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Starship SN10 High-Altitude Flight Test
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raptor1956:

--- Quote from: rdl on March 06, 2021, 03:18:19 am ---They're using three engines, so most of the time during these tests the thrust is not along the centerline. Pretty impressive how well they deal with that. I'm amazed they landed one.

--- End quote ---

Normally, when you use three engines, they are arranged in a row so that you can have balanced thrust with 3 engines, 2 engines or 1 engine -- not sure why that wasn't used.  In an operational rocket requiring more than one engine you would prefer three in a row, five arranged with one in the center and four arranged 90 degrees around the center, or seven with one in the center and the others spaced at 60 degrees.  Again, not sure what SpaceX is trying to prove with the arrangement they're using.


Brian
wraper:

--- Quote from: raptor1956 on March 09, 2021, 11:55:12 am ---
--- Quote from: rdl on March 06, 2021, 03:18:19 am ---They're using three engines, so most of the time during these tests the thrust is not along the centerline. Pretty impressive how well they deal with that. I'm amazed they landed one.

--- End quote ---

Normally, when you use three engines, they are arranged in a row so that you can have balanced thrust with 3 engines, 2 engines or 1 engine -- not sure why that wasn't used.  In an operational rocket requiring more than one engine you would prefer three in a row, five arranged with one in the center and four arranged 90 degrees around the center, or seven with one in the center and the others spaced at 60 degrees.  Again, not sure what SpaceX is trying to prove with the arrangement they're using.

--- End quote ---
Maybe think a little bit and realize you cannot make a round rocket with such arrangement. Then think a bit again and realize you will have thrust vectoring issues in certain directions. Not to say starship will have 6 engines in total (3 of which vacuum engines with large bells). Then think for a third time, and realize you cannot switch between 2 engines and 1 or 3 in a way that thrust remains in center. You either need to fire additional engine during switchover or shut down them all. Or deal with even more off center thrust compared with current arrangement. Just because you have no understanding, does not mean somebody tries to prove anything.

--- Quote ---Normally, when you use three engines, they are arranged in a row so that you can have balanced thrust with 3 engines, 2 engines or 1 engine -- not sure why that wasn't used
--- End quote ---
Normally where? Delta IV Heavy which uses 3 separate boosters and does not even have an option to shut them down separately?

--- Quote ---five arranged with one in the center and four arranged 90 degrees around the center, or seven with one in the center and the others spaced at 60 degrees.
--- End quote ---
These are inefficient in regards to space usage, especially 5 engine variant. A lot of space wasted for nothing.
rdl:

--- Quote ---five arranged with one in the center and four arranged 90 degrees around the center, or seven with one in the center and the others spaced at 60 degrees.
--- End quote ---

The Saturn V used the first arrangement. The Falcon 9 uses the second, though with eight engines in the outer ring. The first version of Falcon 9, at least one of them, had the nine engines in 3x3 pattern which seems really weird. The Shuttle Orbiter's three main engines were in a triangle. It seems the designers use whatever they think is best.
iMo:
They land with help of 1 raptor only - so the arrangement is not so important, imho.
After failing with SN8 and SN9 (due to issues with raptors) a guy in a discussion (or was it a tweet??) asked something like ..why not to reignite all three during the landing, then to decide which one of the raptors works best, then switch the other off...
So it seems Elon has been following the hint :)

PS: below the tweets after SN9 landing..
Medved:
My guess was there was an attempt to keep two engines running at landing, but one of them flamed out just after they shut down the one.
To me the SN10 flight was surprisingly soon after the SN9 failure to have the whole landing sequence redone (first ignite 3, then if successful, shut one down).
To me it looked more like there were two groups of engineers, each group preferring one way (light two vs light 3 and shut down one), arguing about how important the advantages/disadvantages of each approach are, so they designed in actually both scenarios (having no redundancy in case of SN9 vs handling the 4 liquid hammer surges in the fuel piping in the SN10 would be my guesses for the disadvantages). They decided to try first the "light 2" and then later the "light 3, shut down 1".
Well, both have failed so far, so they have some homework to do...
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