Construction, Launch and Loss of a Solar Balloon

Today I wanted to share this “experiment” we carried out quite a few years ago (I hope that if we committed any crime, the statute of limitations has already expired!).

My friend Rodrigo Coca came up with the idea of building a balloon out of black garbage bags taped together with packing tape, so that under solar radiation the air inside would heat up and, as its density decreased, the balloon would rise. He summoned all of us friends and, over several nights (I was working at the Ávila wastewater treatment plant at the time), we got down to work cutting, testing, and taping garbage bags together. Naive as we were, because when the moment of truth arrived and we went out to the countryside to test it, the balloon generated so much lift that, helped by the wind, it snapped the rope we were using to hold it down (paragliding rope! not just any rope) and was lost. We tried to follow it for several kilometers, but in the end we lost sight of it because it rose so high that it disappeared from the sky. Given the time of day we tested it (11 a.m. on a summer day) and the fact that the balloon stays aloft as long as there is sunlight, the device probably ended its journey somewhere outside the Iberian Peninsula. The following summer we built a balloon about ten times larger in volume, but that one never even flew. We were all busier and busier and never managed to assemble the final cone. Maybe one day we’ll see it soaring through the skies. Maybe one day…

The balloon drifting away into the sky

The solar balloon 2.0