Fill with hydrogen (yes, H2, not helium, you can't get enough to waste apparently) ballast until just lighter than air and off you go. Cooling down at night, you dump ballast, warming up in the day you vent gas. Same process to control altitude to be in the layer with the optimum wind strength and direction.
If you enjoy sitting in an open basket for several days and nights, you can go quite a long way.
Thank you very much! Makes perfect sense when you explain it so clearly
