# Balloon Design for Mars, Venus, and Titan Atmospheres
## 4 Balloon Design for Different Atmospheres
### Balloons on Titan  
Titan is a unique place in the solar system [54; 55]. The Cassini-Huygens mission revealed Titan to be a complex and fascinating world with diverse topographical features, and a methane based hydrological cycle [56]. Since then, buoyant vehicles have gained the recognition that they can provide an outstanding and unmatched means of in-situ exploration on a global scale on the surface of Titan [56]. Titan's low gravity, thick atmosphere, and Earth like characteristics make it a perfect candidate for exploration using an atmospheric flight. Titan's air density is 4 times that of the Earth at sea-level, the surface pressure is 1.5 times that of the Earth, and the surface temperature is \(-93\) K. While the air density supports a balloon mission on Titan, the temperature makes it challenging. Too low temperatures can make the material brittle; therefore, the material used for the balloon fabrication on Titan has to be chosen with utmost care. Further, the atmospheric models of aerosols and precipitation indicate methane clouds at 10-35 km of altitude, which suggests that the balloon should be deployed at an altitude below 10 km [57]. On Titan, the near-surface winds are expected to be \(<\)1 m/s up to an altitude of a few hundred meters (the planetary boundary layer thickness). At 10 km altitude, the winds are predicted to be around 1.0-2.5 m/s towards East [58], which enables the global coverage of Titan. Studies suggested three types of balloons, ZP, SP, and Montgolfiere for a mission on Titan [14; 56]. Montgolfiere balloons are a type of ZP balloons, which use heated ambient air instead of helium and hydrogen. The use of OZP balloons on Titan has not been mentioned in the literature. In this paper, the performance of three types of balloons, i.e., ZP, SP, and OZP, with 4 different shapes is analysed. For Titan's cryogenic environment, use of a radioisotope power source (100 W for a mass of 20-40 kg) is needed for all balloon concepts. Some suggestions have been made regarding the payload mass, the balloon envelope material, and the float altitude in the literature [56; 59]; these parameters are used  
Figure 13: Ascent speed variation of different balloon types at a particular fineness ratio on Mars (**a**) SP (**b**) OZP. A fineness ratio of 0.4 for airship and 0.4 for prolate and airship, and 4 for oblate shape is used. for simulating the behaviour of different types of balloons and shapes on the Titan's surface. Table 6 summarizes these parameters. Figures 14-16 present the behaviour of oblate, prolate, and airship shapes for ZP, SP, and OZP balloons and varying fineness ratios. The ZP and OZP balloons tend to reach the desired float altitude. The time taken by the ZP and OZP balloons to reach the stable altitude is more than that of the SP ones for similar shape and fineness ratio. The behaviour of the ZP and OZP balloons is similar (at the same shape and fineness ratio); the time taken by these balloons to reach the float altitude is also similar (Figures 14 and 16). For oblate and airship shape of ZP, SP, and OZP, as the oblateness (increase in fineness ratio) and prolateness (decrease in fineness ratio) increases the amount of time it takes the balloon to get stabilized at float altitude increases. In the case of prolate shape, with the increase in prolateness, the time to reach the stable float altitude decreases. Figure 17 illustrates the envelope and gas mass variation for the ZP, SP, and OZP balloons at varying fineness ratio. The envelope and gas mass of the ZP and OZP balloons are similar and less than that of the SP ones at different fineness ratios. In the case of different shapes, and an increase in prolateness and oblateness, the envelope and gas mass increase. The oblate shape balloons are, in general, heavier than both prolate and airship in terms of both gas and envelope mass as can be seen in Figure 17b. Next, the sphere-shape balloons are compared with the oblate, prolate and airship shapes for the ZP, SP, and OZP balloons.