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Comment by ChuckMcM | Hacker News Reader

Watched the live stream and man, that was pretty awesome! That it passed max-q was what I was waiting for, because that lets them know that 3D printed materials are strong enough to deal with that stress, then their is no need to "rack and stack" ring sections like they do at SpaceX. Riveting and seam welding take a surprisingly long time over all! Also those joints are the most likely to fail when things get stressed.

I am still curious about the 15% that isn't 3D printed. Clearly the avionics, wiring, and carbon-fiber over wraps would not be 3D printed but is that it? Any other fittings or parts?

I am definitely looking forward to launch 2 and the root cause analysis of the second state engine startup issue.

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I am curious why would anyone expects that 3d printed tanks are a good idea. We have sheet metal, it has well controlled and probably close to optimal performance (that is, the maximum mechanical resistance that you can get out out of a given mass of aluminum or stainless steel). The resulting rocket is a long, hollow tube. What exactly do you gain by 3d printing the entire body, other than a nice investor buzzword?

I could see a gradual move to 3d printing, the engine of course with it's complex features, then the bulkheads, downcommer & manifolds, maybe fairing and other aerodynamically shaped pieces etc. But why would you try to print sheet metal transversely, one slice at a time? What possible design you could think of, other than a long, slender tube, that can utilize the flexibility of 3rd printing and provide value to justify the necessarily reduced mass ratio ?

Maybe a 3D printer could me built on the Moon and build rockets there. Like really big rockets:0

Because they're not trying to do the same thing as everyone else. They're also building the worlds largest 3D printer. Something like this could be shipped to the Moon or Mars in the future.

3D printing also takes a lot of time.

I'm not sure but I would bet it takes less time to build a rocket with traditional means than through 3d printing.

There are other advantages (leverage with investors not the least of them, imo) to the 3D printing angle but simplicity of development and speed of production are not them.

I'm far from an expert but it seems like at least some companies use cnc milling very extensively which I can't imagine is all that fast either. Many of the huge parts in this SmarterEveryDay video at ULA have tool markings e.g. at 8:40. I'm also skeptical of 3d printing being as big of a boon as they pitch but I also wouldn't be super surprised if it nets an improvement in speed for some parts.

https://www.youtube.com/watch?v=o0fG_lnVhHw

It's probably easier to land a 3D printer on the Moon than all that other equipment.

I wonder what 3D-printing in a vacuum in low gravity would be like.

Yes and no. Some of the piece you have to make need to be cast, which means having a forge make the molds, test the molds out, and then, if you find an issue, start the whole process over again. That process can take at times around 6+ months, and more if you find an issue or have to redesign. Similarly, because of the limits of machining, 3D printing allows you have to have much more complex parts and geometries, especially for the engines. I was at GE Aviation for a bit, and they showed us some nozzles they printed that would be impossible to make if not for 3D printing just because of the complex geometries.

It takes a long time but a lot less human labor, so the cost can probably be brought way down. Don't know if it can be competitive without reusability though, or at least partial reusability of the engines.

The thing is, Relativity Space doesn't really disclose much about how the rocket is made. They say it's some percentage 3D printed by weight, but that doesn't really tell you if, for example, they use carbon fiber COPVs for the fuel tanks inside.

We don't really know that 3D printing saves them much time. Rockets are large cylinders, which there are other efficient ways to manufacture. Other companies will 3D print parts of rocket engines. I'm sure Relativity Space does as well, but they probbaly do that separately from the main body of the rocket with some hand assembly after.

Believe they’re aiming for a 2 month lead time

Is the engine 3d printed? Or at least components of it? The only footage I’ve seen of their 3d printing process is on, relatively parts like tanks. That may just be to protect IP, but I would be very impressed if they’re printing and using really complex engine components.

I’d wager most modern rocket engines are 3D printed. At the very least SpaceX uses 3D printed engines. It greatly enhances the ability to cool the engine using the supercooled propellant and the technology to achieve it isn’t exactly cutting edge. 3D printing metal using SLS has been around since the eighties

Laser powder bed fusion (L-PBF) of polymers was only in its infancy in the late 80s. This was research out of UT Austin that would eventually lead to DTM. Proper L-PBF of metals (fully melted, fully dense parts) didn't come about until the late 90s in the research world. L-PBF of metals wasn't really commercialized until the 2000s.

In any case, this is lightning speed for an industry that still produces something initially designed in the 60s (Boeing 737).

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