Aerial vehicle with a volatile fluid

An aerial vehicle comprising:

• a first inflatable element;
• a first mass of lifting gas contained within the first inflatable element;
• a lifting gas vent:
• coupled to the first inflatable element;
• and
• configured to vent lifting gas, in the first mass of lifting gas, from the first inflatable element to decrease a net buoyancy of the aerial vehicle;
• a second inflatable element coupled to the first inflatable element;
• a second mass of a volatile fluid:
• contained within the second inflatable element;
• characterized by a saturation-vapor-pressure curve that intersects an atmospheric temperature-pressure profile within an operational altitude range of the aerial vehicle;
• and
• configured to condense during an ascent of the aerial vehicle across a phase-transition altitude, in the operational altitude range, to passively reduce a net buoyancy of the aerial vehicle;
• and
• a controller configured to:
• access a target maximum altitude specified for the aerial vehicle;
• during the ascent of the aerial vehicle:
• before the aerial vehicle reaches the target maximum altitude:
• calculate a first ascent rate of the aerial vehicle;
• and
• estimate a predicted maximum altitude of the aerial vehicle during the ascent based on the first ascent rate;
• and
• in response to the predicted maximum altitude falling below the target maximum altitude:
• withhold activation of the lifting gas vent to withhold venting of lifting gas, in the first mass of lifting gas, from the first inflatable element.