Developing Rocket Engine After Two Years Of Study

It's a quarter to nine in the evening when Barbara Parys, ETH student and safety officer at the rocket test, issues the order: "From now on, nobody is allowed to move until after the firing." Nobody is allowed to leave their position. Parys, like all rocket engineers, transmits in English. She is studying for a Bachelor's degree in interdisciplinary sciences and, together with 19 other colleagues, is a member of the Pegasus team of the Aris student space initiative.

Her colleague is about to ignite a new type of rocket engine for testing. The location is Dübendorf airfield. Parys and her colleagues from the ten-strong test team crowd around the four screens of the control centre in a small hut, shielded and at a safe distance from the propulsion unit.

Several cameras film the hexagonal copper component, which is about the size of a plate and looks a little like an oversized nut. It is mounted on the back of a stainless-steel plate on a car trailer, together with a superstructure of aluminium profiles, various pipes, sensors, cables and pressure tanks forming the test rig.

Liquid oxygen steams out of the engine. It is a propellant component and pre-cooling the system.

Everything glows green in the special light for the high-speed camera. Together with data from pressure sensors, it will later show whether the team has achieved its goal, namely whether a stable detonation wave is forming in the engine. If it succeeds, Aris would be the first student team in the world to ignite an RDRE with liquid fuel. There are only around a dozen countries in the world where such rocket engines have been developed and successfully tested.

You can literally feel the tension in the team. Apart from the brief announcements from the control centre, everything is silent. "Temperature: -100 degrees. Pressure: nominal." Temperature and pressure are OK. And then over to the security guards on the airfield, who take cover behind the earth wall to ensure that nobody enters the test site: "Final surveillance check?" "Clear!"

Project work in the third year of study

Mattia Röösli has already replayed this moment in his mind several times, so the movie is starting to roll in his mind's eye. The team ignited the engine for the first time a week ago but failed to produce a detonation wave. What if it really works today? He and the Pegasus team at Aris have been working towards this moment for almost a year.

Röösli is 21 and in his third year of studying mechanical engineering.

At Pegasus, he developed the injector, the heart of the engine. Rocket engines always need two components: fuel and an oxidiser, which supplies the oxygen required for combustion. The team opted for propane and liquid oxygen. The injector generates the correct mixture during injection.

Some of his work on the engine was carried out as part of his studies: projects such as Pegasus are an integral part of the curriculum for various degree programmes at ETH Zurich. They have existed for some time in the form of Focus Projects for mechanical engineers. Teams of five to ten students develop and realise a product with all the relevant components and accompanying elements over two semesters: finance, conception, design, engineering, simulation, draft design and production. The results include aeroplanes, driverless cars, robots - and even rocket engines.

Controlled detonations for greater efficiency

Pegasus has set itself the goal of developing and testing a bi-liquid RDRE. The project is largely financed through sponsorships. Industrial companies provide the team with a substantial amount of material and services, and in some cases also with funds.

The expectations on such engines are decidedly high: the aim is to deliver around 10 to 20 percent more power with the same amount of fuel.

This is because the fuel in such engines does not burn evenly and steadily, but instead detonates, producing an explosion-like wave that constantly moves in a circle. The shift in burning method leads to the extremely high pressures and temperatures. This means that the energy contained in the fuel is better utilised than in conventional engines.

At the same time, the technology requires fewer complex components to compress the fuel, making the engines more compact and potentially lighter.

Because fuel accounts for 80 to 90 percent of the total weight when launching rockets, even efficiency gains of only a few percent are worth their weight in gold. Rockets could fly more cost effectively - or carry larger loads into space.

Research into such engines has been ongoing for a long time, but they are not yet ready for the market. The challenges are simply too daunting and too numerous.

Consider, for example, material loads and stress: The detonation waves travel through a ring chamber up to 20,000 times per second. At high frequency, the waves expose the material to extremely high pressure and very high temperatures.

Tests with RDREs have already been carried out in various countries. In the USA, NASA has ignited engines on a larger scale on ground-based test stands. A Polish institute has tested RDREs with liquid fuel. Japan is the only country to have actually ignited such an engine in space.

So, if the Pegasus engine produces stable detonation waves for even a single second today, the team members will be able to count themselves among an elite group of genuine pioneers.

After two years of studies: just go for it

While his team colleagues pack the boxes for the test in the hangar, Mattia Röösli tells us how it all began.

He became interested in the subject early on. "Rockets fascinate me because they fly simply by accelerating fuel backwards. The principle is actually quite simple."

After two years of studying the basics, he was motivated by new territory: "There is no one who can tell you exactly how to do it because so much is still unexplored. Working at the forefront of research like this is pretty cool!"

The injector that Röösli has developed is a critical component. RDREs require highly precise injection technology that must mix and deliver the fuel in less than a millisecond, without the detonation wave reverberating back into the supply lines.

How do you approach such a task? He spent three weeks familiarising himself with the subject. Then he just got started. "Maybe I shouldn't have read so much," he says in hindsight. "It's a mistake to think you can fully understand the topic before you start. There are simply far too many unanswered questions."

Sketches, discussions, prototypes

So, he started with something higher-level: the question of which elements belong to such an injector and how they can be connected. "The first thing you do is make sketches and discuss them as a team. The others then draw your attention to things you have not yet considered. Then you continue calculating and sketching. You break big problems down into smaller ones until they become solvable."

The team gradually progressed to the first prototypes from a metal 3D printer. "When the first prototypes are on the table, new challenges become apparent again."

Röösli emphasises: "You don't need to be exceptionally talented to develop a rocket engine after two years of study. You go step by step and help each other."

The predecessors serve as coaches, and a start-up looks on

The expertise of the Aris project team was also very helpful last year - they pass on their knowledge year after year as coaches. If something goes wrong with one team, the next team benefits from this experience. A charred electronic component on a shelf of prototypes in the hangar bears witness to such a lesson.

Pegasus also benefited from the experience of the start-up located right next door, which is also working on RDREs. In any case, the infrastructure and the location in the ETH hangar in Dübendorf simplify many things. There are workbenches, 3D printers, ample space for materials, meeting rooms, workstations and plenty of room for testing right next to the large roller shutter door.

Before an engine can be ignited for the first time, it undergoes a multitude of tests. These include flow tests with water or pressure tests. It is a long way to a controlled detonation, also due to the high safety standards that must always be adhered to. Colleagues spent several months working on the safety concept alone.

Today, the work of the whole team comes together for the second ignition, which is technically known as a "firing".

Gas cylinders, cable reels, snacks: check

Almost six hours earlier, at three o'clock in the afternoon, everyone gathered in the hangar for the safety briefing. All the equipment was already loaded onto handcarts, including cable reels, gas bottles, fire extinguishers and, importantly, a box of snacks to prevent the team from losing concentration due to hypoglycaemia at the airfield.

Everyone stands in a circle. The test conductor reminds everyone of their roles, what must be observed and who is allowed to be where. Each person receives a coloured waistcoat to identify their role: blue for the test conductor, green for the safety officer, orange for the engineers in charge and yellow for the so-called "DACS" the engineers for Data acquisition and control systems.

At four o'clock, Röösli opens the large roller shutter and hitches the trailer up with the high-tech test stand to an old, borrowed estate car. They drive to the neighbouring airfield at walking pace. After a short wait, two military policemen open the gate and wave the colourful procession through. Further back, a squadron of military helicopters is landing. Otherwise, there is not a soul to be seen, nor a car to be heard.

Everyone to their safe positions!

Once they arrive at the test site, the team immediately begins setting everything up. There should be as much time as possible for firings.

Ticking off a long checklist, the test leader guides everyone through the entire test sequence. Two people connect gas cylinders, while a little further away, others are setting up a flaring system to burn off excess propane.

The colleagues in the mission centre operate each valve, while those at the test stand check whether they are working. This is followed by pressure tests. Finally, the engineers in charge, wearing thick gloves, aprons, special shoes and face shields, fill the valves with liquid oxygen. Ice crystals immediately form on the pipes.

The split second of truth

Then comes the moment everyone has been working towards. Everyone is fully focused on the screens in the hut. In the mission control, Mattia Röösli looks eagerly over his colleague's shoulder. It's just after seven o'clock, and it's already starting to get dark outside. The engineer at the mission control is handed the key by the security officer to activate the ignition power circuit. He flips a few switches and starts the cooling process for the engine on the computer. Then the moment has come: "Initiating firing sequence in 3, 2, 1, go!"

There is a hissing sound, a dull bang, followed by screeches in a hoarse, indefinable tone. The beam on the camera images then turns into a flame and goes out. Pressure is released and propane flares up at dusk in the flaring system.

Röösli and his colleagues exchange questioning looks. Was that a detonation wave? The students check the sensor data and discuss what they have seen and heard. Not really. So, everything starts from the beginning.

More propane

The team inspects the engine for damage and refuels with liquid oxygen. By now it's dark. Röösli studies the coloured curves on the screens to see how much propane and how much liquid oxygen flowed into the engine during the previous test. He pulls out a pen, does a quick calculation, then enters the parameter adjustments. The propane should flow a little earlier and a little longer before ignition.

At a quarter to nine, the engine is cooled to minus 130 degrees for the second time. 3, 2, 1, go!

This time, the pressure wave shakes the door of the small wooden hut and a long, steady stream of fire shoots out of the engine, again buzzing and whistling at the highest frequencies.

Röösli glances over his shoulder for a second, a hint of a smile on his face. Nobody says anything, but they all suspect it: that was a detonation wave.

Three detonation waves spark thrills and exuberance all around

Confirmation arrives later by radio, as the colleagues outside examine the video right next to the high-speed camera: "Yes! Guys, that was three detonation waves!" a colleague exclaims jubilantly into the radio. Congratulations all round before concentration returns to the preparations for the third firing.

Later, during dismantling, the excitement has subsided. Gen-Z slang replaces the monotonous mumbling over a checklist. Pride is written all over the students' faces.

Shortly before 10 p.m., Röösli gets behind the wheel of the old estate car towing the rocket engine trailer. He drives back to the hangar at a walking pace. Rap sounds out from the open window as if it were a summer evening, not a night with a cold north-easterly wind blowing at the beginning of April.

Two and a half hours later, the Artemis 2 mission lifts off from California, heading for the moon.