Loon’s envelope used helium. To lift a 15 kg payload (electronics + batteries) plus a 15 kg envelope, the balloon required displacing ~30 kg of air. At 20 km altitude (pressure ≈ 50 hPa), the volume needed is:
Despite technical success, Project Loon was . The reason was not physics but business model. The original assumption—that balloon internet would be cheaper than satellites—collapsed when SpaceX’s Starlink began launching low-earth orbit (LEO) satellites at scale. google gravity balloon
Traditional weather balloons are : they have an open duct at the bottom. As gas expands (daytime heating, rising altitude), excess vents out. At night, the balloon contracts and descends. This is fine for a 2-hour radiosonde flight but disastrous for a 100-day mission. Loon’s envelope used helium