Project IRIDE

Our passion

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.

Our mission

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.

Current situation

Dear Sponsor, Advisor, Friend of ARIS

We are pleased to announce that our test campaign will take place in September and October.

Between March 16th and June 8th, the progress of the project was hampered by the Covid-19 situation, which forced us to home office and virtual meetings, ruling out phyiscal work and impeding the usual close collaboration within the team.
In the last weeks, we were able to assemble our system and finish the procedures. After our exam phase, we will move the container to our testing site.

We warmly thank you for your commitment and trust during these unusual times. This project would not be possible wihtout your support. Now, we are really looking forward to the firings.

Stay healthy,

Your IRIDE team

Our concept

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:

High Safety

A hybrid rocket engine shows generally high safety characteristics since fuel and oxidizer are not only stored spatially separated but they are also in different aggregate states, which makes a spontaneous ignition unlikely.

Low Complexity

Liquid engines show high complexity, especially if turbo pumps are required to achieve sufficient mass flow from the high-pressure tanks. A hybrid engine requires only one fluid while the solid is placed in the combustion chamber.


In contrast to solids, a hybrid engine can be throttled by varying the oxidizer mass flow. This allows achieving the required thrust corresponding on the current demand. During operation, the engine can be aborted at any time.

Research and Innovation

Although hybrids do have some conceptual advantages, they are rarely used since their broad research gap. Our hybrid engine enables us to take steps in development in the less researched areas of the aerospace industry.

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 to enable a wide prior statical test campaign, the following main objectives have been set:





System Overview

Eight equally important subsystems to aim for stable and reliable combustion.

propellant each firing

Total Parts

working hours

Total weight

Max oxidizer pressure

combustion pressure

max temperature

broken cobalt drill bits


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.

Fluid Supply System (FSS)

The main function of the FSS is to store the liquid oxidizer spatially separated from the solid fuel and to deliver the required oxidizer mass flow to the injector of the engine. To ensure safety and high performance of the engine, the oxidizer tank is pressurized with nitrogen as an inert gas. After the firing, the engine will be purged using nitrogen again, while the run tank will be drained from any remaining trace of nitrous oxide. The oxidizer tank will be filled remotely from commercial 50l nitrous oxide tanks, which will be heated using heating pads. This is necessary to increase the vapour pressure of the oxidizer. To control the valves in the subsystems remotely, there is a pneumatic system which also uses nitrogen. The fluid supply system is protected by two shielding walls. Prior cleaning procedures for oxygen service prevent impurities, which could lead to self-decomposition of nitrous oxide.


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 injector ensures the delivery of the required amount of oxidizer into the combustion chamber. The injection method and its level of atomization directly affect the mixing and the flow in the combustion chamber; hence, it has a high impact on combustion efficiency and stability as well as the regression rate of the grain. Therefore, several different injectors with showerhead, swirling and impinging techniques and the corresponding engine configurations are developed and tested. The injector design aims for choked flow to prevent feed-coupled combustion instabilities and allows the integration of Helmholtz dampers. To attain the required oxidizer mass flow of about 2.5 kg/s, empirical parameters are determined in cold flow tests and specific thermodynamic mass flow models for nitrous oxide are applied. The design integrates multiple sensors to measure combustion performance while the modularity allows cost-effective testing of different injection configurations.


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.

Casing (Engine Structure)

The casing builds up the combustion chamber and is all about the engine structure. It contains the further subsystems namely grain, injector, nozzle and igniter as well as various sensors of the DACS, and defines the necessary structural interfaces and sealings to integrate them into one operative system, the engine itself. Key part is a cylindrical tube with about 1m of length, which forms the major part of the casing and allows the engine’s manufacturing with bearable costs. The developed design provides high modularity, which allows interchanging key parts in order to test different engine configurations. While the engine is for static testing only and weight is not of major importance, the concept itself is lightweight. Shape and dimensions of our engine design allow the future integration into a flying rocket without major adaptations.

Test Bench

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.

Data Acquisition and Control System (DACS)

The DACS allows remote control of the fluid supply system and the ignition as well as expansive monitoring of all critical and most performance parameters. For safety reasons, redundant wiring is used to prevent unintended ignition or activation of valves. More than 25 sensors have been selected and integrated to gain valuable data for the evaluation and further development of our engine. Precisely, several thermocouples, piezoresistive and piezoelectric pressure sensors, accelerometers, load cells and even a Coriolis sensor are used. The user interface is programmed with LabVIEW and allows immediate graphical presentation of the sensor data. The circuits are located in a separate compartment of our test container while the control unit can be operated in the bunker.

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.

Our Team

Shady Elshater

Project Manager & System Engineer

Pascal Müller

Control & Testing

Julius Wymann

Injector & Casing

Ianco Cregut

Grain & Casing

Felix Winghart

Fluid Supply System

Mirela Minkova

Control & Media

Philip Wolf

Igniter & Testbench

Stefan Schmid

Nozzle & Testbench

– The Enablers of Project IRIDE –

Academic Partners

Main Sponsors

Gold Sponsors

Silver Sponsors

Bronze Sponsors

White Sponsors

Contact Us

Akademische Raumfahrt Initiative Schweiz ARIS

HPT C 117.1 Auguste-Piccard-Hof 1 8093 Zürich

Did the passion catch you?

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