A new journey
16 September 2019 marks the start of the first ETH Focus Project organized by ARIS. The successor of project RHEA comprises 8 Bachelor students in mechanical engineering and is part of the specialization in energy, flows and processes.Our passion for engineering and our fascination for space motivate us to solve new challenges full time under the supervision of Prof. Lino Guzzella from the Institute of Dynamic Systems and Control (IDSC) of ETH Zürich.
Building a hybrid rocket engine
We are developing the second generation hybrid rocket engine of ARIS. Our aim is to build a reliable hybrid rocket engine which can provide 5 kN of thrust to propel a sounding rocket.
Our engine is named IRIDE (ì-ri-de), Italian for iris, the colored part of the eye. The name is related to the Greek goddess Iris, messenger of the gods and patroness of the rainbow, sea and sky. She is often represented as a flying hybrid creature, just what we aim to achieve with our engine.
Dear Sponsor, Advisor, Friend of ARIS
Since March 16th access to ETH Zurich facilities has been reduced to emergency operations. For the IRIDE team this implies no more physical meetings or access to the ARIS hub. Accordingly, we completely switched the work on the project to home office and virtual meetings. Of course, these restrictions do not stop our project and we are still highly motivated to finish it. Presumably, physical work will be possible as of 8th of June.
The ETH focus rollout will not take place on May 26th. So far, an exhibition over several weeks in September and October in the LEE building of ETH Zentrum is planned instead.
We want to take this opportunity to thank you for your commitment and trust. We can assure you that this project is very important to us and if necessary, we will continue to work on it after the official end. We have worked with great passion on it for more than half a year and each of us has only one goal: We want to successfully fire our hybrid rocket engine! Together with you, we will achieve this goal even under these circumstances.
Your IRIDE team
What is a hybrid rocket engine?
There are three types of rocket engines: liquid, solid and hybrid. Their designation refers to the aggregate state of the used oxidizer and fuel. In our hybrid rocket engine, we use a solid fuel and a liquid oxidizer as common in most hybrids. This offers us the following advantages compared to the other two engine types:
Our main objectives
IRIDE is designated as the first engine of ARIS to be integrated into a sounding rocket in a subsequent project. To allow the implementation by 2021 and a wide prior statical test campaign, the following main objectives have been set:
Eight equally important subsystems to aim for stable and reliable combustion.
The grain is the fuel of our engine, which we specifically cast to fulfill our requirements. A mixture of sorbitol, paraffin, and aluminum is used and casted with a centrifuge to increase the density and improve the mechanical properties. A self-developed centrifugal casting machine allows in-house manufacturing of various grain lengths. The result is a perfectly regulated amount of fuel in a cylindrical shape, even already surrounded by insulation material. The grains are then checked using CT-scans, which allow detecting undesired bubbles and guarantee integrity. The applied technique allows the manufacturing of up to 1-meter long grains as a single part. This prevents potential problems and combustion instabilities that could arise at the joints of multiple shorter grains.
The igniter is the key to a successful start of the engine, which is only possible if an adequate amount of energy is released. This means that the temperature needs to be sufficiently high in order to vaporize parts of the initially solid grain. In a gaseous state, the fuel can mix and react with the oxidizer, releasing even more energy in the form of heat and finally enabling a self-sustaining combustion. To prevent unintentional ignitions that could be caused by induced currents, electrical discharges, vibrations or heat for example, a safety mechanism was implemented. This safety mechanism keeps the ignition circuit open until a very short time before the firing to preclude an unintentional ignition caused by electricity. Several ignition tests have been absolved to prove the igniter design’s functionality. The developed design can be easily adjusted to the engine size and is highly reliable.
The nozzle converts the high pressure coming from the combustion chamber into a high velocity exhaust stream, generating thrust via the impulse. To achieve this, a de Laval nozzle, which accelerates the exhaust gases by compressing and expanding them, is used. The IRIDE nozzle was specifically designed for the average atmospheric pressure at our testing location high up in the Swiss alps. This allows for maximal efficiency of the engine. A water-cooling system for our copper nozzle allows extensive testing while maintaining constant test conditions. Extensive simulations and calculations were carried out to ensure that the system is sound. A high-performance pump generates the necessary mass flow of coolant. On top of that, the mechanical structure was dimensioned in such a way to account for thermal expansion of the copper to avoid deformation of the casing. To protect critical areas at the inlet, a protection ring made out of InconelⓇ is used.
The test bench allows us to perform a static firing campaign and to evaluate the engine’s performance. For this reason, it needs to absorb the generated forces while still allowing undistorted measurements of the engine thrust. The test bench enables limited movement in the axial direction with its hinge mechanism while restricting movements in all other directions. A pretension mechanism facilitates reliable thrust measurements with a load cell of up to 20kN. Further, a special mechanism is used to calibrate the thrust measurement. The long top plate with milled T-slots makes the test bench very customizable, allowing for different test setups with future engines of ARIS. The test bench is a key part of our safety architecture. In consequence, all parts were designed with a high safety factor.
Our test infrastructure
Our container enables us to safely monitor the firing operations
Our container is split into three parts: engine compartment, fluid supply system compartment and electronics compartment. Through our electronics compartment, we can establish a connection to our bunker and monitor the engine performance from a safe distance.
Image Sources: Background Image Title: Launcher (Link); FSS/Igniter/Injector/TestInfrastructure: Project RHEA / ARIS; Logo/Concept/SystemOverview/Grain/Casing/Nozzle/DACS/Container/Team: Project IRIDE / ARIS