Commercial Rockets

TERRAN — USA, 2021?

Relativity Space was a venture I was ignoring, until they signed a launchpad lease at Cape Canaveral, and let it be known that they had already logged a lot of engine firing time on the test stand. They are taking an approach similar to a number of other New Space rockets, in that they have a bottom stage with multiple “Aeon 1” engines (nine) and a second stage with a single vacuum-bell version of the same engine. Unlike any of the others, they’re using methane as a fuel right from the beginning — something that other companies have considered only after they’d gotten themselves well established.

But that’s not what makes them really stand out. The unique thing about the Terran 1 is that they intend to 3D-print the entire rocket. Lots of other companies use 3D printing to make complex engine parts, but nobody else is considering printing the fuselage, fuel tanks, and so on. At first blush, the idea seems ridiculous. A printed material is never going to be competitive on, for instance, optimizing the strength to weight ratio for tank walls. But they say that by printing everything, they can make an Aeon engine with fewer than 100 parts, and a whole rocket with fewer than 1000. (Most traditional rockets have tens or even hundreds of thousands of parts.) In fact, they have said that some versions of their engine have just three parts.

That’s only the beginning of their ambition. The reason they want to 3D print the entire thing, even if it doesn’t result in optimal properties, is so the process can be automated from beginning to end, so they can make a rocket by pushing one button, with no skilled labor required. It would still take weeks for the build to be completed, but that should certainly achieve some reduction in costs.

We're not done. It can’t actually save money to require no human workers at all — there are diminishing returns there, for sure — so why do they want to do it? Well, so the entire factory can be dropped on Mars, and build rockets there. That’s the end goal of this odd approach. It’s also why they picked methane as the fuel. Maybe when they start building it there, they’ll call it the Martian 1 instead of the Terran 1.

This begs the question of what raw materials the printer would use. They mentioned nickel, so it sounds like they might plan to make a lot of parts out of the same inconel alloy which is widely used for the high temperature parts of engines. Inconel mixes are generally at least half nickel, sometimes three quarters, and nickel should be reasonably easy to find on Mars. The crucial second ingredient of inconel is chromium... and it looks like this may also be fairly abundant. Aluminum and titanium are not rare either, and their tanks and frame are mostly aluminum.

Their giant superduper 3D printer is named Stargate. For the large parts such as tanks, it rotates them on a turntable as it builds up the metal on the top edge. (The results look rather rough and grainy in the video they’ve released so far.) Apparently it not only incorporates some proprietary metallurgy, but also some kind of artificial inteligence features, to help make it autonomous. They claim it will learn to build faster as it gains experience. They are now happy enough with the prototype that they are building several more.

Their first rocket, which they claim will in the future be scaleable to different sizes, is fairly small: bigger than an Electron but not bigger than much else. They claim they’ll sell them for $10 million each. The engine itself will probably have to scale in numbers, rather than size, as it uses an expander cycle — a rare choice for a booster engine, but a good fit for 3D printing, as it uses complex plumbing but does not make severe demands on the materials. From pictures, it looks like it’s a semi-closed design which dumps the unburned turbine propellant into the bell... and does it with a single fat pipe, rather than a ring of little holes such as most people would use for the purpose.

This vision has somehow attracted tons of investor capital — a lot more than many of their competitors. As with Virgin Orbit, it’s questionable how it will be possible to make all that money back.

And as every small-launch company eventually seems to do, they announced that they will follow the Terran 1 with a bigger rocket. They will call it the Terran R, for reusable. This one intends to even have a reusable upper stage, looking like a mini Starship. And it would be a big rocket, bulkier than a Falcon or Vulcan. The booster would have seven engines, adding up to around 9.5 meganewtons of oomph. I’m guessing these planned bigger engines will not use the expander cycle.

Terran 1: mass unknown, diam unknown, thrust 621 kN, imp ~3.5 km/s, type ENm?, payload ~1 t, cost $10M/t.