STERN 2 Project Update January 2021

We hope you all had a great start into 2021! For us, this is a great possibility to take a look back at 2020 and our achievements within the DLR STERN program. 2020 was the first full year of our second participation in the program, and despite the challenging situation we have made a lot of progress. Our subscale demonstrator rocket is taking shape with lots of prototyping going on, and we hope to launch it in a few months.

Structure and Aerodynamics:

Over the past year, the structure and aerodynamics team grew to a group of 17 members. With a lot of effort from everyone, we were able to achieve several milestones. Besides a range of manufactured prototypes we stepped up the simulations. A few of our milestones include:

The concept of the wound and etched oxidizer tank was applied to several prototypes. The now approved design will save up to 50 percent weight on our tank for the demonstrator rocket.

We now have an international team working on FEM and CFD simulations which are combined with CFRP testing and in-house development of epoxy resins. This enables us to optimize the structure aerodynamically and in terms of weight, so we can confident it will withstand upcoming loads and temperatures. The trajectory simulation became even more detailed and predicts impressive altitudes for N2ORTH.                                                                                                                           

Tests of different designs and approaches were also conducted for the nose cone, connectors, boat tail and other small parts around the rocket.


Despite the challenging situation with the pandemic, the propulsion team was able to conduct a total of 25 successful hot fire tests with the subscale demonstrator engine HyFIVE in the time between September and December. The tests have shown that our in-house developed fuel enables smooth and stable combustion and our new composite ablative material works reliably. Also, different injector-types (showerhead, impingement, swirl) and nozzle designs have been evaluated.

Additionally, the team has constructed a 4-axis filament winding machine for the production of lightweight composite pressure vessels       (combustion chambers, oxidizer tanks), nozzle components and rocket hull segments. First prototypes of the demonstrator engine have been produced for pressure tests in the new year, using one of our proprietary epoxy formulations with improved temperature- and fatigue properties.

Currently, further engine tests are postponed due to the high numbers of corona cases, but the propulsion team looks forward to even more tests with HyFIVE in the future.

Fluid System:

2020 has certainly been an exciting year for the fluid system team. We made detailed designs for the concepts developed in 2019. Hence, our main work was the design and testing of various prototypes. In particular, the prototypes for the emergency release valve and the main valves of both the demonstrator and N2ORTH rocket yielded promising results. While testing continues, we are using the gathered knowledge for the design of the flight versions of the individual components.


Over the past year, the recovery team has had several successes. While there were only concepts, at the beginning of the year, there have already been the first successful tests and many improvements have already been incorporated into the existing concept.

The first pyro tests with our mortar-like ejection system could already take place in October. In November, we have tested the ejection of the drogue parachute. A prototype of the entire recovery bay has already been built and will be tested in a drop test at the beginning of the new year.

There is still a lot of work ahead of us and many more components to test, nonetheless the results so far make us confident of a successful recovery of the rockets.


We were able to achieve nearly all goals set for this year. We decided onto a final system topology, allowing us to spend all our time onto the individual modules. A major part of our work this year was to select and test components to fulfill every given task like recording the flight trajectory, measuring performance data of the engine as well as transmitting the collected data to the ground station. With the component selection nearly done we are now looking forward to designing and building the flight versions of the demonstrator rocket, which then need to be firmly tested to ensure smooth operation of all modules working together for the launch.

Ground Support Equipment:

In the last year, we have made a lot of progress in the GSE subsystem. We assembled the launch pad which will be used for the demonstrator launch. The arm mechanism, which enables us to undock the fuel interface remotely, is currently being assembled as well.

Progress was also made in our electronic department. It completed development of the system used to control and monitor the fueling process, as well as all other functions of the launch platform. It is also used to schedule and fire all pyrotechnic devices used to light the engine at launch.

The control system was split into three different custom-made PCBs and is managed using a Raspberry Pi running C Code. The graphical user interface running remotely in the control room is currently under development and will allow for easy monitoring and actuation of all functions.

The fueling system has evolved as well. It is planned to use a diving bottle as a buffer tank to fill the demonstrator rocket with oxidizer. The process uses a series of solenoid valves and sensors to ensure the right oxidizer level and pressure in the main tank while also being remotely actuated. In the next couple of months till the launch of the demonstrator rocket, there will be a complete dry run of the entire fueling process in conjunction with the fluid system.

HyFIVE-2: First 800N Demonstrator Engine Tests

After we have successfully conducted our first tests of HyFIVE-2 last week, here are some stunning photos we took. HyFIVE-2 is the 800N version of our test engine which will later – in combination with a lightweight casing – power our demonstrator rocket. We have tested some injector designs to improve fuel regression, thrust and efficiency, reaching a combustion chamber pressure of more than 25 bar. The new ablative nozzle made of carbon phenolic has also proven its ability to withstand the high temperatures in our engine. Since the first tests were very promising, we are looking forward to the next tests in the following weeks to improve the engine even further.Watch our testvideo here:

HyFIVE-1: First Hot Fire Tests of STERN II Project

Our Hybrid Fuel Investigation and Verification Engine (HyFIVE) was tested for the first time on September 2nd, 2020. Since then, three cold flow tests and six hot fire tests were conducted. All engine hot fires had an operational time of 5 seconds and were successful. The goal of the tests was to evaluate different fuel parameters such as regression rate and combustion characteristics. Two different fuel compositions have already been evaluated and we are currently preparing the next tests to further enhance the fuel composition. In a future design stage, the engine will be used as propulsion unit of the demonstrator rocket. For this purpose, we will optimize combustion efficiency and thrust as well as using a lightweight combustion chamber casing. We would like to thank the DLR Institute of Space Propulsion in Lampoldshausen for their help and support even in this challenging times. Stay tuned for more test footage!

STERN 2 participation on track

Although our Preliminary Design Review (PDR) of the DLR STERN Project is being rescheduled due to the outbreak of the corona virus, all HyEnD members are working hard (and from home) in order to bring the project forward. We think this is a great opportunity to give you an update of the current state of the project.

Propelled by its powerful HyLIGHT Hybrid Rocket Engine, our project rocket N2ORTH will fly to an altitude of 20km or higher and will be fully recovered. The engine will provide a nominal thrust of 10kN over an operation time of minimum 15 seconds. It will use a new type of in-house developed polymer-based fuel in combination with nitrous oxide. The whole rocket is designed from the ground up using the experience gained with the previous HEROS rockets. In order to test the different systems of the rocket in advance, we will build a subscale demonstrator rocket which will be launched next year. Currently, HyEnD is focusing its work mainly on this demonstrator. In the following, we will give you an overview of the different systems of the rocket.

Structure and oxidizer tank:

The structure team evaluates different design approaches for several lightweight rocket structure elements. One of the most challenging parts is the oxidizer tank, which is planned to consist almost entirely of composite materials. Several design and manufacturing approaches are investigated, including designs without the use of an aluminum liner. This is challenging since nitrous oxide usually causes problems in a hydrocarbon-based environment.


The propulsion team has already started fuel evaluation tests back in fall 2019 and has built a completely new engine called HyFIVE-1 in order to continue these tests. The first test was scheduled for March 2020 but was canceled due to the corona virus. Currently, the team is working on the design of the demonstrator flight engine, which will use a carbon fiber reinforced plastic (CFRP) combustion chamber hull in order to reduce weight. First design studies for the larger HyLIGHT engine are currently in progress as well.

Fluid System:

In the last weeks and months, the fluid system team has developed a simulation model for the self-pressurizing behavior of nitrous oxide inside the tank. This is crucial in order to determine the required tank size and resulting engine performance. Also, three design studies for every valve were carried out, emergency and relief valve prototypes are currently being manufactured. For the main valve, a pyro charged slider valve is considered.


Since the rocket shall be required entirely, the rocket will be equipped with a two-stage parachute recovery system.  The recovery team has carried out different concepts and decided that the following mechanism will be used. First, the drogue will be ejected with a motar placed between the oxidizer tank and engine. The main deployment mechanism is located near the top of the rocket. It includes the main chute and a pilot chute. The drogue and pilot chute are deployed using pyrotechnical charges. First tests to verify drag coefficients and shock loads for the demonstrator rocket were already done in October 2019.


The Avionics team is currently focused on developing the individual systems. Choosing the right components to implement in the design is crucial to keep the systems as compact and space efficient as possible. For each systems a schematic containing all the used components as well as the connections in between them are designed.

Ground Support Equipment:

Members of the ground support equipment team are working on a custom launch rail for the demonstrator rocket. For N2ORTH, the MRL in Esrange will be used. Also, different concepts for the arm mechanism (responsible for fueling the rocket) were carried out and it was decided to use a rotating arm. Tasks also include the development of an antenna tracking platform, which will enable a life video feed during flight.

EXPLORE is taking shape

EXPLORE is taking shape! During the last few weeks we have worked hard and started the manufacturing of the first components of flight hardware, including the structure, recovery system and tanks. Prototypes of the fluid system and the main valve are also in construction. While the engine is still in its test phase, we have managed to reduce combustion instabilities and improved the design of the engine multiple times. However, tests will continue in order to improve stability, efficiency and burn time.


We’re now one month into the new year! Roughly one year ago we decided to go for EXPLORE, a demonstrator propelled with liquid oxygen (LOx) and solid paraffin-based fuel. Here is an overview over the current status:

The development of the avionics hard- and software is running in high gear. For the first time in HyEnD history, a self-made flight computer shall take control of the most critical functions during flight. First prototypes of many electrical subsystems are already built and about to be tested thoroughly. As for the structure, we have manufactured the tip and have a prototype of a CFK-tank for the LOx. After its ascent, the rocket shall be recovered via a recovery system containing a main parachute and a smaller one for pulling out the first one. It’s now in its final design stage. While some components are already ordered others are being prepared to be manufactured soon. Also, a wind tunnel test campaign is currently being planned, which will finish the development process of the new recovery system of EXPLORE. Very challenging is the design of the fluid system because the oxygen will have gaseous and liquid phases when being transferred to the tanks before the launch and then to the combustion chamber during flight. Safety measures like a mechanic and electronic release valve as well as a burst plate need to be included. Those components are still in a design and re-design process. Gaseous nitrogen under high pressure will deliver the LOx to the combustion chamber. Because of the high pressure, there needs to be a pressure regulator. We already tested a sophisticated design at 50 bar but currently re-designing it to make it lighter and qualify it for 300 bar. At the moment we are looking for suitable sensors for checking the pressure and temperature. Also time-consuming is the development of the engine. A whole thesis concentrated on its first design steps and main parts like the showerhead-injector and pre-combustion chamber are already manufactured. Current stage is the preparation of the test bench. We hope that tests in March will give us promising results on its performance. We also hope that you had a great start in 2019!

CSL Maiden Launch

Great News! Our CanSat Launcher has been launched successfully. CanSat and parachutes were deployed flawlessly and the rocket landed softly in the fields near Lampoldshausen. It is completly intact and can be launched again using a new motor. Below you can see a video of the launch, recorded with several ground cameras and a drone.

CanSat Launcher Progress

Recently, great progress has been made in the development and production of the electronics subsystem. By now there’s a complete hardware package made of an Arduino, a TeleMega and the primary batteries which are mounted on a platform in the nose cone. The software and hardware will be tested soon. The testing of the electronics involves drone flights and a vacuum chamber to make sure the software will trigger the deployment of the CanSat and the parachutes after reaching the apogee.

Lately the fins were attached to the lower end of the rocket. To lower production and development time two identical compartments were produced. One will be used for the CanSat, while the other will contain the main parachute.

Shortly after reaching the apogee, the software will trigger a cable cutter to cut the string used to keep the door of the CanSat compartment closed to the rocket. By releasing the compartment door the CanSat will be ejected immediately via a block of foam material. An ejection mechanism based on foam sounds like a simple solution, but has two main advantages: During the ascent the CanSat is kept in its position in the compartment and the ejection doesn’t need an extra trigger by the software.

HEROS 3 On Display

Three months after its record flight, HEROS 3 made its long trip back from Northern Sweden’s tundra to the exhibition at the German Aerospace Center (DLR) Lampoldshausen site! It is easy to see that HEROS 3 is one of the tallest exhibit in the museum. Here HEROS has found its place next to famous rocket engines and rocket parts like Vulcain 2, Viking, Ariane 5 Upper Stage etc… It’s really a nice place to visit, now even more. Next to HEROS 3 there are some posters and the demonstrator rocket MIRAS.

HEROS Record Flight Video Summary

After carefully evaluating the onboard data from last week’s HEROS 3 flight, we can now happily confirm the maximum flight altitude of 32300m (~106000 ft). This sets a new record for European student and amateur rocketry which was held until now by Delft Aerospace Rocket Engineering and their rocket Stratos II. Furthermore, to our knowledge this is also a new altitude world rocket for hybrid rockets built by students. The maximum speed of HEROS 3 was 2600 km/h with a Mach number of 2.3. The drogue parachute deployed at Apogee as intended and the rocket safely descended to the ground, where the main parachute opened and the rocket landed softly without any damage in 20 km distance to the launch pad.

The launch angle of HEROS 3 was at 80°, which is quite low, since experimental rockets are subject to higher safety requirements at the European Space and Sounding Rocket Range (ESRANGE). Additionally the rocket was only filled to about 70% of the tank volume with oxidizer. The reason for this is that we wanted to make sure with the flight of HEROS 2, that the rocket structure can sustain the high thermal and mechanical loads of supersonic flight. Unfortunately HEROS 2 was not sending any flight data and could not be recovered. Therefore, we decided that also HEROS 3 should not be filled to its maximum level to make the flight as safe as possible. According to analyzed flight data form HEROS 3, a higher launch angle and a fully filled tank would enable a maximum flight altitude of up to 50 km. Currently the team is busy with processing all the data and video recordings. We proudly present a first, short glimpse on our onboard camera footage in the above video. More video material is currently processed and also flight data graphs will be released in the coming days.