Take a 7-foot diameter helium balloon, a box of electronics, and let them go. What do you get?
Space! Well, almost. At 100,000ft (30km) and -50C, it feels awful close.
We've written a rather large tutorial set that documents ultimate failure - I lost the balloon and all the electronics! It's currently sitting somewhere in the plains of eastern Colorado. Learn from our mistake and checkout the High Altitude Balloon intro and the Sensor System, Flight Computer, and Radio System tutorial. We'll get the next tutorial in the set posted next week so check back.