Complex cooling channels support the resurgence of aerospike engines

With about 2,500 satellites deployed annually ^[1] to provide data for telecommunication and navigation systems, the satellite industry is rapidly growing and requires innovation in rocket propulsion technology.

A rocket engine typically comprises a gas turbine, a fuel pump, a combustion chamber with an opening known as the “throat” and the nozzle, through which gas can escape ^[2]. Currently, the exhaust nozzles in all rocket engines are shaped like bells ^[3]. The geometry of this nozzle is crucial to allow rockets to produce enough thrust to get off launchpads and escape Earth’s gravity.

 

Aerospike rocket engines were first conceived in the 1950s as a high-performance alternative to more traditional bell nozzle configurations ^[4]. An aerospike engine relies on air pressure itself, rather than the walls of a bell, to control the exhaust exiting the rocket. This makes the engine capable of adapting to varying air pressures, adjusting to barometric pressure as it is escaping the atmosphere, whereas bell nozzles are essentially designed to work effectively at one particular altitude ^[3].

 

Aside from a demonstrator flown by NASA in the 1990s, the concept had never propelled a real-world rocket until recently. Improvements in additive manufacturing processes and materials for propulsion applications now make it possible to build an economically viable aerospike engine ^[4].

 

 

Demonstrators of additively manufactured aerospike rocket engines

 

In 2021, Pangea Aerospace, a start-up specialising in the development of propulsion systems for the aerospace industry, successfully fired the first liquid oxygen/liquid methane (LOX/LNG) dual regeneratively cooled aerospike rocket engine in history to be additively manufactured ^[4].

 

Rocket engines need to be actively cooled because the flame temperature inside their combustion chamber exceeds 3000 K. “Regenerative cooling” is a popular method for mitigating the wall temperature of the engine, consisting in circulating one of the two propellants (typically the fuel) in small channels within the engine walls.

In their demonstrator, the team at Pangea Aerospace split the cooling system in two circuits: the “pointy” end, called the plug or spike (the latter giving the engine its name), is cooled with liquid oxygen (the oxidiser), while the external housing is cooled with liquid methane (the fuel). Propellants inside the cooling system enter in the liquid state, then undergo a pseudo phase change and leave the channel in a supercritical state. The sharp property variation of the coolant required an equally sharp variation in channel geometry to avoid overcooling or overheating of the material. Find out more in the article published in Metal AM.

The start-up, based in Spain and France, plans to reproduce the system for its first commercial flight at the end of 2027, but make it reusable up to a dozen times, therefore cutting production costs.

 

Video showing scenes of the engine being tested. Credit Pangea Aerospace/ European Space Agency (ESA)

 

In November 2024, German aerospace start-up Polaris successfully fired an additively manufactured aerospike rocket during a three-and-a-half-minute test flight over the Baltic Sea ^[5]. The 1,000 Newton aerospike engine was fuelled by liquid oxygen and kerosene. The company plans to build and fly a supersonic-capable prototype in 2025, to demonstrate safe and repeatable rocket-powered supersonic flight capability at high altitudes using the aerospike engine.

 

In December 2024, LEAP 71, a developer of AI-based engineering technology headquartered in Dubai, United Arab Emirates, successfully fired a 5,000 Newtons aerospike engine powered by cryogenic liquid oxygen and kerosene ^[6]. The engine was AI-generated then manufactured as a monolithic piece of copper through industrial additive manufacturing.

 

 

Sources

[1] The Space Report 2023. https://www.spacefoundation.org/2024/01/23/the-space-report-2023-q4/  

[2] https://www.marks-clerk.com/insights/latest-insights/102jvrr-aerospike-engines-the-next-generation-of-rocket-science/

[3]  https://www.popularmechanics.com/space/rockets/a43756195/aerospike-engine/ 

[4] Making the unmakeable: How metal AM is bringing the aerospike rocket engine to life. Metal AM Vol. 8 No. 1, Spring 2022 https://www.metal-am.com/articles/making-the-unmakeablehow-3d-printing-is-bringing-the-aerospike-rocket-engine-to-life/  

[5] https://www.aerospacetestinginternational.com/news/germanys-polaris-achieves-first-ever-firing-of-aerospike-engine-during-flight.html

[6] https://www.metal-am.com/leap-71-successfully-tests-innovative-ai-designed-aerospike-engine/

 

Image credits (wikimedia). The test of twin Linear Aerospike XRS-2200 engines, originally built for the X-33 program, was performed on August 6, 2001 at NASA's Stennis Space Center, Mississippi.