Printing Rockets

Ethan Wong

May 24, 2024

On May 9th, India developed the PS4 engine made out of 3D-printed material for their PSLV rocket. On Twitter (X), the Indian Space Research Organisation (ISRO) commented on this new achievement, stating that the "engine, now a single piece, saves 97% of raw materials and reduces production time by 60%"

3D-printing rockets is slowly becoming a reality. While the 3D-printed design holds excitement for India's space program and future, a large amount of effort has also been put toward a completely 3D-printed rocket by Relativity Space in the U.S. Earlier last year, the maiden flight of the Terran I rocket marked a new development in spaceflight: the use of 3D-printed materials for over 80% of a rocket. Standing around 110 feet tall, the Terran 1 made it to Max Q before its upper-stage Aeon engine malfunctioned, contributing to the rocket’s descent and failure. The launch vehicle was lifted with nine Aeon 1 engines that were fueled by liquid oxygen (LOX) and liquid natural gas, and carried a second stage with a singular Aeon 1 engine; additionally, all of these engines had been completely made out of metal alloy (ex. aluminum/copper alloy) from a 3D-printing laser. The rocket was built with over 100 fewer parts than standard rockets used today and took drastically less time to assemble (only a few months). After being retired from this failed launch attempt, Relativity Space, the company aimed at constructing a fully 3D-printed and reusable launch vehicle for space, started working and testing designs for their new build: Terran R.

With the potential of 3D-printed rockets being showcased by Terran 1’s flight, Relativity Space is now designing the Terran R rocket, a variation of the Terran 1 with more powerful engines and a height of 270 feet–well over double the size of its predecessor. The Terran R has 2 stages with 13 Aeon R engines on the 1st stage and a single Aeon R engine for the second stage. The Terran R’s payload is significantly larger than the Terran 1 and the Falcon 9, capable of lifting over 33000 kg to Low Earth Orbit. To make this construction even more impressive, Terran R is projected to be made of 95% 3D-printed materials, as opposed to the 80-85% previously guaranteed with the Terran 1. 

Relativity Space uses several techniques to increase efficiency for testing while still maintaining the stable designs of modern rockets. For typical rocket engines, the propellant is passed through fuel injectors to the combustion chamber. Fuel injectors allow a rocket engine to reach its highest possible combustion efficiency by dispersing the fuel and oxidizer into the combustion chamber through thousands of holes and mixing them as they enter the combustion chamber. While being one of the most paramount attributes in a rocket engine’s design, the mechanism requires thousands of parts that take months to manufacture. However, Tim Ellis, the CEO of Relativity Space, states that their Aeon engines use 3D-printed fuel injectors in a single piece of metal alloy, allowing this complicated part of the engine to be made within a few weeks.

The temperatures of rocket engines can rise to 3500K and threaten the structural integrity of the nozzle and walls of the combustion chamber; however, engineers have developed methods to prevent damage to the engine from heat, such as ablative cooling, which uses materials commonly used on heat shields to protect the insides of the nozzle and combustion chamber (like a layer of carbon composite). Another more common option is regenerate cooling, where liquid propellant is passed around the nozzle and combustion chamber through skinny tubes before being looped back into the main system, allowing the exterior to remain cool and fight off the high temperatures produced by the engine. However, the 3D-printed Aeon engines allow Relativity Space to manufacture this exact system in one 3D print, creating tiny tubes while also printing the nozzle. This process cuts down the severely long process of constructing both the nozzle and then the time to place and weld together these tunnels for the liquid propellant; instead, the 3D print can do it without any human labor.

These two processes allow Relativity Space to test their designs rapidly, as they can mass-produce parts and only have to alter changes to their CAD files before scheduling another 3D print that would take 3-4 weeks instead of several months. Despite the absence of several launches by the company, their work has proven a new era of rocket engineering with the utilization of 3D printing.