First Results of the N₂ORTH Post Flight Analysis

Since our N2ORTH Launch Campaign in April, some time has passed, and the team took a well-deserved break. Nevertheless, we had our Post Flight Analysis Review in Bonn at the beginning of June, and we want to share some of the results with you.

Analysis of the 1st Launch:

The first launch took place on Tuesday, April 18. Originally scheduled for Monday, the launch was postponed to Tuesday in order to double check the avionics and launcher interfaces.

The countdown began at 06:15 and went very smoothly. There was a short pause to complete the transfer of nitrous oxide from the intermediate tanks to the rocket tank. This delay was caused by the fact that the boxing of the rocket itself was less insulated than expected. To compensate, the nitrous oxide in the intermediate tanks was heated to a higher temperature. The final oxidizer mass in the rocket was 95 kg and the launch elevation was set at 81.4°.

The launch at 11:05 local time went smoothly without any problems. The rocket reached a maximum speed of Mach 3 / 3,150 km/h after about 20 seconds. The engine provided thrust for about 75 seconds, with a transition to the gas phase after 18 seconds. This data was obtained from the IMU as the lower data acquisition system suffered a cable disconnect at liftoff. This means there is no tank and chamber pressure data for the flight. However, the upper data acquisition system continued to operate and a maximum tip temperature of 240°C was reached.

Apogee was reached at an altitude of 64.4 km after 132 s. This was only a 0.2% difference to the predicted apogee by the simulation.  However, the drogue parachute deployment was triggered 9 s earlier by the Telemegas. The drogue deployed without problems at Mach 0.9-1. However, reviewing the onboard video, it can be seen that the main parachute’s three-ring release system was already activated. Up to this point, the main chute was still held in place by two straps in the recovery section, as the drag generated by the drogue was not sufficient to pull it out. However, during the descent the drag increased until the main parachute was released at an altitude of 36 km and a speed of Mach 1.8. Since the main parachute is not designed for these conditions, it was immediately detached from the rocket together with the drogue parachute.

The rocket then went into a tumble mode with a high spin rate, which helped to keep the descent rate relatively low. The avionics were able to continue transmitting the position up to an altitude of 1.3 km. At this point, the line of sight prevented further data transmission. Thanks to the precise position (downrange: 48 km), the rocket was easily located and recovered by helicopter only 3 hours after launch.

A review of the onboard data showed that the rocket landed at a vertical speed of 36 m/s. The avionics were internally damaged due to the non-nominal recovery sequence and landing speed, but all data could be recovered. Also, the recovery section and one of the fins suffered some structural damage.

The reason for the non-nominal recovery sequence was found during investigations on the following day and was traced to a misconfiguration in the Telemega software. As the cause was quickly found, HyEnD was able to ensure that the second launch would not have the same problem and continued preparations for the second launch.

Analysis of the 2nd Launch:

Having demonstrated with the first launch that our simulations are capable of predicting the rocket’s trajectory with high accuracy, and having quickly identified the cause of the non-nominal recovery sequence, the team decided to continue preparations for the launch of the second rocket.

Unlike the first rocket, the second N2ORTH rocket has a linerless Type V pressure vessel with an ETFE coating on the inside to ensure compatibility with nitrous oxide. The elimination of the aluminum liner reduces the dry mass of the rocket by 7.7 kg (10%). In addition, the Esrange safety and operations team approved an increase in the launch rail elevation. It was decided to target an oxidizer mass of 105 kg for the second rocket, which would result in a >90% chance of reaching an altitude of more than 100 km and thus the Kármán line. A higher oxidizer mass would have been technically possible, but would have resulted in the rocket landing outside the designated landing zone.

The launch attempt took place on Monday, April 24. The Styrofoam box of the rocket was improved in order that the launch team could easily control the temperature and keep it within the desired range. However, during the oxidizer loading process, the solenoid valve in the rocket could not be activated. It was decided to continue the countdown with an adjusted oxidizer loading procedure. With the modified procedure, the target oxidizer mass, temperature, and pressure were achieved with another short countdown pause.  However, the nitrogen content of the oxidizer tank filling was higher than originally simulated.

At 14:10 local time, the rocket launched with an elevation of 82.2°. Unfortunately, the rocket encountered an anomaly that caused it to break up 22.4 seconds after liftoff. At this point, the rocket was at an altitude of 11 km, traveling at Mach 3, and still in sight of the team members and cameras on the radar hill. Due to the anomaly, the rocket disintegrated into several pieces. The avionics were able to send data to the ground station until this point. The timing of the anomaly is interesting because both the transition from liquid to gaseous nitrous oxide and the maximum dynamic pressure occur at this time.

One of the cameras mounted on a theodolite was able to follow the oxidizer tank until it hit the ground. The video and azimuth information allowed the Esrange team to retrieve the tank by snowmobile the next day. The tank and its attached fluid system components were undamaged except for the broken interfaces at both ends. Fortunately, the Rocket Status Measurement System (RSMS) SD card attached to the oxidizer tank was still intact, giving the team access to high frequency (14 kS/s) chamber pressure data.

A review of the cameras on the launcher revealed that the oxidizer release valve was opened at launch, resulting in a slow (<100 g/s) release of liquid nitrous oxide to the side of the rocket. Inspection of the valve (which was still attached to the recovered oxidizer tank) revealed that the pyro charge within the valve was not activated, indicating that the opening was triggered by a shock load at launch. The influence of the vented nitrous oxide on the rockets aerodynamics is still under investigation.

Chamber pressure data shows no indication of engine malfunction until a loss of chamber pressure occurs at 22.4 s, which is associated with the breakup of the rocket. The IMU data shows a continuous increase in lateral acceleration from 0 to 2.5 g beginning at 20 s, with a rapid increase to more than 15 g at break-up. Since the later acceleration begins to increase to a point where the combustion chamber pressure is nominal, a failure of the propulsion system is unlikely. The IMU data also shows a low spin rate of less than 0.52 Hz and no evidence of pitch-roll coupling.

Based on the available data, the final cause of the failure cannot be clearly identified. However, the possibility remains that other components of the rocket will be found by the SSC team in the future. At this point, it can be concluded that the breakup of the rocket was the result of either a structural failure during launch, an unexpected aerodynamic load on the rocket, or a combination of both effects.

Nevertheless, HyEnD is very proud of what has been achieved with the launch campaign – setting new records and pushing the limits of (student) hybrid propulsion. The two weeks in Sweden were an amazing time – thanks to a great team, good logistics and organization as well as the cooperation with DLR and SSC.

Watch the Record Flight Video!

64 km altitude – A new world record for student-built hybrid rockets and for European student-built rockets in general! We are very happy and proud that we have almost doubled the existing record that we set with our HEROS 3 rocket in 2016. This achievement is the result of almost four years of hard work and dedication by our team. With N2ORTH, HyEnD has shown what students can achieve when they work together towards an ambitious goal. We are grateful for the support we received along the way – especially the funding from the DLR STERN program. Without it, this project would not have been possible. We hope you enjoy the videos of the record flight as much as we do. Stay tuned for more footage, including the full on-board videos, in the coming weeks and months.

Mission Success: New Record for Student-built Hybrids

On Tuesday 18th April 2023 at 11:05 local time, HyEnD successfully launched its first N2ORTH rocket from the European Space and Sounding Rocket Range ESRANGE in Sweden.

The countdown started at 06:15 and went very smoothly. There was a short hold to finish filling the nitrous oxide from the intermediate tanks to the rocket tank, but otherwise there were no delays. With a final oxidizer mass of 95 kg and a launch elevation of 81°, the rocket reached an altitude of more than 64 km after about 2 minutes. This almost doubled the previous altitude record for student-built hybrids. The altitude was measured by GPS and the data will be released in the coming days and weeks.

The drogue parachute was successfully deployed and inflated shortly after reaching apogee. However, there were some issues with the recovery sequence that need to be investigated. This resulted in an increased landing speed and some damage to structural components, but the team was able to recover the entire rocket by helicopter.

The team is currently analyzing the data and preparing for the launch of the second N2ORTH rocket early next week. Depending on the weather situation and the results of the investigation, the oxidizer load and launcher elevation will be increased to reach an even higher altitude.

HyEnD would like to take this opportunity to thank the managers and reviewers of the DLR STERN programme as well as the launch and operations crew at ESRANGE. Their support is greatly appreciated, and we are very happy to be working together.

HyEnD’s N₂ORTH Rocket passes Acceptance Review

HyEnD is proud to announce that it has passed its Rocket Acceptance Review (RAR) with experts of the DLR today. The event took place at the Institute of Space Systems (IRS) and Materialprüfungsanstalt (MPA) of the University of Stuttgart. The review included detailed discussions about qualification testings, design changes and plans for the launch campaign. Also, the fully assembled rocket was shown for the first time. At the end of March, the components of two complete N₂ORTH rockets will be transported to Esrange in Sweden.

Here are some impressions of the event as well as the assembly of the rocket:

The review and presentation of the rocket was also covered by the German television SWR:

Launch Campaign Announcement

We are proud to announce the date of our launch campaign! From 11th to 25th April this year, 16 HyEnD team members will visit the European Space and Sounding Rocket Range (Esrange) close to Kiruna, Sweden. And we plan to not bring one – but two N2ORTH rockets with us!

The launch of the first N2ORTH rocket is planned with 80° of elevation and with limited propellant mass, in order to ensure a safe downrange and landing area. If all goes according to plan, N2ORTH will reach an altitude of more than 50 km at its first flight and we will get the permission to increase the elevation for the second rocket launch. The launch of the second N2ORTH rocket is currently planned with a higher elevation and increased propellant mass.

As of now, a space shot is not off the table but will also depend on the results of the first launch and weather conditions. We are looking forward to share more details about the launch campaign in the upcoming weeks.

Successful Validation of Thermal Protection System

In order to complete final research concerning thermal loads, HyEnD conducted thermal tests on December 20th, 2022. The thermal tests were a crucial milestone and provided us with valuable insights into the expected in-flight behavior of N2ORTH.

During a test campaign, we tested the nose cone, fins, and 3-ring system of the parachute. The tests were conducted under realistic conditions corresponding to a speed of Mach 2.5, equivalent to the predicted max Q conditions. Thus, with this test, the maximum aerothermal load that we expect during our flight could be tested.

First the fins were tested. Due to the surface standing perpendicular to the flow direction, high heat loads are expected here. During the test, the leading edge of the fins was able to withstand the thermal load expected at max Q for over a minute. This is significantly longer than expected in flight, so we are confident in our design.

Subsequently, the nose cone was tested. We tested not only the structure of the nose cone, but also potential camera recesses. We confirmed that the thermal loads can be safely withstand even at the location of a recess. With this test, we validated for a second time that our thermal protection at the nose cone can withstand the loads with a high degree of reliability.

By testing the 3-ring-system of the recovery, it should be verified whether a premature triggering of the pyro-cutters can occur due to the heat load. It should be mentioned that our recovery system will never be exposed to such thermal stresses during our flight compared to max Q. In order to perform a maximum estimation here as well, the system was also tested at max Q conditions. The thermal tests showed that the cutters are not triggered prematurely by thermal stresses. In a subsequent test in which the cutters were intentionally triggered, it was demonstrated once again that the 3-ring system reliably releases the connection when the cutters are ignited.

Many thanks to the DLR Institute of Space Propulsion in Lampoldshausen. Due to their support at the M11 test bench and access to the air heater for supersonic tests, we were able to successfully carry out our tests.

Final Propulsion System & Loading Procedure Test of N₂ORTH

HyEnD has successfully conducted its final system test on Thursday, 8th December! The test included the oxidizer loading procedure using the Ground Support Equipment as well as a hot fire with the hybrid engine and rocket’s fluid system components.

During the oxidizer loading procedure, temperatures and pressures were measured across multiple parts of the Ground Support Equipment and 160 L oxidizer tank. We are happy to report that the test showed a high level of precision during the loading procedure, as we were able to precisely set the amount of oxidizer as well as temperature and pressure conditions in the tank.

The hot fire of the propulsion system showed stable and efficient combustion throughout the operation time. With a peak thrust of more than 15 kN and a total impulse of 255 kNs at sea level, we are confident that the propulsion system is capable of pushing N2ORTH to the frontier of space. The in-flight impulse of this configuration will be even higher since effects like flow separation will occur later in the operation time due to lower ambient pressure at higher altitudes. Moreover, the test showed good accordance to the simulation carried out in advance. This is especially important to ensure a safe flight trajectory of the rocket.

A video of the test can be found on YouTube:

As this was our final hot fire within the scope of the STERN 2 project, we would like to thank the DLR Institute of Space Propulsion for their fantastic support during the last years. Since September 2020, more than 60 hot fires were conducted, and we learned a lot! We are now fully focused on the final production and assembly steps and are looking forward to our launch campaign in April 2023.

Recovery System Test successful

Flying up to 16,000 feet and dropping 79 kg from an aircraft: Under these conditions, we were able to perform the first system test of the entire recovery system of our sounding rocket N2ORTH. By evaluating the drop sequence, we could determine whether all components of the two-stage system work nominally in interaction with one another. At the same time, we wanted to investigate the canopy behavior during deployment in subsonic conditions as well as the integrity of all structural components.

Apart from minor design flaws in structural components, the test was completed successfully. Both parachutes withstood the occurring loads and showed a stable descent. The load switch from the drogue the main parachute worked out properly with a nominal main parachute deployment at about 1,000 m above ground. After descending 300 s, the drop test demonstrator landed safely in the designated landing zone of the Heuberg military training area.

We would like to take this opportunity to thank all our partners who supported us in the successful realization of this project during the last month. Big thanks to the companies like “LIROS GmbH” (ropes), “Amann & Söhne GmbH & Co. KG” (yarns), “Güth & Wolf GmbH” (aramid bands/harness), “EDELRID GmbH & Co. KG” (shock absorber), “Heathcoat Fabrics Limited” (drogue parachute aramid fabric) and “EVOTEC” (main parachute) for providing materials/components together with technical support.

Furthermore, a special thanks goes to the German Armed Forces and “Skydive Saulgau GmbH“ for the safe conduction of our test.

N₂ORTH Rocket Unveiled for the First Time

Our new rocket N2ORTH was unveiled for the first time at an event at the Materialpruefungsanstalt (MPA) Stuttgart on Wednesday, 26th October.
In the days before, three years hard work of more than 60 students came together for the first time. The project is funded by the STERN programme of the German Aerospace Center. Thanks to its dry mass of less than 70 kg, up to 145 kg of propellant mass and the efficient propulsion system, N2ORTH is HyEnD’s most powerful rocket. We are proud to announce that N2ORTH is also technologically capable of reaching the frontier of space, the Kármán line. However, the targeted altitude is still subject to change and will be chosen in accordance to our trajectory simulations, safety regulations at Esrange and weather conditions. The launch of the rocket is currently planned for April 2023.

The unveil of the rocket took place in the presence of representatives of the University of Stuttgart, the German Aerospace Center and partners from industry. We especially want to thank the Coordinator for Aerospace of the German Feder Government, Dr. Anna Christmann, for her visit.

Read more about the event here:

The German press also covered the event:

Photos: HyEnD, MPA Stuttgart

Interested to join? Meet us!

English version below

Wir, die Hochschulgruppe Hybrid Engine Development – kurz HyEnD – sucht neue Mitglieder. Im Jahr 2016 haben wir mit unserer Rakete HEROS den Höhenrekord für studentische Hybridraketen (32 km) aufgestellt. In wenigen Monaten möchten wir diesen Rekord mit unserer Rakete N2ORTH brechen. Parallel dazu beginnt JETZT die Vorbereitung für das nächste Projekt – und wir brauchen dich!

Ein paar Infos vorab:

  •  Mitmachen können Studierende der Universität Stuttgart aus ALLEN Studiengängen
  •  Ein Einstieg im ersten Semester ist ohne Problem möglich und oft sinnvoll.
  •  Vorteile: Du sammelst Erfahrung in einem technisch herausforderndem Projekt, kannst dein theoretisches Wissen aus dem Studium anwenden und bekommst erste Kontakte zu Industrie und Wirtschaft
  • Zeitaufwand: 2 Meetings pro Woche (Gesamt + Subsystem) + Zeit zur Erledigung deiner Aufgaben

Du hast Interesse?

Dann komm zu unserem Treffen für alle Interessierten und nimm Kontakt mit uns auf. Beim dem Event gibt es weitere Infos und du hast die Chance unsere Rakete N2ORTH aus nächster Nähe kennenzulernen.

We are looking for new members! In 2016, we set the altitude record for student hybrid rockets (32 km) with our rocket HEROS. In a few months we plan to break this record with our rocket N2ORTH. In parallel, the preparation for the next project starts NOW – and we need your help!

Please note:

  • You have to be a student at the University of Stuttgart. All study courses from all semesters are welcome!
  • Usually, every team member participates in two meetings per week (overall team meeting and subsystem meeting). You will need additional time to work on your tasks.
  • Meetings are usually in German.

You are interested?

Come to our meeting and contact us. At the event you will get more information and have the chance to get to know our rocket N2ORTH up close.