Flying research

For planets and moons that support an atmosphere, such as Venus, Mars and Titan, flying robots (aerobots) can provide a practical solution to the problem of extended planetary surface coverage. Not only can aerobots be used for terrain mapping and surface/sub-surface composition surveying, they could also be used for the transportation and deployment of science packages or even microrovers at geographically separate sites. Using aerobots for planetary exploration represents a highly innovative concept. Although rover technology is clearly competent at facilitating useful science, their application is terrain limited. Aerobots in comparison have no such limitations.

The technological challenges posed by planetary aerobots are significant, and the Space Robotics Group at the UWA are investigating the design and control of helium filled balloon robots that can fly autonomously to designated landing sites. To study these problems the ALTAIR (Aberystwyth Lighter Than Air Intelligent Robot) research programme has been proposed. The ALTAIR aerobots have a modular design that allows rapid prototyping and experimentation within a controlled environment.

The challenge of flying a planetary aerobot encompasses mobility control and autonomous navigation in a constantly changing 3D environment. Inter-planetary distances prohibit real-time communication and control. An aerobot's long term endurance and ultimate survival can be achieved only if sophisticated autonomous flight control and navigation methods are employed.

Interest in aerobots for planetary exploration is increasing due to the ability to traverse large areas of a planet's surface rapidly, when compared to a rover vehicle. For an aerobot to function autonomously within a dynamic 3D environment, it must possess the necessary sensors and actuators for control and navigation purposes. These areas are addressed in the ALTAIR research program where the problem of sensor and actuator hardware and software performance is tested. Although software simulation methods have a very important role within an aerobot development programme, there is no substitute for tests on a real aerobot. Controlled experiments are required to advance our understanding of autonomous aerobot navigation and control.

The main area of interest for balloons in the immediate future, especially on Mars, is planetary ultra-high resolution imaging, although later aerobots could carry additional scientific payloads or provide information for control of surface robots. With limited resources of memory and power on a planetary aerobot, the main problem is the economic storage and use of images acquired, until communication with an orbitor can be established, during which the data can be uploaded. To provide context for the gathered data the aerobot will have to calculate its position within the environment. Although other means of navigation could be provided, using already available imagery would be the most economic. Thus the UWA Space Robotics Group have begun an ESA (European Space Agency) study that is designed to investigate the localisation of an aerobot using environmental images, economic use of memory to store the vast quantity of images, and the problem of predicting the next communication window with an orbitor, so that the best use of storage can be made to meet the mission targets without loss of any important information.

The main outputs of the mission are to be, a 3D map of the surface (Digital Elevation Model) and images of the surface at various resolutions. There is however another problem associated with any image processing in real time, the processing power available. Image manipulation, especially on high resolution images, requires many operations. Although for this study a PC is available, in practice the processing power is likely to be much less. No one process should therefore produce a bottleneck, for this process will limit the continuous image acquisition rate possible, and therefore the maximum speed of the aerobot before processing overload leads to areas of the surface having to be missed. This speed is, of course, a function of the aerobot's height, and image resolution requirements. The study should address this major problem.

A proposed Martian site for aerobot activities is the "Dao Vallis" region of Mars which is situated at approximately -36 degrees latitude and 269 degrees longitude (North East of the Hellas Basin). This site was chosen because it is believed to contain features caused by running water, from melting permafrost. As the sides of the valley are too steep for rovers an aerobot solution offers the greatest success, but only time will tell.