Clark Lindsey posted some links on Hobbyspace to a recent presentation given by SpaceX at COMSTAC. The Briefing had some interesting pictures and information, and this one at least doesn’t appear to have any sort of statement saying it shouldn’t be distributed, so if they don’t mind, I’m going to post a few of the pictures and a couple brief thoughts.
There isn’t really all that much that’s new in the presentation, but I did notice that apparently my understanding of their tank design was a little bit off. I thought they were using a design that had the tank walls, with a couple of ring stiffeners, but no stringers. I was wrong. So, in a way this is just a 21 century Friction Stir Welded version of how an aircraft wing is designed.
It’s also interesting to note that they appear to have resolved their supply issue with Lithium Aluminum. That’s good. LiAl is interesting stuff–really good fracture toughness, with excellent strength-to-weight. And if you’re using FSW for the welds, you get around a lot of the weird processing issues.
But the coolest bit from the summary was their pictures of the Merlin 1C. Apparently the powerpoint file has some pretty sweet high-res pictures. Back in the summer of ’03, before I got involved with Masten Space Systems, I paid a visit to their rocket factory. Their VP of Business Development, Gwynne Shotwell was nice enough to give me a tour of the place, and I was interviewed by Chris Thompson (then VP of Operations and Manufacturing). During the interview, we got talking about pintle injectors, since I had a fascination with the design, and SpaceX was using it. Chris told me that he and Tom Mueller and a few others of the original SpaceX crew had done some ameteur pintle injector based rockets over the years. When I showed him my designs I had done as part of a special projects class at BYU, he smiled and said something along the lines of “my, that looks familiar”. I’m not trying to be rude or belittling in any way, but when I saw those pictures I thought the same thing–“my, that looks familiar.”
Those first two are pretty obvious, and quite gorgeously done. This last one I think is a tube-wall nozzle extension, possibly for the upper stage version of the Merlin-1C. But I could be wrong. It might also be part of the closeout for the milled-wall chamber. Either way, it is rather impressively done. Though having a swirl like that in the nozzle tends to create a torque on the stage, which will induce a roll unless counteracted by the turbopump exhaust or RCS thrusters. My curiousity is definitely piqued.
Overall, I’d say that these engines look very nice, and I hope they have as much luck and success with their regen cooled pintles as we have–it’s definitely the right way to go. The designs are a lot more complicated than our designs, but probably a lot higher performance and a lot lighter weight than ours too. Tom Mueller’s team has outdone themselves. Having a real cooling system on their engines I think compliments an already quite impressive design. Now if only we could talk them into getting a real landing system to go with that stage…
Jonathan Goff
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Intrigued by you last comment, what kind of landing system are you suggesting they should use?!?!?!
My understanding is that Jon is talking about landing on the thrust and landing legs, like XA does, instead of chutes and airbags.
Anonymous,
The second commenter nailed it. I work for a VTVL rocket company in Mojave, and I’ve got a natural bias toward powered landings. Especially when the alternative is fishing the stage out of the ocean, and refurbishing it. I don’t know if Elon still reads this blog ever, but it was just some good natured razzing.
I say the same snarky thing about Kistler’s vehicle.
~Jon
Well, maybe you could demonstrate the powered landings first before trying to sell them. 🙂
Btw, any insights why they’re using tubewall nozzle instead of milled channels like RD-170/180?
I thought the latter was the way to go in modern times…
Mz,
You have a perfectly valid point. There’s a reason why I’m still just mentioning the idea as a half-serious zinger in a blog post, and not spending hours writing up a technical proposal and trying to pitch it directly to SpaceX. Until we’ve flown that, while it’s still a good idea, it’s an unproven good idea. So yeah, for now I’ll keep it at some good-natured friendly razzing between alt.space companies.
At least until we’ve flown stuff enough that I feel legit with making a more serious case.
~Jon
Yeah, it was meant as a good-natured joke. 🙂 I’m really appreciating the work you’re doing. I also like your personal contribution here on the publicity side of things.
How far are your first holddown firings?
Mz,
Well, as you notice they do have a milled-wall chamber even though they have a tube-wall nozzle. That’s actually similar AIUI to the way the SSME is done (at least that’s the way it looked when I was poking my head up in the one they had at Las Cruces). I’m not as familiar with the Russian engines. Do they really use a milled channel for the actual nozzle section, or only the combustion chamber and throat?
The issue being that since the outside perimeter of the nozzle will often be much, much larger than the outside perimeter of any section of the actual chamber, it may make it difficult to get channels of the right aspect ratio (ie not very wide and very shallow for instance). Not really sure. I’ve never personally tried doing one with that kind of expansion ratio, and I don’t know enough about the milled channel wall ones that do to be sure….
I’m rambling.
Anyhow, it’s a fairly reasonable approach, but we have at least one idea that we think may be better. If we get the chance to try it out (I’m seeing if I can switch my thesis topic to investigating the manufacturing method for that concept), we’ll definitely brag about it if it works… 🙂
~Jon
Mz,
I’m really appreciating the work you’re doing. I also like your personal contribution here on the publicity side of things.
Thanks!
How far are your first holddown firings?
Well, we made some really good progress towards them today, but we’re still a bit off. We had tried to get the microcontroller-based engine firing to work pre-Las Cruces (the day before we packed up in fact), but had had some weird instability. We ran across what we thought was the cause, eliminated it, and did a bunch of testing today which verified that that problem is gone. Much better now. Unfortunately we ran out of LOX before we could move on to the throttle testing we wanted to do, so we’ll have to wait till Wednesday for the next Praxair shipment. If that works out, we can probably have the dynamic throttling concept proven out before the end of the week.
At that point we’ll be done with all the “development” work we needed to do for the engine, and we’ll be on to assembling the engines, qualifying and tuning them, and then we can do hold-down tests and then flight tests….
So, we’ve got a long way to go yet, but we’re almost out of the woods on what ended up being our biggest developmental headache for this vehicle.
~Jon