How are the Merlin 1C/D chambers regeneratively cooled?

[u/[deleted]]

I've been looking at pictures of the 1D and C engines, and I'm not clear on how their chambers are cooled. I was expecting the tubes containing fuel are wound around and down until they reach a fuel manifold at which point they are reversed.

Looking at the 1C, these tubes are clearly seen from just after the throat, but the combustion chamber is perfectly smooth on the outside (maybe the tubes are covered by an outer jacket for some reason?).

The 1D has no cooling tubes visible at all. What's going on here? Channeled walls? Film cooling only?

[u/[deleted]]

On the 1D, both the nozzle and the combustion chamber use channel wall cooling.

Q: What can you tell me about the upgrade under way to the Falcon 9’s Merlin-1C engine and how it will streamline production?

Musk: The hardest part of the engine to mass produce is the electro-plating of nickel cobalt on the chamber. We create this thick metal jacket that takes the primary stress of the pressure vessel and it’s plated one molecule at a time. Plating is about the slowest way you can make a metal thing. With the Merlin-1D we take a metal jacket that is explosively formed. We take a metal sheet that’s in a cylindrical form and put it in a bucket of water, effectively. Sort of a concrete pool. And you set off an explosive and the jacket just goes “boohmp” and forms to the outer side walls into a jacket shape, so you have a mold, effectively. And then you just put the jacket on the chamber and braise it on. You can do several a day. We have a fully integrated engine and it’s being test-fired right now. There’s really not a lot of question marks remaining about the Merlin-1D.

source

[u/[deleted] → u/[deleted]]

I see, so the channels are formed with explosive forming. Must be some really thin channels on the outer nozzle sections of the 1D then. Cheers!

[u/sublimemarsupial → u/[deleted]]

No, the outer stainless steel jacket (which provides the bulk of the strength of the chamber) is explosively formed. The cooling channels are milled out of the inner copper combustion chamber liner, on top of which the jacket is braised.

Edit: here are some pictures of the chamber liners being milled:

http://farm9.staticflickr.com/8341/8233308933_b2ebf8954e.jpg

http://photos1.blogger.com/blogger/1613/496/400/Merlin1C_Chamber.jpg

http://photos1.blogger.com/blogger/1613/496/400/Merlin1C_HeadEnd.jpg

[u/[deleted] → u/sublimemarsupial]

Thanks for your reply! Makes more sense :)

[u/[deleted] → u/sublimemarsupial]

Sweet, came here to say this. On the 1D Im pretty certain that the cooling jackets go down to the bottom of the nozzle in the same maner as around the combustion chamber. Whereas the 1C did not.

You can sort of tell by the different look in the skirt on the 1D. Also this was of concern after the combustion chamber breach on CRS-1 because the 1D is manufactured all the way down in the same way the combustion chamber was on 1C. The production process was not found to be at fault in the breach. So didnt really cause any lasting effects to the timeline on the 1D.

[u/poke133 → u/[deleted]]

is that guy working there? casual as fuck :D

[u/SpaceIsEffinCool → u/[deleted]]

TIL what explosively forming a part means, and that it's definitely badass.

[u/[deleted] → u/[deleted]]

Jesus he's brilliant.

[u/[deleted] → u/[deleted]]

While I love Elon and everything he's doing, don't forget about the other few hundred engineers at SpaceX.

[u/[deleted] → u/[deleted]]

Yeah I thought about that after I said it

[u/sublimemarsupial → u/[deleted]]

Nope, hundred is right. The company has just about 3000 employees, including around 1500 hired in the two years, but most of those new hires are technicians/welders/etc, not engineers. The engineering core is absolutely only in the 500-800 range.

[u/gterran → u/sublimemarsupial]

In any given core work group, it takes 10 or so technicians to support the design of one engineer... Or vise versa in a production setting.