# Balloon Design for Mars, Venus, and Titan Atmospheres
## 4 Balloon Design for Different Atmospheres
### Balloons on Mars  
The atmosphere on Mars has a low density in comparison to those of Earth and Venus, which makes the balloon flight operation difficult on the surface of Mars. Mars also has extreme temperature variations (\(\Delta T\sim 100\) K and \(\Delta T/T_{min}\sim 50\) %) which increases the challenges related to the balloon flight. At low altitudes on Mars, the balloon flight is similar to flying in the Earth's stratosphere as pressure and density are similar, and, therefore, the performance metrics in terms of the balloon  
Figure 8: Mass variation of different balloon types at varying fineness ratio on Venus (**a**) Airship and Prolate (**b**) Oblate. Note that the lines for ZP gas mass and OZP gas mass are superimposed, as well as the lines for ZP envelope mass and OZP envelope mass. Figure 9: Ascent speed variation of different balloon types at particular fineness ratio (**a**) Zero pressure (**b**) Super pressure (**c**) Over-pressurized zero pressure. A fineness ratio of 3 is chosen for oblate shape, 0.6 for prolate shape, and 0.4 for airship shape. material mass per unit area and volume are comparable [50; 51]. On Earth, ZP balloons are typically flown at these altitudes, but due to the high temperature variation in day-to-night, these balloons are impractical in the Mars atmosphere, as they have to deploy significant amount of ballast in order to stay afloat, fact that the lifetime of these balloons brief, i.e., few days. This characteristic of ZP balloons makes them unattractive for operation on Mars as they have to carry extra mass, and in addition are not able to collect enough data 'geographically and temporally' [52] due to limited lifetime in order to justify the high cost of the mission. The two types of balloons that seem viable options for Mars are the SP and OZP. Over the years, a number of conceptual and experimental studies have been done for balloon missions on Mars [50; 51; 53]. In [17], the authors suggest that for lifting a 15.8 kg net payload mass (i.e., without gas tank), a balloon with a diameter of around 8 m would be required. While none of these studies have given a detailed analysis of different shapes for the balloon mission on Mars, they do suggest some important design parameters. Table 5 shows the parameters that will be used for simulating the balloon behaviour on the surface of Mars. Similar to the case of Venus, balloons will be aerially deployed to minimize the risks [52]. Figure 10 presents the behaviour of prolate, oblate, and airship shapes at different fineness ratios for the SP balloons. All three shapes of SP balloons reach the desired float altitude. In the case of oblate shape SP balloons, the time taken by the balloon to reach the float altitude increases with the increase in oblateness (increase in fineness ratio). As the oblateness increases, the cross-sectional area of the balloon increases, so does the drag, and due to the increase in drag, the velocity of the balloon decreases. Therefore, with the increase in oblateness in Figure 10a, the time taken by the balloon to reach the float altitude also increases. The behaviour of the prolate shape SP balloons is illustrated in Figure 10b. With increase in prolateness (decrease in fineness ratio), \(A_{xy}\) decreases, which reduces the drag. Consequently the balloon ascends faster, which leads to larger oscillations around the float altitude. In the case of airship (Figure 10c), with the increase in prolateness (decrease in fineness ratio), \(A_{xy}\) increases, and, hence, the drag. Therefore, the time taken by the balloon to reach the float altitude increases. The behaviour of the OZP balloons with varying shape and fineness ratios can be seen in Figure 11. The OZP balloons reach the desired float altitude. The time to reach the stable float altitude for different shapes at varying fineness ratio illustrates a behaviour similar to that of the SP balloon oblate, prolate, and airship shapes.