I get that this is Slashdot and almost nobody reads TFAs, but seriously, the last time this thing was discussed there were plenty of comments pointing out that it had already been replicated in three different labs around the world... *last year*! True, I don't know if the "... in a vacuum" result has been replicated yet (though at least one lab has offered to do so) but considering that the results in the vacuum were consistent with the atmospheric results (and also considering the care that was taken to ensure that the result wasn't being caused by the atmosphere anyhow, like comparing the operational device with a dummy load that still generates the same heat, or turning the device around) I don't think that the error in our expectations is due to vacuum-vs.-atmosphere, so the other experiments are useful examples of the same effect.
100KW is the theoretical energy that you might be able to make a deep-space craft out of with this drive. The power it's been tested with so far is three orders of magnitude lower.
BUT it certainly stands to reason from our observations of the universe that some frequencies of EM are better suited to this purpose than others, as well as various drive configurations
BS. That most certainly does not "stand to reason". Higher-energy photons have more momentum, not less, yet this thing uses microwaves (much lower energy than visible light) and gets orders of magnitude more thrust than could be explained by the quite-well-understood thrust from EM radiation. Besides, why would there be a net thrust in one direction? The microwaves should escape the cavity in all directions, not just out the back, if they're escaping at all. A light drive has to be open at the back, or the photons would bounce off the rear wall and counter the thrust they imparted to the ship by bouncing off the reflector around the emitter.
First of all, you need to be careful of your pronouns. "They" the inventor of the device is mostly just saying it can be used to replace satellite thrusters, which would be a huge weight saving (no need for maneuvering or stationkeeping fuel). "They" NASA are saying that, *if* it scales up the way their current model says (yes, they have one), then after a lot of refinement and with a nuclear reactor powering it, this thing could produce hundreds of Newtons of thrust at a scale that would be feasible for spacecraft propulsion. Some people have worked out, based on the predicted thrust and the likely mass of such a craft generating that thrust, that it can be used to reach Alpha Centauri in under a century. The first of these is an obvious use case for anything that can generate a tiny thrust for a long time. The second is a straightforward application of the current-best (though probably still in need of major refinement) model of thrust detected to power input, which has been measured. The model is a guess, but the fact that more power = more thrust has been demonstrated; it is, as you say, a concrete fact. The third thing - the starship drive - is simply once again a straightforward application of the results of the model. Nobody is saying that the EmDrive makes starships possible, just that if we *had* a starship, and if it was propelled by an EmDrive that corresponds to the current model of power output, then it could reach Alpha Centauri in N years. That's simple mathematics; you can do the same for chemical rockets or solar sails or any other form of propulsion that works in vacuum.
Second, I don't know why you're calling the idea of scaling up an observed result "delusional". The first Wright Flyer could barely get one person off the ground for a few seconds, flew slower than a horse could run, and was so fragile that it was shattered by a gust of wind after only four flights. But, once you've demonstrated that it *works* - that heavier-than-air flight is actually possible (which should have been obvious to everybody, given that birds and bats and insects exist, but plenty of people thought humans would never achieve it) - then scaling that up to WW2 bombers was pretty straightforward: more-powerful-for-their-weight engines (the Wright brothers had to design their own engine; the existing ones at the time didn't have enough power to weight ratio), stronger-for-their-weight materials, lots of refinements to the design (the Wright brothers pioneered the use of wind tunnels and used them to fix several significant errors in the equations that govern aspects of flight like lift, but their first Flyer was still a very primitive design with many compromises or outright flaws), and other simple, iterative improvements. Breaking the sound barrier was a bigger challenge than getting across the ocean in one flight, in terms of theoretical challenges. All this from a craft that could barely get one guy a few hundred feet down a beach.
If somebody had watched the Wright Flyer and said "one day, people will be able to fly to Europe from the US in less than a day" would you have called them "totally delusional" too?
No offense, but even an AP physics class could point out that this doesn't make any sense. Yes, the perpendicular (sideways) moments (instances of thrust imparted by bouncing particles) would cancel out, but the thrusts at the normal to the back plate (that is, inline) would also cancel out. The inline component of the thrust has to exactly equal the inline-but-opposite component of the thrust caused by the bounce. You don't get to start out the set of all emitted photons with a net velocity in one direction.
If you think about it in terms of where the particles end up, it's pretty obvious this doesn't work: if there's always more thrust on the front side of the chamber (towards the thruster) than on the back, then that means the photons would all end up at the back of the chamber. For that to happen, the back of the chamber must have absorbed their perpendicular components towards itself, or the particles would have bounced back to the front of the chamber. But that would produce a thrust pushing the back plate away, which (since it's attached to the whole assembly) would counter the forward thrust.
Also, your idea just flat-out doesn't make sense: the sloped section is the forward part of the thruster (the cone points in the direction of travel). The back plate perpendicular to the direction of thrust. By what you're saying, the full component of the particle's bounce-imparted momentum would be acting *against* forward thrust, while only part of the thrust in the other direction would. The net thrust would be opposite the observed direction.
Yep. An ion engine also can't be closed at the back the way the EmDrive is; the emitted particles (ions) would hit it and bounce, canceling out the thrust they provided.
That's an excellent example. Gravity is still, in some ways, a mysteroius answer. We know a lot about it, and we can use what we know to make a lot of predictions, but we also know there's a lot that we don't know, and some of our theories about its properties are better termed guesses than predictions.
Now, obviously the EmDrive is far more mysterious than gravity, both because it's much more conceptually novel and unexplored, and because we can really easily detect there's *something* causing the effect called gravity while only a handful of labs around the world are equipped to test the thrust of an EmDrive. I'm not attempting to equate the two. But, as you say, the actual mechanism of gravity has never been observed directly, and the theories about it are still unconfirmed. Similarly, the EmDrive offers some (much less mature) theories as to its operation, but nobody has actually been able to confirm or deny those theories.
Of course, the EmDrive itself hasn't been confirmed yet, at least not to the degree that makes it practical for anything real-world. We have repeatable experiments saying that emitting microwaves into a specially-shaped resonant cavity causes a *tiny* thrust, and we've accounted for some of the likely errors in the experiment (atmosphere, whether the same result happens with a dummy load that doesn't generate the microwaves, etc.), but as of writing this, we have no direct evidence that it scales to useful sizes.
A small monohull is also a lot cheaper than a house, at least in most of the developed world. Even a fairly nice "yacht" (which just means "private non-business vessel") is probably affordable if you can sell your house. My parents have lived aboard for 13 years now, and their 48' (14.5m) catamaran cost significantly less than their house near Seattle.
It's actually really annoying when people assume that yachties must be rolling in dough. Most have very little income, so even though the lifestyle is cheaper than living ashore there's not a lot of disposable income.
Makes sense. Even if Dragon 2 takes over completely from the initial Dragon, if SpaceX gets anywhere near the reusability out of it that they're aiming for (and, unlike the Falcon 9 first stage, Dragon 2 is designed from the start for safe landings and reusability) they won't need to manufacture that many of the rocket motors. Certainly not enough for economies of scale, at least not for the first revision or two. In the meantime, they (and ULA, and everybody else doing this) will be driving down the cost of this kind of manufacturing.
Indeed. Leaving aside the fact that things Medicaid and food stamps and emergency rooms that are obliged to treat you mean that even the most destitute Americans are already better off than a lot of the world, I've yet to see an American community - population in the thousands - who live in the following conditions:
* Rough shacks (a trailer home is a mansion by comparison; I've seen outhouses bigger than some of these shacks)
* No electricity
* No running water (the luckier ones don't have to carry water very far)
* No water sanitation (it probably comes out of a stream or lake)
* No sewers (hope you can draw your water upstream of most of the community...) I'm talking about people who literally live on top of trash dumps, or in shantytowns outside of cities. In some ways, the arguably-even-poorer people who live in the middle of nowhere actually have it better; they may not even have the leavings of civilization (in the sense of "city dwellers") to live on, but their population is low enough to be supported by well water and to grow or gather plant crops and to not shit where they eat.
Considering that SpaceX has started printing *entire* rocket motors - not primary launch motors, to be sure, but rocket motors for production spacecraft nonetheless - I don't think ULA playing "me too" with building a few parts this way is going to make them as cool as SpaceX!
Yep. Some parts of the Merlin 1D are built additively, I think, but the *entire* SuperDraco thruster (which uses Hydrazine rather than cryogenic fuels like RP1/LOX) is printed. http://en.wikipedia.org/wiki/S...
It's really cool to see this technique taking off (pun not initially intended, but let's go with it). People think of 3D printing as making rough plastic parts, but it can be used to create extremely precise parts out of various metals, too.
If they're renting (as most low-income people do), they won't be (directly) paying property tax.
I suspect Lucas doesn't actually expect to turn a profit on doing this, possibly not by a long shot. 200M isn't exactly pocket change, but he can easily afford to write off the whole thing if needed.
It's pretty sad that "rich guy flips the bird to other rich people in revenge for not getting his way" pleases you more than "rich guy helps people get housing in one of the most expensive parts of the world". I mean, I enjoy the feel of a good "fuck you!" too, but if you like that *more* than what's essentially charity, well, that's kind of screwed up of you...
Seems like a reasonable claim to me! Resource supply is one of the key determiners of land value, and always has been. If it rains on my land, and I catch that rain before it wanders onto somebody else's land, how is that not my water?
I mean, there's lots of arguments for (and against) communal ownership of natural resources, but the current (and, for as far back as I'm aware, historical) rule is that they are part of the land value. You're going to have a hell of a time overturning that view. Some things, like rivers, tend to get a bit complicated - it's really awkward if your upstream neighbor feels like using his water (immediately before it ceases to be his) as an arsenic dump - but taking ownership of the water falling from the sky or coming up through the ground has never, so far as I know, *not* been part of land property rights.
I'm not actually sure which of use that tweet backs up; I thought he meant "I estimate we have an 80% chance of at least one landing by year's end, because there are lots of launches between now and then and there's a pretty good chance at least one will succeed." It would be pretty awesome if what he meant was "By the end of the year, we'll have so much more launch practice that, even though each launch has less than 50% chance of recovery right now, by year's end it should be about 80%." I hope the latter is the case, but the two are very different statements and the latter is much more optimistic. I was hoping you could indicate which one was more accurate.
Not clear whether or not you realize this, so to give you the benefit of a doubt:
A) In orbital launch booster rocketry terms, that's a pretty damn small fireball. B) At the time he sent that tweet, nobody (Musk included) had seen the video from the barge. I doubt he even had the video from the airplane, probably just the telemetry data that showed touchdown followed by a loss of telemetry.
Explode when it crashes, there's a difference. SpaceX has demonstrated powered vertical landings on their test vehicles, there were no explosions.
Hydrazine is nasty stuff, but you don't need very much of it (a few second's worth, maybe) and the *entire point* is to avoid the crash, so what happens in the event of a crash is much less important.
I thought that was him estimating an 80% chance of at least one success by year's end, which (considering that they have a lot of launches this year) is a very different thing. Do you have a source for that?
Nitpick: The first attempt ran out of hydraulic fluid (for the guidance fins), not out of propellant for the RCS thrusters.
The rest of what you say is generally true, although a larger target *would* help. The advantage of a larger target is that, while you still have to zero your horizontal velocity, you don't have to zero it anywhere terribly precise. You can pick an optimal set of thrusts that results in the correct orientation and velocities (horizontal and vertical) without worrying overmuch *where* that series of thrusts has you touching down. Both attempts so far clearly demonstrate the ability to do an excellent good job of targeting a (relatively) tiny barge, but currently, if the rocket would come down even 100' (30m) to one side of its target spot, it needs to induce a horizontal momentum (which requires leaving a vertical attitude as well, it can't just translate sideways) and then null that momentum at the right moment (and fix its attitude). That's hard.
To clarify for the person who keeps misunderstanding my posts: they should, of course, plan for the barge-level of landing precision. They should aim for a precision of inches, and within a year, they may get it... 90% of the time. Stuff goes wrong, though, and (especially early in the testing of such a system) it behooves them to use a larger landing area so that there's some margin for error. I'd say their land attempt (possibly next CRS launch, in a couple months) has a very good chance of being their first success.
The thrusters aren't even supposed to be needed there, actually. They're only supposed to fire in very short bursts, not a continuous stream like in the video. As for the legs holding up, just one of them supported the whole rocket for a few seconds; all four should have had no trouble. We know a hell of a lot more than just that it crashed. To claim otherwise is to embrace ignorance.
There is literally no point at all to living in a world where you are only concerned with the things that you absolutely know. You don't absolutely know *ANYTHING*, you could be a simulation in some advanced being's AI-run world, along with everything the program running you has ever simulated observing. The only way to achieve anything difficult is to analyze the differences between failures and successes, and a part of that analysis is to determine how close you came to success.
But then, you probably already knew that and are just a naysayer...
I'm not trying to fix the wrong problem, I'm trying to add a backup for the fix. Shit happens. Parts will fail, valves will stick, unexpected winds or waves will occur.
I thought the fact that the primary goal was to correct the problem that caused the excessive lateral velocity was so bloody obvious that it didn't need saying, but I guess I forgot I'm on the Internet. The purpose of my idea was not "fuck it, fixing a little problem is hard, let's do something much more complicated", it's "shit happens. What can we do to survive the likely error modes?"
A) You've mastered "dictionary", "bookshelf", and "somewhere", but an eight-letter word is too big for you?
B) Welcome to the Internet. You probably got here using "the blue e", right? Tip: highlight (whoops, big word) the scary word with your mouse, right-click on it, and click the option that will search or define the word for you! No need to go over to your bookshelf at all, and you get to avoid looking like a lazy ignoramus (sorry, is that one too long?) at the same time!
Seriously, I get that you're probably joking, but that is a really stupid thing to complain about. Definitions don't belong in a summary, especially not a summary delivered through the biggest inter-connected information network humanity has ever created.
You saw the part where the reaction control thruster at the top (little white plume) is trying to keep the rocket upright, didn't you? Lasts about four seconds. The rocket had already touched down (on at least one leg, with engines shut off) at that point. If the stage had been even a *little* closer to upright, or the thruster a *bit* more powerful, the rocket would have settled onto all four legs and that would be it.
Also, the stage swings through vertical in the moment before touchdown. It's that half-second of overcorrection that doomed it. It was over the barge and in the correct orientation less than 1000 millisecond before touchdown. I'd say the only reason that "seconds away from what would have been the first successful landing" is wrong is because it was more like *one* second.
So, I asked this in the last thread but the discussion there was already mostly dead: what would it cost (presumably mostly a matter of weird) to upgrade the nose thrusters? These are cold-gas (nitrogen) thrusters, and I can't imagine they have a lot of power.
The Dragon uses hydrazine-based "Draco" thrusters for its RCS system; might it be worth adding a hydrazine thruster with a few seconds of fuel in place of the cold-gas thrusters, enabling the rocket to correct its orientation in the moment of touchdown (when it can no longer use engine gimbaling)? For that matter, how does the thrust of a hydrazine thruster (I think a Draco goes to about 90 lbf) compare to a cold-gas thruster? Wouldn't want to bend the rocket with excessive pressure at the top, after all.
Alternatively, the rocket contains a bunch of compressed gases (helium is used for pressurizing the fuel/oxidizer tanks, I believe). Would it be possible, on landing, to vent some of that pressure to provide additional attitude control? It might reduce the rocket's rigidity a bit, which could be bad, and it's a high-pressure valve (of course), but when your concern is that the rocket land upright (you'd want to use this in the moment before touchdown, to avoid excessive pressure on just one leg as appears to have happened here) it might be worth it. The obviously don't have a *lot* of excess pressure - fluids cost weight, pressurized ones moreso - but they probably have some and it might be suitable for a last-second thruster.
Slashdot Mirror
I get that this is Slashdot and almost nobody reads TFAs, but seriously, the last time this thing was discussed there were plenty of comments pointing out that it had already been replicated in three different labs around the world... *last year*! True, I don't know if the "... in a vacuum" result has been replicated yet (though at least one lab has offered to do so) but considering that the results in the vacuum were consistent with the atmospheric results (and also considering the care that was taken to ensure that the result wasn't being caused by the atmosphere anyhow, like comparing the operational device with a dummy load that still generates the same heat, or turning the device around) I don't think that the error in our expectations is due to vacuum-vs.-atmosphere, so the other experiments are useful examples of the same effect.
100KW is the theoretical energy that you might be able to make a deep-space craft out of with this drive. The power it's been tested with so far is three orders of magnitude lower.
BS. That most certainly does not "stand to reason". Higher-energy photons have more momentum, not less, yet this thing uses microwaves (much lower energy than visible light) and gets orders of magnitude more thrust than could be explained by the quite-well-understood thrust from EM radiation. Besides, why would there be a net thrust in one direction? The microwaves should escape the cavity in all directions, not just out the back, if they're escaping at all. A light drive has to be open at the back, or the photons would bounce off the rear wall and counter the thrust they imparted to the ship by bouncing off the reflector around the emitter.
First of all, you need to be careful of your pronouns. "They" the inventor of the device is mostly just saying it can be used to replace satellite thrusters, which would be a huge weight saving (no need for maneuvering or stationkeeping fuel). "They" NASA are saying that, *if* it scales up the way their current model says (yes, they have one), then after a lot of refinement and with a nuclear reactor powering it, this thing could produce hundreds of Newtons of thrust at a scale that would be feasible for spacecraft propulsion. Some people have worked out, based on the predicted thrust and the likely mass of such a craft generating that thrust, that it can be used to reach Alpha Centauri in under a century. The first of these is an obvious use case for anything that can generate a tiny thrust for a long time. The second is a straightforward application of the current-best (though probably still in need of major refinement) model of thrust detected to power input, which has been measured. The model is a guess, but the fact that more power = more thrust has been demonstrated; it is, as you say, a concrete fact. The third thing - the starship drive - is simply once again a straightforward application of the results of the model. Nobody is saying that the EmDrive makes starships possible, just that if we *had* a starship, and if it was propelled by an EmDrive that corresponds to the current model of power output, then it could reach Alpha Centauri in N years. That's simple mathematics; you can do the same for chemical rockets or solar sails or any other form of propulsion that works in vacuum.
Second, I don't know why you're calling the idea of scaling up an observed result "delusional". The first Wright Flyer could barely get one person off the ground for a few seconds, flew slower than a horse could run, and was so fragile that it was shattered by a gust of wind after only four flights. But, once you've demonstrated that it *works* - that heavier-than-air flight is actually possible (which should have been obvious to everybody, given that birds and bats and insects exist, but plenty of people thought humans would never achieve it) - then scaling that up to WW2 bombers was pretty straightforward: more-powerful-for-their-weight engines (the Wright brothers had to design their own engine; the existing ones at the time didn't have enough power to weight ratio), stronger-for-their-weight materials, lots of refinements to the design (the Wright brothers pioneered the use of wind tunnels and used them to fix several significant errors in the equations that govern aspects of flight like lift, but their first Flyer was still a very primitive design with many compromises or outright flaws), and other simple, iterative improvements. Breaking the sound barrier was a bigger challenge than getting across the ocean in one flight, in terms of theoretical challenges. All this from a craft that could barely get one guy a few hundred feet down a beach.
If somebody had watched the Wright Flyer and said "one day, people will be able to fly to Europe from the US in less than a day" would you have called them "totally delusional" too?
No offense, but even an AP physics class could point out that this doesn't make any sense. Yes, the perpendicular (sideways) moments (instances of thrust imparted by bouncing particles) would cancel out, but the thrusts at the normal to the back plate (that is, inline) would also cancel out. The inline component of the thrust has to exactly equal the inline-but-opposite component of the thrust caused by the bounce. You don't get to start out the set of all emitted photons with a net velocity in one direction.
If you think about it in terms of where the particles end up, it's pretty obvious this doesn't work: if there's always more thrust on the front side of the chamber (towards the thruster) than on the back, then that means the photons would all end up at the back of the chamber. For that to happen, the back of the chamber must have absorbed their perpendicular components towards itself, or the particles would have bounced back to the front of the chamber. But that would produce a thrust pushing the back plate away, which (since it's attached to the whole assembly) would counter the forward thrust.
Also, your idea just flat-out doesn't make sense: the sloped section is the forward part of the thruster (the cone points in the direction of travel). The back plate perpendicular to the direction of thrust. By what you're saying, the full component of the particle's bounce-imparted momentum would be acting *against* forward thrust, while only part of the thrust in the other direction would. The net thrust would be opposite the observed direction.
Yep. An ion engine also can't be closed at the back the way the EmDrive is; the emitted particles (ions) would hit it and bounce, canceling out the thrust they provided.
That's an excellent example. Gravity is still, in some ways, a mysteroius answer. We know a lot about it, and we can use what we know to make a lot of predictions, but we also know there's a lot that we don't know, and some of our theories about its properties are better termed guesses than predictions.
Now, obviously the EmDrive is far more mysterious than gravity, both because it's much more conceptually novel and unexplored, and because we can really easily detect there's *something* causing the effect called gravity while only a handful of labs around the world are equipped to test the thrust of an EmDrive. I'm not attempting to equate the two. But, as you say, the actual mechanism of gravity has never been observed directly, and the theories about it are still unconfirmed. Similarly, the EmDrive offers some (much less mature) theories as to its operation, but nobody has actually been able to confirm or deny those theories.
Of course, the EmDrive itself hasn't been confirmed yet, at least not to the degree that makes it practical for anything real-world. We have repeatable experiments saying that emitting microwaves into a specially-shaped resonant cavity causes a *tiny* thrust, and we've accounted for some of the likely errors in the experiment (atmosphere, whether the same result happens with a dummy load that doesn't generate the microwaves, etc.), but as of writing this, we have no direct evidence that it scales to useful sizes.
A small monohull is also a lot cheaper than a house, at least in most of the developed world. Even a fairly nice "yacht" (which just means "private non-business vessel") is probably affordable if you can sell your house. My parents have lived aboard for 13 years now, and their 48' (14.5m) catamaran cost significantly less than their house near Seattle.
It's actually really annoying when people assume that yachties must be rolling in dough. Most have very little income, so even though the lifestyle is cheaper than living ashore there's not a lot of disposable income.
Makes sense. Even if Dragon 2 takes over completely from the initial Dragon, if SpaceX gets anywhere near the reusability out of it that they're aiming for (and, unlike the Falcon 9 first stage, Dragon 2 is designed from the start for safe landings and reusability) they won't need to manufacture that many of the rocket motors. Certainly not enough for economies of scale, at least not for the first revision or two. In the meantime, they (and ULA, and everybody else doing this) will be driving down the cost of this kind of manufacturing.
Indeed. Leaving aside the fact that things Medicaid and food stamps and emergency rooms that are obliged to treat you mean that even the most destitute Americans are already better off than a lot of the world, I've yet to see an American community - population in the thousands - who live in the following conditions:
* Rough shacks (a trailer home is a mansion by comparison; I've seen outhouses bigger than some of these shacks)
* No electricity
* No running water (the luckier ones don't have to carry water very far)
* No water sanitation (it probably comes out of a stream or lake)
* No sewers (hope you can draw your water upstream of most of the community...)
I'm talking about people who literally live on top of trash dumps, or in shantytowns outside of cities. In some ways, the arguably-even-poorer people who live in the middle of nowhere actually have it better; they may not even have the leavings of civilization (in the sense of "city dwellers") to live on, but their population is low enough to be supported by well water and to grow or gather plant crops and to not shit where they eat.
Considering that SpaceX has started printing *entire* rocket motors - not primary launch motors, to be sure, but rocket motors for production spacecraft nonetheless - I don't think ULA playing "me too" with building a few parts this way is going to make them as cool as SpaceX!
Yep. Some parts of the Merlin 1D are built additively, I think, but the *entire* SuperDraco thruster (which uses Hydrazine rather than cryogenic fuels like RP1/LOX) is printed. http://en.wikipedia.org/wiki/S...
It's really cool to see this technique taking off (pun not initially intended, but let's go with it). People think of 3D printing as making rough plastic parts, but it can be used to create extremely precise parts out of various metals, too.
If they're renting (as most low-income people do), they won't be (directly) paying property tax.
I suspect Lucas doesn't actually expect to turn a profit on doing this, possibly not by a long shot. 200M isn't exactly pocket change, but he can easily afford to write off the whole thing if needed.
It's pretty sad that "rich guy flips the bird to other rich people in revenge for not getting his way" pleases you more than "rich guy helps people get housing in one of the most expensive parts of the world". I mean, I enjoy the feel of a good "fuck you!" too, but if you like that *more* than what's essentially charity, well, that's kind of screwed up of you...
Seems like a reasonable claim to me! Resource supply is one of the key determiners of land value, and always has been. If it rains on my land, and I catch that rain before it wanders onto somebody else's land, how is that not my water?
I mean, there's lots of arguments for (and against) communal ownership of natural resources, but the current (and, for as far back as I'm aware, historical) rule is that they are part of the land value. You're going to have a hell of a time overturning that view. Some things, like rivers, tend to get a bit complicated - it's really awkward if your upstream neighbor feels like using his water (immediately before it ceases to be his) as an arsenic dump - but taking ownership of the water falling from the sky or coming up through the ground has never, so far as I know, *not* been part of land property rights.
I'm not actually sure which of use that tweet backs up; I thought he meant "I estimate we have an 80% chance of at least one landing by year's end, because there are lots of launches between now and then and there's a pretty good chance at least one will succeed." It would be pretty awesome if what he meant was "By the end of the year, we'll have so much more launch practice that, even though each launch has less than 50% chance of recovery right now, by year's end it should be about 80%." I hope the latter is the case, but the two are very different statements and the latter is much more optimistic. I was hoping you could indicate which one was more accurate.
Not clear whether or not you realize this, so to give you the benefit of a doubt:
A) In orbital launch booster rocketry terms, that's a pretty damn small fireball.
B) At the time he sent that tweet, nobody (Musk included) had seen the video from the barge. I doubt he even had the video from the airplane, probably just the telemetry data that showed touchdown followed by a loss of telemetry.
Explode when it crashes, there's a difference. SpaceX has demonstrated powered vertical landings on their test vehicles, there were no explosions.
Hydrazine is nasty stuff, but you don't need very much of it (a few second's worth, maybe) and the *entire point* is to avoid the crash, so what happens in the event of a crash is much less important.
I thought that was him estimating an 80% chance of at least one success by year's end, which (considering that they have a lot of launches this year) is a very different thing. Do you have a source for that?
Nitpick: The first attempt ran out of hydraulic fluid (for the guidance fins), not out of propellant for the RCS thrusters.
The rest of what you say is generally true, although a larger target *would* help. The advantage of a larger target is that, while you still have to zero your horizontal velocity, you don't have to zero it anywhere terribly precise. You can pick an optimal set of thrusts that results in the correct orientation and velocities (horizontal and vertical) without worrying overmuch *where* that series of thrusts has you touching down. Both attempts so far clearly demonstrate the ability to do an excellent good job of targeting a (relatively) tiny barge, but currently, if the rocket would come down even 100' (30m) to one side of its target spot, it needs to induce a horizontal momentum (which requires leaving a vertical attitude as well, it can't just translate sideways) and then null that momentum at the right moment (and fix its attitude). That's hard.
To clarify for the person who keeps misunderstanding my posts: they should, of course, plan for the barge-level of landing precision. They should aim for a precision of inches, and within a year, they may get it... 90% of the time. Stuff goes wrong, though, and (especially early in the testing of such a system) it behooves them to use a larger landing area so that there's some margin for error. I'd say their land attempt (possibly next CRS launch, in a couple months) has a very good chance of being their first success.
The thrusters aren't even supposed to be needed there, actually. They're only supposed to fire in very short bursts, not a continuous stream like in the video. As for the legs holding up, just one of them supported the whole rocket for a few seconds; all four should have had no trouble. We know a hell of a lot more than just that it crashed. To claim otherwise is to embrace ignorance.
There is literally no point at all to living in a world where you are only concerned with the things that you absolutely know. You don't absolutely know *ANYTHING*, you could be a simulation in some advanced being's AI-run world, along with everything the program running you has ever simulated observing. The only way to achieve anything difficult is to analyze the differences between failures and successes, and a part of that analysis is to determine how close you came to success.
But then, you probably already knew that and are just a naysayer...
I'm not trying to fix the wrong problem, I'm trying to add a backup for the fix. Shit happens. Parts will fail, valves will stick, unexpected winds or waves will occur.
I thought the fact that the primary goal was to correct the problem that caused the excessive lateral velocity was so bloody obvious that it didn't need saying, but I guess I forgot I'm on the Internet. The purpose of my idea was not "fuck it, fixing a little problem is hard, let's do something much more complicated", it's "shit happens. What can we do to survive the likely error modes?"
A) You've mastered "dictionary", "bookshelf", and "somewhere", but an eight-letter word is too big for you?
B) Welcome to the Internet. You probably got here using "the blue e", right? Tip: highlight (whoops, big word) the scary word with your mouse, right-click on it, and click the option that will search or define the word for you! No need to go over to your bookshelf at all, and you get to avoid looking like a lazy ignoramus (sorry, is that one too long?) at the same time!
Seriously, I get that you're probably joking, but that is a really stupid thing to complain about. Definitions don't belong in a summary, especially not a summary delivered through the biggest inter-connected information network humanity has ever created.
Agh, bloody autocorrect and stupid failure to proofread. First paragraph:
What would it cost (presumably a matter of weight) to upgrade the nose thrusters?
You saw the part where the reaction control thruster at the top (little white plume) is trying to keep the rocket upright, didn't you? Lasts about four seconds. The rocket had already touched down (on at least one leg, with engines shut off) at that point. If the stage had been even a *little* closer to upright, or the thruster a *bit* more powerful, the rocket would have settled onto all four legs and that would be it.
Also, the stage swings through vertical in the moment before touchdown. It's that half-second of overcorrection that doomed it. It was over the barge and in the correct orientation less than 1000 millisecond before touchdown. I'd say the only reason that "seconds away from what would have been the first successful landing" is wrong is because it was more like *one* second.
So, I asked this in the last thread but the discussion there was already mostly dead: what would it cost (presumably mostly a matter of weird) to upgrade the nose thrusters? These are cold-gas (nitrogen) thrusters, and I can't imagine they have a lot of power.
The Dragon uses hydrazine-based "Draco" thrusters for its RCS system; might it be worth adding a hydrazine thruster with a few seconds of fuel in place of the cold-gas thrusters, enabling the rocket to correct its orientation in the moment of touchdown (when it can no longer use engine gimbaling)? For that matter, how does the thrust of a hydrazine thruster (I think a Draco goes to about 90 lbf) compare to a cold-gas thruster? Wouldn't want to bend the rocket with excessive pressure at the top, after all.
Alternatively, the rocket contains a bunch of compressed gases (helium is used for pressurizing the fuel/oxidizer tanks, I believe). Would it be possible, on landing, to vent some of that pressure to provide additional attitude control? It might reduce the rocket's rigidity a bit, which could be bad, and it's a high-pressure valve (of course), but when your concern is that the rocket land upright (you'd want to use this in the moment before touchdown, to avoid excessive pressure on just one leg as appears to have happened here) it might be worth it. The obviously don't have a *lot* of excess pressure - fluids cost weight, pressurized ones moreso - but they probably have some and it might be suitable for a last-second thruster.
Thoughts?