I'm a big fan of arrestor lines around the sides. Basically as the stage lands, stand up four outrigger arms with a cable going through them from the corners of the barge. If it falls over then catch it and lower it gently. But easy to armchair, hard to do! That they have arrived exactly where the barge is (or would have been) 3 times now is pretty awesome in itself.
The question is always whether you remove more risk than you add. That's a big part of why it's easy to armchair but hard to do. In this case, for example, I'd bet that the odds of the rocket getting tangled in the lines and ruining a landing are better than the odds of the rocket being saved by the lines.
From my armchair observations, it looks like they just need to tweak some constants in their control algorithm to avoid control-induced oscillation. This is the first time that the rocket has reached the ship while still under control (the first landing attempt ran out of hydraulic fluid and went out of control, and of course the second not-quite-attempt didn't have the ship there so it probably wasn't as obvious what was going on) and I imagine there's a fair amount of "oh, duh, how did I overlook that?" going around SpaceX headquarters now that they've finally seen it in action all the way to the end.
I love the beer can analogy. Agreed it is a really interesting problem. Which I don't doubt SpaceX will solve. I was not impressed with the ULA "lets just catch the engines with a helicopter" idea.
I would hesitate to say it's going to be easy to fix because I would have thought this would have come up in simulations, BUT... They got this in the bag. It's going to be very exciting on the fist landing, but I think it's a forgone conclusion at this point that what they are trying to do will work.
Just how bad is salt water for the engines? Cut a hole in the landing barge and hit that, with struts mounted 2/3 of the way up to catch on the sides of the hole.
Actually -- make the hole a steel cavity projecting below the waterline, with smooth sloped sides. Thus a miss hits the cavity side and the rocket slides down. Put thrusters at the top of the rocket to push against the pitch torque when the thing contacts the cavity. Drop your struts from the top of the rocket on to the barge.
Now you've got a lower center of mass and wider "legs". You will for sure bang up the side of the rocket, but so what, it is the engines that you really want to recover. (Hmm, actually it will be the rocket exhaust that hits the well first anyway, does pressure in the well from the rocket exhaust help at all? Might slow down the descent, might increase the pitch torque.)
Having KSP stock aero in real life would be so amazing. For one, it would solve air transportation - just put a bunch of control surfaces in a circle and you get free lift!
That's the Kerbal way. First they hit it from the side because they run out of control fluid (say, electricity, in Kerbal terms); then they landed a-ok but tipped over. Next time they'll probably miscalculate the suicide burn and - because it's SpaceX - fourth time's a charm.
There is an opportunity here for some clever control system design. If the mobile platform is brought into the control system loop, it can move to adjust for excess lateral velocity.
Won't be easy, but if anyone can do it, it's SpaceX.
This barge is in a turbulent ocean, so it's already doing a lot of work just to stay somewhat still. Plus the vision tracking on the rocket is already accounting for the movement of the barge.
How can that make sense? Until they actually get a successful landing they can't be sure they don't have a problem that causes a failure 100% of the time.
Presumably they've tried to estimate that probability and factored it into the 20% probability of not succeeding. (I don't know though, since I haven't seen the calculation.)
But you shouldn't also pretend you have zero information. They hit the barge last time, engineering principles are sound, so those two things alone give you an estimate of "quite likely". Yes, 80% is kind of arbitrary, but it tells you the same story as "quite likely" with an added benefit of being able to plug it into some math that will yield you better results than going with just words.
(Note that I think that starting with a good 50/50 coinflip and revising it based on evidence in this case is reasonable, I just think it's nice to have a reasoned opposing opinion sometimes.)
>But you shouldn't also pretend you have zero information.
If you've never done something before you really have no idea if it's going to work, and in rocket launch everything that occurs after the last failure is a complete unknown in terms of failure modes.
Now, if he'd made successful flyback stages before, or it was a relatively routine thing for the industry he might have a good enough feel to assign a ballpark number. But that's not the situation.
In the link you provided he uses computer failure as an example, where a person who is familiar with computers does have some information - I've owned my current rig for three years and it's never failed. If you told me you thought it has a 50% chance of failure next month I can pretty confidently say that's an overestimate.
But it's useless to pull numbers out of the air for something as complicated as SpaceX is trying to do.
If you have an expectation, you have a probability. Not a numeric one, but a probability nonetheless.
Nobody has ever landed a rocket before. But we don't expect the rocket to turn into an alarm clock or suddenly develop antigravity. In fact, we have quite reasonable expectations on what behaviors the rocket will exhibit. We might, for instance, expect the rocket to crash more than we expect it to land. What else does that say rather than p(crash) > p(land)?
(Of course, this may well come down to "probability as ratio" vs. "probability as anticipation", which is probably a matter of preference.)
I think he's referring to the fact that every time they do one of these they have more experience with everything, therefore with each new launch the chance of failure should be reduced. He said there will be more than one launches until the end of the year. So by then, the chance of success should rise to 80%.
Yes, I do, and that's why I'm laughing at what you wrote. Just how do you arrive at a numeric probability for an event for which you have no way of assessing the likelihood of occurring?
If one had complete clairvoyance and absolute understanding of every element in a system then there would be no estimates, no probabilities, merely outcomes foretold in advance.
For an estimate one needs to gather up what evidence and information is available; make a judgment on how well understood the system is, and its components; determine how predictable the behavior of the system has been in the past; figure out how close what is attempting to be done is to any previous testing or operations; and so on. Then take all of that and make an informed estimate of the likelihood of something occurring.
That's what an estimate is, a statement about how well a system seems to be understood and the probability of some event occurring. An estimate can build in uncertainty in the understanding of the system quite easily, by simply making a more cautious or pessimistic assumption.
SpaceX designed and built these rockets. They've flown them numerous times. They've done test flights exploring landing operations. They've done re-entry flights and landing attempts multiple times. All of these things increase confidence in understanding how the rocket operates under different conditions during landing, making it possible to come up with a reasonably informed estimate of the probability of a successful landing over a given number of attempts.
Perhaps they are wrong, perhaps they have made a key error in their modeling, who knows. That's why these are estimates, because there's always the possibility for unknown variables to affect outcomes. But to say that there is no basis for SpaceX's estimates is patently ridiculous.
I feel like a truer estimate would be "100% chance of success unless some unknown factor causes failure." It's saying that the unknown factor subtracts 20% that makes me go hmmm.
Musk is a mastermind/strategic/INTJ personality. Much of someone skill of someone like this it often from making assumptions based on hunches. It could just be a hunch. And that's totally fine.
As an INTJ, I'm curious why you mentioned that trait in such a sentence. Also, remember: everything you see around you, what you call the world, was built be people no smarter than you.
The HR screen was a bit off. I applied as a Python developer and was given a purely C memory-leak multiple-choice quiz. Sort of annoying, considering I told the recruiter explicitly that I don't know C.
EDIT: My broader qualm is this. If you've got hundreds of open req.s, but fail a candidate based on a quiz that you know the candidate doesn't know (but which aligns with one specific job posting), you're maybe doing hiring wrong.
You guys regularly fire some portion (3% to 5%) of your employees every year yes? I love what you're doing and I'd love to be part of it, but the press doesn't make it out like a great place to be an employee. It makes sense I guess, given the risk involved in launching rockets, but this kind of work environment is probably not for everyone.
Being fired for low performance is okay — if you feel you're continually perform poorly, you should start to look for another job well ahead of this moment. California is not a particularly saturated market for software developers.
Not following the legally required procedure is bad, though.
The problem is that companies following the "fire at least 10% every year in every department" Jack Welch philosophy tend to let some good people go. It's a management philosophy that just assumes that there's no such thing as a really good team, full of worthwhile players.
Its an attitude that works better in professional sports, where hyper-competitiveness is more often an asset than a liability. The knock-on effects of a bunch of coworkers trying to outdo one another to make the cut seem as though they'd make for a crappy work environment, which I believe is what VieElm was talking about.
It's not appropriate for me to comment on company HR policy. All I'm going to say is that my impression of the atmosphere on the software team is not at all "a bunch of coworkers trying to outdo one another to make the cut".
lutorm, I should have put a disclaimer in there. I know nothing about SpaceX policy and so I wasn't trying to cast any aspersions. (and frankly, the 3% figure VieElm mentioned sounds more like attrition than Neutron Jack policy)
Well it's well documented that what happens is that the system ends up being gamed. For example managers hire people to fire so they don't have to fire the people they've friended. See Microsoft Stack Ranking.
I applied to the same Linux Admin position in Cape Canaveral 3 times over a year that sat vacant, having 14 years of Linux experience and willing to take the ~60%+ paycut. No response ever.
> To conform to U.S. Government space technology export regulations, applicant must be a U.S. citizen, lawful permanent resident of the U.S., protected individual as defined by 8 U.S.C. 1324b(a)(3), or eligible to obtain the required authorizations from the U.S. Department of State.
Optimistic that in the distant future we will be eligible.
Do you have any particular insights how to get a reply from the HR? Applied twice through this form to a super relevant position with matching skills -- no reply, not even a negative one.
All at the time when I'm rejecting other offers expecting to have a chance to talk to SpaceX.
Hey, I work at SpaceX, and made the initial contact through HN. What kind of position are you looking for? If it's software, I can at least make sure someone internally looks at your resume.
I actually went through a few stages of the interview process at SpaceX but was offered only a fraction of my current income.
Regardless, I greatly admire the company's ambition and goals. The methane powered Raptor engine for the MCT is just sheer insanity. I love it. SpaceX inspires many of us, young and old.
That stage 2 engine nozzle really glows hot! Looks hot enough to melt, but holding together impressively. Also, the exhaust into the vacuum looks like a messy grey cloud, not the bright cone I might have expected. Very cool. Or hot.
Yes! Amazingly, although the nozzle looks just like a bell-shaped piece of sheet metal, it in fact uses "regenerative cooling" which means the nozzle is full of small pipes which wind back and forth like a radiator. The rocket fuel is passed through these pipes before combustion, resulting in a heat exchange which is doubly beneficial, keeping the nozzle (relatively) cool and also heating up the rocket fuel so it combusts more efficiently.
> the exhaust into the vacuum looks like a messy grey cloud, not the bright cone I might have expected
Yep, since there is no atmospheric pressure squeezing it into a cone shape, the exhaust just kind of flies everywhere!
Merlin 1C Vacuum had a regeneratively cooled combustion chamber but radiatively cooled expansion nozzle. I'm not sure if Merlin 1D Vacuum differs from this though.
You're correct for the last generation of engines - Merlin 1C Vacuum was radiatively cooled. However I haven't found any confirmation one way or the other for the 1D Vacuum engine, which they're using currently. It's possible they haven't made this info public yet due to ITAR.
FTS means flight termination system. Meaning the thing that blows it up if it goes off course and is going to crash into people. They were saying "safed" not "saved", meaning, no longer armed.
FTS is the flight termination system. I believe that is a self destruct mechanism in case things go very wrong. They arm it before liftoff and disable it after it's well over the ocean.
I'm guessing they don't show it live because if something went wrong, they'd like to figure out why before releasing the video, like last time. Instead of just having a failure without the known cause...
It's about managing expectations. The landings are part of an experimental R&D program, they don't necessarily need constant coverage all the time, though it is exciting to follow the progress.
SpaceX is preparing the technology to land on Mars. While this particular rocket will not go to Mars, the next iteration will. There are no soft floating areas on Mars, therefore that solution will not work. This is also the reason there are no parachutes, etc. Vertical rocket landings work on Earth, Mars, the moon, pretty much all surfaces in the accessible solar system. So having a rocket that can land vertically, refuel, and take off again is important for space travel, and that's the primary goal here. You can think of the Falcon 9 rocket and its tests to be like a revenue-generating prototype, so they're testing a bunch of future technology when they do these landings.
The structure of the rocket is designed to support itself upright. It would likely fall apart (or at least get damaged) if you lay it on it's side, without a whole lot of (heavy) re-enforcements to the structure.
I have an idea for how to improve the landing of the rocket stage: instead of fold-out landing-legs, why not fold-out wings? Or, a combination of both - legs with wing-like features - they function as wings until close to touch-down and then feather to support the rocket laterally upon landing?
They'd be on the wrong end of the rocket. The centre of mass is close to the engines, but not that close; the landing legs have to go at the bottom for obvious reasons, but any aerodynamic surfaces have to go near the vehicle's stern, as it moves through the air. Since it's descending vertically, this means the top. This is what the pop-out grid fins way up are for.
Fun fact: if the F9 first stage had traditional fins at the bottom, they wouldn't be able to do this. The vehicle would tumble in the upper atmosphere and end up either nosediving into the ground or breaking up.
I believe you and I understand the problem (I make planes for fun, so know a little bit about aerodynamics and CG) .. but what I think is that the wings could indeed be mounted to the rocket higher up the frame, over the legs - so when the legs deploy at the bottom, the wings deploy as well over the top - they'd be part of the same leg structure, only extended all the way to the top of the rocket body. Actually they'd need to be rotors, a kind of mini-wing, to spin the rocket body on descent, for drag .. like maple seed wings that flip out in the last stage of the flight envelope.
Well of course all this sounds easy, but KISS principles apply I suppose. Still, I could see this happening at some point in the future ..
I never watched one of these before ... T+13 shows Dragon deploying solar panels (really should to be called 'wings' I think). I think a second stage camera shows the Dragon with a some fairing panel spinning away from it. This is amazing!
They also have a camera inside the liquid oxygen tank. You can see it drain away as the second stage engine runs... and then it cuts off. What do you think happens to the remaining fuel? What happens is that it's awesome.
Let's say you're driving along the highway and come up on another car. Try to get behind him and gently nudge his bumper. (Don't try this in real life.) Not too hard, right? That's docking with the ISS.
Now, do the same thing, except he's stopped on a steep downhill slope, and you're going 70MPH. You can use your brakes, but you have to push them pretty hard if you push them at all. If you come to a stop too early, the hill will accelerate you into his bumper. If you start on the brakes too late, you'll hit too hard. You have to time it precisely.
That's more or less landing on the barge, except you also have to steer in two dimensions, and you're coming it at more like 700MPH.
One of the factors is that the whole landing operation is a very tricky balancing act.
The 9 Merlin engines are designed to life the fueled and loaded rocket into space, and it's hard to design these engines for a wide range of thrusts - meaning big penalties in weight, performance, efficiency, etc. Thus, when you're dealing with just the first stage, nearly empty of fuel, even minimum thrust from one engine will accelerate it up pretty hard. It can't hover because of this, so they have to take the rocket falling down with considerable velocity and fire the engine at exactly the right time so that when it passes through zero vertical velocity, it's on top of the barge with no lateral velocity either, and then shut it off at exactly that moment.
Then fuel is a whole 'nother factor. There isn't much of it at landing time, and it probably still makes up a lot of the weight of the stage. So you also have to handle the weight constantly decreasing and any motion of the fuel, and not run out before your landing burn.
You need a huge amount of precise control, and your only tools for the job are a vastly over-powered rocket engine, a stage body not exactly designed for stable aerodynamic flight, and some teeny little hydraulic fins. It's gotta be a minor miracle that they can hit the barge at all, and not with some massive destroy-everything velocity.
My guess is that it primarily an issue of time. When you are trying to dock with the ISS, you are effectivly in a 0g environment, so you can take as much time as you want. This means that you can cancel out your relative velocity at a safe distance and crawl your way towards the ISS at whatever speed you like.
When you try to land on a barge, you essentially need to do a suicide burn, where you wait until the last second to fire your engines enough so that you have zero relative velocity at the instant you hit the barge [0].
Added to this is the fact that landing is largly an afterthought.They would not build, let alone launch, the rocket before they were confident it could dock. However, because the marginal cost of a landing attempt is (relativly) low, they decided that it is cheaper to attempt landings with low confidence and get data instead of attempt to engineer a perfect landing with high confidence before they attempt anything.
[0] If I recal correctly, their margin of error is stopping within one second of hitting the barge.
Just wild guesses here but anyone who has played Kerbal Space Program knows that while docking is no piece of cake, it happens slowly and you can back off and try again until you run out of fuel.
Landing on a moving target shouldn't be that hard except you get (almost) zero weight budget, you're relying on atmospheric braking which means intense heat, and at the end you're hoping the engine doesn't malfunction.
In case it wasn't clear there, the real challenge here is using something that wasn't designed for landing - it was designed for liftoff - to do the landing.
Musk is probably just happy it hit the barge, and tried to slow down some. We'll find out later if it:
a) ran out of fuel
b) misjudged the position and velocity of the barge at the moment of impact
c) landed at the intended speed because there were technical concerns that kept it from landing any slower
d) something else entirely
But keep in mind, the stage landed on the barge. That means it can be salvaged! Pretty cool, if you ask me.
In addition, even one engine on the F9 first stage, throttled down to its minimum, generates way too much thrust for the vehicle to do a gentle landing. They have to do a suicide burn --- they fall towards the launchpad unpowered and then at the last possible moment light up the engine, and hope that when they come to a halt they've landed. There is no margin for error.
KSP doesn't really have an equivalent, but you can compare it to trying to land on the moon using a solid rocket fuel engine. (The difference with SpaceX is that at least they can turn it off.)
> KSP doesn't really have an equivalent, but you can compare it to trying to land on the moon using a solid rocket fuel engine. (The difference with SpaceX is that at least they can turn it off.)
Minmus suicide burn with a Mainsail could probably compare.
Docking with the ISS involves floating in a mostly gravity free environment, with no wind/air resistance, and moving via small controlled jet bursts.
Landing a rocket on a barge involves dealing with gravity, wind resistance, air currents and the crazily unstable centre-of-gravity of a large vertical tube balancing on some rockets.
In mutual freefall, on orbit, it's possible to take as much time as you want, reducing relative velocities as much as you want, and keep things gentle.
When landing on the Earth (or a barge) you can only control speed so much before you run out of fuel, so you're stuck with high speeds, high accelerations, and large forces. The margins are much thinner and you have an extremely limited amount of time to get things done.
Additionally, the landings are an R&D program being carried out for very little cost, the ISS cargo trips are a commercial service being bought at around $130 million per flight, so the engineering resources available to either are considerably different. If SpaceX could plow hundreds of millions of dollars just into developing the operational capability of landing their rockets they'd likely have done it many times by now.
From what I understand, the reason they don't show it live is because they don't have enough bandwidth to transmit live video from the barge. They get a frame every second or two, and lots of telemetry, but not video.
Which is probably because they don't want to show it live. If they wanted to, I'm sure they could find a way to get enough bandwidth to it.
Their PR is very well-run, and not only will they not show a live video for something that they aren't sure is going to go right, they'll also have a plausible technical excuse for why they can't do it.
Not that I have anything against running your PR well, just admiring it.
I don't buy it. I'm sure Musk (and many others) would like nothing more than to watch the event live. Just having the stream doesn't mean they'd have to show it to anybody. It could be kept private. The fact that they don't have a stream at all means it must be pretty hard. Certainly it can be solved, but it's hard or expensive enough that other things take priority.
(Note that the seeming ease with which they send live video back from the rocket during the launch tells us nothing. It's relatively easy to receive high-bandwidth data from a rocket above the horizon to a tracking station with a big dish that it can point at the rocket.)
In the early launches, whenever something went wrong the stream would be cut off instantly --- sometimes they'd even leave the connection open but just stop sending frames, which made my video player very sad.
I sympathise: they don't want to be associated with failure. But on the other hand, there were an awful lot of people, including me, who would have been utterly fascinated to see a first-hand view of the failure modes.
They're getting ever closer. And they have a great setup to experiment with. They have paying customers funding the whole thing, and they can take their time to get it right.
If this was some pure R&D project, today's events would probably be a major setback. But SpaceX still made a healthy profit on this launch even with the bang at the end. That's the genius of their approach, and it's why I think they'll succeed where others have failed.
So far SpaceX has used approximately a third of a billion dollars in launch hardware in reusability testing, almost entirely subsidized through commercial launches. It's a very savvy way to do R&D. Note that it takes a lot of foresight to design a rocket which can serve as both a good expendable booster and also be sensibly made reusable, and most of the optimizations for expendability would push the design away from being good for reuse.
It takes some smarts and will to realize that fully optimizing for reusability isn't the right move, too. It's a constant refrain in these comment threads to ask, why don't they use parachutes? Why don't they use wings? Why not do all sorts of things that would make it easier to reuse, instead of trying a crazy vertical landing suicide burn onto a boat?
The paradox is that making reusability easier would make it harder, because you'd have to get it right from the start, and spend a lot more money developing it, and ensure you can reuse each vehicle many times to make up for the increased cost.
So instead of inventing something new, they started with something known to work, and then adapted it. Because it's cheap, you can keep tweaking it in live tests and not worry too much when you break the stuff.
People often compare this stuff to the Space Shuttle, since that's the one example of a reusable rocket that actually flew, and it was never cheaper than expendable launchers. Imagine what would have happened if the Shuttle had crashed on its first two landing attempts. The program would have been dead before it got anywhere. Now imagine what would have happened if the Shuttle had been so cheap that they could build and launch one for $60 million, instead of $2 billion per orbiter and $500 million per launch (and imagine that somehow they could be lost without killing anybody). It would have been an enormous success even if a bunch had crashed.
Indeed. Just look at Blue Origin. They've well funded, they've got tons of high caliber engineers (rocket scientists even), they've been "bending metal" and building real hardware for years, and they've had pretty good designs, but they're far behind SpaceX in terms of progress. While SpaceX was launching rockets, earning dollars, and doing R&D with launch vehicle leftovers Blue Origin was still mired in the midst of building an orbital launcher.
This is a good example of both "worse is better" and the MVP concept. The Falcon 9 is not the best design for a reusable launcher that one could put together, I could list easily half a dozen optimizations that would lead to a vastly superior reusable vehicle, for example. But by going the expendable mode first route, and building a dead simple vehicle (2 stage LOX/Kerosene, a 60+ year old design) they've been able to iterate, do full-scale testing, and earn income. Income is the life blood of any operation, so being able to bring in profits early made it easier for SpaceX to invest in rocket R&D. And by using the expendable -> reusable route they're able to gain a lot of confidence in the behavior of their rocket as well as get multi-million dollar test vehicles to play with, all financed by their customers.
One of the most impressive things about SpaceX (and don't take this wrong, it's not intended as a snark to your comment) is that nobody cares about the payloads any more --- they just work. We just assume that when they launch something it'll get there. Their first ISS mission was in early 2012! That's less than three years ago! That's amazing!
There is no higher compliment for a rocketry company than to be considered boring.
That said... I'm waiting for the first stage landing footage. squee
Edit: "Looks like Falcon landed fine, but excess lateral velocity caused it to tip over post landing" @elonmusk