New shorter nozzle compared to regular.
reddit.com/gallery/12mtk6d
reddit.comPosted Apr 15, 2023, 7:07 AM UTC
11723
reddit.comI vaguely remember Elon making an offhand remark during one of his walk-around interviews/tours mentioning how surprisingly expensive and annoying that last portion of the big extended bell on the mvac engines are, and how they are like the most expensive part of the whole engine (or something roughly along those lines), in I think it was one of the interviews he did with Tim Dodd (the EverydayAstronaut) a year or so ago, if I'm remembering it right.
So, had a good chuckle when I was watching the launch and saw the shortened nozzle on this non-maxed launch, almost immediately when I saw it, my mind flashed back to that memory of that comment from Elon, and started laughing to myself, like "ah, alright, I think I see what happened here..."
19
They have launched a slightly shortened nozzle a while ago -- it was a famous story where there was a crack in the nozzle and they just used shears to shorten it, because there was enough performance for the mission regardless.
Somebody must have remembered that, so now they decided to make shorter nozzles intentionally, as a cost saving measure. Why not, unless there is some serious hassle to re-qualify this version for flight.
5
Almost makes you wonder if these shortened nozzles came off the reject pile with just a little trim.
3
I don't really see how a shorter nozzle on the second stage leads to faster launch cadence. It's one of the only pieces that gets discarded and not reused, how can it contribute to faster turnaround times?
Unless it allows for other changes in the interstage like a different stage separation mechanism. Or perhaps it makes the nozzle stronger so they don't need to treat it so delicately?
16
Well a larger nozzle could take longer to manufacture. But based on the 2 tweets linked here they just mentioned performance, not about manufacturing time. A vaccum engine could theoretically be infinitely large + expanding to get the maximum performance but eventually you hit diminishing returns vs weight. They've just decided here they can use less material and still reach the intended orbit with the performance of a smaller nozzle. It will capture less thrust from the exhaust but they don't need it.
43
It costs ~$45 per kilogram (US$45,000 per tonne) for standard ferroniobium metal. Considering thickness of vacuum nozzle rim (<1mm) cost saving for material should be negligible. Implies cost to manufacture at that thickness is high, probably due to a relatively high proportion of rejected items.
32
When visiting the factory in 2016, I saw a large (double-digit) # of mVac nozzles on the side of the building that were being discarded.
May have just been timing, but it also could mean you are spot-on with your theory.
19
Thanks. There's a great Ars Technica article describing how they had a cracking problem on the rim of an early Merlin Vacuum engine nozzle. They managed to remove crack by trimming back the nozzle, creating something similar to these shorter nozzles currently in use. Wonderful insight into what makes SpaceX special.
4
They have reached the point with first stage refurbishment that the manufacturing time of second stages is the limiting factor for launch cadence.
8
I want a stage 2 with a short skirt and a looooooooooooooooooong jacket.
14
Sounds like you want to have your cake and eat it too
;-)
8
After seeing so many glowing MVac nozzles on video, looking at this one is hurting my brain. It looks like a video glitch.
11
Just when you think F9 flights are getting routine, they pull this on you. This is inline with no part is a good part, but since they couldn't get rid of it, they optimized it further for a specific case scenario. Bravo SpaceX.
6
And not just a little!
2
Is this the same nozzle as the sea level variant or just a shorter vacuum optimized one? It seems like the F9 upper stage often has performance to spare so this makes sense, but it is definitely out-of-the-box thinking.
This is the nozzle extension which is radiatively cooled and made of niobium. The nozzle on the sea level variant is even smaller and shaped differently, it's regeneratively cooled, and is made of copper with an inconel jacket
So is it is basically the same nozzle without the niobium extension. That makes lots of sense. I was confused that SpaceX would create a new nozzle design, but if they are just omitting the extension then that makes lots of sense.
The niobium extension is definitely still there, just shorter.
Interesting, I am surprised the material cost savings per unit exceeded the engineering cost of the design. Engineering hours are expensive, but I guess niobium is expensive too? Clearly somebody gave a compelling cost/benefit analysis but that is really interesting.
This is a shorter vacuum engine.
[deleted]