The Hunt

A rainy day leading up to Christmas. But the prediction was promising. The probe was expected to land near Schwäbisch Gmünd which is just a mere 50 kilometer drive. Felix was unfortunately busy with school, so I went on my own. Near the main station of Schwäbisch Gmünd, I found a parking spot and got my gear ready.

The prediction places the landing site of the Probe near Schwäbisch Gmünd

I just had to stick my antenna out of the window, and there the probe was. Altitude was 33 km above the ground, and it was still climbing. 6 minutes later, the balloon burst. Using the position at the burst point, I ran the predictor again: The probe was predicted to land near Pfahlbronn, about 15km to the North-West of Schwäbisch Gmünd. I started driving. The roads were small and winded their way through the forest. Visibility was poor. Hence the progress was slow.

En Route: The sun was not exactly shining.

When I reached Alfdorf, I decided to stop to acquire the signal of the probe again, and track it to the ground. Good choice, as the probe had already dropped to 5200 m. And the signal looked good.

The Signal of the Probe looks nice and strong

Decoding worked until an altitude of 780m. 10 seconds later I had lost the signal also.

[ 9361] (M1453318) (2017-12-21) Do 13:09:56.640 lat: 48.94878 lon: 9.54362 alt: 800.8 (d:4.4) vH: 10.1 D: 84.9° vV: -6.1 DOP[16,6,9,23,7,13,5,2,30,29] 1.8
[ 9362] (M1453318)
[ 9363] (M1453318) (2017-12-21) Do 13:09:58.640 lat: 48.94877 lon: 9.54385 alt: 783.4 (d:4.5) vH: 8.7 D: 99.4° vV: -7.1 DOP[16,6,9,23,7,5,2,30,29] 2.0
[ 9364] (M1453318)

I tried to regain the signal — and here it was again strong and clear. About 30 seconds later, the decoder spit out telemetry data. But what was that ? Now the probe was in 11,5 km height and over Poland. And the signal came from the rear and no longer from the side. Not plausible. The GPS receiver of the probe must have gone mad.

[ 8949] (M1723428) (2017-12-21) Do 13:10:58.360 lat: 48.66929 lon: 14.09622 alt: 11794.9 (d:3.5) vH: 37.5 D: 172.1° vV: -9.9 DOP[5,7,13,6,23,29,9,16,2,30] 1.8
[ 8950] (M1723428) (2017-12-21) Do 13:10:59.360 lat: 48.66897 lon: 14.09630 alt: 11783.8 (d:3.6) vH: 37.2 D: 171.2° vV: -11.4 DOP[5,7,13,6,23,29,9,16,2,30] 1.8

I decided to go the location from where I had received the last consistent telemetry. The GPS coordinates brought me to Sechselberg. As there was a construction on the way, I could not directly reach Sechselberg and had to detour. Consequently, It took roughly an hour to get there instead of 35 minutes. And as the battery capacity is limited, time is of the essence.

Once I arrived in Sechselberg, I was able to reacquire the signal of the probe, but could not decode it. Armed with a radio, a mobile phone for google maps, and a directional antenna, I made my way through the rain and the fog towards the point from which I had received the last GPS coordinates of the probe. On the way, I discovered a sign warning of a battue. It looked a bit worn — but then again who knows. And those hunters, they often are of age and have bad eye sight. Then barking, and the silhouettes of 2 dogs and 2 persons began appearing in the fog. It turned out to be a couple taking out their dogs. They did not know of an ongoing battue and also had not seen a weather probe, so I pushed on.

As someone, who lived most of his life in the city, this looked a bit eerie to me. And a sign warning about a battue did nothing to lessen that. The signal was however coming in strong…

A couple of minutes later, I saw the probe in a meadow.

The probe with the parachute, a threaded rope, and the rest of the balloon in the back

The parachute and the rest of the balloon

Post-Flight Analysis

Even though the balloon burst in more than 35 km altitude, the flight distance was shorter than predicted. The distance between actual and predicted landing point is about 30 km.

When I received the last telemetry data in Alfdorf, I was 20 km away from the probe. After that, the probe continued for about 40 seconds and 200m.

I could also solve the secret of the mysterious telemetry. I realized that the probe ID is different. I had received telemetry of a probe about 320 km away that used the same frequency and was launched at the same time in Kümmersbruck (see also https://radiosondy.info/. Probe Id is M1723428).