Since September 2020 a group of members of the student association ÆSIR was delegated the task to design and build a stratospheric probe with the task to record a video as of a commercial request from a Swedish media production company. The client was the Swedish food brand “Eldorado” and the task was to record a package of fresh tofu hailed to 35000 meters by a scientific weather balloon. Non of us had any previous experience in designing high altitude probes and to make the construction as light and easy to work with as possible the material was chosen to polystyrene, what in Sweden is more commonly known as “frigolit” or “cellplast”.

A conceptual drawing was deciding on, with two carbon fiber ribs to support the package of tofu with the ribs protruding out on the back of the box to support counterweights, two cameras mounted on the front to record the tofu and one camera facing upwards to record the balloon bursting when reaching the top altitude. Inside the box a battery was mounted to charge the cameras during flight and as well test hardware for the upcoming rocket project Mjollnir, including one GPS, temperature sensors and hardware for sending telemetry data live to the ground station.

The construction went quite straight forward with polystyrene being a soft and easy material to work with, allowing for both drilling with tools and easily cutting with knives. Drilling the long vertical holes for the supporting ropes was a bit of a struggle, but with the help of the mechanics at the plasma and fusion lab next door and their pillow drive the holes were done in a moment. Cameras were ordered and delivered and experiments with optimal camera angles were carried out.

When the carbon fiber parts were ordered and received we built the support structure for the tofu with some epoxy and the carbon fiber rods. Meanwhile the electronics team were designing their platform to support the internal electronics.

Approaching launch day the probe was painted, electronics fitted and cameras mounted. Center of gravity and all-fly-weight was measured and within limits with some counter weights added. The launch location was in western Sweden somewhere close to the town Malung where we spent the night before launch. Batteries were charged, electronics tested and last checks carried out. 

The early morning was frost filled, with a couple of minus degrees until the sun rose. One hour drive later, towards the Norwegian border on roads way too rough for my non-terrain car, we were all gathered at the location where we met the responsible team for the balloon, as that was carried out by a separate company. Our probe was assembled, Eldorado logos painted, cameras armed and the balloon was slowly filled up with hydrogen. Some time later we were all ready for lift-off. The cable from the balloon was attached and slowly the assembly was hailed out until the only grip there was left was on the box itself, pulling hard towards the sky. When released it ascended fast across the three tops with the airborne drone recording it’s fly-by. 

The hunt began. Live data was received from the onboard telemetry system and the altitude was increasing fast. When we lost contact with the telemetry we got support by a nation wide system of ground based receivers that could track its progress with help from the onboard system. Cars back on the road to get as closed as we could. Some hour later and 150 km further away the balloon was on the way down under it’s parachute. The radio contact was lost some kilometers above the ground with a trajectory dangerously close to the big lake Siljan. Thanks to another team with hand held receivers the balloon could be tracked down just a few hundred meters from the shore line, in the forest close by a small road beside a local village.

The probe was found some 5 meters up in a three with the parachute way up in the three top, but thanks to a local farmer and his ladder we got it down after some struggle. The internal battery did for some still unknown reason not charge the cameras, so the video clips were not as long as planned for, but one camera made it all the way to the peak of the flight. The shots were extracted from the cameras and the results almost mind blowing. 

Written by Anton Vannesjö, ÆSIR, December 2020.