Originally Posted by
Recc
That would have been true a few decades back, but if you have onboard power (e.g. solar) , then you can use pumps and valves to inflate or deflate a separate bladder in order to adjust the buoyancy (and therefore control altitude) indefinitely. These are known as "air ballast" systems and have been used in research balloons since at least the turn of the century.
Ballonets for buoyancy control (reducing the need to jettison gas or ballast) go right back to the start of ballooning:
https://en.wikipedia.org/wiki/Ballonet
The ballonet was first described in 1783 by Jean Baptiste Meusnier, then a lieutenant in the French Army.
A ballonet is an air bag inside the outer envelope of an airship which, when inflated, reduces the volume available for the lifting gas, making it more dense. Because air is also denser than the lifting gas, inflating the ballonet reduces the overall lift, while deflating it increases lift. In this way, the ballonet can be used to adjust the lift as required.
Ballonets may typically be used in non-rigid or semi-rigid airships, commonly with multiple ballonets located both fore and aft to maintain balance and to control the pitch of the airship.