Sky-sailor Design of an Autonomous Solar Powered Martian Airplane

For more than two decades, Mars has been of great interest for scientific exploration, using orbiting spacecrafts or landers. Orbiters like “Mars Express” cover large areas and give images of the surface with a resolution limited to several meters. Rovers missions, like “Pathfinder” or “MER”, offer the ability to maneuver to scientifically interesting sites, perform analysis of soil and rock composition, but are limited in range to the immediate surroundings of the landing site. There is a strategic gap for systems that would combine high-resolution imagery and extensive coverage. This gap can be addressed by micro-airplanes that will give more accurate images than satellites, thanks to their proximity to the ground (about 0.5 to 2 km) and cover much larger areas than rovers without being limited by terrain roughness. This paper presents a feasibility study and the first design of a very lightweight solar powered airplane for Mars exploration. Called Sky-Sailor, it was investigated in an ESA definition study within the framework of the Startiger technology program. INTRODUCTION AND MOTIVATION The enabling technology for the realization of a solar powered micro-airplane with continuous flight capabilities on Mars is available today or in the near future. In fact, significant progress has been made recently in the critical fields for such a project that are: Efficiency, weight and flexibility of solar cells, power to weight ratio of batteries, miniaturization of MEMS and CMOS sensors, performance of single board computers, etc. However, major interdisciplinary effort is necessary in order to optimize and integrate concepts and technology to a fully functional system. Therefore, a strong collaboration of specialists from the fields of autonomous systems design, aerodynamics, solar cells, micro-sensors, light-weight structures, energy storage and much more is needed. The Autonomous Systems Lab (ASL) at EPFL is already very active in the field of VTOL (Vertical Take-Off and Landing) indoor flying robots (OS4 project), ultra-light airplanes (Celine, 10 [g]) and bio-inspired vision-based flying robots (Blimps, F2). With the Sky-Sailor project, the ASL enters the new field of outdoor flying robots. The goal of the project is to develop and test on Earth a prototype of solar powered micro-glider that will be fully autonomous in navigation and power generation and thus validate the feasibility of a Mars dedicated version. OTHER PLANETARY UAV PROJECTS AND ORIGINALITY OF SKY-SAILOR The idea to explore the red planet using UAV (Unmanned Aerial Vehicle) is not very recent and had given rise to many projects. In the 1970’s, the earliest one was the Mini-Sniffer, a 6.7 [m] wingspan and hydrazine powered airplane, designed, built and flown by NASA [1]. Since this time, considerable improvements, in particular in propulsion concepts, energy storage and materials, have led us to more advanced Martian UAV proposals; the most famous are ARES (Aerial Regional-scale Environmental Survey) from NASA Langley Research Center [2] and the AME (Airplane for Mars Exploration) from NASA Ames Research Center [3]. Several other planetary UAV projects with a large variety of concepts are in study, like inflatable wings glider [4], special helicopters [5,6], lighter than air balloons [7], flapping insect robots [8], etc. ARES and AME can embed an important payload for scientific operations but they are quite heavy and have a short autonomy (Table 1). On the opposite, Sky-Sailor will be limited to lightweight sensors and scientific instruments, but its coverage possibilities and autonomy will allow it to achieve very long period missions. In Proceedings of the 8th ESA Workshop on Advanced Space Technologies for Robotics and Automation 'ASTRA 2004' ESTEC, Noordwijk, The Netherlands, November 2 4, 2004