Issue 11/23

Rise and fall of a weather balloon

Jürgen Beckmerhagen

Sunday morning in Ambach on Lake Starnberg: 22 degrees, bright blue sky, white clouds drifting leisurely south-eastwards in a light wind. Glorious weather. Ideal weather for flying. The Rosenbruch family has an exciting day ahead of them on this 4 June: son Ilian is planning to launch his weather balloon, which he built himself, to round off his year eight project. The balloon, parachute, probe and helium bottle are loaded into the boot. Father, mother, brother and sister are also there. The destination is a meadow in nearby Münsing.
Alongside politics and football, the weather is a widely discussed phenomenon that many people think they understand, but few really comprehend. This realisation had already prompted Ilian three years ago when he made the weather the subject of his project in year eight. He is now delving deeper into the topic on a scientific level.
On the websites of the company Stratoflights and the Ludwig Maximilian University, Ilian came across instructions for building a weather balloon and a data logger. The technology required was clearly outlined: circuit board, sensors for temperature, pressure and humidity, data logger, GPS tracker with transmitter, two mini cameras, power bank and mounting materials. Setting to work with a soldering iron, Ilian assembled the elements into a complex system and stowed it in a polystyrene box.
He downloaded the required software from the Internet and soon realised that it was unfortunately not compatible with the current versions of the components. He found support in the forum, where other stratosphere voyagers hang out, and soon received the updated software code.
The system worked. The cameras recorded images. The data logger recorded the flight path, temperature, air pressure and humidity inside and outside the probe. The GPS tracker sent the exact position via satellite. Ilian's weather balloon was ready for launch.
A glance at the weather forecast showed today, Sunday, to be an ideal day. But anyone who thinks they can simply release a balloon into the sky has not reckoned with the conscientious German authorities. The Southern Bavarian Aviation Office was responsible for issuing the take-off permit, but required aircraft operator liability insurance and authorisation from the local public order office. And this only five days before the scheduled start date!
Liability insurance with coverage of five million euros was quickly found and taken out, but the person responsible at the Münsing public order office was not due to come into the office until Wednesday. But in return, he immediately approved Ilian's application on Wednesday. There were two working days left until the launch. Ilian submitted the authorisation and proof of insurance to the Southern Bavarian Aviation Office, pleaded for permission to launch and received it within 24 hours. Three cheers for officials who respond swiftly!
Arriving at the meadow near Münsing, Ilian checks the functioning of his probe once more. Despite repeated attempts, the data logger always switches off after exactly one minute. Ilian's blood runs cold. A short circuit? Is a component defective? At home, everything had worked according to plan. Then the crucial thought occurs to him: "The battery!". At home, he always had the data logger connected to a mains adapter. When Ilian switches on both cameras and the data logger together, everything runs as desired – even for more than a minute. Evidently the battery switches to power-saving mode when the power requirement is too low.
Ilian's sister and brother connect the probe to a small parachute via a ten-metre line and this to the balloon using a five-metre line. Ilian marks the probe with bright orange duct tape so that he can see the balloon better in the sky.
His father prepares the helium bottle for launch, while Ilian and his mother hold on to the balloon together. They ensure that it does not rise prematurely. The filling process takes 15 minutes.
The time has come. Ilian once more checks all the knots on the lines, the parachute and finally the probe. Everything is fine. He gives the launch signal. Slowly, the balloon and its cargo rise into the sky in front of the family. But immediately the next scare follows. The GPS tracker no longer sends position information. Can't believe it. «How am I supposed to find the balloon after it lands?», Ilian asks himself desperately. The balloon rises higher and higher. For the first eight to 15 kilometres, it crosses the troposphere at a speed of around five metres per second. The temperature drops to minus 60 degrees. Only commercial aircraft usually travel up there.
The balloon passes the tropopause and reaches the stratosphere. Here, the ozone layer filters a large part of the sun's UV radiation and allows the temperature to rise slightly. At this altitude, the radio probe at most crosses the path of supersonic jets. The balloon rises to 30 kilometres and in doing so reaches a diameter of ten metres, helped by the low air pressure. Below it, light clouds gleam in the bright sunlight, while infinite space appears on the curved horizon, as seen on the films afterwards.
At an altitude of 37 kilometres, the balloon has increased in size by a factor of 300. At exactly 37,553 metres, the envelope made of natural rubber material bursts and falls back to earth together with the probe and parachute. The GPS tracker continues to remain silent. All ten eyes of the Rosenbruch family scan the sky. No trace of the balloon.
Half an hour later, Ilian enters the coordinates of the launch site into an Internet application, which calculates the approximate landing site based on the weather data: Planegg, about 30 kilometres north of Münsing. Ilian and his father set off and find themselves in a place where it is impossible to see anything: lots of trees, privacy hedges, high fences, plots of land that are hard to see into. They see a white tarpaulin in a tree on the railway embankment of the S-Bahn line to Munich. It is not Ilian's balloon. Far and wide, there is no sign of the probe or the parachute in the sky – the hope of finding the probe is diminishing by the minute.
At this moment, Ilian receives a smartphone notification: his Bluetooth tracker is located in Forstenrieder Park, three kilometres south of Planegg. Originally developed to locate lost keys, Ilian added the tracker to the probe at short notice and forgot about it. They can use the app to locate the probe in a wooded area within a 30-metre radius. A red stripe shimmers through the trees. The probe hangs in dense branches. After a few strong shakes of the tree, it falls into Ilian's arms. Father and son celebrate their joint success. Next destination: return home to Ambach.
Ilian opens the polystyrene box and switches off the camera. He then connects the data logger to the PC. It has accurately recorded air pressure, humidity and even the flight path. Only the temperature sensors did not provide any data at times. Over the next few days, Ilian transfers the data into a table and creates the first graphs for the written part of the project.
Although he continues to be very interested in aerospace, Ilian does not intend to launch another probe into the stratosphere any time soon. «That was some adventure. I was pretty excited and at the same time was very afraid of losing the probe,» Ilian sums it up.


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