Relativity Space printed its Terran 1 rocket’s second stage in a few weeks

By Eric Berger

Relativity Space tests a development version of its Terran 1 second stage at Stennis Space Center.
Enlarge / Relativity Space tests a development version of its Terran 1 second stage at Stennis Space Center.

When Relativity Space was founded with the audacious idea of using 3D printing to manufacture pretty much the entirety of a small rocket, the premise sounded revolutionary. But if the company could pull it off, Relativity would have the potential to upend traditional rocket manufacturing, which in many respects remains a hands-on job.

There remain very real questions about whether or not this approach is ultimately feasible. The acid test will come when Relativity attempts to reach orbit. Nevertheless, the company's 3D printing technology does seem to be working. Two recent milestones in the development of the company's Terran 1 rocket, in fact, suggest the tech is working really well.

Second stage print

In an interview, Relativity CEO Tim Ellis said the company recently printed the second stage that will be used on the inaugural flight of the Terran 1 rocket, which is presently scheduled to take place before the end of 2021. The stage was printed at a rate of about 1 linear foot per day, so in printer time it took about three weeks in total to produce the 20-foot tall second stage.

"We're now confident in this build process," Ellis said. "Not only is the second stage now completed, but we're 75 percent of the way through printing the rocket's first stage."

Relativity Space prints a second stage.

With the printing complete, the company has begun installing an Aeon vacuum engine, avionics, and a separation system for the first stage. The California-based company intends to ship the second stage to its facilities at Stennis Space Center, in Mississippi, for testing this summer. Assuming a successful test campaign, the stage will then be moved to Florida, where it will be integrated with the first stage for launch.

This inaugural mission of the Terran 1 rocket will carry no commercial payload so Relativity can focus on the rocket itself. Asked about the chances of reaching orbit with this first flight, Ellis said he was confident the company would gain a lot of knowledge about the launch vehicle. "The expectation is that we're going to learn a lot," he said.

The company's second launch will carry a payload for NASA. With a maximum capacity of 1.25 metric tons to low-Earth orbit, the Terran 1 rocket has a base price of $12 million. It will slot into an increasingly competitive market for small launch vehicles.

Copper engine

Relativity has also been able to prove the merits of 3D printing by rapidly changing the metal used in the thrust chamber of its Aeon engine—nine of which will power the rocket's first stage. Engineers started out using a nickel-based alloy inside the thrust chamber because it was an easier material to work with during the manufacturing process. But a copper-based alloy has better conductivity and allows for higher combustion temperatures—and therefore a higher-efficiency engine.

The Aeon engine, with a copper-based thrust chamber, undergoes testing at Stennis Space Center.
Enlarge / The Aeon engine, with a copper-based thrust chamber, undergoes testing at Stennis Space Center.

Because Relativity will need this technology for future rockets, such as the larger Terran R rocket that will use a larger version of the Aeon engine, it decided to go ahead and make the change to a copper-based thrust chamber and nozzle now. To be clear, the company did not need to do this for the Terran 1 rocket, but it decided to make the new engine now because it turned out to be relatively simple to make the materials swap using additive manufacturing.

Ellis said the new engine was put on the test stand this year at Stennis for its initial short hot fire test. Only five days later, he said, it completed a full duration test firing. This new technology will therefore fly on the Terran 1 rocket's first mission as well.