# Balloon Design for Mars, Venus, and Titan Atmospheres
## 1 Introduction  
Buoyant aerial vehicles are potential candidates for future space missions, as these vehicles can provide extensive, low-altitude geographical coverage over multi-month time scales with minimal power at low costs on planets and moons with a significant atmosphere [1]. The details of other aerial vehicles that have been suggested for different atmospheric bodies can be found in [2; 3; 4; 5]. In 1986, the Vega mission deployed balloons in Venus atmosphere to demonstrate the technical feasibility of using balloons on other planets for scientific observations [6]. Since then, there has been a number of flagship studies by NASA and ESA which suggest the use of aerial vehicles for atmospheric explorations [7; 8; 9; 10]. In 2009, the Venus Flagship Mission (VFS) study by NASA suggested the use of two helium-filled, super-pressure (SP) balloons for a 30-day mission at an altitude of 55 km for the study of Venus clouds and atmosphere [7]. In the same year, ESA suggested a mission called European Venus Explorer (EVE) [11], which considered a balloon as the primary platform for Venus explorations. Another mission that is currently in the planning phase is Venera-D which includes three elements, i.e., orbiter, lander, and a balloon [12; 13]. In the case of Titan, there are three flagship mission studies, namely, Tandem and Enceladus Mission (TANDEM) [8], Titan Explorer Flagship Mission (TEFM) Study [14], and Titan and Saturn System Mission (TSSM) [9], all of which suggest the use of aerial vehicles as a high priority for the mission. These studies ([7; 9; 10; 12; 13; 15; 16]) suggest a particular aerobot type for the exploratory mission, but only a few of these studies focused on how different aerobot types can add different characteristics to the mission [17]. The type of aerobot that can be deployed to different planets/moons are: zero-pressure (ZP), super-pressure (SP), or over-pressurized zero-pressure (OZP). Zero-pressure (ZP) balloons are those whose internal-external pressure differential is zero; in super-pressure balloons (SP), the pressure of the buoyant gas inside the vehicle exceeds the ambient pressure in an almost uniform manner. An over-pressurized zero-pressure (OZP) balloon is a hybrid which combines the features ofboth ZP and SP balloons, i.e., first the balloon should be able to handle a higher than ambient pressure and then it should be able to safely achieve float and relieve pressure in excess of the design limits for over-pressure [18]. The different characteristics that these different aerobot types might add to the mission are, for example, an SP aerobot might be more stable on a planet/moon than a ZP aerobot, the mass, volume, and lifetime of different types of aerobots might differ as per the atmosphere of planets/moons, etc. Therefore, it is interesting to study the behaviour of different types of aerobots in different atmospheres as this will help in laying the groundwork of what type of aerobots could be used to fulfil the different mission requirements. In general, the spherical shape is the preferred shape for any balloon type as the ratio of the volume to surface area, i.e., the balloon efficiency is highest for the sphere shape [19]. However, this ratio might not be the most important factor for balloon operation on different planets/moons as different shapes can complement the balloon mission with other characteristics, for e.g., a mission might demand a faster or slower ascent, or a balloon that can continuously do altitude excursions, etc. Further, it is expected that a balloon with a fineness ratio \(f\) much greater or much less than 1 will be unstable as it will not have enough buoyant force for different balloon types. Therefore, it is interesting to study the behaviour of different balloon shapes and types for varying fineness ratio. Further, there is a need for proper tools for the synthesis and analysis of exploratory robots.