# Balloon Design for Mars, Venus, and Titan Atmospheres
## 4 Balloon Design for Different Atmospheres
### Balloons on Venus  
The wind circulations and high density of the Venusian atmosphere make it an interesting candidate for balloon exploration [7]. The VEGA balloons deployed in the Venusian atmosphere in 1985 as a collaboration between USSR, French, and US scientists were the first planetary exploration balloons [44]. These spherical SP balloons operated for about 2 Earth days at an altitude of 50-54 km over the surface of Venus and succeeded to observe the wind pattern at such altitudes until their batteries were depleted. Since then various studies have suggested the use of balloons for Venus exploration [45]. The main advantage of using SP balloons is their ability to maintain a stable altitude under atmospheric turbulence and diurnal solar flux variations. While various studies have illustrated the importance of spherical SP balloons for Venus [43; 46; 47], not much is said in the literature about the feasibility of ZP and OZP balloons for Venus explorations. This Section presents a comparative analysis of the three types of balloons (ZP, SP, and OZP) for exploring Venus. At an altitude of 52-53 km, Venus resembles the atmosphere of Earth except for the presence of sulphuric acid and haze-like clouds. Permanent winds of magnitude 65 m/s to 100 m/s in clockwise direction are common and provide many advantages to balloon flights [48]. To survive the contact with the sulphuric acid, the balloon envelope has to be chosen with utmost care. The Jet Propulsion Laboratory (JPL) has suggested the use of fluoropolymers, PTFE (polytetrafluoroethylene) & PFA (perfluoroalkoxy polymer) as a protective layer on the Mylar film as this combination has extremely low permeability and can cease the effect of sulphuric acid [49]. For deploying the balloon on Venus, aerial deployment is preferred. In [17], the authors suggest that for lifting a 0.31 kg net payload mass (i.e. without gas tank), a balloon would have a diameter of around 0.4 m. For an exploratory balloon  
Figure 4: Altitude variation of real and simulated flights for three types of balloons which were launched from Esrange Space Centre: (a) 12,000 m\({}^{3}\) (FL-1); (b) 50,000 m\({}^{3}\) (FL-2); (c) 1,120,546 m\({}^{3}\) (FL-3). on Venus, certain envelope characteristics, payload mass, and float altitude have been suggested in the literature [43; 47; 50], and on the basis of these studies, the parameters used for simulating the balloon flight on Venus have been chosen and are listed in Table 4.  
Figures 5-7 illustrate the ascent behaviour of oblate, prolate, and airship shape ZP, SP, and OZP balloons for several fineness ratios. The behaviour of oblate, prolate, and airship ZP balloons can be seen in Figure 5. In the case of oblate shape ZP balloons, with the increase in oblateness (increase in fineness ratio), the cross-sectional area \(A_{xy}\) of the balloon increases, and as a result the drag acting on the balloon also increases. Consequently, the ascent speed of the balloon decreases. In the case of prolate shape ZP balloon, with the increase in prolateness (i.e., decrease in fineness ratio), the \(A_{xy}\) decreases, as a result the drag acting on the balloon decreases. Hence, the balloon with high prolateness ascends faster than the balloon with low prolateness. For the airship shape balloons, with the increase in prolateness, the \(A_{xy}\) increases and as a result, the drag increases and the ascent speed of the balloon decreases. For the prolate shape ZP cases, balloons with prolateness between 0.1-0.4 reach the float altitude but then start to descend again. While the balloon ascends, the temperature of the lifting gas decreases due to adiabatic expansion at a faster rate than the temperature of the surrounding atmosphere, which follows the atmospheric temperature lapse rate. Initially, this leads to the lifting gas being colder than the atmosphere. However, with increasing temperature difference, convective heat transfer becomes more important. Eventually, at the float altitude, thermal equilibrium is reached.