Fly a DIY weather station to 30 km+ on a latex weather balloon. Capture pressure, temperature, humidity, GPS track, and live video while complying with local aviation rules.
In the US, unmanned free balloons are regulated under FAR Part 101. In the UK, CAA-mandated NOTAMs may apply. File a NOTAM request with your aviation authority and plan launch/landing zones away from controlled airspace.
Use a balloon trajectory predictor (e.g. habhub, CUSF) with your expected ascent rate (~5 m/s), burst altitude (30-35 km with 1600 g latex) and descent rate (~5 m/s on parachute). Rerun daily for 48 hours before launch.
Assemble an APRS (or LoRa) tracker with GPS. Test beacon rates — 1 per 60 s is usually enough. Set aprsfi or RadioLabs to push to your phone. For ground redundancy, also carry a cellphone GPS reporter that starts reporting below ~3 km on descent.
Mount the BME280 outside the payload box (sensor in free airflow); keep the Pi inside the insulation. Configure the camera for 1080p video + a timelapse still every 15 seconds. Write timestamps to SD so you can align with ascent data.
Use foam at least 25 mm thick on all sides. Tape handwarmers beside the GPS (it can cold-lock). Pad sharp edges so nothing cuts the shroud lines on descent. Weigh the fully-loaded payload and record it.
Fill the balloon to the neck-lift required for the chosen ascent rate (tables available online). Attach parachute above the payload so the balloon remnant cannot snag on descent. Release upwind of any obstacles.
Drive towards the predicted landing zone but keep at least 15-30 km behind during ascent (safety from burst debris). Listen/track live. After landing, approach carefully — payloads may end up in trees or water.
Plot altitude vs temperature — you should clearly see the tropopause inversion and warming into the stratosphere. Stitch the timelapse into a 60 s video.