The next milestone on the road to the CHAOS launch is completed. On July 30th, two experts from ZARM visited us in Kiel to check on our integration process. We told them about the changes we have made since the CDR in Nordwijk and shown them our assembled instrument. The successful integration took place around two weeks ago, where we assembled the sensor head as well as the electronics to form a successfully measuring instrument. We are currently running a lot of test measurements to fully understand the instrument since it is the first time that an instrument-design as such has been integrated.
This current progress was presented to the experts from ZARM who were happy with the status. We hope to get the official pass soon. Then, the next step is the thermal vacuum test and the EAR (experiment acceptance review) at ZARM in Bremen, Germany in the first week of September. Until then, we will finalize the integration process and continue with the testing to minimize errors. Stay tuned for the journey!
From 15th to 17th May 2024, we went to ESTEC (European Space Research and Technology Centre) in Noordwijk, Netherlands. There we had our CDR (Critical Design Review). Again, we presented progress we made on our experiment to the review board, which was made up of experts from DLR, ESA, ZARM and SSC. Even though the board had some useful comments and tips for us, we passed the review, and our experiment design was accepted. Now, we can focus all our efforts on integrating the CHAOS instrument. The next milestone will be the IPR (Integration Progress Review) at the end of July. Two experts from ZARM will visit us in Kiel and inspect the integration process.
Although it was an exhausting couple of days, we had a lot of fun in the Netherlands and used the time to explore the cities of Leiden and Amsterdam. Stay tuned for more information on CHAOS!
The heart of our experiment CHAOS is the Cherenkov detector. High energy particles travelling through this detector will create photons and because only few photons are created, a Photomultiplier Tube (PMT) is needed to detect them. This makes the use of High Voltages (HVs) necessary to operate the PMT and poses a security risk for our experiment. During the BEXUS balloon flight CHAOS will be exposed to low pressure environments. The combination of high voltages and low pressures can lead so-called corona discharges which could possibly harm the experiment. The easiest way to mitigate this risk is to place the experiment inside a pressure housing which ensures the same ambient pressure as on ground.
Here you can see the CHAOS pressure housing. It consists of an aluminum base plate on which a die-cast aluminum box is screwed. We use two additional U-profiles which press the box onto the base plate.
But we cannot simply put our pressure housing onto the BEXUS balloon. First, we have to prove that our design really works. This is why we performed several tests:
In a first step, we inflated our pressure housing with a tire inflator. Maybe not the most scientific way, but it worked. Sometimes scientists have to be creative. We were able to show that our pressure housing has no problems to withstand an additional pressure of 1.2 bar. During the BEXUS balloon flight the maximum pressure difference between the inside and outside of the pressure housing can be 1 bar.
But that was not enough. We decided to put our experiment in the vacuum chamber at our university to perform a professional vacuum test. For the test we placed a pressure sensor inside the pressure hosuing as seen in the following pictures:
The pressure housing was put in the vacuum chamber which was then evacuated to a pressure of 0.1 mbar. We left the pressure housing inside the vacuum chamber for a total of four days. The results can be seen in the following plot:
The red curve is the temperature inside the pressure housing and the blue curve the pressure. The big spikes in temperature and pressure are caused by the heating plate inside the vacuum chamber which we turned on for several hours. The measured pressure was corrected for the temperature using the ideal gas law. This is the green curve. We can see a linearly decreasing pressure. This leakage was expected because a perfectly airtight pressure housing is hard to build. But we only lost around 100 mbar in four days. This is totally acceptable because the BEXUS balloon flights only last several hours. To quantify our results, we performed a linear regression on our pressure measurements. This regression was then used to calculate a leakage rate of around Q = -0.003 mbar*l/s.
We are very happy with the results of our tests. Hopefully, they will convince the board of experts at our Critical Design Review (CDR) as well. The CDR will take place at ESTEC in the Netherlands in May. So, stay tuned and follow us on our journey!
