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Background on the Falcon 9 Launch
- mannykannot 11y ago"[100Km altitude] is the equivalent of the starting line of a race. The race itself is the kinetic energy." Did you get that, Jeff? The truth is, they have both achieved an astonishing amount.
- andys627 11y agoComparing apples (going up then down) to oranges (getting into orbit). Pretty awesome to see these guys putting their cash towards this! Hope a rivalry heats up and I can goto Mars for $3.50.
- lotyrin 11y ago3.50? But then you'll get ancient cryptids asking you for rocket fare.
- mikeash 11y agoBlue Origin is cool but it's certainly not astonishing to me that a billionaire is able to send a rocket on a suborbital trajectory and recover it. It's certainly more than I've ever done by a long shot, but it's not a very interesting achievement unless you're interested in five-minute space tourism. I don't think BO's achievement here has many implications for space travel.
- fixermark 11y agoI wonder its implications for terrestrial travel, though? We are in a post-Concord era, after all, but suborbital flight could get you to any point on the planet pretty quickly if the price is right.
- thomashabets2 11y agoThis may be interesting to you: http://www.antipope.org/charlie/blog-static/2015/01/why-were-not-going-to-see-sub-.html http://www.antipope.org/charlie/blog-static/2015/01/why-were...
- erikpukinskis 11y agoIt's amazing in 10 years we've gone from an X-prize to do exactly that to "not interesting".
- alerkay 11y agoYou're right, both achievements are huge. That said, I'm not too sure I understand the line "the kinetic energy transfer at a 100 km reference altitude is what matters"... What is the "kinetic energy transfer at 100km" ? Why not say that what matters is the "kinetic energy transfer", period? It doesn't make any sense to me to put it the former way.
- mrec 11y agoOne thing I've not seen mentioned in the coverage so far: how much payload is sacrificed by the need to keep fuel in reserve for the return to base? I'm guessing the sacrifice is roughly equal to the mass of unburnt fuel in the booster at the point of booster separation, but don't much trust my intuition on these things.
- msandford 11y agoYou're right not to trust your intuition! Good call. It's actually going to be much, much less than that due to the nature of the rocket equation. https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
- msandford 11y agoGiven that I'm not wrong as the above link shows (http://aviationweek.com/blog/nasa-cnes-warn-spacex-challenges-flying-reusable-falcon-9-rocket http://aviationweek.com/blog/nasa-cnes-warn-spacex-challenge...) would anyone care to explain to me for a second why I'm getting downvoted? I'm happy to be less stupid if that's the problem, but I don't know what thing it was that I did that was stupid.
- rory096 11y agoAbout 30% returning to landing site, 15% returning to a barge downrange. Note that the rocket's still perfectly capable of running an expendable mission if the payload requires it. The mass figure on their website[1] is for reusable. [1] http://www.spacex.com/falcon9 http://www.spacex.com/falcon9
- mannykannot 11y agoI don't think you could allocate all of the landing fuel load to payload as any addition to the payload also requires additional 2nd. stage fuel.
- mikeash 11y agoYou can run the first stage longer without any extra second stage fuel. Adding performance to either one (within limits) increases the performance of the system. Using the landing fuel for a launch would allow for a heavier payload without changing the second stage. The first stage would do more of the total work.
- nathanielc 11y agoMy favorite way to describe orbits is 'constantly throwing yourself at the ground but moving so fast that you just keep missing', hence the constant free-fall/zero-g.
- Swizec 11y ago"The knack of flying is learning how to throw yourself at the ground and miss." ~ Douglas Adams
- nathanielc 11y agoYep, that's the origin of the quote. Thanks.
- yellowbeard 11y agoThere is an XKCD "what if" that explains this: https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/ "The reason it's hard to get to orbit isn't that space is high up. It's hard to get to orbit because you have to go so fast."
- logicallee 11y agoHow fast do you have to go? Easy. Look out at the horizon far enough that you can see it drop (for example a mountain etc). You have to go so fast that in the time it takes you to reach that point, you only drop by the amount the horizon falls.
- chrisseaton 11y agoCould you make a cruise missile that didn't need any wings or other surfaces for lift - only forward propulsion - that just went so fast that it was effectively in orbit, but nor far above the ground?
- lordnacho 11y agoThe loss from atmospheric drag would be enormous. If you were on a planet with no atmosphere it would be no different from any other orbit though.
- sixQuarks 11y agoElon is actually great at explaining things in simple terms. The writing on WaitbutWhy.com is very similar.
- dcgoss 11y agoElon has said himself that he is a fan of WaitbutWhy.com
- sixQuarks 11y agoWaitbutwhy did a few in-depth articles about him and his companies after Elon invited him over for interviews.
- veritas3241 11y agoTim Urban, the author of waitbutwhy.com hosted the launch event. He's the goofy guy with the black pocket on the right side of the screen.
- blizkreeg 11y agoClearly this man's intellect is through the roof. Reading this post and him explaining these concepts in such first-principle terms (despite not being a physicist/rocket engineer) indicates his in-depth understanding (nothing new there). I know he has a Bachelors in Physics but bear with me. But, I'm just in awe and I keep thinking 'how does he do it?'. He's running two intensely technical and risky companies. Yet he seems involved in and knowledgeable about every aspect of their operations and tech. And finds the time to write a post like this before what is an incredibly important and defining endeavor. What can us, mere mortals learn from him? We can't change our baseline raw intelligence (which effects how quickly and deeply you can learn new things), but are there other patterns we can replicate in our lives?
- the_economist 11y agoHe has a reputation for being an extremely hard worker.
- marktangotango 11y agoIndeed, I'd wager that raw intelligence is highly overrated. Hard work trumps intelligence. Hard work and intelligence are an unbeatable combination. >> What can us, mere mortals learn from him? We can't change our baseline raw intelligence (which effects how quickly and deeply you can learn new things), but are there other patterns we can replicate in our lives? Become an autodidact, and study, study, study.
- madaxe_again 11y agoIntelligence undermines hard work all too often. I wasted years of my life coasting, as coming top of the class in everything was easy, and only actually started applying myself after university, when it rapidly became clear that intelligence alone doesn't cut it. You've gotta be smart, you've gotta be prepared to work insane and thankless hours, you've gotta be tough as nails to hear but ignore the naysayers, you've gotta be willing to lose everything, and above all, you've gotta believe in yourself. Only when you put all of those together (with krazy glue, of course), only when you are leading yourself, can you hope to lead others.
- panic 11y agoNice article, but I couldn't pass up a chance to correct Elon Musk's math: It is important to note that the amount of energy needed to achieve a given velocity increases with the square, so going from 1000 km/h to 2000 km/h takes four times as much energy as going from 0 km/h to 1000 km/h, not twice as much. Three times, not four--you already spent a quarter of the energy getting to 1000 km/h. Getting the rest of the way to 2000 km/h takes the remaining three quarters.
- notdonspaulding 11y agoI believe you've misunderstood his English. If it takes 1 Joule to accelerate the mass from 0-1000km/h, it will take 4 Joules to accelerate the same mass from 0-2000km/h. Elon is calling that four times as much as because he's considering the total energy required to accelerate from 0 in both numbers. I think you're just accounting for it differently by saying it takes 3 times as much as the original energy input to go from 1000km/h to 2000km/h. I'm a complete physics novice, I'm open to being schooled on this if I'm completely missing both yours and Elon's concepts here.
- pbreit 11y agoI don't think he worded it quite right but the inclusion of "not twice as much" makes it clearer that he was referring to "0 to 1,000" vs "0 to 2,000" (not 0 to 1,000 vs 1,000 to 2,000). So I believe the error was in the writing, not the math or understanding. Which he even pre-apologized for presumably in an attempt to assuage the nit-pickers.
- w_t_payne 11y agoIf we can land the rocket accurately enough to put it down on a tiny barge only slightly larger than the rocket itself, then why do we need to tolerate the weight of the landing legs? We already have industrial robots that can move and grasp heavy weights relatively quickly over distances of several metres -- it doesn't take much imagination to conceive of a similar contraption being used to arrest the descent of the rocket over the final few tens of metres of its' descent - a sort of brobdingnagian robotic catcher's mitt. Granted, this might be a bit on the expensive / elaborate / bizarrely over-engineered side -- but it would look utterly awesome.
- w_t_payne 11y ago... or (as a less mechanically complex solution ...) use the same concept as the arrester cables on an aircraft carrier flight deck -- but upended to catch a vertically descending vehicle. (No flight deck required -- just cables suspended between two towers and an arrester hook at the top of the rocket -- which just has to be lighter than folding legs at the bottom).
- mrfusion 11y agoThat's a great idea. But I think they want something really general purpose that can land anywhere and possibly even on Mars. Also the empty rocket might be too weak to be grabbed by anything. They compare the thickness to a tin can.
- ggreer 11y agoThere are several reasons why landing legs make more sense: – Any flat chunk of cement is a landing spot. That means more places to land in case of contingencies. For yesterday's mission, SpaceX had one primary and four alternate landing zones.[1] – I doubt industrial robots can withstand rocket exhaust. As helicopter footage shows, the landing pad got lit-up pretty good.[2] Remember, the first stage is over 40 meters tall. Those are some massive flames. …and most importantly: – Landing legs work on other planets. 1. Map: http://www.americaspace.com/wp-content/uploads/2015/12/LZ1.jpg http://www.americaspace.com/wp-content/uploads/2015/12/LZ1.j... (from http://www.americaspace.com/?p=89910 http://www.americaspace.com/?p=89910) 2. https://www.youtube.com/watch?v=ZCBE8ocOkAQ https://www.youtube.com/watch?v=ZCBE8ocOkAQ
- kibwen 11y agoThe article mentions that the water landing requires less fuel to return the rocket because it doesn't have to spend fuel overcoming its initial ballistic trajectory. In the water landing scenario, how far away from the launchpad is the landing barge? I'm wondering about the economics of launching from a site where your first stage trajectory is entirely overland, to avoid the complications of landing on a barge that's being tossed in the sea. Though it might be hard to find such a site in U.S. territory that's both near the equator and sparsely populated.
- timdierks 11y agoI found a reference that the barge was 320 km downrange in the earlier tests. The Bahamas look to be an appropriate distance from Florida, although to the southeast of Cape Canaveral. From SpaceX's planned Texas spaceport, there's nothing at that range but gulf.
- fixermark 11y agoHypothetically, I imagine they could anchor a stable ocean platform out there if they find it's easier than the barge. No idea if it actually would be easier than the barge though.
- skykooler 11y agoIt would probably use much less fuel to boost the trajectory to land in Florida than to turn around and fly back to Texas.
- grecy 11y agoI was wondering about that too. It would be cool if they could launch from somewhere south of San Antonio, TX on the water, and land in Florida so it doesn't fly over land mass for safety reasons.
- pbreit 11y agoThe cost of the fuel or opportunity cost of "lost" cargo space is a fraction of the value of saving the rocket. It's not really worth worrying about.
- idlewords 11y agoI'm having some trouble with the opening salvo here: "Now imagine placing a marble somewhere on that slippery sheet -- it is guaranteed to fall into one of the funnels. " This holds for the case where there are two objects initially at rest, but I don't see it as obviously true if there are more than two objects in the universe.
- jholman 11y agoI see two aspects to your question/comment: at-rest, and two-objects. The whole point of that comment was to apply only to at-rest things (he goes on to contrast it with objects with velocity), though I think maybe you got that. If you have a marble and two other objects, the other objects make two funnels, and there is a saddle (itself curved) where the two objects's funnels are equipotent. That's the three-body case. If it were possible to balance perfectly on this line of equipotence, you'd just slide to the lowest point on that line, and stay there, out of the funnels. This, IIUC, is one of the Lagrange points... L1, I think. In theory it's possibly-stable, but its stability exhibits negative feedback, so in practice it's impossible (although with station-keeping rockets, it's cheaper to hover there than most places). As you add more funnels, you just get more of these saddle lines intersecting. There are many infinitely-fussy places in the universe where you could in-theory-but-not-in-practice hover without falling into a funnel (if it weren't for brownian motion and maybe some other quantum effects that disturb your infinitely-difficult equilibrium). Of course, this whole analogy doesn't account for the fact that all of the bodies are acting on each other, not just the funnels acting on the marble.
- idlewords 11y agoRight, the fact that all the bodies are acting on the other is what makes me feel the analogy is not kosher. The funnels are going to start moving around based on their mutual attraction, and I could see the marble being ejected to infinity, for example. It's less clear to me (but possible) that it could enter a stable orbit.
- mrfusion 11y agoIsn't the universe expanding? If you start in the right place couldn't everything be moving away from you faster than you'd be pulled in?
- marcus_holmes 11y agohaha they gave the drone ship a Culture ship name! SpaceX just became my favourite company
- dcgoss 11y agoElon's whole gravity explanation is essentially a textual version of this excellent video/demonstration: https://www.youtube.com/watch?v=MTY1Kje0yLg https://www.youtube.com/watch?v=MTY1Kje0yLg (19 million views). Highly recommended, very memorable.
- enraged_camel 11y agoYep, came here to post this. The funny thing is that there was a post about that video a while back, and the HN crowd criticized it pretty heavily for being a bad way to explain gravity. But... whatever. :)
- mturmon 11y agoHere is the discussion, which was interesting but inconclusive about the merits of this rubber sheet model: https://news.ycombinator.com/item?id=8542244 https://news.ycombinator.com/item?id=8542244
- alerkay 11y agoCool video, thanks!
- tempestn 11y agoIt's a good summary, but I'm not sure the repeated digs at Bezos are really necessary. I think anyone who would bother to read this already gets the differences. Not sure that he really needs to point out, twice, that height doesn't matter at that stage of testing. Edit: Just got to the end and saw this was prior to launch, so before Bezos' "welcome to the club" tweet. I guess in that context it's a bit more subtle at least, but still seems like he was making a point of the difference from Blue Origin.
- sopooneo 11y agoNot trying to nit-pick, just trying to confirm my own understanding. But actually, accelerating a mass from 1000km/hr to 2000km/hr should take three times as much energy as from 0km/hr to 1000km/hr, right? I assume the quantity of "four times as much" was just used to get across the notion of energy being proportional to the square of velocity.
- rimantas 11y agoIt ment going from 0-1000 to 0-2000, i.e. increasing target speed twice will increase total energy neede four-fold.
- marcosscriven 11y agoThis all seemed reasonable except this paragraph: "The reason they are floating around is that they have no net acceleration. The outward acceleration of (apparent) circular motion, which wants to sling them out into deep space, exactly balances the inward acceleration of gravity that wants to pull them down to Earth." There is no "outward acceleration". The weightlessness is because the craft they are in is accelerating towards Earth with exactly the same acceleration. The reason they don't hit the ground is that they have a suitably high tangential velocity.
- 1stop 11y agoIs "tangential velocity" not just another way of saying "outward acceleration"?
- marcosscriven 11y agoI'm not sure if that's a question or a statement.Firstly, velocity and acceleration are different things. Velocity is change of distance with time (km/s), acceleration is change of velocity with time (km/s per second or km/s^2). Secondly, an acceleration on a mass requires a force. Supposing there were an 'outward acceleration', where do you propose the 'outward force' is?
- 1stop 11y ago... We are talking a tangent on a circle that is changing every second. So that is a change of velocity, which is acceleration. Outwards is clearly "out" of the circle. The tangent (on the curve) would be a snapshot of that "outward" velocity. As a said: Tangential velocity is the same as saying outward acceleration. Unless you were referring to just that single "snapshot" in a frozen time scenario. That "outward" force usually comes from a massive rocket... It is then maintained by the inward force of gravity.
- marcosscriven 11y agoNothing is accelerating outward. There's only one acceleration here, and that's towards the centre of the mass of Earth.
- v4n4d1s 11y agoGreat and easy to understand article, thanks for posting it. Does anyone know it the spacex team uses the imperial or the metric system for development? Elon switches between both systems and it's messing with my head.
- exDM69 11y agoFwiw, on their public webcast, they had on-screen telemetry showing km/h for speed and km for altitude (and no downrange distance). Not necessarily what they use internally, though. Aerospace engineers traditionally uses knots, thousands of feet and nautical miles. SI units typically have km/s (not /h).
- caio1982 11y agoJust for the record, the biggest newspaper in Brazil has an incredible picture of the launch/landing on its front page today :-) http://f.i.uol.com.br/folha/homepage/images/1535742.jpeg http://f.i.uol.com.br/folha/homepage/images/1535742.jpeg
- IshKebab 11y ago> Getting back to everyday reality, the impression that most people have is that gravity stops once you reach a certain altitude above Earth, at which point you start floating around in "zero g", but, as we just talked about, this is obviously not true. The force of gravity drops proportionate to the square of the distance between the centers of two objects. I'd like to meet the person that is both uneducated enough to think that gravity suddenly stops and after that is "zero g", and also undestands what "proportionate to the square of the distance" means!
- soperj 11y ago"nitrogen attitude thrusters" Think that was supposed to be altitude? edit: just saw this at the bottom and it made me smile; "Apologies for any typos in the above."