A geodesic sphere is not two domes put together. If you did that, you'd have two center rings, and the 'sphere' would actually look ovoid. A sphere is globular, and using the Sonostar hardcore geohubs, you can make a sphere as easily as you can make a dome. To get the calculations, I suggest you go to Desert Domes website. Be sure to subtract the 2.28 inches from each strut length, to account for the width of the hubs. The smallest you can go with the Sonostar hubs is a 2' radius or 4' diameter 2V.