Two Techniques for Controlling Altitudes of Lifting Balloons

Two techniques have been proposed (see figure) for controlling the buoyancies and thus the altitudes of robotic lifting balloons (aerobots) that would carry scientific instruments for exploration of Mars. Buoyancy-control techniques other than these have been, variously, used on Earth and/or proposed for use in exploring planets other than Mars, but have been found inadequate for providing the requisite altitude control in the thin Martian atmosphere and at the low nighttime Martian surface temperature. The proposed techniques could also be used on Earth; for example, for carrying instruments to perform surveillance, monitor weather, or measure pollution.