4 ms·

Yes. They need 1 to land - more than one means too much thrust. Last time they only lit one, it failed to light, and boom. This time they lit all three hoping

Yes. They need 1 to land - more than one means too much thrust. Last time they only lit one, it failed to light, and boom. This time they lit all three hoping at least one would work, then turned off the ones they didn’t need. I assume they had the idea independently of the guy who asked musk why they didn’t light more than one and shut down — musk replied “because we’re dumb”, but I guess that tweeter could claim to be a rocket scientist now.

eightysixfour 6y ago
Quick edit to this - they need two for the rotation to happen. Last time they lit two and one failed, so they did not have enough thrust to rotate it. This time they lit three and turned off one for the rotation, then turned off a second once it was rotated.
- GeneralAntilles 6y ago
  It was three engines through the whole rotation. They turned off two within about a second of one another after transitioning out of rotation.
  - eightysixfour 6y ago
    Yep, you’re right, just saw the video from SpaceX. Good call. This actually makes me wonder if they significantly changed the landing profile since they’re scrubbing velocity so much faster with three thrusters, it may explain why the single thruster landing portion seemed slow compared to previous attempts.
payamb 6y ago
Link to the tweet: https://twitter.com/elonmusk/status/1357256507847561217 https://twitter.com/elonmusk/status/1357256507847561217
avmich 6y ago
To start both main and backup engine was standard procedure planned for Soviet lunar landing LK, at liftoff. If everything's fine, backup engine shuts down. "The rocket company", https://en.wikipedia.org/wiki/The_Rocket_Company https://en.wikipedia.org/wiki/The_Rocket_Company , a great and quite realistic book, reminds about importance of knowing history; there, a company explicitly maintains a library of previous technical solutions to problems encountered.
- sitkack 6y ago
  This is very interesting. Blending fiction and non-fiction, it sounds like a very finely detailed position paper.

eightysixfour 6y ago

Quick edit to this - they need two for the rotation to happen. Last time they lit two and one failed, so they did not have enough thrust to rotate it. This time they lit three and turned off one for the rotation, then turned off a second once it was rotated.

GeneralAntilles 6y ago
It was three engines through the whole rotation. They turned off two within about a second of one another after transitioning out of rotation.
- eightysixfour 6y ago
  Yep, you’re right, just saw the video from SpaceX. Good call. This actually makes me wonder if they significantly changed the landing profile since they’re scrubbing velocity so much faster with three thrusters, it may explain why the single thruster landing portion seemed slow compared to previous attempts.

payamb 6y ago

Link to the tweet: https://twitter.com/elonmusk/status/1357256507847561217 https://twitter.com/elonmusk/status/1357256507847561217

avmich 6y ago

To start both main and backup engine was standard procedure planned for Soviet lunar landing LK, at liftoff. If everything's fine, backup engine shuts down. "The rocket company", https://en.wikipedia.org/wiki/The_Rocket_Company https://en.wikipedia.org/wiki/The_Rocket_Company , a great and quite realistic book, reminds about importance of knowing history; there, a company explicitly maintains a library of previous technical solutions to problems encountered.

sitkack 6y ago
This is very interesting. Blending fiction and non-fiction, it sounds like a very finely detailed position paper.