Rocket Factory Augsburg (RFA) has revealed the second stage for its upcoming RFA ONE rocket. The company’s tweet showed a second stage, integrated with a Helix engine. This engine will power both the first and second stages. NASASpaceflight spoke to RFA about the reveal and RFA’s test campaign for the second stage pathfinder.
The company called the next step in the test campaign “Integrated Systems Test” (ITS). In this test, the second stage will test all necessary flight hardware, including propulsion and avionics. The second stage already includes tanks, umbilical connections, and the vent system. It also has the flight control system and engine control system integrated. The test campaign will start in the upcoming weeks.
About the test, the company said “The campaign will feature three main tests: The first test will last a few seconds, followed by one for around 10 seconds, then the full flight duration. Every engine is acceptance tested. Then each engine is fired a second time during stage acceptance and then started a third time for flight. We have already proven that we can fire the same engine 3x without switching out components with our long-duration hot-fire campaign. Now we want to repeat that achievement with a full upper stage.”
The test campaign will start in the coming weeks and ensure qualification and further development of our upper stage and Helix engine. Btw: we use a sea-level nozzle for these first tests and replace it with the vacuum variant before flight 😉 (3/3)
— Rocket Factory Augsburg (@rfa_space) November 7, 2022
The test of the upper stage will be conducted in Kiruna, Sweden. Previous tests of the company were also conducted there, at the Swedish Space Cooperation (SSC).
Regarding if this is a test pathfinder or actual flight hardware, the company confirmed, that this upper stage currently is desired to fly on the first flight of the RFA ONE rocket. The test campaign is expected to last up to six months, which includes buffers in the test timings. This would mean that the stage would complete its testing somewhere in the area of summer 2023.
RFA ONE Render. (Credit: RFA)
As of right now, the second stage is equipped with a Helix engine, which is outfitted with a sea-level nozzle. This will change later in the test campaign, with a change to a vacuum-optimized nozzle. Regarding this, the company said: “The vacuum nozzle is still in the design and prototyping phase. However, we need to carry out system-level testing as early as possible to maintain the speed of the overall development process. That’s why we’re testing with the SL nozzle. Which is not an uncommon process at all, and it also saves us from having to use expensive vacuum test rigs.”
Related to this, RFA also clarified that their vacuum nozzle extension is able to be tested at sea level, thanks to their robust 3D-printed design. Down the line, the company plans to conduct tests with the vacuum nozzle extension and engine throat.
Helix during a hot-fire test. (Credit: RFA)
Regarding the build cadence of the Helix engine, RFA said that this is the third engine they have built. Before these three, there was also a prototype engine: “The first one was a prototype engine we called “SLE” (System Level Engine). Here the main components were further apart, so not as tightly built as the flight configuration. This made it easier to work on, and we could replace parts more easily. If something had gone wrong, we wouldn’t have lost the whole SLE, too. But all went well.”
For the full RFA ONE rocket, the company will need 10 engines. Nine will be in a sea-level configuration on the first stage, while one vacuum-optimized Helix engine will power the second stage. The third stage will be a kick stage, based on nitromethane, which will be used to boost the payloads to their final orbits. RFA ONE wants to lift up to 1,600 kg into a low Earth orbit (LEO) and 1,300 kg into a Sun-synchronous orbit (SSO).
You can learn more about the design of the rocket and the third stage in NASASpaceflight’s interview with Dr. Stefan Brieschenk, COO of Rocket Factory Augsburg.
Previously, the company conducted a full test campaign of a Helix engine with a series of tests. This included hot fire tests of 30 and 40 seconds with one engine and an up-throttling of the engine to 130% of nominal design levels. NASASpaceflight asked RFA about learned lessons for the engine, after these test campaigns.
“Yes, we improved many details as we took the engine to 130% of its nominal power to see where the first weak points were. The changes relate to seals, coatings, and various wall thicknesses, for example.”
Next to the second stage, the first stage for the first orbital flight is also moving into its testing to prepare for the orbital flight. Regarding the test campaign for this part of the rocket, RFA said: “Parallel to the IST, we are already planning the hot-fire of our first stage. This will take place in mid-2023 and is the last milestone before the initial launch. Before that, there will still be smaller drain tests, compression tests, pressure tests, etc. We are also working on our launch infrastructure and orbital stage at RFA Portugal.”
A look through a carbon fiber interstage 👀 This particular part is far too often underestimated. Interstages connect…rocket stages. And powerful forces are at work here.
Tricky for us: connecting the carbon fibers of the interstages to the stainless steel of the tanks. (1/4) pic.twitter.com/Ms5i5hJuik— Rocket Factory Augsburg (@rfa_space) November 1, 2022
Recently, the company also showed the carbon fiber interstage of RFA ONE. This will connect the two stainless steel tanks. Carbon fiber was used to reduce weight on the interstage. The main tanks are built out of stainless steel as it is low-cost and durable. It also supports the company’s goal to reuse the rocket stage.
The maiden launch for RFA ONE will carry a Ukrainian research satellite. RFA confirmed that the maiden launch is currently scheduled for Q4 of 2023.
(Lead image: RFA ONE Second Stage. Credit: Rocket Factory Augsburg)