# Balloon Design for Mars, Venus, and Titan Atmospheres
## 4 Balloon Design for Different Atmospheres
### Balloons on Venus
Because of solar heat input, \(T_{\rm g}\) may then be higher than the atmosphere, as is the case for the Venus simulations. The state of neutral buoyancy and thermal equilibrium is complex due to all involved heat flows and forces and the balloon oscillations around this equilibrium state. The instability in case of more pronounced prolateness may be due to the increased surface area, affecting the heat flows, and the decreased \(A_{xy}\), reducing the drag. Both effects combined lead to increased balloon speed before and during the oscillations around float altitude, which in turn can cause instability. \begin{table}
\begin{tabular}{c c} \hline \hline Film area density (g/m\({}^{2}\)) = 176 (ZP \& OZP) & = 200 (SP) \\ Payload mass (kg) = 50 & Gas = Helium \\ Strength (kN/m) = 71 & Elongation (\%) = 7.0 \\ Solar absorptivity = 0.17 & Infrared emissivity = 0.56 \\ Permeability = \(\sim 0\) & Deployment altitude (km) = 49 \\ Float Altitude (km) = 55 & Thickness (mm) = 0.25 \\ Over-pressure (Pa) = 7000 (SP), 500 (OZP) & Drag coefficient = Variable \\ Diurnal cycle = Yes & Time step (s) = 1 \\ Start day of mission = & 1 (224.68 days on Venus) \\ Venting \& Ballast (kg) = No & Free lift (\%) = 12 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Venus aerobot parameters. Parameters are based on [43; 47; 50]. Figure 5: Altitude variation of the ZP balloons for different shapes with varying fineness ratio \(f\) in order to find the stable fineness ratio on Venus: (**a**) oblate (\(f\): 2–8) (**b**) prolate (0.1–0.8) (**c**) airship (0.1–0.8). Figures 6 and 7 illustrate the behaviour of SP and OZP balloons for the different shapes with varying fineness ratios. Similar to the ZP oblate balloons, both SP and OZP oblate shape balloons achieve stability for different fineness ratios. Also, in the case of prolate shape, unlike ZP, both SP and OZP balloons are able to stay afloat at all the fineness ratios. SP and OZP balloons allow higher than atmospheric pressure, and therefore, have a fixed volume at the float altitude, i.e., the volume does not increase or decrease with a change in gas and atmospheric temperature, and, hence, these balloons tend to stay afloat for long durations, irrespective of the configuration of the shape. Figure 8 presents the envelope mass and gas mass variation for ZP, SP, and OZP balloons at varying oblateness and prolateness. The envelope mass of ZP and OZP balloons are very similar as the envelope properties for these balloons are the same. The SP balloon envelope mass is heavier in comparison, as the envelope used has higher density in addition to a larger balloon volume required. The envelope and gas mass increase linearly with an increase in oblateness for all three types of balloons and can be seen in Figure 8a. For prolate and airship, the envelope and gas mass decreases linearly as the prolateness decreases towards a spherical shape (Figure 8b). For ZP and OZP to reach the same float altitude as SP, slightly less gas mass is needed. Next, the behaviour of different shapes of ZP, SP, and OZP balloons were compared with a sphere shape. A fineness factor of 3 was chosen for oblate shape, 0.6 for prolate shape, and 0.4 for airship shape as all three types of balloons are stable at these fineness ratios. Figure 9 presents the ascent speed variation for the three types of balloon and four different shapes. The balloon ascent speed increases or decreases in accordance with the variation in altitude and fluctuates around zero when the balloon reaches the stable altitude. After reaching the stable altitude, the balloon moves in the direction of the wind and only ascends or descends if ballasting and valving operations are applied to the balloon system. The flight behaviour of the different shapes varies. The prolate shape has the highest velocity while the oblate shape has the least velocity, for all three types of balloon.