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I'm wondering if they'll be using the vertical equivalent of arresting gear on aircraft carriers[0]. See when fighter jets land on aircraft carriers? There's a

I'm wondering if they'll be using the vertical equivalent of arresting gear on aircraft carriers[0]. See when fighter jets land on aircraft carriers? There's a cable that decelerates them. That, but for vertical landing. The way these chopsticks are set forces the booster into a dangerous, snake like maneuver (a SnakeX maneuver) at the last second from a vertical setting, to get into the chopsticks. This maneuver is due to the fact chopsticks are short and the booster has to land on one point in space. No degrees of freedom. Now, imagine if the chopsticks were long. The booster wouldn't have to land at one specific point, but it could now land on a line. One degree of freedom. Now replace the long chopsticks with cables, and then add another pair of cables perpendicular to them. So you have a pair of parallel cables perpendicular to a second pair of parallel cables. Now the booster doesn't have to land on a line, but can land anywhere in the grid that's covered by the cables. Two degrees of freedom. Pushing this thought leads to having a sort of iris diaphragm, like the ones in optics, but an iris diaphragm of cables. The diaphragm is open when the booster is about to land, then closes in quickly. Imagine this[1], but it's cables cinching in. Now, it's a diaphragm of cables, not a diaphragm of rigid beams, so I imagine the deceleration to be even smoother as the cables elongate, and an additional system of springs and dampers to counter the weight of the booster. The booster is vertical and stays vertical. Granted, an unstable equilibrium, but it beats doing the SnakeX maneuver to get to the chopsticks, and that's another story. Now, imagine the iris cable diaphragm can move up and down like equipment handling containers, and now you have three degrees of freedom. That's less control to worry about on the booster's side at the worst possible moment, landing, where you can't make adjustments anymore. This not only means being more forgiving on mistakes related to position, but also on speed and angle. The diaphragm catches the booster at any angle, and given that it cinches way above the center of gravity, the booster goes back to a more stable vertical position. For the fire, maybe you just need a big hole down there. - [0]: https://en.wikipedia.org/wiki/Arresting_gear https://en.wikipedia.org/wiki/Arresting_gear - [1]: https://en.wikipedia.org/wiki/File:Iris_Diaphragm.gif https://en.wikipedia.org/wiki/File:Iris_Diaphragm.gif

T-A 2y ago
That's how the Chinese are planning to do it: https://youtu.be/OYWBmu6H0ik?feature=shared&t=35 https://youtu.be/OYWBmu6H0ik?feature=shared&t=35
jve 2y ago
SpaceX likes to simplify and not to complexify things. And they demonstrated they can do landing accurately. Moreover I think Elon discusses the mechazilla arms in one of Tim Dodd interviews. They dont want longer arms, ratger shoeter. Think about physics involved for longer arms and how much more stress you will putt on the connection points.
- Jugurtha 2y ago
  >SpaceX likes to simplify and not to complexify things. And they demonstrated they can do landing accurately. Yes. Something falling into a web of cables. I'd say it may be simpler than optimally controlling that last SnakeX maneuver to be hugged by a short-armed T-Rex. >Think about physics involved for longer arms and how much more stress you will putt on the connection points. That's why I wasn't talking about arms, but cables, as explained by most of the reply.
  - jve 2y ago
    Good luck not ruining rocket with that cable web. Now you got other problems to target into some cell. Moreover cables could be lingering depending on thrust. Or maybe thrust will just cut em easily.
    - Jugurtha 2y ago
      >Good luck not ruining rocket with that cable web. What do you mean? >Now you got other problems to target into some cell. Moreover cables could be lingering depending on thrust. Or maybe thrust will just cut em easily. It's an iris diaphragm that's open but cinches on the booster.
  - Faaak 2y ago
    Did you think about how you support the cables ? Surely they must be tensionned or else they will hang. How do you tension them ? Of course you know that the more the cable is tensionned, the more force you need. So you need a big-ass structure to hold all of these cables. They must be able to circulate around the perimeter, while being in tension, while not collapsing the structure that holds them, etc.. I'm sure you think it's easy, but I'm sure some people thought a bit more
Cthulhu_ 2y ago
This is a solution for a problem that's already solved, that is, booster maneuverability and accuracy. But they've just demonstrated that the booster is accurate and controlled enough to land on the chopsticks, and they have over a decade of experience in making rockets land accurately in a specific zone.
nkoren 2y ago
Next year, China says it will be testing a concept very similar to what you've described, with its Long March 10A rocket: https://www.youtube.com/watch?v=27TvGDpPLNw https://www.youtube.com/watch?v=27TvGDpPLNw It will be interesting to see how these two approaches fare vs. one another.
- Jugurtha 2y ago
  That's exactly it, thank you! What worries me with the current one that landed is the gradient: because the arms are short and the spot is tight, the burden is on the booster to make very sharp corrections (especially on pitch) to get caught when there's literally a few meters left, with an increased risk at the worst time (no altitude, and structures around), as opposed to leaving the pitch as is and landing vertically. In other words: the possibility to screw a perfect launch by introducing irremediable risk in the last few seconds and meters. Then again, I just watched the launch and that was the first thing that popped into my mind, and the first "design" that popped into my mind as I was replying to the thread, so not much thought went into it.
tvier 2y ago
One thing to note is that the "Snake" maneuver was designed to keep the tower safe during the test, and not forced on the rocket by the chopsticks. The rocket was set to come down on the pad just in front on the tower and launch mount until the final 3-engine landing burn started. This kept the infrastructure safe until the last moment, but also required that lateral translation you referred to.

T-A 2y ago

That's how the Chinese are planning to do it: https://youtu.be/OYWBmu6H0ik?feature=shared&t=35 https://youtu.be/OYWBmu6H0ik?feature=shared&t=35

jve 2y ago

SpaceX likes to simplify and not to complexify things. And they demonstrated they can do landing accurately. Moreover I think Elon discusses the mechazilla arms in one of Tim Dodd interviews. They dont want longer arms, ratger shoeter. Think about physics involved for longer arms and how much more stress you will putt on the connection points.

Jugurtha 2y ago
>SpaceX likes to simplify and not to complexify things. And they demonstrated they can do landing accurately. Yes. Something falling into a web of cables. I'd say it may be simpler than optimally controlling that last SnakeX maneuver to be hugged by a short-armed T-Rex. >Think about physics involved for longer arms and how much more stress you will putt on the connection points. That's why I wasn't talking about arms, but cables, as explained by most of the reply.
- jve 2y ago
  Good luck not ruining rocket with that cable web. Now you got other problems to target into some cell. Moreover cables could be lingering depending on thrust. Or maybe thrust will just cut em easily.
  - Jugurtha 2y ago
    >Good luck not ruining rocket with that cable web. What do you mean? >Now you got other problems to target into some cell. Moreover cables could be lingering depending on thrust. Or maybe thrust will just cut em easily. It's an iris diaphragm that's open but cinches on the booster.
- Faaak 2y ago
  Did you think about how you support the cables ? Surely they must be tensionned or else they will hang. How do you tension them ? Of course you know that the more the cable is tensionned, the more force you need. So you need a big-ass structure to hold all of these cables. They must be able to circulate around the perimeter, while being in tension, while not collapsing the structure that holds them, etc.. I'm sure you think it's easy, but I'm sure some people thought a bit more

Cthulhu_ 2y ago

This is a solution for a problem that's already solved, that is, booster maneuverability and accuracy. But they've just demonstrated that the booster is accurate and controlled enough to land on the chopsticks, and they have over a decade of experience in making rockets land accurately in a specific zone.

nkoren 2y ago

Next year, China says it will be testing a concept very similar to what you've described, with its Long March 10A rocket: https://www.youtube.com/watch?v=27TvGDpPLNw https://www.youtube.com/watch?v=27TvGDpPLNw It will be interesting to see how these two approaches fare vs. one another.

Jugurtha 2y ago
That's exactly it, thank you! What worries me with the current one that landed is the gradient: because the arms are short and the spot is tight, the burden is on the booster to make very sharp corrections (especially on pitch) to get caught when there's literally a few meters left, with an increased risk at the worst time (no altitude, and structures around), as opposed to leaving the pitch as is and landing vertically. In other words: the possibility to screw a perfect launch by introducing irremediable risk in the last few seconds and meters. Then again, I just watched the launch and that was the first thing that popped into my mind, and the first "design" that popped into my mind as I was replying to the thread, so not much thought went into it.

tvier 2y ago

One thing to note is that the "Snake" maneuver was designed to keep the tower safe during the test, and not forced on the rocket by the chopsticks. The rocket was set to come down on the pad just in front on the tower and launch mount until the final 3-engine landing burn started. This kept the infrastructure safe until the last moment, but also required that lateral translation you referred to.