It sounds like an interesting idea, but I'm not sure I buy it.
It makes sense that building single use rockets is expensive, and with only one launch to amortize the construction cost, labor is a huge factor (materials in a rocket are pretty normal: a lot of carbon fiber, aluminum, titanium, etc). But with reusable rockets, you are bringing that cost way down. If you are able to launch and land 5 times on the same rocket, then effectively you've brought the cost of the rocket to 1/5th of what it used to be.
"a handful of the arms can work together to create the rocket’s entire body as a single piece"
Once you get into reusable rockets, I'm not sure that trying to 3d print the whole thing will turn out. Why? Because you need replaceable parts. You need to be able to tear down, inspect, and replace parts as each part of the rocket has a different lifetime. If you make the rocket as one giant piece, and use efficient methods (reduce weight, size, etc), that it would be much less serviceable over its lifetime.
"We want to get to 1,000 moving parts, fewer than a car."
This is why subassemblies of cars are so expensive, even if you only need to replace a small part of one assembly.
My gut feeling about rocket building is that it's not the labor for building parts and putting them together which makes them expensive but the labor for inspecting, reinspecting and then reinspecting once more before putting parts together, only to do some more inspecting on the combined subassembly. The launch is the first true dress rehearsal and the rocket equation leaves little room for "engineering math" (calculate to seven digits, then multiply by two for safety).
My gut feeling about 3D printing is that it just makes it worse. How do you inspect a welding line as long as a rocket's dry mass?
For a liquid fueled rocket you have many opportunities before launch such as firing the engine in a test stand, etc. For the whole rocket you can do a static fire, or even a full duration fire to test the components. Mostly when you are moving you are worried about the mechanical loads on the rocket instead of having to worry if parts were put together correctly. Of course, even this level of testing takes a lot of money, capital, and of course labor.
For a solid fueled rocket, you're right that pretty much you have one shot, and you can't turn it off if something goes wrong.
> My gut feeling about 3D printing is that it just makes it worse. How do you inspect a welding line as long as a rocket's dry mass?
In general, the way you do this is to move it lengthwise through an x-ray scanner, so you can inspect the full length by moving the rocket through. I'm not sure if 3d printing makes this easier (because there's not really welds, it's one piece) or harder (you have to be able to inspect the inside of something), but it is certainly tricky.
I guess you can think of it that way, but it probably depends on the technology used by the printer at that point. My thought was that for the 3d printer, at least it's one consistent piece with no seams or edges that are later welded together. The welds can have imperfections/weaknesses and need to be inspected. Materials can also have weaknesses and imperfections, either on a batch level or individual area level, and need to be tested/inspected. For a printed piece, I would expect the strength to be generally consistent throughout the piece (of course still might be weaknesses based on design shape, thickness), but of course, you'd still want to inspect it.
PS - totally not an expert on 3d printers or materials or welding
I am not an expert on either, but in general 3D printers lay out the material in thin layers (with each layer laid out line by line). Thus you have lots of potential seams everywhere two points laid at different times touch.
I think modern technologies prevent seams forming at most of those points, but the potential (impurities, dirt, etc.) still remains so must be tested.
I could imagine some technology that takes advantage of future layers not being there yet to validate the most recent layer on the same pass, and the one that the current layer will be built upon (as that might have suffered in the time since it has been laid) in a way that is exclusive to this manufacturing method. But as you move to bigger and bigger one-piece parts, you would probably also want your process to support undoing a few layers on failure detection to forego scrapping the whole part.
The printers are going to make the exact same rocket every time.
And you could anneal the rocket after, which would improve the strength.
Also spacex seems to be doing it with their Dragon engine. Is there another rocket part that undergoes more strain? (vocab cringe, not a materials scientist)
The superdraco engines in Dragon have a printed combustion chamber. But these are (relatively) low pressure engines.
Chamber pressure is limited by the fuel injection pressure. The simplest, fastest response time way to provide the fuel pressure is to use a high pressure bottle of gas to push the fuel through. Since those are important features in a launch escape system, that's how superdracos work.
But... chamber pressure is directly correlated with efficiency, so a main engine uses an extremely powerful fuel pump to achieve higher pressures.
That fuel pump is itself, a rocket engine with a gas pressure fuel system like the superdracos.
My actual knowledge of the industry says that it's both. The metalurgy, production prcesses etc. are very very intricate and the inspections are also very very intricate.
A 3d printed rocket would be cheaper right from the start, so they wouldn't need to bother with repairs, they can print another module or whole rocket again. Even a 3d printed rocket is going to be made of parts that can be replaced, because I presume we can't print the whole thing in one piece.
> I'm not sure that trying to 3d print the whole thing will turn out. Why? Because you need replaceable parts. You need to be able to tear down, inspect, and replace parts as each part of the rocket has a different lifetime. If you make the rocket as one giant piece, and use efficient methods (reduce weight, size, etc), that it would be much less serviceable over its lifetime.
I think the idea is to 3D print parts that are currently welded together. I don't see anywhere that they are planning to print as one piece anything that is ever disassembled with current practices.
> I think the idea is to 3D print parts that are currently welded together. I don't see anywhere that they are planning to print as one piece anything that is ever disassembled with current practices.
I would agree that 3d printing smaller parts and putting them together by hand seems more reasonable, but I don't get the impression that is what they're doing (but it's hard to tell from the article).
This is what led me to that conclusion:
"Ellis and Noone say a handful of the arms can work together to create the rocket’s entire body as a single piece, guided by custom software that monitors their speed and the metal’s integrity."
Entire body - single piece. I don't hear any talk of welding or putting it together (which would involve multiple pieces).
Also just as a point of reference, making the bodies or the fuel tank is actually the easier part. It's either metal or carbon fiber. What takes a long time is assembling complex engines, and getting the whole thing together (including wiring).
You won’t be reusing the parts without some refurb work. It’ll be more labor than the initial inspection. For one you’ll be poking around for signs of wear you might not look for on a new part.
Think about how expensive it was to replace the heat shield tiles on the shuttle. The shuttle was “reusable” but the repairs were hell.
In theory, I don't see any reason why 3D printing a reusable rocket is impossible. With advances in 3D, it may become a reality where this company is a complimentary company for SoaceX and not a competitor company.
It makes sense that building single use rockets is expensive, and with only one launch to amortize the construction cost, labor is a huge factor (materials in a rocket are pretty normal: a lot of carbon fiber, aluminum, titanium, etc). But with reusable rockets, you are bringing that cost way down. If you are able to launch and land 5 times on the same rocket, then effectively you've brought the cost of the rocket to 1/5th of what it used to be.
"a handful of the arms can work together to create the rocket’s entire body as a single piece"
Once you get into reusable rockets, I'm not sure that trying to 3d print the whole thing will turn out. Why? Because you need replaceable parts. You need to be able to tear down, inspect, and replace parts as each part of the rocket has a different lifetime. If you make the rocket as one giant piece, and use efficient methods (reduce weight, size, etc), that it would be much less serviceable over its lifetime.
"We want to get to 1,000 moving parts, fewer than a car."
This is why subassemblies of cars are so expensive, even if you only need to replace a small part of one assembly.