10 ms·

An Analysis of SpaceX’s Falcon 9 Crash Landing

99 points by jonah 12y ago

Animats 12y ago
A key piece of information we don't have, but Space-X does, is how much fuel was left at landing. Landing has to be done with minimum fuel, since it comes out of the fuel budget for putting payload into orbit. They have thrust vectoring on the main engines, and have attitude jets near the nose. They have to land vertical, at near zero velocity, with near zero angular rate, with an underactuated system. Underactuated means there are more degrees of freedom to control than there are controllable parameters. They have 5 controllable degrees of freedom - 2 axes of engine vectoring, main engine throttle, and 2 axes of relatively weak nose thrusters. They have to hit a point with three translation constraints, three linear velocity constraints, two angular constraints, and two angular rate constraints. So they have 5 DOF in and 10 DOF out. That, mathematically, is what "rocket science" is. This under-actuated maneuver has to be solved as a two-point boundary problem, or, in practice, re-solved continuously to cope with problems such as wind gusts. You can see what happened; they had too much angular rate at landing, requiring more torque than the nose thrusters could impart to keep the rocket upright once the main engines could no longer help. It looks like they made a big correction shortly before landing to hit the target, and lost angular stability doing so. If they'd had a bigger landing area, so they didn't have to apply big corrections to hit the tiny target, this would have worked.
- pixie_ 12y ago
  Elon - "Looks like the issue was stiction in the biprop throttle valve, resulting in control system phase lag. Should be easy to fix." AKA lost constrol of the engines. It could of landed in a field and it would of still crashed. Man there are so many armchair rocket scientists.
  - Animats 12y ago
    Aviation Leak says that message was "withdrawn."[1] [1] http://aviationweek.com/space/spacex-checks-throttle-valve-after-flawed-falcon-9-recovery-attempt http://aviationweek.com/space/spacex-checks-throttle-valve-a...
    - pixie_ 12y ago
      [2] ITAR.
  - LoSboccacc 12y ago
    as KSP player and armchair engineer: when the rocket touched on the barge, thrust vectoring couldn't rotate the rocket anymore, since legs become a fixed pivot. and rcs didn't had enough trust to upright the rocket. now I don't think the issue is as easy as 'rcs didn't had enough thrust' what looks like is that the control system minimized vertical/horizontal velocity but allowed the rocket to touch down with too much rotational momentum. whether this was caused by software or hardware has to be seen. if they are storing the landing fuel in the same storage as the ascent fuel, sloshing may be a big factor. but I honestly have no idea, just like the speculation.
    - baq 12y ago
      musk says throttle got stuck, in KSP terms the ctrl key didn't work as the computer expected it to.
      - cronin101 12y ago
        Ugggh. StickyKeys activating and crashing my spaceship AGAIN.
      - LoSboccacc 12y ago
        yeah I was so happy when they added X
      - madaxe_again 12y ago
        Their wireless keyboard ran out of batteries. Honestly, I've had several missions to Jove which have ended in disaster because my keyboard died during orbital insertion.
        Rooster61 12y ago
        Jool, you mean? I think you are confusing Jupiter's adjective with the the KSP counterpart's name. And that would be so annoying. It's no trivial task to get all the way out there and bleed off all that velocity.
  - imaginenore 12y ago
    You fail at basic grammar. I don't think you're ready to judge anybody. It's "could have" and "would have", not "could of", nor "would of".
    - smoyer 12y ago
      I don't know pixie_ but non-native English speakers hear "could of" and "would of" when we use the contractions "could've" and "would've".
      - saraid216 12y ago
        I'm too lazy to go turn on showdead for GP, but... > I don't know pixie_ but non-native English speakers hear "could of" and "would of" when we use the contractions "could've" and "would've". You actually hear "could ov" and "would ov", but since the latter aren't actually words, there's an automatic shunt to the nearest known word. Sometimes this occurs in the speaker; sometimes this occurs in the listener. It occurs in the speaker because of loopback: you say "could ov"; you hear "could of"; you say "could of".
        hollerith 12y ago
        >You actually hear "could ov" and "would ov" All occurences of the English word spelled "of" are pronounced "ov": pronouncing it with an F sound instead of a V sound would sound strange to an English speaker even where spelling it "of" is correct usage. Your explanation still applies, though, provided that we assume that the listener actually hears "could v" and "would v", but since there is no word pronounced "v", there's an automatic shunt to the word that is pronounced "ov".
      - nacs 12y ago
        I actually see this ("could of" and "would of") more in native speakers than non-native speakers actually. I have also seen it used many times in writing so it's not just a "heard it wrong" issue. Here in the South (US), it's disturbingly common.
  - Shivetya 12y ago
    I would lay claim to the idea its far easier to land in a field than on a floating barge. For one thing the field doesn't move, second its an awfully easier target to hit with greater room for error
    - lmm 12y ago
      The point was that this particular problem (oscillation due to control lag) would still have caused a crash even if it had been landing in a field.
- hyeonwho 12y ago
  That is a very interesting way of thinking about the landing. If you are going to use DOF, you should also mention the grid fins (4 DOF (1)), and how control over parameters can be "time-shifted". Early in the descent the rotation of the craft doesn't matter so much as its trajectory, and so the grid fins can control pitch to aim for the landing site (2 DOF). Once the trajectory for landing is mostly established, the grid fins can be used to eliminate the vehicle rotation (3 DOF). At the time of landing, the grid fins are no longer useful, but they have set one degree of freedom that none of the other controls will change (rotation about the central axis of the rocket), so essentially they have "6 DOF in" at the time of landing. (1) In addition to control over rotation, the fins can be turned so that they cancel each other out overall, and thus slow down the vehicle without changing its rotation. I don't know whether the fins are actually used this way given the stresses involved.
- mdda 12y ago
  You can't count position and velocity (i.e. d(position)/dt) as separate degrees of freedom. If you insisted on doing so, then you should also count rocketthrust and rocketthrust changes through time. IMHO, the constraints here (as an armchair engineer) are more that the 'big rocket' isn't very responsive to requested changes in thrust, whereas the 'little nose rockets' may be responsive, but very weak compared to the mass of the thing they're trying to control.
  - phkahler 12y ago
    >> You can't count position and velocity (i.e. d(position)/dt) as separate degrees of freedom. Sure you can, and must. velocity is a controllable and it's also very important that it be controlled as close to zero as possible when Y=0. Parent is correct, technically they care about 11 degrees of freedom, but rotation rate about the length is either a non issue or well regulated somehow. I'd really like to see the controller they're using. Wonder if it's fancy, or fairly simple with some large matrices.
    - Animats 12y ago
      I ignored rotation about the rocket's axis, since the rotational position at landing doesn't matter. The controller for this almost has to be a predictive controller. You can't do this on feedback alone. The control goal is not stability; it's end state - stopped, vertical, and on target, all achieved at the same moment. With enough fuel, you could do this step by step. Get into stable hover while vertical, then move slowly sideways over target, then descend slowly. NASA's Morpheus rocket works that way. Space-X is using much more aggressive control strategies; in the last seconds it's clear that all the goals are being sought simultaneously. Landing should work much better on land, with a bigger, stationary target in a less windy place.
      - grecy 12y ago
        > I ignored rotation about the rocket's axis, since the rotational position at landing doesn't matter. I agree the position at landing doesn't matter, but surely the rotation about the rocket's axis needs to be controlled so that it isn't spinning with any great speed - if it were, the RCS thrusters would have a hell of a time doing their job, as would the gimble of the main engine
- tsotha 12y ago
  They were able to do just fine with the F9R. I don't think this is a problem.
sunstone 12y ago
The video shows a lot of white caps in the ocean so the wind was blowing pretty hard. If the wind was gusting on top of that it's not hard to see why it would be hard to keep the rocket from being blown over even if it landed properly.
- foobarge 12y ago
  There's some white caps but not a whole lot. Wind speed at sea level might have been around 8 to 11m/s. http://en.wikipedia.org/wiki/Beaufort_scale http://en.wikipedia.org/wiki/Beaufort_scale
- david-given 12y ago
  The first stage will be empty of fuel and is basically a big empty metal balloon with a huge lump of metal at the bottom. The centre of gravity is very low, so while it looks really unstable it's much less bad than it looks --- like a double decker bus. OTOH, as you say, there'll also be a huge amount of windage from that big empty metal balloon... SpaceX seem to be competent, so I assume they'd factor this in. I'd be interested to see an analysis, though.
ridgeguy 12y ago
It's interesting to think about a case where Just Read The Instructions (the barge) might cooperate in the landing. Perhaps it could have an XY stage that could help compensate for residual X,Y or X,Y roll rates at touchdown. Looking at the video, if JRTI could have slewed a platform quickly to the left after contact, it might have been able to return the tilting booster's center of mass to a stable position. That's probably not much of an incremental engineering effort over what SpaceX has done already in this work. I'm completely awed by what they've accomplished so far. (edited because I can't do word->initial strings late at night...)
- grecy 12y ago
  I keep hearing lots of great ideas about how something other than the rocket could help the rocket land (catch it, move the platform, use a net, etc. etc.) I honestly think SpaceX have no intention of learning how to do any of those (even though some might work great) because they want to learn how to land it in a place with no "smart" landing pad already setup. i.e. Mars
  - ehmmm 12y ago
    Yes. That is also the reason they will not try to move the barge in unison with the rocket even if that was possible. Barge is trying to representing land. The maneuver made by the rocket to land at an angle is intentional. The rocket wasn't trying to correct some unknown balance issue with it. The reason for too fast sideways speed came from the problem with the rockets response time, signal->engine. The big sideways maneuver is made so the rocket will not hit the barge at high speeds in case of any problems.
  - robszumski 12y ago
    Can a Falcon Heavy get the full center core of the rocket, including the first stage into orbit? Maybe with no payload? If so, this would mean transporting and landing a stage on Mars, for use as a return launcher, would be possible. Is this a possible long term plan?
    - 12y ago
petrosh 12y ago
I would not call such an article "an analysis".
- simonh 12y ago
  Oh come on. Generating graphs of the rocket's vertical position and angular deflection from vertical over time, using a video analysis and physics modeling package, is not analysis? Sure, having the actual telemetry data from the rocket would be better, but suppose you were a competitor to SpaceX and wanted to understand what their capabilities were and whether this approach is feasible, this is exactly the sort of investigation you'd want to do.
paulsutter 12y ago
Guys please. The sideways oscillation of the rocket is an obvious control loop problem. When it's working correctly, the booster will remain rock solid vertical and land gracefully. Elon's (now deleted?) tweet said as much. Let the real rocket scientists fix their rocket. They know how. It's really unbelievably close to working. Amazing really.
- tsotha 12y ago
  The fact that he deleted it implies they decided that wasn't the case after all, or at least wasn't the whole story. They didn't handle media very well this launch, what with the fumbled video release and then a retracted tweet.
  - hahainternet 12y ago
    > The fact that he deleted it implies they decided that wasn't the case after all, or at least wasn't the whole story. It doesn't. That's just your impression you are placing upon the tweet. Deleting it says nothing when you are the head of multi billion dollar organisations. Perhaps he didn't want to give their competitors information that could help them model F9. > They didn't handle media very well this launch, what with the fumbled video release and then a retracted tweet. This is just ridiculous nitpicking. SpaceX usually gives us camera views from inside the goddamn LOX tanks on the stages. 'Didn't handle media very well' my arse.
  - weego 12y ago
    Didn't handle the media well? Some dickhead multi-millionaire who puts all his money into hedge funds and is pretty much just a negative drain on humanity can worry about their media image but how about we let the people putting their money into building space rockets do the space rocket thing.
  - ceejayoz 12y ago
    He also deleted a tweet to John Carmack telling him to work for SpaceX. Don't read too much into a deletion.
  - saraid216 12y ago
AdamTReineke 12y ago
I didn't see a mention of Musk's tweet, which labeled the YouTube video as "slow motion". That will make a difference (though likely just a scalar?) in the calculations.
Already__Taken 12y ago
I'm interested in why they haven't built another grasshopper to primarily use for the pad abort and inflight abort to get some bonus testing with. Does SpaceX have a location they could fly such a test rocket? They can't go over a km in their texas location.
Trombone12 12y ago
The title is misleading, should say "analysis of video of F9 crash". I know the current tittle is the title wired put in it, but the crash is not actually analysed at all, just the video of it, and that analysis doesn't provide any information of importance.
sebastianconcpt 12y ago
They were so close! Previous landings where more elegant, this one "looks anxious" (like done in a hurry). If they leave more fuel towards the end for error margin maneuvering then it can aproach landing with less momentum
whoisthemachine 12y ago
Overall, I'm very impressed by SpaceX's efforts. However, I'm wondering why they haven't tested the Grasshopper out on a water barge? It may be no different than on land, but that seems like a large assumption to make and a crucial variable to ignore.
- maxerickson 12y ago
  Would that save them much development effort? I would think they would have to do a lot of refit each time they dumped it in the ocean.
  - whoisthemachine 12y ago
    Very good point. It may not in terms of pure time or money. But in terms of eliminating "unknowns", it will certainly save them many headaches. Generally the unknowns are what cost you in development efforts. In this case, was it the variability of a water platform (however minute) that caused the over correction, or was it a fault of a piece (i.e. valve or something similar) in the rocket? When doing something new it's much easier if you eliminate all unknown variables except for one. So first, develop a controlled rocket that can hover and land on land (grasshopper). Next develop one that can hover and land on water. Now all major unknowns are eliminated except for the big one, landing a rocket from space, on either a water platform or a land platform. However, you will now be able to discern whether the issue is related to the water platform or just the general difficulties of landing a rocket hurtling down from space.
    - maxerickson 12y ago
      Wouldn't saving either time or money (or both) be the entire point of using a specialized test vehicle? They are anyway working their way through the unknowns by trying to recover the boosters. I think they are also pricing the launches so that at least all the direct costs are covered, so these tests are 'free'.
- mrfusion 12y ago
  Or put a barge in a wave pool or lake to test the grasshopper. That would save on transport costs.
mrfusion 12y ago
This doesn't seem to take into account that the video was in slow motion?
motoboi 12y ago
Landing attempt video: https://youtu.be/rAzwuEmZcmE https://youtu.be/rAzwuEmZcmE
deepix5 12y ago
Learn the language with the best people http://preply.com/en/skype/english-native-speakers http://preply.com/en/skype/english-native-speakers

99 points by jonah 12y ago

A key piece of information we don't have, but Space-X does, is how much fuel was left at landing. Landing has to be done with minimum fuel, since it comes out of the fuel budget for putting payload into orbit. They have thrust vectoring on the main engines, and have attitude jets near the nose. They have to land vertical, at near zero velocity, with near zero angular rate, with an underactuated system. Underactuated means there are more degrees of freedom to control than there are controllable parameters. They have 5 controllable degrees of freedom - 2 axes of engine vectoring, main engine throttle, and 2 axes of relatively weak nose thrusters. They have to hit a point with three translation constraints, three linear velocity constraints, two angular constraints, and two angular rate constraints. So they have 5 DOF in and 10 DOF out. That, mathematically, is what "rocket science" is. This under-actuated maneuver has to be solved as a two-point boundary problem, or, in practice, re-solved continuously to cope with problems such as wind gusts. You can see what happened; they had too much angular rate at landing, requiring more torque than the nose thrusters could impart to keep the rocket upright once the main engines could no longer help. It looks like they made a big correction shortly before landing to hit the target, and lost angular stability doing so. If they'd had a bigger landing area, so they didn't have to apply big corrections to hit the tiny target, this would have worked.

pixie_ 12y ago
Elon - "Looks like the issue was stiction in the biprop throttle valve, resulting in control system phase lag. Should be easy to fix." AKA lost constrol of the engines. It could of landed in a field and it would of still crashed. Man there are so many armchair rocket scientists.
- Animats 12y ago
  Aviation Leak says that message was "withdrawn."[1] [1] http://aviationweek.com/space/spacex-checks-throttle-valve-after-flawed-falcon-9-recovery-attempt http://aviationweek.com/space/spacex-checks-throttle-valve-a...
  - pixie_ 12y ago
    [2] ITAR.
- LoSboccacc 12y ago
  as KSP player and armchair engineer: when the rocket touched on the barge, thrust vectoring couldn't rotate the rocket anymore, since legs become a fixed pivot. and rcs didn't had enough trust to upright the rocket. now I don't think the issue is as easy as 'rcs didn't had enough thrust' what looks like is that the control system minimized vertical/horizontal velocity but allowed the rocket to touch down with too much rotational momentum. whether this was caused by software or hardware has to be seen. if they are storing the landing fuel in the same storage as the ascent fuel, sloshing may be a big factor. but I honestly have no idea, just like the speculation.
  - baq 12y ago
    musk says throttle got stuck, in KSP terms the ctrl key didn't work as the computer expected it to.
    - cronin101 12y ago
      Ugggh. StickyKeys activating and crashing my spaceship AGAIN.
    - LoSboccacc 12y ago
      yeah I was so happy when they added X
    - madaxe_again 12y ago
      Their wireless keyboard ran out of batteries. Honestly, I've had several missions to Jove which have ended in disaster because my keyboard died during orbital insertion.
      - Rooster61 12y ago
        Jool, you mean? I think you are confusing Jupiter's adjective with the the KSP counterpart's name. And that would be so annoying. It's no trivial task to get all the way out there and bleed off all that velocity.
- imaginenore 12y ago
  You fail at basic grammar. I don't think you're ready to judge anybody. It's "could have" and "would have", not "could of", nor "would of".
  - smoyer 12y ago
    I don't know pixie_ but non-native English speakers hear "could of" and "would of" when we use the contractions "could've" and "would've".
    - saraid216 12y ago
      I'm too lazy to go turn on showdead for GP, but... > I don't know pixie_ but non-native English speakers hear "could of" and "would of" when we use the contractions "could've" and "would've". You actually hear "could ov" and "would ov", but since the latter aren't actually words, there's an automatic shunt to the nearest known word. Sometimes this occurs in the speaker; sometimes this occurs in the listener. It occurs in the speaker because of loopback: you say "could ov"; you hear "could of"; you say "could of".
      - hollerith 12y ago
        >You actually hear "could ov" and "would ov" All occurences of the English word spelled "of" are pronounced "ov": pronouncing it with an F sound instead of a V sound would sound strange to an English speaker even where spelling it "of" is correct usage. Your explanation still applies, though, provided that we assume that the listener actually hears "could v" and "would v", but since there is no word pronounced "v", there's an automatic shunt to the word that is pronounced "ov".
    - nacs 12y ago
      I actually see this ("could of" and "would of") more in native speakers than non-native speakers actually. I have also seen it used many times in writing so it's not just a "heard it wrong" issue. Here in the South (US), it's disturbingly common.
- Shivetya 12y ago
  I would lay claim to the idea its far easier to land in a field than on a floating barge. For one thing the field doesn't move, second its an awfully easier target to hit with greater room for error
  - lmm 12y ago
    The point was that this particular problem (oscillation due to control lag) would still have caused a crash even if it had been landing in a field.
hyeonwho 12y ago
That is a very interesting way of thinking about the landing. If you are going to use DOF, you should also mention the grid fins (4 DOF (1)), and how control over parameters can be "time-shifted". Early in the descent the rotation of the craft doesn't matter so much as its trajectory, and so the grid fins can control pitch to aim for the landing site (2 DOF). Once the trajectory for landing is mostly established, the grid fins can be used to eliminate the vehicle rotation (3 DOF). At the time of landing, the grid fins are no longer useful, but they have set one degree of freedom that none of the other controls will change (rotation about the central axis of the rocket), so essentially they have "6 DOF in" at the time of landing. (1) In addition to control over rotation, the fins can be turned so that they cancel each other out overall, and thus slow down the vehicle without changing its rotation. I don't know whether the fins are actually used this way given the stresses involved.
mdda 12y ago
You can't count position and velocity (i.e. d(position)/dt) as separate degrees of freedom. If you insisted on doing so, then you should also count rocketthrust and rocketthrust changes through time. IMHO, the constraints here (as an armchair engineer) are more that the 'big rocket' isn't very responsive to requested changes in thrust, whereas the 'little nose rockets' may be responsive, but very weak compared to the mass of the thing they're trying to control.
- phkahler 12y ago
  >> You can't count position and velocity (i.e. d(position)/dt) as separate degrees of freedom. Sure you can, and must. velocity is a controllable and it's also very important that it be controlled as close to zero as possible when Y=0. Parent is correct, technically they care about 11 degrees of freedom, but rotation rate about the length is either a non issue or well regulated somehow. I'd really like to see the controller they're using. Wonder if it's fancy, or fairly simple with some large matrices.
  - Animats 12y ago
    I ignored rotation about the rocket's axis, since the rotational position at landing doesn't matter. The controller for this almost has to be a predictive controller. You can't do this on feedback alone. The control goal is not stability; it's end state - stopped, vertical, and on target, all achieved at the same moment. With enough fuel, you could do this step by step. Get into stable hover while vertical, then move slowly sideways over target, then descend slowly. NASA's Morpheus rocket works that way. Space-X is using much more aggressive control strategies; in the last seconds it's clear that all the goals are being sought simultaneously. Landing should work much better on land, with a bigger, stationary target in a less windy place.
    - grecy 12y ago
      > I ignored rotation about the rocket's axis, since the rotational position at landing doesn't matter. I agree the position at landing doesn't matter, but surely the rotation about the rocket's axis needs to be controlled so that it isn't spinning with any great speed - if it were, the RCS thrusters would have a hell of a time doing their job, as would the gimble of the main engine
tsotha 12y ago
They were able to do just fine with the F9R. I don't think this is a problem.

sunstone 12y ago

The video shows a lot of white caps in the ocean so the wind was blowing pretty hard. If the wind was gusting on top of that it's not hard to see why it would be hard to keep the rocket from being blown over even if it landed properly.

foobarge 12y ago
There's some white caps but not a whole lot. Wind speed at sea level might have been around 8 to 11m/s. http://en.wikipedia.org/wiki/Beaufort_scale http://en.wikipedia.org/wiki/Beaufort_scale
david-given 12y ago
The first stage will be empty of fuel and is basically a big empty metal balloon with a huge lump of metal at the bottom. The centre of gravity is very low, so while it looks really unstable it's much less bad than it looks --- like a double decker bus. OTOH, as you say, there'll also be a huge amount of windage from that big empty metal balloon... SpaceX seem to be competent, so I assume they'd factor this in. I'd be interested to see an analysis, though.

ridgeguy 12y ago

It's interesting to think about a case where Just Read The Instructions (the barge) might cooperate in the landing. Perhaps it could have an XY stage that could help compensate for residual X,Y or X,Y roll rates at touchdown. Looking at the video, if JRTI could have slewed a platform quickly to the left after contact, it might have been able to return the tilting booster's center of mass to a stable position. That's probably not much of an incremental engineering effort over what SpaceX has done already in this work. I'm completely awed by what they've accomplished so far. (edited because I can't do word->initial strings late at night...)

grecy 12y ago
I keep hearing lots of great ideas about how something other than the rocket could help the rocket land (catch it, move the platform, use a net, etc. etc.) I honestly think SpaceX have no intention of learning how to do any of those (even though some might work great) because they want to learn how to land it in a place with no "smart" landing pad already setup. i.e. Mars
- ehmmm 12y ago
  Yes. That is also the reason they will not try to move the barge in unison with the rocket even if that was possible. Barge is trying to representing land. The maneuver made by the rocket to land at an angle is intentional. The rocket wasn't trying to correct some unknown balance issue with it. The reason for too fast sideways speed came from the problem with the rockets response time, signal->engine. The big sideways maneuver is made so the rocket will not hit the barge at high speeds in case of any problems.
- robszumski 12y ago
  Can a Falcon Heavy get the full center core of the rocket, including the first stage into orbit? Maybe with no payload? If so, this would mean transporting and landing a stage on Mars, for use as a return launcher, would be possible. Is this a possible long term plan?
  - 12y ago

petrosh 12y ago

I would not call such an article "an analysis".

simonh 12y ago
Oh come on. Generating graphs of the rocket's vertical position and angular deflection from vertical over time, using a video analysis and physics modeling package, is not analysis? Sure, having the actual telemetry data from the rocket would be better, but suppose you were a competitor to SpaceX and wanted to understand what their capabilities were and whether this approach is feasible, this is exactly the sort of investigation you'd want to do.

paulsutter 12y ago

Guys please. The sideways oscillation of the rocket is an obvious control loop problem. When it's working correctly, the booster will remain rock solid vertical and land gracefully. Elon's (now deleted?) tweet said as much. Let the real rocket scientists fix their rocket. They know how. It's really unbelievably close to working. Amazing really.

tsotha 12y ago
The fact that he deleted it implies they decided that wasn't the case after all, or at least wasn't the whole story. They didn't handle media very well this launch, what with the fumbled video release and then a retracted tweet.
- hahainternet 12y ago
  > The fact that he deleted it implies they decided that wasn't the case after all, or at least wasn't the whole story. It doesn't. That's just your impression you are placing upon the tweet. Deleting it says nothing when you are the head of multi billion dollar organisations. Perhaps he didn't want to give their competitors information that could help them model F9. > They didn't handle media very well this launch, what with the fumbled video release and then a retracted tweet. This is just ridiculous nitpicking. SpaceX usually gives us camera views from inside the goddamn LOX tanks on the stages. 'Didn't handle media very well' my arse.
- weego 12y ago
  Didn't handle the media well? Some dickhead multi-millionaire who puts all his money into hedge funds and is pretty much just a negative drain on humanity can worry about their media image but how about we let the people putting their money into building space rockets do the space rocket thing.
- ceejayoz 12y ago
  He also deleted a tweet to John Carmack telling him to work for SpaceX. Don't read too much into a deletion.
- saraid216 12y ago

AdamTReineke 12y ago

I didn't see a mention of Musk's tweet, which labeled the YouTube video as "slow motion". That will make a difference (though likely just a scalar?) in the calculations.

Already__Taken 12y ago

I'm interested in why they haven't built another grasshopper to primarily use for the pad abort and inflight abort to get some bonus testing with. Does SpaceX have a location they could fly such a test rocket? They can't go over a km in their texas location.

Trombone12 12y ago

The title is misleading, should say "analysis of video of F9 crash". I know the current tittle is the title wired put in it, but the crash is not actually analysed at all, just the video of it, and that analysis doesn't provide any information of importance.

sebastianconcpt 12y ago

They were so close! Previous landings where more elegant, this one "looks anxious" (like done in a hurry). If they leave more fuel towards the end for error margin maneuvering then it can aproach landing with less momentum

whoisthemachine 12y ago

Overall, I'm very impressed by SpaceX's efforts. However, I'm wondering why they haven't tested the Grasshopper out on a water barge? It may be no different than on land, but that seems like a large assumption to make and a crucial variable to ignore.

maxerickson 12y ago
Would that save them much development effort? I would think they would have to do a lot of refit each time they dumped it in the ocean.
- whoisthemachine 12y ago
  Very good point. It may not in terms of pure time or money. But in terms of eliminating "unknowns", it will certainly save them many headaches. Generally the unknowns are what cost you in development efforts. In this case, was it the variability of a water platform (however minute) that caused the over correction, or was it a fault of a piece (i.e. valve or something similar) in the rocket? When doing something new it's much easier if you eliminate all unknown variables except for one. So first, develop a controlled rocket that can hover and land on land (grasshopper). Next develop one that can hover and land on water. Now all major unknowns are eliminated except for the big one, landing a rocket from space, on either a water platform or a land platform. However, you will now be able to discern whether the issue is related to the water platform or just the general difficulties of landing a rocket hurtling down from space.
  - maxerickson 12y ago
    Wouldn't saving either time or money (or both) be the entire point of using a specialized test vehicle? They are anyway working their way through the unknowns by trying to recover the boosters. I think they are also pricing the launches so that at least all the direct costs are covered, so these tests are 'free'.
mrfusion 12y ago
Or put a barge in a wave pool or lake to test the grasshopper. That would save on transport costs.

mrfusion 12y ago

This doesn't seem to take into account that the video was in slow motion?

motoboi 12y ago

Landing attempt video: https://youtu.be/rAzwuEmZcmE https://youtu.be/rAzwuEmZcmE

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