a hyperloop track, or have it blocking their natural sunlight.
Hyperloop might see some savings as it requires less land than high speed rail, but you'll easily offset that by physically how many resources go into the tunnel and pillars (and raising the tunnels into position and sealing them).
If all hyperloop was was a tunnel in the sky it might be easier to imagine the financials making sense. But then you add negative pressures within, and you're talking about aircraft skin the entire length of the thing, and then dealing with attaching these pieces of loop together on-site (so presumably double-riveting them like aircraft skins are, which is time consuming/expensive).
Imagine you need to cross a tightrope to do something amazing and everyone is afraid of heights.
Some forms of criticism are useful but yelling out "Hey, it's 2300 meters to the bottom, be careful!" is not very useful.
People often know the negatives, it's just easier to do the task when you don't look down. Often this requires self delusion. Otherwise "Don't look down, or think of white polar bears" would work for everyone.
Could you give an example of a constructive comment that was killed? While certainly there is a lot of optimism around what Elon is trying to do, I don't think that "I feel like I at a One Direction concert surrounding by a bunch of screaming teenage girls" is a reasonable reaction.
> Elon Musk likes to make fun of the competition quite publicly when they have an issue, while ignoring his project's own failures.
This seems pretty harsh. It's not like he went home, curled up in a blanket with a hot cocoa and told the engineers to figure it out by the time he came back to the office.
It would seem that the hyperloop is just an invented charade developed for use as a carrot to manipulate states into dropping their laws against direct sales from car manufacturers. That would explain why Texas is being courted now. They lost out on the gigafactory and may be more willing to capitulate to get a piece of other Musk projects.
it's not only hyperloop, "Musk said Texas could be a contender for future Tesla car or battery factories." And I am sure he will build them there as he needs plenty of them in order to produce millions of cars "by 2025"
Tell me about it. Close but no cigar, who else even has the gumption to try? NASA has been pushing rockets into space for fifty plus years and I have never seen them trying it; granted I may have missed it but I have pretty much watched most televised stuff since the moon landings.
From a political standpoint, privatization of space is probably for the best. Some people are automatically fearful of anything a private company does as if government entities were beyond reproach. There's probably nothing evil that Musk could do in space that a government couldn't do. Privatization in this case should have the effect of diffusing access to space which I should think was an overwhelmingly good thing. Unless you expect him to pull a Moonraker, I don't really see the problem.
Also consider, a lot of what happens in space is already accomplished through private companies. Lockheed and Boeing already launch most US military satellites. SpaceX really is just another launch company. They provide competition for government monopolies. That's probably a good thing.
"I have never been more impressed with a human being"
... in technology - I would add. Otherwise I agree. But let's not forget that technology is a niche, there area many other achievements of mankind, literature, arts, civil organizations etc.
The naysayers will most likely be those with less creative minds - can't blame them if they currently don't have the ability to understand fully what he's doing; unfortunately there's plenty of bullshit in this world to make people skeptical about everything - only a few are lucky enough during our time to get the opportunity to fully realize their own potential.
Interesting. It had quite the lean, And close to zero vertical velocity. Then it looks like it accelerated at the last second in an attempt to move sideways back the center of the barge.
I wonder if the top of the rocket was at or very near the center?
Also you can clearly see the landing legs deployed, jeez they look tiny.
Must just tweeted "Next rocket landing on drone ship in 2 to 3 weeks w way more hydraulic fluid. At least it shd explode for a diff reason."
From what I can tell, and I think you can see a bit in the video, when the grid fins ran out of hydraulic pressure they locked full in one direction.
The last burn this thing does is often called a 'suicide burn' as there are a couple complications to landing it. First, it only has enough fuel left for a short burn. Second, it's not possible to run the single engine they use to land it at a low enough thrust level that it can hover. i.e. 1 of 9 engines at the lowest possible thrust it can operate at is more than enough to accelerate the empty stage body upward. As a result they have to 'blip' it just before landing and cut at the exact time needed to reach 0-ish velocity at landing. This means the thing is moving _fast_ just before the video starts.
I'm guessing that with the grid fins locked in an extreme direction 24 seconds before getting to the barge they still had a lot of influence over the flight path since it was still moving fast. This pulled the top to an angle. The engine fired and the vectoring capability of the engine tried to toss it back over the ship but it just couldn't correct the lean before hitting the barge.
Hm, if I was the guy designing the control loop on that thing (not gonna happen in real world, but bear with me), I would definitely take into account the fins position - the real position, not the one I want them to be in.
Not that it would have helped anyway in this case.
I suspect that the code takes the fin's starting position into account in each planning cycle but also assumes that the fin will move as directed in the future.
To me, the video has an optical illusion effect, caused by the bright light from the engine. The rocket is not directly over the platform, it’s actually off the far corner by about 50-100 feet, it comes horizontally into the platform and crashes over it. Meaning it’s not close to the center of the platform and trying to accelerate off of it, it was laterally moving over it from the side and crashed the engine into the barge, which kicked it up over the platform.
Maybe they could improve the failure behaviour with some failsafe mechanism? *If the rocket is not within a certain envelope, gain as much distance to the pod as possible? Later when they want to have landing on land, a designated area for aborting could be used.
Looks like it did not come down vertically but at a slant, but they got the positioning better than I thought they would on this try. One thing to note is that it is from now on officially a very bad idea to piss off Elon Musk if he knows where you live, being able to hit stuff with this kind of accuracy using rockets from space is normally enough to get you placed on the 'axis of evil' list. Incredible precision.
Cheaper to use drones / cruise missiles / HE carried by a flock of small robot helicoptors; many simpler schemes that are less traceable, unless developing a reputation is your intent. There are uncountable ways to kill people without needing to invoke Hollywood class exotica.
[NB: I thought about not posting this, because people who are paid to not have a sense of humor about these things almost certainly read HN, but fuck that, screw "chilling of speech"]
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.
A kitchen knife can work across intercontinental distances. Buy plane ticket to city where target lives, buy knife in local store, get taxi to location of target, stab target to death with knife. It's less glamorous than drones and missiles, but it's just as effective in the scenario that kicked off this thread, where one civilian decides to kill another even though he'll be writing off his own life in the process. Shinier weapons don't change that fundamental.
Drones, at the very least, would not be that hard. They're already developing a solar-powered drone that can stay in the air for years; crossing a few oceans are definitely in the realm of possibility.
I'm trying, but not succeeding, to imagine a non-fiction situation where a corporation has any business advantage in owning and/or controlling an ICBM. Can you expand on your comment? What would a corporation do with this, other than to perhaps implement same day delivery of packages around the globe?
The best historical example is the British East India Company whose private army conquered India and ruled it for about 100 years. Another example is the United Fruit Company in South America that bought local armies to crush rebellions.
Since the US government has become so corrupt American companies have found it easy to use the power of the US government to coerce other countries, for example for intellectual property treaties. But it’s feasible that in the future companies might want their own military power to get their way.
I don't necessarily believe this to be a possibility... but if the US contracted out "security" to companies like Blackwater, it seems at least.... plausible that they could contract out "missile defense."
Space launch systems are so deeply dual-use it's not even funny. Orbital rockets are very similar to early, low-readiness ICBMs - modern systems prefer solid fuel, since they can be safely kept fueled for longer periods of time, but aside from that the biggest differences between a Falcon 9 and an ICBM is how ridiculously overpowered the Falcon is, and its lack of re-entry countermeasures (MIRVs, decoys, etc.). Which is why anyone working at a company like SpaceX is subject to the same technology export restrictions as weapons companies.
For example, if SpaceX can get e.g. the Dragon capsule to land with a reasonable accuracy on thrusters, and then put a warhead in it (or multiple warheads) , that's quite a capable weapons system right there. In fact, it's even capable of fractional orbital bombardment, which was considered so destabilizing during the Cold War that it was specifically banned in SALT II.
tl;dr - Elon Musk will, within a couple of years, control a system that can be adapted into an ICBM within a very short period of time and with minimal investment.
Theoretically, they could be mercenaries, hiring themselves out to some corrupt dictatorship, guerillas, drug lords, state-sponsored terrorists, or similar groups. They would collect a bunch of money and launch a missile at their enemies. Turning that into a sustainable business model has ... hazards, of course.
The Economist had an interesting book review on a book positing a return to medievalism -- where the state does not have a monopoly of force -- and it's interesting: a little far-fetched and unlikely, but just this side of plausible. http://www.economist.com/news/books-and-arts/21638096-how-pr...
One notable bit was the incident where "a famous actress turned humanitarian [...] with various human-rights groups, wanted to hire Blackwater to set up safe havens in Sudan to protect civilians fleeing the janjaweed militia" but decided against it.
It's basically the company-as-government idea, wherein a company is so big it begins to function like a government, including military operation to further its goals.
Which, tangentially, is the model presented by extreme libertarians as the way of the future and how we can do away with government for good.
I feel like I remember seeing a steampunk variant of this idea in some animation/comic (maybe in the Flight series or Bolt City?)
Scene: ten miles over a major metropolitan city, an ICBM is racing in. Seconds later the nose cone is jettisoned and a cluster of small cones begin pouring out. Little grid fins pop out and they scatter out like dandylion seeds to the wind. Zooming on one, we watch it hurtle towards an enormous skyscraper. The cone's nose begins blinking from green to red, blinking faster as it approaches its target. Screaming closer and closer, we see the tower suddenly open a panel showing a large tank and the cone slams into it with an enormous splash. As it settles a platform gently captures it and raises it up to a crew of people with mail carts ready to distribute the packages.
That is awesome! I appears the stage has maybe 10 m/s horizontal velocity and less than that vertical, but at that angle I can see how difficult it would be for just engine gimballing to get get it vertical again. I wonder if the barge is equipped to record a downlink of telemetry from stage. Once it gets close enough you should be able to shoot over at least some data which the barge could presumably keep 'safe' in a blast protected storage system.
Could an aeronautics person kindly explain why it's so hard to get this thing to land as it's supposed to? I'm not being judgmental at all here; I am saying that as a software engineer with no aeronautics experience, I simply don't understand the problem. Assuming all of the sensors indicating tilt, altitude, etc. are accurate, the software portion coordinating where and how much thrust needs to deployed to keep it level and descending at an appropriate speed should be relatively straightforward to write. And yet, with at least dozens of undoubtedly brilliant people working on this very problem, the result is the world's most expensive fireworks show.
Not aeronautics, but control systems engineer and I've seen the explanation. The rocket engine they use is too powerful to hover and move towards the destination in a slow adjustment loop. And there is no throttle control on the engine, 70% minimum which is still too powerful. In order to land you turn the engine off and wait to pick up some vertical speed, then in the last N seconds you turn the engine on to kill the speed you picked up from the freefall just before you hit the ground. Best described as a hover-slam. If your position during the freefall is off, you can't just keep the engine running to hover around and fix it (like they do in their dev rocket), it would fly up quickly if they do. In this video they still have lots of fuel in the rocket so they were trying to hover a little, however in the real landing presumably the rocket will be empty thus the hover-slam will be harder.
> The rocket engine they use is too powerful to hover and move towards the destination in a slow adjustment loop. And there is no throttle control on the engine, 70% minimum which is still too powerful
I've seen this a lot, and I've also read about how many times each engine can be re-lit. Can you talk a bit about why the engines have a limited number of times they can be lit?
If there were no limit on that, I'd want to just turn the engine on and off a bunch to get the right amount of thrust to hover.
While there's a limit in the amount of (highly toxic) TEA/TEB hypergolic fuel that's carried in the ignition system I'm not sure it's the bottleneck.
The limited number of times the Merlin 1D can be relit is probably referring to the re-usability aspect (from memory they tested "cycling" the engine something like 40 times in qualification testing, but it's a little unclear exactly what a cycle entails). It's the associated "coking" of the engine with hot and sticky carbon/soot from the incomplete combustion of the kerosene that's been speculated to be a major hinderance to the long-term engines survivability.
Other than consumables, it's probably the high (and variable) latency in the switching time that restarting the engine in quick succession that would make it problematic, in addition to the engine damaging aspects you mentioned.
Hover-slamming a first-stage with a Merlin 1D has been heavily tested by F9R-Dev1/2 - it's a completely workable solution that minimizes engine restarts over the flight profile to 3 (boostback, re-entry burn, hoverslam).
While the switching the engine may be made to be workable solution which can effectively throttle the engines between 0% and 70%, a hoverslam with a vehicle with thrust/weight ratio > 1 gives less stress on the entire (~$40 million F9R first stage) vehicle to be reused.
One limiting factor of reignition is the mechanism for lighting it. Some for example use a very combustable fuel that ignites in the presence of air to then ignite the main fuel flow. Depending on what mechanism the Merlin uses, this could limit their number of reignitions.
Thank you. I assume there are legitimate reasons for not having throttle control, but perhaps they should look into adding it. The hover-slam seems risky.
Elon mentioned the problem was that they ran out of hydraulic fluid about 30 seconds too soon. The rocket had to try to right itself using only engine gimbaling instead of using the waffle paddles, which didn't work out so well.
The great thing is they've already fixed the problem for the next flight.
I wonder if the thin cylinder shape is to blame and if it would be easier to land if it sported a stabler shape. Can aerodynamics be compatible with something like a tetraedron mesh?
I wonder what actually exploded there? Part of the argument for why the landing was supposed to be relatively safe was that the stage would be mostly empty of fuel by the time that it landed, so there wouldn't be much to explode if something went wrong. So is that an explosion of the remaining fuel in the rocket, or something on deck?
Not easy to do with Vine's crappy interface but if you step through it and stop you will see that the rocket is decelerating and when it gets close to the platform it adds thrust which then increases its pitch over (which would be expected without anything on the top to control pitch) and then it increases thrust still more (presumably to right itself) but the back end of the stage is already below deck level at that point. It comes across the back of the barge and clips the engine section which separates the engines from the fuel supply. The fuel and oxidizer continues coming out and burns rapidly. That ends up tossing the remains of the rocket off the screen to the left.
We can't tell of course from the video if the barge was moving (by virtue of the camera being fixed to the barge it makes it appear to be unmoving in the video).
If you are reading this SpaceX, here is my suggestion for capturing more data in future flights. Install quad copters on the barge which launch once the barge detects the landing stage is inbound, have them position themselves using the GPS from the barge 100 yards out in four directions. Then have four reference lights on the corners of the barge (can be LEDs) to give you the ability to back compute angles from the video. Stream video from the quad copters back to a secure video storage facility in the barge which is designed to withstand rapid disassembly of the barge and float. Could make for some awesome videos too.
I've been watching an old scifi series this days, called Starhunter. They had that obvious (but unusual) concept of drones that gripped on prey and delivered it to the mothership.
> If you are reading this SpaceX, here is my suggestion for capturing more data in future flights. Install quad copters on the barge which launch once the barge detects the landing stage is inbound
I'm sure they will do that - once the landings become predictably successful.
This is the tweets by Elon Musk on this
"Tks. Turns out we recovered some impact video frames from drone ship. It's kinda begging to be released…"
" Before impact, fins lose power and go hardover. Engines fights to restore, but …"
"Rocket hits hard at ~45 deg angle, smashing legs and engine section"
"Residual fuel and oxygen combine "
"Full RUD (rapid unscheduled disassembly) event. Ship is fine minor repairs. Exciting day!"
"Next rocket landing on drone ship in 2 to 3 weeks w way more hydraulic fluid. At least it shd explode for a diff reason."
https://twitter.com/sacca/status/556107612396457984
A landing stage will still have some fuel and oxidizer on board, to keep burning all the way to the deck, though not much compared to when full. But 1% of ~385,000kg of propellant is still enough to go bang. There's also a fair bit of energy in the pressurized tanks. (It's a turbo-pump engine, so the tanks are not kept at high pressure, but they still have 3-5 bar/40-70 psi and it's 70m tall structure.) That's what tears the stage apart.
Looks like it hit the fuel tank, so the pressurized kerosene was exposed to the atmosphere and a burning engine. Thus fireball. It would have been worse were the LOX tank ruptured at the same time. But it's not a very big explosion; doesn't even overexpose the camera for more than a frame.
You need some margin for error to assure that you have enough fuel during the last fuel seconds to hit the marge at a safe speed, this means that there will likely be some fuel left over. In terms of a rocket exploding, that explosion seemed tiny. Compare it to the Antares [1], which exploded just a few seconds after launch.
That was pretty small and safe as rocket explosions go. Launch pad explosions with a full load of fuel and oxidizer are huge and would have engulfed the whole ship in flames.
It doesn't take much to make the kind of explosion you see in the video (those chemicals are quite volatile). I think the safety comes from that being the extent of the explosion. Compare that to a fully-fueled stage, which would have 90x more fuel, a 90x larger fireball, shock wave, etc.
"Mostly" != "entirely". Also, don't forget the rocket engine itself
My guess would be the explosion was of the remaining fuel in the rocket engine and tank. Either that or it wasn't actually an explosion, just burning fuel-air mix spewing about after the rocket nozzle deformed too much.
I figured it was just the automatic aperture on the camera causing the flame to simply appear bigger. I'd point out that the sound didn't change (no boom) but then maybe the mic was already clipping. Still, I'd like more detail to be certain whether something exploded.
Edit: no, you're right. I just mis-remembered. When I reviewed the video, it looks like the thing breaks open and I'd suspect the last remnants of fuel are spilling out.
I'm amazed it's taken this long for innovation to happen in rocketry. Here's an entire industry that -expects- your production model to explode and crash after one use. Literally anything that doesn't explode and crash is a step forward. And it's been this way for 50 years!
Wow, what an amazing feat to come this close. To think just ~100 years ago humans took flight for the first time. Now we are able to launch a rocket in orbit, then fly the first stage to land on a small platform floating in the middle of the ocean.
>Now we are able to launch a rocket in orbit, then fly the first stage to land on a small platform floating in the middle of the ocean.
You know we landed on the moon, right? I mean, this is cool, but from a sheer "fascinating achievement" standpoint, this is at least a few notches behind that.
Can't we just appreciate how both are fascinating for entirely different reasons? I think it's pretty amazing we were able to get a rocket to land (edit: well, almost land) to this precise a spot - and all by itself, without human pilots. Sure, it's no moon landing, but it has certain other challenges the moon landing didn't have. I think both are really cool.
Landing on the moon was a historic achievement, but this work with reusable rockets is on the same scale. In order to colonize space and no longer be bound to just the Earth, we will need transportation that costs less than a billion dollars per person. Apollo showed us that the stars are in our grasp, SpaceX wool provide the means of actually grasping them.
As others noted, it's not, but for different reasons. The moon landings were sort of a different task (get people to the moon and back and don't kill 'em). SpaceX is trying something a bit different though: make this whole thing boring and industrialize it.
The first is a historic series of one-shots that really can't be repeated for any sane economic purpose. The second is an attempt to automate and ruggedize it.
It's sort of why the sky-crane landing on Mars was such a historic achievement, arguably far more complex than the Apollo work. Don't let that diminish the greatness of Apollo, though. Today we have tools bording on magic, while they literally used wax pencils and slide rules. But don't let that diminish the accomplishment here, where the tools are being properly leveraged to make LEO an everyday occurrence.
You have two methods of putting hydraulic fluid into a system: closed and open. Closed systems require a pressure system to keep the pressure up, open ones use a pressurized hydraulic that is expended. The open system was used in this situation to reduce the weight necessary to run a closed system.
As I understand it, there are fins that deploy in order to steer the rocket on the way back down (the first stage). They are really cool "Grid Fins" [1] that work even in supersonic flight. In particular, they are used to prevent the rocket from spinning, and to keep the rocket upright.
The rocket can also steer by "gimbaling" the motor (pointing it in different directions), but that has limitations; changing the rocket's orientation will also change its velocity (like balancing a broom on your hand).
In this case, the hydraulic fluid is used to rotate the grid fins and therefore keep the rocket upright. When the fluid ran out, the fins wouldn't work, which is why the rocket comes down tilted.
The hydraulic oil is not used as a 'fuel' to burn but to control the actuators for the grid fins. So if you lose control because you run out of hydraulic oil the last bit of the descent will be uncontrolled. So they almost made it with enough hydraulic oil, which means that next time the grid fins will work all the way down, which leaves a ton of other possibilities for mishap (too high a descent rate, rogue waves, barge being slightly at an angle and so on). Makes you wonder why the hydraulic circuit isn't closed, probably they figured an open loop system is more reliable than a closed one (half the gear and no need for a sump, which comes in handy when you have to deal with gravity coming from all directions).
Open loop is lighter than closed. No need for a closed loop if you have a set time of operation. I thought I heard they were also pumping the fuel through the system as well so I imagine this amounts to just a bit more propellant and another go.
The fins turn and are powered by hydraulic fluid. When it ran out, the fins stayed pointing in a certain direction, which meant the stage couldn't steer. Then it hit the ship.
It's from a time when it was common to offer cigars as rewards for playing carnival games. If you missed the target or milk can or whatever, "close, but no cigar!".
> From the practice of giving cigars as prizes at carnivals in the US in the 19th century; this phrase would be said to those who failed to win a prize.
I'm annoyed by this trend of having posts with 0 context or analysis on the top of the frontpage. Yesterday we had a link to some bitcoin chart showing a sudden drop in price (why? I still don't know). A few days ago it was a gif of a flowchart for some brainfuck interpreter (I had to dig into the comments to find the link to the source code). And now... Vine?!
The problem with that kind of submissions (images, short videos...) is that they're quick to overtake more in depth articles because people upload it in seconds without 2nd thought. I don't want the front page of HN be overtaken by imgur posts, if you see what I mean.
On most sites like this a little context can be added by the title on the social news site, but Hacker News does not allow that. Moderators will change the title to whatever the page has.
I wonder what the cost savings to space there are for buying a trip for a satellite on a "used" booster. Also if SpaceX is recycling the 1st stage, I wonder if they have plans to "Recycle" the 2nd stage in orbit.
We'll just have to see on that - it depends a lot on how many times the 1st stage can be reused, how much the refurbishment costs, and what the risk involved is. The first launch is pretty low-risk at this point, but how risky is the tenth launch on the same 1st stage?
IIRC, they are on record as wanting to eventually recover the 2nd stage as well. It's a much tougher problem though - the 2nd stage has much higher velocity at engine cutoff, its engine is a variant designed to operate in vacuum and reportedly can't be made to operate in the atmosphere easily, and any additional hardware added to the 2nd stage has a much higher penalty on the rocket's performance than on the 1st.
That's interesting, though it doesn't take into account all the non-rocket costs in the launch.
Also the factory has to exist, probably the yearly cost does not scale linearly with the number of engines produced.
That said, once you go there, if launch prices drop to one tenth, all kinds of other things can start to happen.
I imagine the cost savings would be huge. The fuel and oxidizer for a typical satellite launch is only a few hundred thousand dollars, but the rocket is in the 10's of millions. Even if you add a million or 2 for refurbishing the used booster it's still huge.
IIRC SpaceX's next generation of rockets will be designed so a reusable second stage will be possible.
I feel if the 1st stage booster had an attitude control system toward the top like the BRAHMOS missile [1], the lean could've been corrected to at least have the rocket be upright when it impacted the platform. Although the choice to add an attitude control system would probably take up more space and add mass which is critical for a stage rocket.
The Falcon 9 does have attitude control system towards the top: the nitrogen cold gas thrusters in the Reaction Control System is located in the interstage portion of the vehicle - right at the top of the first stage
The gimballing engines give attitude control at the bottom, as far as I understand
Nitrogen cold gas thrusters don't give enough "oomph". Maybe if the rocket was inclined at angles x<10 degrees with respect to the vertical axis it would've been able to correct but this rocket was leaned over at what seems to be 20<x<=45 deg. In other words they wouldn't of have been powerful enough to correct that much of a drastic lean the Falcon had coming down.
But I'm sure with the hydraulic fluid corrections a stronger control system won't be needed to fix large angles of attack but it would be nice to have as an emergency system.
"Have it and not need it/Need it don't Have it" really doesn't work with rockets because of the mass requirements
Those are just grid fins which are used more for steering than attitude control.
If I kick the rocket over those fins won't do any thing because they can't correct the force I applied to kick the rocket over. An active thruster (an attitude control system) can recorrect the force of my kick and reorient the rocket vertically.
How are you going to kick a rocket falling from outer space? You don't need active thrusters (and all the extra weight that comes with it) when gravity and wind will do the job for you just as well.
> How are you going to kick a rocket falling from outer space?
I meant if there was some external force like a wind shear or grid fin/hydraulic line failure that pushes the rocket hard enough on descent to alter it's vertical orientation, those grid fins won't really do much to correct that force.
> Gravity and wind will do the job for you
You cannot control gravity or wind. You just have systems that manipulate those forces. Grid fins are a passive system in that they manipulate the fluid the rocket is in to steer it on course but not to correct drastic attitude alterations.
But again, if the updates to the hydraulic lines work out, then they won't need the active thruster system. Adding an active thruster system is just engineering for worst case scenarios.
On this video the trajectory seems a bit weird. It looks like the rocket does its approach slightly to the right and afar, and then when it gets closer it changes direction and goes towards the camera, more or less in the direction of its tilt. As if the rocket began to tilt only around the end to a point the engine could not compensate anymore except by adding a large horizontal acceleration.
The rocket ran out of power for its control fins at some point during the descent, so this is indeed partially out of control. The engine is doing a lot more than was intended during this video.
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.
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.
love that they're trying something new and exciting.. you're gonna fail when you're going for it.. but at least someones going for it. looking forward to hyper loop.
People always compare him to Jobs but I don't think it's right. Jobs hated any sort of public failure. He pushed the envelope in some ways, but never put something out there until it was polished and consumer-ready. Jobs was great at seeing how technology could be combined in novel ways and how to boil products down to exactly what they needed, but he didn't push forward entirely new tech, and I can't imagine Jobs publicly showing a video of his flagship product exploding into a fiery mess.
More business sense than Tesla. Less in the way of personal technical/scientific achievements.
He's not very popular on the internet for a variety of reasons, but I think that Edison is a better comparison. Not the first person I'd compare him to, but I'd sooner compare him to Edison than Tesla.
My point was using 'Tesla' in the same sentence as Elon Musk is ambiguous and mildly confusing in this case. I was saying the poster should have used Tesla's first name as well to remove confusion.
> 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.
So the rocket just explodes and the trash goes in the ocean? Thanks for polluting our oceans. Can I take all my household trash and just dump it in your living room?
Getting a sub-orbital rocket traveling at multiple Mach to decelerate and land (vertically, nose up) on a point in the ocean that's about 200 square feet in size?
At the relative ranges we are talking about here, those numbers are probably more comparable than many would realize. Consider, Mars at its closest, is over 6700km away. The space station at its furthest is 418km. (Assuming I looked up the correct numbers, of course.)
Considering it came down from 60 miles up and 5x the speed of sound, yes, this is pretty damned close. Especially given the probable cause, needing just a little more hydraulic fluid, and the fact that it's literally the first try for real landing.
This wasn't really a screw up, though. The mission was accomplished - successful resupply flight to the ISS. The landing was a R&D test - the first of this nature - with the leftover pieces.
I'll bite, the second phrase never happens. NASA isn't trying in the same way that SpaceX is trying at all, they are doing amazing stuff, incredible feats like Mars rovers. When that feel of commentary comes around is when the bureaucracy of the government gets in the way of taking the risks to make the discoveries possible. We cheer SpaceX because we see them taking action, taking risks, and making progress.
We get frustrated with NASA because we've gotten use to the idea of go fast break things. However http://www.nasa.gov/missions/schedule/index.html shows they are launching 3 new projects, they just aren't the sexy science right now so don't get all the cheering. You better believe there was a lot of ooo's and aaahhh's around the new Hubble photos. So they come out with something amazing like that, then you hear that the government (in 2004 mind you) is not willing to fund them enough to keep Hubble alive, combined with the feature of loss of human life from the 2003 Columbia disaster making them risk averse.
When we see SpaceX taking risks and making discoveries, or SpaceShipOne doing the same and exploding, but then the team keeps going, we cheer that, we rally around the against all odds determination to make space accessible.
NASA has done amazing things, but they are hamstrung by the government and their own bureaucratic growth. What once was a warm blanket in the space race is now being used to try and smoother them to death now that there isn't a commercial or war time payout.
SpaceX is certainly doing great things, but where was this vid a couple days ago?
When I first heard of the hard landing I jumped online to see the vid. But no vid appeared. Then I realized what was happening. A vid of a crashing rocket is never a good thing for a spacelaunch company. It's just bad PR. Thinking back, we don't see many vids from SpaceX that aren't unqualified successes.
They surely had this vid withing minutes, of not seconds of the landing attempt. But they delayed its release until the media and the public were educated sufficiently to understand that, despite the flames, this landing was not a failure.
Usually when there's an error or a failure on a mission, there will be an immediate lockdown of all PR, videos etc to analyze the problems first and understand what happened before the official release of material. This might seem trivial but I'll type it anyway.
First off, if SpaceX released videos and didn't know what happened, the press would obviously speculate and SpaceX's brand would lose value somewhat. If the videos were released and the problem is a little harder to solve, well now you have a video of your error circulating and you don't even know what to tell the press what happened.
If you watch the Mission Control footage during Columbia's fatal reentry, when Houston realized the worst had happened, Flight Director Cain said over the intercom "G.C., FLIGHT, Lock the doors". This was meant figuratively and literally; He told Ground Control to lock the doors of Mission Control so no one could leave, and that all information regarding the incident would not leave that room. Not even the President could enter that room after Ground Control locked the doors.
I think you're getting downvoted for the perceived negative tone, which I'm not sure if you intended. It's true, but I don't see anything wrong or sinister about it. If I was in charge of SpaceX, I would have done the same thing.
Even without the video, several news sources jumped into calling the mission a failure, even though the actual mission of resupplying the ISS went perfectly, and the landing was a long-shot experiment. Those calls would only be louder with a flashy explosion video with no backing explanation on hand, ready to go out with the news of the landing failure. By the time more info was available, the story would be gone, and the explanation would be ignored. This would damage SpaceX's brand, ability to get Government missions and private contracts, etc.
It's also entirely plausible that they didn't bother to install a high-speed data link from the barge to the mainland for the purpose of getting the video instantly. It would probably be an expensive and finicky way for them to instantly distribute video that would more likely than not be damaging to their brand.
It would be embarrassing for SpaceX if somebody from the public discovered something in the video that SpaceX had missed. It therefore makes sense that they would sit on the video for a while, making sure they had learned as much as there was to learn from it before releasing it to the public.
The guy is pushing the envelope on perhaps the most difficult engineering/technological endeavor ever attempted by a private company - and he's making it look cool and futuristic.
As if that wasn't enough, he's doing this in two different industries simultaneously.
I'm not saying he can do no wrong, but I'm just flabbergasted that there are still so many armchair critics and naysayers when it comes to Elon Musk.