LEAP71
LEAP 71 has successfully hot-fire tested an additively manufactured aerospike engine with 5,000 Newtons of thrust and powered by cryogenic liquid oxygen and kerosene.
The engine was generated autonomously with the company's Noyron Large Computational Engineering Model. It follows LEAP 71's successful hot fire testing of the a computationally engineered rocket engine in June 2024 - believed to be a world first.
By using Noyron, the thruster was developed in a matter of weeks and manufactured as a monolithic piece using a laser powder bed fusion 3D printing process. Aconity3D printed the engine in an advanced aerospace copper alloy (CuCrZr) before Solukon depowdered the piece and Fraunhofer Institute for Laser Technology heat treated it. The University of Sheffield’s Race 2 Space Team then prepared the engine for the test site and provided active support during the campaign. Once put on the test stand, it was successfully hot fired on the first attempt.
Aerospike engines are considered to be more compact and more efficient across various atmospheric pressures, including the vacuum of space, while their design forgoes the conventional bell-shaped nozzle in favour of a spike in the centre of a toroidal combustion chamber. With up to 3,500°C of hot exhaust gas surrounding the spike, cooling it can represent a significant challenge. So much so that very few teams have 'mastered the challenges' of aerospike engine design in the last 30 years.
Josefine Lissner, CEO and Co-Founder of LEAP 71, said: “We were able to extend Noyron’s physics to deal with the unique complexity of this engine type. The spike is cooled by intricate cooling channels flooded by cryogenic oxygen, whereas the outside of the chamber is cooled by the kerosene fuel. I am very encouraged by the results of this test, as virtually everything on the engine was novel and untested. It’s a great validation of our physics-driven approach to computational AI.”
Lin Kayser, Co-Founder of LEAP 71, added: “Despite their clear advantages, Aerospikes are not used in space access today. We want to change that. Noyron allows us to radically cut the time we need to re-engineer and iterate after a test and enables us to converge rapidly on an optimal design.”
LEAP 71's aerospike was fired on December 18th, 2024, as part of a four-engines-in-four-days campaign conducted by LEAP 71 at Airborne Engineering in Westcott, UK. The company will now process the collected data to fine-tune Noyron for the next iteration of engines and continue testing in 2025, with the goal of making Aerospikes a viable option for modern spacecraft.
Behind the scenes
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After the successful world-first in June, LEAP 71 immediately set about integrating the data collected - including information spanning manufacturability to practical questions about connector layouts - to develop the second generation of its Noyron computational engineering model (Noyron g.2.).
The company came to the conclusion that rather than look to adapt the engine its computational model had developed, it would instead look to enhance the model. It believes the data created from testing similar designs, thrust levels and material would be relatively narrow compared to the data it would generate from testing a radically different type of engine, such as the aerospike.
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Cross section of LEAP71 aerospike engine.
While challenging to achieve success with an aerospike engine, the potential advantages are numerous. In theory, aerospikes can operate at any atmospheric pressure without loss in performance, while traditional engines require a different nozzle length depending on what altitude they fly. This can make vacuum nozzles for upper stages long and heavy and the engine less efficient.
Aerospikes, however, can adjust to changing air pressure. The drawback of an aerospike is in how you go about cooling the spike. It is why experimental rocket programmes have turned to alternatives to power their spacecraft.
For Lissner and Kayser, however, the successful development and testing of an aerospike engine has been among their many objectives. In additive manufacturing they see a technology that can facilitate the complex geometries required in a functional aerospike engine and in their Noyron computational model they see a way of designing the piece in such a way that ample cooling can reach the spike.
One of the results from its hot fire campaign in June was that the copper engine performed better than expected in terms of cooling. The cryogenic liquid oxygen (-200°C) used in June cooled down the injector such that the heat sink effect could be measured all around the chamber, with temperatures remaining around 140°C.
Read more | Exclusive: Behind the scenes at world first hot fire test of computationally engineered rocket engine
In response, LEAP 71 updated Noyron's thermal models and the design logic for the aerospike, while building new iterations of the traditional bell nozzle engine to be tested on the three other days as part of the company's four-engines-in-four-days campaign. The aesthetic of the aerospike compared with the bell nozzle engines is completely different, but the calculations used to develop them are said to be very similar.
LEAP 71 worked with trusted partners, then, to bring the aerospike engine into the real world. Aconity3D had previously given the company confidence it could print the challenging geometry, with very shallow unsupported overhang angles, in a single piece, while Solukon and Fraunhofer Institute for Laser Technology had also proved out their respective expertise in post-processing and treatment.
LEAP71
Printing, depowdering and heat treatment was all that stood between Noyron and the test stand. Once on the test stand the inside spike was cooled using Liquid Oxygen, which went downward into the spike, inducing a spiral movement by the rifling of the spike and then by the vanes. Then, the liquid oxygen was injected into tiny cooling channels that swirled beneath the skin of the spike. At the end of the cooling channels, at the top of the engine, sat the injector head, which collected all the now gaseous oxygen and injected it into the combustion chamber.
From the fuel manifold, the Kerosene was injected into tiny cooling channels, which swirled around the outside of the combustion chamber. The kerosene ran all the way to the top of the engine, just like the oxygen in the spike, before going into the manifold and connecting to the injector elements which shoot the liquid kerosene into the combustion chamber, opposite the injectors of the gaseous oxygen. Both combined and combusted to provide the exhaust gases that drive the rocket.
LEAP71
The thruster was a 5000N thruster - the same class as was tested in June - and is said to have performed well on the first run. Since 'virtually everything' on the engine was novel and untested, LEAP 71 did not expect the test to be successful first time, despite its confidence in the theory behind the engine. It figured, since the only way to inspect certain aspects of the design was through a CT scan, than resistance in the cooling channels might affect the performance on the first run. The company, of course, had data from the previous tests in June, but the angles of the aerospike were said to be much shallower. "These angles," Kayser said, "are dictated by physics, so you have to live with what you get."
What they got was a successful hot fire test. The company is now set to cut the engine in half to inspect it, knowing already that improvements can be made to the oxygen flow since the engine ran hotter than intended. Instead of risking additional runs on the test stand, obtaining this information encouraged LEAP 71 to feed the data back into Noyron for further refinement.
All three of the engines were also successfully hot fire tested across the four-day campaign, with that data also now set to inform future LEAP 71 projects. As soon as the test data has been evaluated and encoded, the company will start another round of tests. The aerospike engine was generated by Noyron g.2c and the company is already at Noyron g.2e, with revised versions of all engines already generated.
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