5 ms·

... Are they the same engines though? Don't get me wrong, it's impressive that the pressure tanks can take that many cryogenic cycles, but I am not sure I woul

... Are they the same engines though? Don't get me wrong, it's impressive that the pressure tanks can take that many cryogenic cycles, but I am not sure I would call it the same "rocket".

dylan604 2y ago
Does it matter if they are the same? If they have an inventory of engines that get rebuilt after launches but enough that they do not need to delay launches, it's good enough for my use. It's similar to a NASCAR race. They pretty much tear those down and rebuild after each race as well, but it's the "same" car.
- jauntywundrkind 2y ago
  It matters and it doesn't. It doesn't affect turn around because you can have a ready to go inventory. But it matters how much an engine can be reused because it's a significant material and labor effort to produce them. Are the 9 engines from each flight reusable, and to what extent? Does half the motor get replaced each time or is it generally ok? The Ship of Theseus debate doesn't have a hard answer to it. We can -like the Persian Immortal - respect the continuity of the thing. But so too we should track and follow the churn of the pieces, acknowledge the parts decayed. I for one am very curious how much of the ship and how much of the motor needs replacement, and how often.
  - Isamu 2y ago
    In the context of rockets, what is important and salient here is reuse, and even if some motors are swapped out, they are still available for refurbishment, rather than destroyed on reentry.
    - jauntywundrkind 2y ago
      Unless they have to be written off cause they are wrecked? Tesla's kept this one close to the chest. We really don't seem to have much data at all on how the rocket engines are doing after re-entry. The rocket engine itself might well be it's own Ship of Theseus, requiring considerable replacement. We just don't know, it's just not clear.
      - dylan604 2y ago
        Would launches be as cheap if they had to keep replacing the most complicated part of the ship? Could they hide the expense of replacing the engines with subsidized pricing like Uber?
- fdfdfdfdfdddf 2y ago
  Ship of Theseus The engines are the most expensive part of any rocket by far. Clearly SpaceX has produced some incredible economies from reuse, but it's definitely not as clear cut as simply "reusing a single rocket twenty times".
johlindenbaum 2y ago
https://en.wikipedia.org/wiki/Ship_of_Theseus https://en.wikipedia.org/wiki/Ship_of_Theseus
anovikov 2y ago
Booster processing between launches sometimes takes as little as 7 days. That probably rules out any engine replacements at least on some launches.
- _joel 2y ago
  They seem to be able to switch out a Raptor 2 in a couple of hours, even quicker sometimes. It's not impossible there will be some need for maintenance on the Merlins, probably on the injectors I'd imagine, as there'll be some coking build up (it's RP1 not CH4).
ericcumbee 2y ago
not as many as you would think. They don't do very many static fires of falcon 9 at all anymore. https://aviationweek.com/defense-space/space/spacex-building-airline-type-flight-ops-launch https://aviationweek.com/defense-space/space/spacex-building... "For example, the company changed its requirement to perform a static firing every time an engine was removed. “Now we have to drop three engines before we go do a static fire because we determined we can put the high-pressure joints together, verify that they’re leak-tight and everything works,” Gerstenmaier says. “We’ve removed like 14 static fires out of the flow that would have been required under our old criteria, and all 14 of those flights launched on the first attempt.”"
abc_lisper 2y ago
[flagged]
- ceejayoz 2y ago
  > According to ChatGPT... No. Stop it. edit: I asked it the same question and it answered entirely differently. https://chat.openai.com/share/d214702c-561d-4e4f-96c2-8c66f125a0da https://chat.openai.com/share/d214702c-561d-4e4f-96c2-8c66f1...
jve 2y ago
Is there any source you can provide that says they have to swap the engines out?
grecy 2y ago
> ... Are they the same engines though? The answer is we don't know. SpaceX have not published much detailed information about exactly what they do during booster refurbishment, how much is simply inspected, how much is replaced and how much is "swapped out". The fastest turnaround for a booster is 21 days (and plenty have been less than 30). [1] [1] https://en.wikipedia.org/wiki/List_of_Falcon_9_and_Falcon_Heavy_launches https://en.wikipedia.org/wiki/List_of_Falcon_9_and_Falcon_He...
avmich 2y ago
It's possible to make rocket engines able to perform for quite a long time. http://www.lpre.de/sntk/NK-33/tests.htm http://www.lpre.de/sntk/NK-33/tests.htm В 1976 г. один из двигателей первой ступени НК-33 вместо 140 с, требуемых техническим заданием, проработал на стенде 14.000 с. In 1976 one of NK-33 rocket engines instead of 140 seconds required by the specification run on the test stand for 14,000 seconds.

... Are they the same engines though? Don't get me wrong, it's impressive that the pressure tanks can take that many cryogenic cycles, but I am not sure I would call it the same "rocket".

dylan604 2y ago

Does it matter if they are the same? If they have an inventory of engines that get rebuilt after launches but enough that they do not need to delay launches, it's good enough for my use. It's similar to a NASCAR race. They pretty much tear those down and rebuild after each race as well, but it's the "same" car.

jauntywundrkind 2y ago
It matters and it doesn't. It doesn't affect turn around because you can have a ready to go inventory. But it matters how much an engine can be reused because it's a significant material and labor effort to produce them. Are the 9 engines from each flight reusable, and to what extent? Does half the motor get replaced each time or is it generally ok? The Ship of Theseus debate doesn't have a hard answer to it. We can -like the Persian Immortal - respect the continuity of the thing. But so too we should track and follow the churn of the pieces, acknowledge the parts decayed. I for one am very curious how much of the ship and how much of the motor needs replacement, and how often.
- Isamu 2y ago
  In the context of rockets, what is important and salient here is reuse, and even if some motors are swapped out, they are still available for refurbishment, rather than destroyed on reentry.
  - jauntywundrkind 2y ago
    Unless they have to be written off cause they are wrecked? Tesla's kept this one close to the chest. We really don't seem to have much data at all on how the rocket engines are doing after re-entry. The rocket engine itself might well be it's own Ship of Theseus, requiring considerable replacement. We just don't know, it's just not clear.
    - dylan604 2y ago
      Would launches be as cheap if they had to keep replacing the most complicated part of the ship? Could they hide the expense of replacing the engines with subsidized pricing like Uber?
fdfdfdfdfdddf 2y ago
Ship of Theseus The engines are the most expensive part of any rocket by far. Clearly SpaceX has produced some incredible economies from reuse, but it's definitely not as clear cut as simply "reusing a single rocket twenty times".

johlindenbaum 2y ago

https://en.wikipedia.org/wiki/Ship_of_Theseus https://en.wikipedia.org/wiki/Ship_of_Theseus

anovikov 2y ago

Booster processing between launches sometimes takes as little as 7 days. That probably rules out any engine replacements at least on some launches.

_joel 2y ago
They seem to be able to switch out a Raptor 2 in a couple of hours, even quicker sometimes. It's not impossible there will be some need for maintenance on the Merlins, probably on the injectors I'd imagine, as there'll be some coking build up (it's RP1 not CH4).

ericcumbee 2y ago

not as many as you would think. They don't do very many static fires of falcon 9 at all anymore. https://aviationweek.com/defense-space/space/spacex-building-airline-type-flight-ops-launch https://aviationweek.com/defense-space/space/spacex-building... "For example, the company changed its requirement to perform a static firing every time an engine was removed. “Now we have to drop three engines before we go do a static fire because we determined we can put the high-pressure joints together, verify that they’re leak-tight and everything works,” Gerstenmaier says. “We’ve removed like 14 static fires out of the flow that would have been required under our old criteria, and all 14 of those flights launched on the first attempt.”"

abc_lisper 2y ago

[flagged]

ceejayoz 2y ago
> According to ChatGPT... No. Stop it. edit: I asked it the same question and it answered entirely differently. https://chat.openai.com/share/d214702c-561d-4e4f-96c2-8c66f125a0da https://chat.openai.com/share/d214702c-561d-4e4f-96c2-8c66f1...

jve 2y ago

Is there any source you can provide that says they have to swap the engines out?

grecy 2y ago

> ... Are they the same engines though? The answer is we don't know. SpaceX have not published much detailed information about exactly what they do during booster refurbishment, how much is simply inspected, how much is replaced and how much is "swapped out". The fastest turnaround for a booster is 21 days (and plenty have been less than 30). [1] [1] https://en.wikipedia.org/wiki/List_of_Falcon_9_and_Falcon_Heavy_launches https://en.wikipedia.org/wiki/List_of_Falcon_9_and_Falcon_He...

avmich 2y ago

It's possible to make rocket engines able to perform for quite a long time. http://www.lpre.de/sntk/NK-33/tests.htm http://www.lpre.de/sntk/NK-33/tests.htm В 1976 г. один из двигателей первой ступени НК-33 вместо 140 с, требуемых техническим заданием, проработал на стенде 14.000 с. In 1976 one of NK-33 rocket engines instead of 140 seconds required by the specification run on the test stand for 14,000 seconds.