Tag REXUS

Almost four years after our letter of intent to participate in the REXUS program with Experiment S Cephei 2019, the long-awaited and already twice postponed launch campaign in Esrange, Sweden, finally arrived at the end of March 2023. Six members of our team were invited to Esrange Space Center to perform the final preparations on our experiment and to attend the launch. 

On March 21, we traveled from Dresden via Stockholm to Kiruna in northern Sweden. Besides us, the student teams Deadalus2 of the University of Würzburg, HERMESS of the University of the German Armed Forces Munich, ECRIDA of the University Politehnica Bucharest and RaPTeX of the Arctic University of Norway also traveled to Kiruna. For the REXUS30 campaign taking place at the same time, the teams IMFEX of RTWH Aachen, µMoon of FH Aachen, B2D2 of the Royal Institute of Technology Stockholm and ASTER of Luleå University of Technology were also there. They already knew each other from previous reviews and events within the REXUS program and so it was a joyful reunion. The bus took us from the airport to the Esrange Space Center about 45 km outside of Kiruna.

Since Esrange is a restricted civilian area, we first had to pick up our badges at the entrance gate, which then gave us access to all the premises that corresponded to our security level. In addition, the quite strict security instructions were explained. These include, for example, the absolute ban on taking photos of antennas and satellite dishes.

Shortly after midnight we finally made it to the charming Hotel Aurora (the guesthouse in Esrange), seeing the first auroras as we got off the bus.

The next day, after breakfast, the first morning meeting was scheduled, in which we received a detailed briefing on the implementation of the launch campaign. Several institutions were involved on site for the organization and implementation of the launch as well as for the support of the student teams: ESA, DLR, MORABA, SSC and the ZARM Bremen, as well as all the teams, of course. After the introduction, we went to the Dome, a very large hall, where we had the opportunities to sight our experiment and put it back into operation after its long journey.

The experiment had survived the transport well, but the used light guide plate was broken. Replacing the lighting with the very sparse spare parts also filled the next day. Nevertheless, the result was very convincing! One could almost think it was better than before.

On the evening of the second day, the launch of the BROR mission took place on a sounding rocket (about 250 km altitude), which in several pulses produced a kind of artificial aurora by ejecting substances. The whole thing resembles an oversized firework. Scientists want to gain further knowledge about space weather and winds in high altitudes. For us as observers it was also very beautiful to see how many colorful dots gradually appeared in the sky.

In the following three days, we finalized the preparation of the S Cephei experiment. This included filling the four chambers with the CNT suspension already mixed in Dresden. The completed experiment was then ready for communication and timeline tests with the other experiment modules and the on-board computer. These procedures were performed very often to rule out errors and problems during proper launch. All tests were successful, allowing the payloads of the rocket to be finally bolted together.

On March 27, all those participating in the campaign met at 5 a.m. in the Dome for a group photo. The two fully assembled rockets were seen for the last time before they were transported to the launch complex and connected to the rocket motors. Early rising characterized the rest of the time in Sweden from now on, as the many (test) countdowns were started well before sunrise to have as flexible a launch window as possible. This was especially true for the people who were allowed to operate our ground station.

After the handover of the experiment, the tension decreased somewhat and we were able to enjoy waiting for the rocket launches in accordance with Swedish conditions. Especially the exchange with the other students and employees of the supervising institutions brought a lot of new inspiration. This is what makes the REXUS/BEXUS program so special.

In order to represent our favorite city in Saxony with respect and honor, we hired the best designer we know from Team S Cephei to create a logo for this year's campaign. The announced logo contest promised incredible fame. Our design was very well received - especially by the German teams and support staff:

With the experts working on the rocket, there was some free time for us. So the next few days for us were marked by the idyllic snowy landscape of northern Sweden and the again excellent food. We were able to do a few laps on the advanced trails over the balloon launch site or even make our own tracks through the untouched snowy landscape of the forests.

We also tried our hand at ice fishing. At least the necessary hole could be successfully drilled into the half meter thick ice after some effort. But then the fish didn't really want to bite. Therefore it remained with snow walks over the icy and snowy river courses. Physical training was provided accordingly.

To pass the time with learning effect, there were also anecdote-filled lectures by Koen about the work at ESA. The entertaining and well-attended events allowed interesting to bizarre insights in an entertaining manner. There was also the opportunity to visit Isar Aerospace's test stand. In Kiruna, the German company wants to test its developed engines and we were allowed to take a first look at the test stand.

In the evenings, the gaze always went to the aurora forecast with the hope of capturing the impressive natural spectacle again. However, the first evenings could truly no longer be surpassed. Instead, the available sauna was often exploited with the one or other snow infusion.

On March 29, we were able to witness the launch of REXUS30. At 5 o'clock in the morning we were driven by car and bus to Radar Hill, from where there was a wonderful view of the launch complex. It was then only a matter of waiting an hour in the freezing cold at about -10°C until the warning siren finally sounded. This is the signal that there are only 15 minutes left until the start. The launch was successful and really impressive! Experiencing the launch of a real rocket from such a short distance is really different from the impressions you know from videos! Back in the dome we got first information how the experiments of the other teams went.

The next day was the rollout of REXUS29. That means we had the chance to see the rocket with integrated rocket motor before it is finally moved to the launch building. There was also a tour of the Skylark Launch Tower and the refurbished rocket assembly building. In the afternoon, it was also time for us to confirm by signature that our experiment was officially ready for launch. This was done in an almost ceremonial session where all team leaders signed on the launch contract.

As expected, the first launch attempt was aborted due to excessive winds. The weather balloon, which was released before the rocket was launched, showed considerable lateral movements. A launch that day was out of the question. The next day, April 1, the promising second attempt took place. Our motivated ground station crew was allowed to perform their important tasks from the beginning on this day as well. Driven by their urge to explore, they pushed the buttons that needed to be pushed. Said the things that needed to be said.

Shortly before takeoff, another weather balloon was launched. Unlike the day before, it glided almost vertically into the cloudless sky, illuminated by the rising sun. A few minutes later the rocket with our experiment followed. It quickly disappeared into the heights and we went to have breakfast.

At noon we saw our experiment again. Together with the other experiments, the payload was dropped by a helicopter in front of the Dome. Everyone's excitement was high to finally inspect the experiments after years of development. Our experiment looked surprisingly intact both externally and after the extensive disassembly. 

The most important data, the video recordings of the cameras, were backed up and sifted right away. The recording of all six cameras worked. Since the expected results could not be observed directly, investigations were started immediately. However, a result is still pending here.

Afterwards, the experiment module was prepared and packed for transport. In a meeting, the preliminary experiment results were presented by all teams, which showed a broad spectrum of successes.

The last evening traditionally included the campaign dinner, where all participants of the campaign enjoyed specialties of Swedish cuisine in a relaxed atmosphere. Thereby some summarizing closing words and speeches were given and the teams received a campaign certificate. The conclusion of the last evening was to be the prepared skits of the individual teams. We complemented the funny anecdotes, pointed plays and engaging interludes with an acoustic-visual masterpiece of contemporary art.

On April 2, we returned to Dresden after eleven full but exciting and partly relaxing days. Now we have to evaluate the recorded measurement data.
At this point, we would like to thank all the staff of the numerous space organizations that make it possible for students from all over Europe to gain such experiences. This program cycle will certainly remain in our memories for a long time, also because of the multiple postponements due to Corona, but we are all the more grateful that the campaign could still take place! More information about the REXUS/BEXUS program can be found at the official Website.

Autor: Jonathan Bölk

Im Mai 2022 ging es für vier unserer Mitglieder aus dem BEXUS-Team CASTOR zum CDR (Critical Design Review). Dazu wurden Georg, André, Arwed und Florian zum ESA ESTEC Gelände in der Nähe von Leiden in den Niederlanden eingeladen. Georg aus dem Elektrotechnik Team durfte bereits 2 Tage eher anreisen, um an einem Lötkurs teilzunehmen.

Während des Kurses zeigte ein Ingenieur der ESA, wie man nach den ECSS (European Cooperation for Space Standardization) Normen lötet und Elektronik verbaut. Ergänzt wurde der Kurs außerdem mit kleinen Besichtigungen in verschiedene Labore auf dem ESTEC Gelände. Dabei bekamen alle Kursteilnehmer die Chance mit Mitarbeitern zu reden und mehr über ihre Arbeit zu erfahren.

Am Dienstagnachmittag kamen dann Florian, Arwed und André dazu. Gemeinsam bereiteten wir uns auf das bevorstehende CDR am nächsten Tag vor. Danach konnten wir zusammen mit einem weiteren BEXUS Team aus der Schweiz die schöne Universitätsstadt Leiden besichtigen.

Am Mittwoch begann schließlich unser CDR um 15:30 Uhr. Verschiedene Experten vom ZARM, der ESA, dem DLR und des Esrange Space Centers (SSC) hörten sich den aktuellen Entwicklungsstatus von unserem Experiment an und stellten Fragen oder gaben Hinweise und Verbesserungsvorschläge. Am Ende haben wir das CDR mit einem Pass bestanden und konnten sehr viele konstruktive Hinweise für unser weiteres Vorgehen mitnehmen. Zur Belohnung ging es dann am Abend für unsere Gruppe auf eine Sightseeing-Tour durch Amsterdam.

Donnerstag früh 8:30 Uhr hörten wir uns zunächst Vorträge vom ZARM und dem SSC an. In diesen lernten wir, was wir während des Ballonstarts zu beachten hätten und wie der Start in Esrange durchgeführt wird. Danach gab es ein Buffet mit leckeren Sandwiches und Getränken. Während der „Ask-your-Expert“-Session kamen ESA-Experten aus den Bereichen Mechanik, Software und Elektrotechnik, mit denen wir uns austauschen konnten. Nachdem wir alle unsere Fragen gestellt hatten, nutzten wir unsere Freizeit am Nachmittag, um in das Museum „Space Expo“ zu gehen. Das Museum befindet sich direkt am Eingang von ESTEC. Dort ausgestellt waren z.B. ein Triebwerk der Ariane 5 sowie auch Mondgestein und vieles mehr.

Am letzten Abend gab es dann für uns einen schönen Abschluss: die ESA lud alle Teams von BEXUS zum Abendessen ein. Bei guten Getränken und leckerem Essen lernten wir die anderen Teams besser kennen. Sie kommen zum Beispiel aus der Schweiz, Schweden, Polen, Italien und Rumänien. Dabei lernten wir viel Interessantes, nicht nur über die jeweiligen Projekte, sondern auch über das Leben als Student in diesen Ländern. Freitag früh ging es dann für unsere Gruppe zurück in die Heimat. Der Aufenthalt in ESTEC war wundervoll und hat uns viele großartige Eindrücke, Freude und Spaß gegeben, die wir noch lange in Erinnerung halten werden.

Corona also left its mark on the S Cephei team. In spring 2020, we were informed that the REXUS campaign would unfortunately have to be postponed by one year. This was sobering news, as the experiment was already well on its way to being operational. But due to the advanced state of development of the experiment, ZARM from Bremen offered us the opportunity to test the experiment in their drop tower before the actual rocket flight and thus already collect first scientific data.

The Center of Applied Space Technology and Microgravity (ZARM) is one of the organizers of the REXUS/BEXUS program. The institute has a 146 m high drop tower in which experiments can be exposed to microgravity for up to 9.8 s. This short time is suitable for our experiment, since the alignment process of CNTs (carbon nanotubes) does not take much longer than a few seconds at certain power parameters. Although we have to limit ourselves to half of the chambers due to the short microgravity and limited electrical power, the high repeatability of up to two flights per day made the drop tower campaign a welcome opportunity to perfectly prepare the experiment for flight in the sounding rocket in Kiruna.

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The campaign ran from May 10 to 22, 2021. The experiment was already sent to Bremen the week before the campaign. The team members Robin, David, Jonathan and Joshua then followed the experiment to Bremen on May 9. We were accommodated in apartments of the 7THINGS-Hotel, which is centrally located on the university campus and only 5 minutes away from ZARM.

The first week was scheduled for testing and integration of the experiment.
The PoC (Pillars of Creation) system, the electronics standard developed by STAR, had already been tested for functionality prior to the campaign, but had never actually been used. Patience had to be maintained here, as commissioning was delayed due to sometimes unknown problems. Due to PoC's modular principle, troubleshooting required a certain degree of precision, but at the same time, any errors found could be fixed in a very short time by replacing the damaged module. When the hardware and software were finally ready for use, nothing stood in the way of installing the PoC stack. The experiment was controlled via the ZARM ground station, which is in direct contact with the capsule inside the drop tower.

In addition to working on the project, there was of course time to visit the city of Bremen. In addition to impressive architecture, Bremen's old town also has some natural retreats to offer, such as the meadows and green spaces along the Weser River. The campus of the University of Bremen also offered the opportunity to relax with a visit to the nearby campus lake.

The second week in Bremen was the flight week. We started on Monday with the calibration of our drop tower capsule, in which the S Cephei experiment was installed. The center of gravity of the capsule was determined with a special measuring device and brought to the desired position by attaching mass pieces. If the center of gravity of the capsule was not exactly in the middle of the capsule, rotation would occur during the fall, which could have fatal consequences.
For a drop tower flight, our experiment was first installed in the drop tower capsule, which also contained an additional on-board computer for power and communications. This capsule was sealed airtight by an outer shell and then moved to the inside of the drop tower. Inside the tower is a very large vacuum chamber, which consists of a room on the first floor and the actual drop tube. The lower room contains the launch and recovery equipment. Our capsule was lifted onto the catapult at the bottom of the drop tower and then the vacuum chamber was evacuated. Since this process takes about 90 minutes, there was enough time to establish communications with our experiment from the control center. Once the chamber was pumped empty of air, the hydraulically operated catapult could be preloaded. After that, it was up to us to launch via the ground station. The catapult accelerates the capsule with up to 35g, while the on-board computer of the capsule simulates the signals of the REXUS rocket and can thus control our experiment. After about 9 to 10 seconds, the capsule gently lands again in the recovery container. This container, filled with damping Styrofoam beads, can swing over the launcher after the catapult shot and thus catch the capsule again. As soon as the chamber pressure was equalized again, the capsule was lifted out of the catching container by a crane and we could immediately evaluate all data. However, due to a live video transmission from a camera, it was already possible to observe the alignment process of the CNTs during the flight.

We had already extensively tested various parameter combinations in our experiment setup in Dresden as a reference and were thus able to set up a precise plan with the experiments to be performed at ZARM. The first launch was actually scheduled for Monday afternoon. Due to difficulties with the capsule's on-board computer, we eventually had to postpone the first flight until Tuesday. During this particularly exciting first flight, our experiment worked smoothly. On the second flight of the day, however, unexpected complications arose. Already during the evacuation procedure, it turned out that the communication via WLAN was heavily lossy. Even a restart of the communication systems could not solve this problem. But it got even worse when, during our routine test run, an erroneous command corrupted the program. Recompiling the program and copying it to the on-board computer failed because of the weak connection to the capsule. This was due in part to the fact that the catapult was already in the cocking process and thus the capsule had disappeared into the tube of the catapult, which did not improve the quality of the connection. The catapult may remain tensioned for a maximum of two minutes, because otherwise the hydraulic oil would become too hot. All attempts to get the experiment ready to fly failed during this time, so we had to start the flight without a running experiment.

This failure made us realize that we should not take the time before the launch lightly either. From then on, before the upcoming flights, the software was copied to the on-board computer with Ethernet cables and the test run was done with the catapult untensioned and only with a good connection.
With this lesson learned, we were then able to perform two more flights each on Wednesday, Thursday and Friday. Particularly exciting and impressive for us were also the acquired insights into the technology that makes the drop tower operation possible. Among other things, we were shown and explained the catapult equipment located several meters below ground. In addition, we were able to take the elevator up to the top of the drop tower, from where we had a great view over the flat Bremen countryside.

In total, we were able to perform seven successful flights, each with two different experiment configurations. This result has definitely exceeded our expectations and is thus a complete success! All recorded videos of the experiments have to be evaluated now, and we are currently testing different software solutions for tracking the individual CNT particles during the alignment process. The capsule's on-board computer also recorded some flight and performance parameters during the flights, which means we now have even more data to optimize our systems for the Kiruna flight.
During the campaign, however, we not only gained scientific knowledge, but also gained many skills in terms of conducting such a campaign. The biggest insight for us is that you can never do too much testing in advance.

The departure went as planned and on Friday evening the IC in the direction of Leipzig departed punctually from the main station in Bremen. On the train we could use the several hours of travel time to reflect on the eventful stay in Bremen.
However, there will still be some work to do before the campaign in Kiruna. For example, the electronics still have to be tested for their thermal behavior in a vacuum, the ground station has to run without errors, and the lighting of the chambers has to be reworked. In addition, there will be small quality-of-life improvements on the mechanics side and then nothing should stand in the way of a successful start in Kiruna.

Finally, we would like to thank ZARM again for their support both with REXUS and with this campaign. Without you all this would not have been possible! The drop tower campaign was very valuable for us and our experiment. We would also like to thank all of the staff for their support during any complications. We are very excited to be back at ZARM during the upcoming Benchtest week and to see all the people again.

This year's REXUS/BEXUS Student Training Week took place from February 10th to 14th at the Esrange Space Center in the far north of Sweden, witch we, members of the S Cephei Team, participated. Two weeks before was the deadline of the first version of the SED (Student Experiment Documentation) in which we presented a draft of our experiment. Freed from the burden of the deadline, the anticipation of the Training Week for the team members Alexander, Robin, David and Felix began.

The journey to Esrange on February 09th was by plane from Dresden via Frankfurt (Picture 1) and Stockholm to Kiruna. Luckily, we just made it out of Frankfurt before the storm Sabine hit and the airport was closed. From Frankfurt, a lot of other teams and employees of the organizing structures accompanied us already. The flight over the North Sea had the expected stomach-churning effect.

Arriving in Kiruna, a transfer service drove us the last 40 km to Esrange, where we got our room keys and security passes at the entrance and then finally, after a short midnight snack, fell asleep.

For the much too short night we were rewarded by the culinary pleasure of a heavenly breakfast. At this point I would like to thank the kitchen team, who delighted us 3 times a day with the best warm meals, on behalf of everybody. Day 1 of the Training Week started with a few introductory words on safety and rules of conduct, before we were introduced to some important topics, including Systems Engineering, Requirements and REXUS Flight Mechanics. These lectures were interrupted by a couple of coffee breaks, where we had the chance to exchange ideas with the other teams and to meet some people from the Selection Workshop. In addition, there were presentations of all REXUS teams, where the experiment and possible influences on the experiments of the other teams were roughly discussed.

The 2nd day started after an obligatory morning meeting with a round trip over the Esrange area. We were shown the local museum (Picture 2), where some of the defining moments of the Esrange Space Center are exhibited (highly recommended!).

Afterwards, we went to the Balloon Pad, where we witnessed the launch of a small altitude research balloon, before we were shown the preparation halls for the REXUS rockets for motor and payload integration. At last, we went to the launch tower of the MEXUS rockets (Picture 3) and on our way back, we passed the REXUS Launcher.

It was still quite warm with -8 °C for a February day in Esrange, but after this spectacular roundtrip our fingers and feet were happy about the warmth in the Dome, where the lectures continued afterwards. Lectures on BEXUS systems were on the schedule, but in the afternoon we had our PDR, which we had been preparing for since the SED deadline. The board consisted of experts from a variety of disciplines and institutions. Members of the ZARM (Zentrum für angewandte Raumfahrttechnologie und Mikrogravitation) and ESA (European Space Agency), as well as MORABA (Mobile Raketen Basis) asked questions after a 20-minute presentation from us and explained weaknesses in our experiment design and our development schedule. All in all, the PDR was a success and we were able to take a lot of input for further experiment development. In the evening there was a teambuilding session, where we built a Lego model of a space transporter under certain rules (Picture 4). Ten teams were put together, which then competed against each other. A great opportunity to get to know other team members a little bit closer and to build new bonds.

Now that we had the PDR behind us, we could look forward to the rest of the week in a more relaxed manner. On Wednesday we had some subsystem specific topics on the agenda. Among other things we were introduced to possibilities and approaches to solve common problems in the design of the flight software and to improve the thermal experiment design. Many helpful tips, especially on open source software, will help us to improve our experiment. In the afternoon, project and risk management were on the agenda. After all, a space project consists not only of calculations and design, but also of an organizational part.

In this respect we continued with Outreach on day 4. An important part of the RX/BX projects is that teams try to find partners in the industry, in order to enable the development of the not always cheap projects and to guarantee the financing besides the help from the DLR through ZARM. In the afternoon there was another important appointment on the agenda, the "Ask the experts" session. Here we were able to address questions that were still open after the lectures or questions that had arisen from the lectures to a number of experts from the various disciplines. Thanks to their commitment the last problems were solved.

The last day was mainly devoted to organizational matters concerning the upcoming tests and the final mission campaign in March 2021, with the Critical Design Review scheduled for June, by which time the experiment design must be finalized. This will be followed by the Integration Progress Review at the end of August, before the system tests (Vibration test at ZARM, Benchtest at MORABA and finally the Spin & Balance test in Esrange) complete the qualification phase. In the afternoon we visited Kiruna and the Ice-Hotel (Picture 5) nearby. With a great farewell dinner (pulled pork of reindeer), where everybody had a lot of fun, the last days were reflected and with a final visit in the sauna the training week came to an end.

Departure started very early in the morning of Saturday. Two buses brought us back to Kiruna to the airport (Picture 6), from where we went via Stockholm and Munich back to Dresden. Most of the teams were said goodbye to in Stockholm and the last German teams left us in Munich.

Back in Dresden we were looking forward to our beds to catch up on the sleep we missed. The next few days were spent processing all the information. The participation in the Training Week was a great experience, for us participants and for the entire team.

We would like to thank everyone who made the Training Week possible, who patiently answered our questions and who provided us with a lot of input for the upcoming CDR.

Text: Felix Scharnhölz

Im November haben Frederik, Lucas und Karina aus dem Star-Team ein neues Projekt für REXUS vorgestellt und im Dezember die Bestätigung für die Förderung des DLR erhalten.

REXUS ist das Äquivalent zu BEXUS, bei dem diesen Oktober schon zwei andere Star-Teams gestartet sind (Gamma-Volantis und Ooxygen). Es ist ein Projekt für Studenten, das vom DLR und der SSC ins Leben gerufen wurde. Die Studenten bauen ein Experiment und dieses wird mit einer Höhenforschungsrakete in Schweden gestartet und verbringt ca. 2 Minuten in Mikrogravitation, bevor die Rakete sich wieder in Richtung Erde bewegt.

Frederik, Lucas und Karina haben unser Experiment S Cephei (Suspension of Carbon Nanotubes under dieelectrophoretial Influence) vorgestellt, an dem gerade 10 Mitglieder arbeiten. Unter Mikrogravitation soll der Ausrichtungsprozess von Kohlenstoffnanoröhrchen(CNTs) untersucht und dokumentiert werden. Die CNTs werden mittels Dielektrophorese ausgerichtet. CNTs können die thermischen, elektrischen und mechanischen Eigenschaften ihrer Trägermaterialien gezielt beeinflussen. Sie können daher zum ESD und EMI-Schutz, für Sensoren, Aktuatoren und zur Armierung eingesetzt werden.

Mit der Untersuchung des Ausrichtungsprozesses der Kohlenstoffnanoröhrchen unter Mikrogravitation tragen wir nicht nur zur Material-, sondern auch zur Grundlagenforschung bei. An der TU-Dresden wird derzeit an der Ausrichtung von CNTs geforscht, was sich sehr gut zum Vergleich unserer Ergebnisse mit terrestrischen Versuchen eignet.

Bis jetzt ist die grobe Auslegung unseres Experiments fertig und im Februar geht es dann zum PDR (preliminary design review) nach Schweden. Unsere Experimenteinheit besteht aus Behältern, die mit einem Fluid und den CNTs gefüllt sind. Mit Hilfe von Kameras wird der Ausrichtungsprozess beobachtet. Durch die Viskosität des Fluids kann die Ausrichtungsgeschwindigkeit gesteuert werden. Außerdem hat das Elektrische Feld, sowie Elektrodengeometrie, Spannung und Frequenz, wie auch der CNT-Anteil und die CNT-Art einen großen Einfluss. Die Ausrichtung der CNTs in en Behältern findet nacheinander statt und dauert etwa 10-30 Sekunden pro Behälter. Das Experiment muss durch eine einschließende Metallhülle vor elektromagnetischer Strahlung abgeschirmt und zusätzlich thermisch isoliert werden. Ein Fluidabsorber dient dazu, mögliches austretendes Fluid aufzufangen.

Unterstützt werden wir vom ILR durch Teststände, Werkzeug, Materialien und natürlich auch der fachlichen Expertise der Mitarbeiter. Außerdem erhalten wir die REXUS-Förderung des DLR und hoffen auf die Zusammenarbeit mit einigen Sponsoren.