Planetary aerobots - A program for robotic balloon exploration

Abstract

The exploration of the solar system has proceeded in several phases beginning with flyby missions, proceeding to orbiters, then to probes and landers and finally mobile vehicles that operate on the surface and in its atmosphere. For the most accessible planetary bodies, Venus and Mars, we are now entering this phase of mobile exploration of the surface and atmosphere. This paper is concerned with the use of robotically-controlled and autonomous balloons aerobots and their use in planetary exploration. Conceptual designs of aerobots capable of vertical mobility in planetary atmospheres using various altitude control systems are discussed. The use of prevailing wind patterns to enable global exploration is also examined. Emphasis is placed on the discussion of approaches to autonomous navigation for achieving desired latitudes and longitudes in planetary atmospheres using on-board flight dynamic models and a combination of real-time sensory perception (surface topography, balloon state and atmospheric conditions) and periodic independent position updates. The design of a planetary aerobot testbed vehicle is described mat will conduct a series of terrestrial technology demonstrations which will: 1) move gradually from manual teleoperated control of the robotic vehicle to fully autonomous altitude change and landings; 2) achieve increasingly long-range mobility from widely separated launch and landing sites (first predicted sites followed by designated sites). The missions that may use this technology include both scientifically motivated missions and technology demonstration opportunities at Venus, Mars, Titan and the outer planets. Introduction and Background At the Jet Propulsion Laboratory (JPL), we are now involved in planning and developing technology for the next phase of planetary exploration using buoyant vehicles. This phase will draw on the technical experience of earlier missions but will employ telerobotic and autonomy technologies to control motion hi three dimensions. There are significant parallels in these systems to the capabilities needed for mobile surface vehicles. However, there are also significant new challenges in atmospheric exploration that demand distinctly different approaches. The original motivation for developing this new class of buoyant vehicle was to advance the exploration of Venus. Following the exploration of the surface of Venus by short-lived Soviet landers and the Vega balloons, JPL carried out the Magellan mission, which mapped the surface of Venus using radar sensors. The radar revealed a surface with a great variety of structural and volcanic features. There has been no clear pathway, however, to follow up the Magellan mission with a long-lived in situ mission. Venus, Earth's estranged sister planet, has a dense atmosphere exceeding 92 bars hi pressure and surface temperatures in excess of 460°C (733K). Its surface is obscured from view at visible wavelengths by high-altitude haze and clouds as well as the molecular scattering of the clear atmosphere beneath. The Soviet Venera landers were able to function for less than two hours exposed to the high-temperature environment on the Venus surface. With advanced thermal techniques and the use of vacuum insulation, it may be possible to extend surface lifetime to a few days. Much longer lived systems, however, will require radioisotope power and temperature control systems which will be costly and present Earth environmental concerns. An aerobot on the other hand can turn the environmental challenges of Venus to advantage. The Venus Flyer Robot (VFR) concept, conceived at JPL in 1993, could make brief excursions to the hot surface environment of Venus to acquire data and return to higher altitudes to cool down and telemeter those data to an orbiting relay station or directly to Earth. This concept takes advantage of new technologies hi lightweight and low-power electronics and instruments for rovers that were developed at JPL. However, hi the