https://phys.org/news/2018-07-clever-recover-weather-balloon-radiosondes.html > Radiosondes are carried aloft by giant helium-filled weather balloons that expand as they rise through the air – in some cases to an altitude of 30 kilometers – until they eventually pop. A small parachute attached to the onboard equipment automatically opens once the maximum altitude has been reached, preventing the radiosondes from causing damage when they touch down. > The students' focused their attention on the parachute release. "Our system controls the exposed surface area of the parachute, directing the radiosonde towards air currents that will guide it to an accessible landing spot," says Hugo Cruz, a student in Environmental Sciences and Engineering. His classmate Lorenzo Donadio adds: "The main thing is to make sure the radiosonde doesn't end up on the side of a mountain, at the bottom of a lake or in some no man's land."