Microlaunchers are an alternative to conventional launch vehicles. These medium-sized transport systems can carry payloads of up to 350 kilograms, and soon they can launch small satellites into space. Researchers at the Dresden Fraunhofer Institute for Material and Beam Technology IWS, together with space experts from TU Dresden, have developed an additively manufactured rocket engine with aerospike nozzle for microlauncher. The scaled metal prototype is expected to consume 30 percent less fuel than conventional engines. It was presented on February 12 at the Hannover Messe Preview and from April 20 to 24, 2020 at the Hannover Messe (Hall 16/Stand C18).
Great Britain is planning the first spaceport on European soil in the north of Scotland, and the Federation of German Industries (BDI) also considers a spaceport in this country. From there, small to medium-sized launchers will bring research instruments and small satellites into space. These microlaunchers are designed for a payload of up to 350 kilograms. An efficient way to drive these microlaunchers are so-called aerospike engines. These not only offer the prospect of a considerable reduction in mass, but also significant fuel savings. During the last two years, a research team of the Fraunhofer IWS and the Institute of Aerospace Engineering at the TU Dresden has developed, manufactured and tested such an aerospike engine. The project is funded by the German Federal Ministry of Education and Research BMBF. The special feature: Fuel injector, combustion chamber and nozzle are manufactured layer by layer by Laser Powder Bed Fusion (L-PBF), an additive manufacturing process. The nozzle itself consists of a spiked central body through which the combustion gases are accelerated.
"The technological concept of aerospike engines first appeared in the 1960s. But it is only through the freedom of additive manufacturing and the embedding of these in conventional process chains that we are able to produce such efficient engines at all," says Michael Müller, research associate at the Additive Manufacturing Center Dresden (AMCD), which is jointly operated by the Fraunhofer IWS and TU Dresden. Aerospike Rocket Engines promise fuel savings of about 30 percent compared to conventional rockets. Furthermore, they are more compact than conventional systems, which reduces the mass of the overall system. "In space travel, every gram saved is worth its weight in gold, since less fuel has to be taken into orbit. The heavier the overall system, the less payload can be transported," explains Mirko Riede, group leader 3D Generation at the Fraunhofer IWS and colleague of Michael Müller. The Dresden Aerospike nozzle of the Fraunhofer IWS and TU Dresden adapts better to the pressure conditions on its way from earth to orbit. Therefore it is more efficient and requires less fuel than conventional engines.
Additive manufactured nozzle with conformal cooling
"When manufacturing the rocket from metal, we decided to use additive manufacturing because the engine requires very good cooling and internal cooling ducts. This complex regenerative cooling system with internal, intertwined structures cannot be conventionally milled or cast," says Mirko Riede. The powder is applied layer by layer and then selectively melted by laser. This gradually creates the component including the one-millimeter-wide cooling channels that follow the contour of the combustion chamber. The powder is subsequently sucked out of the channels. The requirements for the metal: It must be solid at high temperatures and conduct heat well to ensure optimum cooling. "Temperatures of several thousand degrees Celsius prevail in the combustion chamber, so active cooling is required," explains Michael Müller.
In the project CFDμSAT, which started in January 2020, scientists of the Fraunhofer IWS and TU Dresden focus on the injection system to further increase the efficiency of the drive systems. Associated partners in the project are the ArianeGroup and Siemens AG. The production of the injectors makes particularly high demands on design and manufacturing. "The fuels are first used to cool the engine, they heat up and are then introduced into the combustion chamber. Liquid oxygen and ethanol are supplied separately and brought together via an injector. The resulting gas mixture is ignited. It expands in the combustion chamber, then flows through a gap in the combustion chamber and is expanded and accelerated via the nozzle," Müller explains the process of thrust development.
Engine in hot fire test
The Dresden researchers have already tested the prototype of the aerospike engine on the test stand of the Institute of Aerospace Technology at the TU Dresden. They achieved a burn time of 30 seconds. "This is a special process, because there have hardly been any tests of aerospike nozzles so far," says Müller. "We have proven that a functioning liquid jet engine can be manufactured using additive manufacturing."
The project is an example for the close cooperation of the TU Dresden with non-university research institutions within the framework of the scientific network DRESDEN-concept. In the project, TU Dresden is responsible for the design and layout of the engine, the Fraunhofer IWS is responsible for the process chain: In the first step the design was adapted to the additive manufacturing process, followed by the selection of the material and the determination of the material characteristics. Using Laser Powder Bed Fusion the engine was printed from two components and reworked on the functional surfaces. The components were then joined by laser beam welding and inspected for flaws and other defects using non-destructive computer tomography. For example, it can be determined whether cooling channels are blocked by sintered powder. This shows across all industries how AM processes can be integrated into existing process chains in a meaningful way in order to drive developments forward.