Project RHEA

ARIS’ First Engine Firing – Project RHEA

It was a cold winter night in Ochsenboden, Switzerland, after 15 months of hard work: The whole team RHEA stared out of a bunker’s small slits in silence as the countdown started to run down. The pulse increased faster and faster until the heart beat was the only thing we perceived in our heads.
Three. Two. One. The ignition started, the opening of the main valve was signalled with a click, and before we even realized what we’re about to see, a bright shining exhaust flame exited the nozzle and turned the night into day.

Hybrid Rocket Engine

As second project of ARIS, project RHEA launched in September 2018. 
RHEA lays the foundation for future hybrid rocket engine developments. The built test infrastructure is expandable to thrusts up to 20 kN. RHEA’s first-generation engine focusses on high safety factors and a high degree of modularity to test a variety of different key parameters. A perfect baseline to scale up the engine and make it flight ready in future.


As a first step, a 500N hybrid rocket engine is developed laying the foundation for future engine developments at ARIS. This engine was designed, manufactured and tested until the end of 2019.


The second generation will be developed by the ETH Focus Project IRIDE, aiming for a thurst of 5000N. Different nozzle types and grain structures will be tested to increase the performance.


To test the engine, project RHEA will set up a test facility with a fluid supply system for the oxidizer as well as a data acquisition and control system to control the valves.

Test Facility

Two shipping containers are used as an enclosure in which the whole test equipment is integrated. The containers are divided into three compartments: engine compartment, fluid supply system (FSS) compartment and data acquisition and control system (DACS) compartment.

To validate the test infrastructure, a small scale hybrid rocket engine was designed and manufactured. This first-generation engine will help to understand the hybrid engines’ working principles by allowing to study grain regression rates, the effect of injector geometries and of the pre- and post-combustion chamber.

The Test Infrastructure

The facility consists of a 20 ft and a 10 ft shipping container split in three compartments.

Engine compartement

The first compartment features the engine and its testbench. Temperature, pressure and force sensors are connected to the engine or the testbench to gather valuable performance data and observe the state of the system to ensure safe operations.

FSS compartement

The engine is connected to the Fluid Supply System (FSS) in the second compartment, which controls the flow of the oxidizer into the combustion chamber. The FSS itself consists of 4 different lines needed to fill, drain, pressurize and purge the liquid oxidizer.

DACS compartement

All the sensor signals are transmitted into the 10 ft container, where the electronics are located. The signals are processed in an NI cDAQ which sends control signals to the valves and igniter as well as transmits the data to the remote-control room.


Test Containers

It was a moment of great joy when the containers arrived at our basis at ETH Hönggerberg. First, the 20ft container for the engine and FSS followed by the smaller 10ft container for data acquisition.


Assembling the system

During June and July 2019, the system was united. First, the shielding plates, which separate the engine and FSS compartment, and the testbench were integrated, followed by the FSS system and cable trays. In parallel, the electronic boxes were assembled.


Test campaign

The system assembly was finalized in October 2019, and the facility was moved to Ochsenboden for the testing campaign in November and Decemeber 2019. After completing the dry test and a cold flow test, the rocket engine finally got fired in December 2019.

The Test Location

Safety comes first. Besides many measures in the design and operations, an additional fall back was included by firing from a dedicated testing site with a bunker in Ochsenboden on the property of Rheinmetall Air Defence. The team stepwise moved closer to the firing by weekends of dry running the system, component-wise and then combined, functionality checks, a successful cold flow test. 

Performance data

A first firing was performed using 1.5 kilogram of nitrous oxide oxidizer, 1 centimeter pre- and post-combustion chamber length, cylindrical port whole grain and shower injector, yielding to 3.5 seconds of burning time, 838 N of peak thrust and a chamber pressure of 25 bar.

A second firing was performed with the configuration of the swirl injector which yielded an even higher peak thrust of 1253 N. Due to the higher discharge coefficient of the swirl injector, the oxidizer mass flow into the combustion chamber increased and thus the regression rate of the grain.

burning time

peak thrust

chamber pressure

The Team

The team consisted of 9 students with the goal to bring ARIS closer to a fully self-developed sounding rocket by building and testing ARIS first hybrid rocket engine together with its infrastructure.

Without you we would not have succeeded

The successful completion of project RHEA would not have been possible with the tremendous amount of help we received through our academic and industrial partners.

Special thanks to ETH Zürich and the IDSC headed by Prof. Lino Guzzella for sharing knowledge, providing infrastructure and supporting the project financially. Furthermore, we want to thank Swagelok for their supply of all our fluid supply system parts and helping us with their expertise in selecting and installing the components.
We are most thankful to Maxon for manufacturing all our parts as well as Rheinmetall for giving us the unique opportunity of using their test location, Werner Steiger Stiftung for their support and RUAG Space for reviewing our designs.