AIRSHIPS MODELING AND CONTROL STRATEGY FOR TITANEXPLORATION

Lighter-than-atmosphere (LTA) systems provide significant advantages for planetary exploration due to their potential role for extended mission duration, long traverse, and extensive surface coverage capabilities. Robotic airships, in particular, are ideal platforms for airborne planetary exploration. Airships have modest power requirements, and combine the extended airborne capability of balloons with the manoeuvrability of airplanes or helicopters. Their controllability allows precise flight path execution for surveying purposes, long-range as well as close-up ground observations, station-keeping for long-term monitoring of science sites, transportation and deployment of scientific instruments and in-situ laboratory facilities across vast distances to key science sites, and opportunistic flight path re-planning in response to the detection of relevant science sensor signatures. Furthermore, robotic airships provide the ability to conduct extensive surveys over both solid terrain and liquid-covered areas, and to reconnoitre sites that are inaccessible to ground vehicles. Understanding and modelling airship's dynamics and control is a crucial point for different applications: i.e a realistic navigation system must takes into account the characteristics of the motions of this type of vehicle and a power budget analysis has to consider forces and moments applied by actuators. By numerical integrations it's possible to compute the pressure forces and moments without an explicit analytical expression for them, simply including in the equation of motions the added mass contribution. On the other hand, numerical techniques can nowadays allow the calculations of the added mass considering the geometric property of the rigid body. A complete airship simulator has been developed and two different kind of vehicles have been modelled, for terrestrial and planetary applications. Also a control strategy, for path planning, has been designed with a particular attention to its robustness in case of wind disturbances. In this work we analyse the dynamics of the airship in response of the encountered environment of Titan satellite. Possible trajectories for an extended survey are investigated; this allows to have a precise quantitative analysis of the power necessary for a journey on the satellite. A 1 km x 1 km region is selected as baseline: time necessary for performing a complete survey is investigated. Analysis are conducted both in a quiet situation with no wind and in wind conditions: considered winds are in the range 0.5 – 2 m/s parallel and orthogonal to the ground track. Trajectories are followed at 1, 3, 5 and 10 m/s velocities; surface science and high altitude (\>1000m) scenarios are proposed.