Energy Modeling of VTOL Aircraft for Titan Aerial Daughtercraft (TAD)Concepts

Aerial vehicles are of considerable interest for exploration of Saturn's icy moon Titan. The concept of Titan Aerial Daughtercraft (TAD)was introduced in 2014, where small-scale (e.g. <; 10 kg)VTOL aircraft would conduct multiple sorties from a mothership (lander or balloon), recharging batteries from a radioisotope power source (RPS)on the mothership between sorties. More recently, NASA has funded a study of a much larger Titan rotorcraft ( ~ 450 kg)that would carry its own RPS. The TAD concept is still worth further analysis as a low-cost element of mission architectures where the mothership is a lander, balloon, or other large mobility system. To compare the potential performance of daughtercraft that are rotary-wing only or fixed/rotary-wing hybrids, this study examines potential flight durations and flight radius for small-scale (4 to 10 kg)quadcopters and tailsitters. For notional system parameters, a payload mass fraction of 25%, and a conservative battery model, energy estimation modeling for lander-based scenarios shows maximum flight endurance at Titan's surface for 10 kg quad-copter and tailsitter as 9.3 hours and 12.4 hours, respectively, and maximum sortie radius from a lander as 89 km and 125 km, respectively. Modeling of balloon-based scenarios estimated the mass potentially available for payload as a function of the total TAD mass and the float altitude of the balloon. For a balloon floating at 10 km above the surface and a 10 kg TAD, the model gave available mass of about 2.8 kg for a quadcopter and 3.5 kg for a tailsitter. Non-aerodynamic power dominates aerodynamic power at the lowest mass, but becomes a less significant fraction of the total as mass increases. The tailsitter has little or no advantage over the quadcopter at the lowest mass, but increasing advantage as mass increases.