Learned a lot even without the measurement data
The past few weeks have been a rollercoaster ride in many ways for the participants in the “OG goes Stratosphere” student project at Hochschule Offenburg: First, the planned stratospheric flight of their balloon had to be postponed several times. Later, conditions were ideal, the balloon launch went smoothly, and all systems functioned perfectly. Then, however, the GPS transmission suddenly cut out. Later, position data could be received again, and a probable landing site was determined. Despite an intensive search, nothing could be found on site due to the nearly jungle-like vegetation. But let’s take it one step at a time.
For months, the interdisciplinary team of ten students from such diverse fields as Maschinenbau, Biotechnologie and Wirtschaftspsychologie—led by Prof. Dr. Dragos Saracsan—had been preparing for the stratospheric flight. Literally at the last minute, a mirror for the tracking antenna was produced on a 3D printer to improve signal reception. After very little sleep, the group finally met early in the morning on June 17 at the Kehl-Sundheim airfield. There, they filled the latex balloon envelope with approximately 5,900 liters of helium and tested the contents of the payload capsule one last time: the data logger, which records GPS data, external and internal temperature, humidity, altitude, speed over ground, and pressure; the cameras; and the actual “passengers”—bacteria of the species “Bacillus spizizenii” (DSM618, Bacillus subtilis wild type), yeast cells, and mung bean sprouts. Studies of these organisms before and after the flight were intended to provide insight into the effects of the extreme, Mars-like conditions in the stratosphere on living organisms, in order to derive information for the construction of space stations or transport rockets.
At 8:37, the moment had arrived: The stratospheric balloon launched and ascended at a constant speed of less than four meters per second. All measurement and communication systems, including GPS and the LoRa radio antenna, were transmitting stable signals. About an hour later, at an altitude of roughly 12,000 meters, came the shock: The GPS module suddenly stopped transmitting position data. However, since the balloon had been moving exactly along the pre-calculated flight path up to that point and the other signals remained stable, the team members decided—after some deliberation—around 10:30 a.m. to head for the calculated target area.
And indeed: Just under three hours later, they were briefly able to receive GPS data there again, which confirmed their calculations of the flight path. The balloon had continued to expand as planned at high altitude, where air pressure is lower, and had eventually burst. The capsule attached to it had then descended to the ground on a parachute. However, the probable landing site determined using the GPS data was located in the middle of a hard-to-reach wooded area between Wasenweiler and Gottenheim.
Four days of intensive searching followed, using multiple antennas, directional microphones, and even drones. Using the tracking antenna, the search area was narrowed down to a radius of 50 to 75 meters. Nevertheless, the balloon debris and the 2.5-kilo capsule containing the measuring instruments remained untraceable in the rugged terrain.
“There are trees more than 30 meters tall standing very close together there. Presumably, the remains of the balloon and the capsule are hanging in one of the treetops, so we can’t see them from above or below,” explained Prof. Dr. Dragos Saracsan when the active search was finally called off. “But even though we lost the capsule and the samples, I draw a positive conclusion: Our students gained valuable practical experience in interdisciplinary collaboration, detailed mission planning, and working with measurement and communication technology as well as 3D printing. The search in the field, which lasted several days, also provided them with important insights—they learned a great deal even without measurement data.”
