BEXUS Projects of Kiel University
SETH – CHAOS – FaNS – TANOS – ADAM – PING – FRED
We’re excited to announce that Nicolas, our team lead, has officially submitted his Bachelor’s thesis titled “Implementation of the Attitude Determination System (ADS) of the Scintillation Event Triggering Hodoscope (SETH).”
His work on the ADS will play a crucial role in advancing the SETH project. Congratulations from the whole team, Nicolas — we’re proud of your dedication and hard work!
After the CDR, we decided to revise the design of the photodiode holder so that it could be 3D-printed as a single piece. This change simplified the assembly process and improved the structural integrity.
We completed the first assembly and fit check of the sensor head – a big milestone for the team! The 3D-printed parts fit together nicely overall. May we present the SETH frog 🐸
However, we did have to slightly enlarge the holes on the “front feet” to make it work properly.
Next up: we’ll need to reopen the shells (the silver parts that hold our crystals) to solder the coaxial cables to the photodiodes, which are glued onto the BGO crytals. Step by step, it’s all coming together!
Some impressions from CHAOS’s trip to CERN. We got the chance to perform measurements in the CERF radiation field which is supposed to recreate the radiation environment at commercial flight altitudes. Although there were some problems with the particle beam which is used to create the radiation field, we were finally able to take our measurements during the final night of our stay. Now, we are looking forward to evaluate the data.
Yesterday, on May 15th 2025, we had our Critical Design Review. After 20 minutes of information packed presentation by us we had a discussion about our design, requirements and general SED content.
During the presentation we showed around our preamplifier, ADC and NMRENA boards which represent the signal flow from the detector to the SD Card. We also presented the wrapped BGO scintillation crystal in its holder, complete with the mounting mechanism of the photodiodes that go on top and below the BGO holder. Here, the board gave some input on possible design improvements for easier and more light-weight fabication and mounting. After the review the experts said that they were happy to see the progress we made in real life instead of just pictures on a slide.
The board critisised our thermal design requesting more information and more calculations. However the overall progress of the project seemed to be satisfactory for the reviewers and we get to go ahead with finishing up fabrication and moving on to sub-system wise integrating and testing of our parts.
Today it’s time to say “Goodbye, CDR!” and head home. We are set to arrive in Kiel at 17:22 after traveling via Amsterdam and Osnabrück.
Today is the day that team SETH is set to join up in Leiden, near ESA’s ESTEC facility in Nordwijk!
The route from Kiel to Leiden should only take about 7h20 by train. However with a signal failure and damage to the overhead line in Hamburg and a cancelled train from Osnabrück to Amsterdam, the journey is all but straight forward. After getting off in Osnabrück HBF at short notice, we caught a local train to Hengelo. The Netherlands welcomed us by canceling the next few stops of our newly made up route due to an broken train on the track.
After checking the next options, we chose an Intercity train going to Amsterdam and connecting to an IC heading to Vlissingen via Leiden Centraal! We arrived in Amsterdam with a delay of about 25 minutes, missing this train.
Thankfuly there was another train departing for Rotterdam over Leiden. With a total travel time of 10 hours and 10 minutes we will finally make it to our destination at 19:13.
The next Review on our journey is the Critical Design Review, or CDR for short, from 14th May to 17th May. There, the reviewers will critically review the proposed design. After the Preliminary Design Review (PDR) in February, this is the second and last of the two design reviews.
We have submitted the second version of the Student Experiment Documentation (SED) for the review and will give a 20-minute presentation on the changes we have made since the last review.
Once this review is approved (fingers crossed), we will receive the official go-ahead to begin manufacturing all parts. We will start with single-part testing before gradually integrating and building more complex sub-groups and sub-functions. Each will be tested until the Integration Progress Review (IPR), where the initial functionality will be assessed by the reviewers visiting our institute.
Am Dienstag Mittag, nach dem Essen in der Uni-Mensa, sind wir in den Botanischen Garten gezogen, mit Spaten, Hämmern, Pürckhauer, Tüten und Dosen, um Bodenproben rund um den Neutronenmonitor auszubuddeln.
Das Wetter der letzten Monate war trocken, sehr trocken. Vorher hatte es über ein Jahr durchgeregnet, die Böden ware also sehr feucht. Nun beginnen die oberen Horizonte auszutrocknen.
Der Neutronenmonitor war lange kaputt. Dann wurde das Zählrohr ausgetauscht. Danach war die Zählrate deutlich niedriger als vorher. Das ist zu erwarten, wenn der Boden mehr Feuchtigkeit enthält. Oder liegt es doch am neuen Zählrohr?
In rot ist die gemittelte (2σ=4h) Zählrate der Monitors in Amerika zu sehen
Die blaue Kurve zeigt zum Vergleich die Zählrate des Kieler Neutronenmonitors, der die Intensität der kosmischen Strahlung anzeigt.
Beide Kurven sind um den Einfluss des Luftdrucks (grün) korrigiert.
Man sieht, daß die rote Kurve in diesem Frühjahr im Vergleich zur blauen Kurve wieder ansteigt. Die Bodenproben sollen nun hergeben, genau wie viel Wassen jetzt im Boden ist, bis in 30cm Tiefe und bis zu 150m Entfernung vom Monitor.
Der Neutronenmonitor zählt Neutronen, die von der kosmischen Strahlung im Boden erzeugt werden, als schnelle Neutronen durch die Gadolinium-Hülle des Rohres fliegen, in der Röhre von einem Plastikmoderator auf Umgebungstemperatur gebremst, und endlich von einem ¹⁰B Atom im Geiger-Müller-Zählrohr eingefangen werden. Dabei etsteht ein α-Teilchen, das im Zählrohr ein Signal auslöst. Wenn Wasser im Boden ist, dann werden die erzeugten Neutronen schon dort gebremst. Langsame Neutronen werden von der Gadoliniumhülle eingefangen und machen kein Signal im Zählrohr. Also, je höher die Zählrate, umso trockener ist der Boden.
The next extraterrestrial BEXUS project SETH shall include a new module called SETHAT, to measure the magnetic and gravity field vectors. Of course, this needs to be tested on a weatherballoon mission. The launch was scheduled on Tuesday, April 1st, 11 o’clock, after we watched the forecasts for weeks, while the landing was firmly predicted in the baltic sea between Gdańsk and Malmö. Now, it would land between Rendsburg and Hohenwestedt, safely right in middle of Schleswig-Holstein, with a clear blue sky.
Prediction for a launch on 11:00 CEST from Kiel: Red dot: launch position, green dot Landing, balloon pops at 40km: explosion.
At 10 o’clock the press arrived to follow the launch preparations. The reporters were underwhelmed by the crowd of three students and one graybeard. But then, unexpectedly, Matti and his Nawi class came along, from the Ricarda-Huch-Schule. The crowd was there, and the class was immediately put to work. Inflating the balloon, calculating and watching the Helium pressure, giding the payload gondola. But the graybeard (me) immediately recognized the bad omen, that Matti’s arrivals induced: all three of Matti’s own Balloons landed off shore.
Matti’s students did a good job, though, the liftoff on 10:42 was prefect.
The Helium bottle went back into storage, we had a quick lunch, and soon where on the road to Schachtholm airport, close to the Breiholz ferry. We got a coffee and some icecream, waiting for the balloon to land on the runway in front of us. In any case, we could quickly get to either side of the canal.
The satellite tracker provides positions of our balloon every five minutes. It went to Wischhafen, a little further south than expected, but quickly came back north and turned west heading straight to the airport where we were sitting, almost exactly as expected. Even after the balloon popped, the satellite tracker was still providing positions, from heights up to 40km. Usually, there are no GPS solutions above a height of 20km from those surface trackers.
And those positions were rapidly going south, much faster than the forcasts predicted. Soon, we realized that it would land south of the river. Overhead of the Elbe, our box was still four kilometers high in the sky, … and then it turned west. It came down right in the water, close to Neufeld.
We were on the way to the ferry in Glückstadt, when we turned around towards Brunsbüttel and Neufeld. There was only one boat in the harbour, belonging to Hafenmeister Hein Claußen. We got on bord, heading towards the last coordinates submitted by the satellite tracker.
In the beautifull weather it was no problem at all to spot the payload of our mission.
The parachute was full of sand, serving as an anchor. The box was very slowly drifting towards Hamburg with the tide. The anchor kept the box upside down, the custom payload electronics on the bottom of the box was held high above the water line. It turned out that is it still fully functional.
The avionics (SIM trackers, datalogger, video camera) are all corroded beyond repair. Salty water and with the batteries still connected quickly destroyed those units. Only the watertight satellite tracker survived unscratched.
All three storage cards in the gondola were recovered and are readable. We have video from launch and until the battery run out at 35 km height. The card from the datalogger provides pressure, temperatures, further environmental data, and precise GPS coordinates. The later are the source of the flight track shown above. The SD-card in the Raspberry Pi bord computer faithfully recored the output of the SETH Attitude sensor, the 3Diodes cosmic ray detector and furher environmental data.
The mission is a full success.
Outside temperature got as low as -50°C. The electronics stayed above 0°C. The sensor temperature is shown here with a wrong calibration. The battery voltage was good until the end. When the pressure reached 800mbar on descent, the unit turned itself off, to protect the electronics against fatal transients on impact. The storage cards are particularly sensitive to transient power disconnections .
The comic ray count rates are highest at around 50 to 80mbar. This is called the Regener-Pfotzer maximum. (This pressure sensor is not rated for pressures below 10 mbar.) The colors denote various trigger conditions. The yellow line is the overall trigger rate.
The pulse height spectra for the whole mission. Each detector diode (A, B, and C) individually count about the same number of hits, with a broad spectrum due to variable path lengths in the sensitive volume. Coincidences for vertically aligned diodes A and B show a narrow sprectrum (blue line, purple dots), due to the contrained path lengths. Coincidences for diodes A and C (red line, green dots) detect particles from a zenith angle around 45°. The path lengths are longer, the spectrum is shifted to larger energy deposits. The projected area is smaller and the flux from that angle may be different. The dependence of the flux on the zenith angle depends on the height, which is not resolved in this picture.
This week, four members of the team travelled all the way from Kiel to Oberpfaffenhofen, Bavaria, to take part in the training week. Here we hear all kinds of lectures on all topics related to a space project. This includes for example mechanism design, implementation, system engineering but also outreach. Furthermore, we are guided through the huge premises of DLR and MORABA and get to know the other teams even better. We are looking forward to this great time and are grateful for the great experiences.
We will of course keep you up to date throughout the week, especially as our PDR (preliminary design review) is coming up soon. Stay tuned and follow us on Instagram at “seth.bexus”.
SETH was successfully accepted for the 16 cycle of the BEXUS programme! We are very happy about the acceptance and are looking forward to the new year. Many thanks to @germanaerospacecenter for this great opportunity.
Next up is the Preliminary Design Review (PDR) in February. For this, we are travelling all the way to the south of Germany and are going to Oberpfaffenhofen as a team to present our current status. We will have more meetings in the course of the year, which we will of course keep you informed about.
Finally, in autumn this year, we will head to Kiruna, Sweden, for the flight campaign, where SETH will conquer the skies!
