Figure 1. Prototype mobile instrument deployment device (MIDD) (Courtesy of DLR).
Résumé
Les sondes à poste fixe destinées à l'exploration de la surface de Mars ou d'autres astres doivent être en mesure d'analyser la matière constituant le sol qui les entoure. On a besoin pour cela d'un micro-véhicule simple, compact, léger et robuste consommant peu d'énergie et apte à mettre en place une série d'instruments scientifiques. Deux activités sont décrites, l'une relative à la conception d'ensemble et au prototypage des micro-véhicules, l'autre consacrée à la mise au point des composants électromécaniques critiques.
Contractors:
DLR (D),
Von Hoerner und Sulger (D),
Steinbeis Transferzentrum ARS (D),
Mecanex (CH),
Oerlikon Contraves Space (CH),
Max-Planck-Institut für Chemie (D),
Funding:
Basic Technology Research Programme, Max Planck Gesellschaft and German national funding.
Recent conceptions of a relatively inexpensive mission to Mars assume the use of a small, stationary lander, carrying scientific instruments for chemical and mineralogical analysis and close-up visual inspection of the planetary surface. The scientific return of a planetary mission can be greatly enhanced by extending the range of these measurements from the immediate vicinity of the landing station to a wider radius of several tens of meters, enabling numerous rock surfaces and samples of surface soil to be analysed.
The term 'micro-rover' is used to describe a mobile robot lighter than 10 kg. It must operate reliably and with a fair degree of autonomy over difficult, unknown terrain, under extreme conditions of temperature and pollution by dust or sand. It must be designed to meet very tight constraints on mass, volume, and power. A miniaturised vehicle has been identified as a means to maximise the use of the resources available to the scientific equipment and to minimise development cost.
The micro-rover is purpose-designed around the needs of a model instrument payload tyical of a planetary mission. By limiting the mobility and other capabilities of the vehicle to those which are strictly needed to meet scientific requirements, a very high ratio of payload mass to net rover mass (1:1) should be achievable. With this approach in mind, ESA has funded two industrial activities. The first is the study of a mobile instrument deployment device which serves to identify and develop critical electro-mechanical components. The second is a development of micro-robots for scientific applications in which a system level trade-off will be followed by the design and prototyping of two alternative micro-rover concepts.
Although a mission to Mars is considered to be the primary target, the results of these developments could be applied to missions to the Moon and other celestial bodies with only minor modifications.
The model payload assumed to be accommodated on the micro-rover has a mass of 2 kg and includes instruments such as spectrometers and a close-up imager. The measurement locations of primary interest to geo- and cosmo-chemists are the vertical surfaces of rocks.
The micro-rover must house the scientific instruments, transport them from the lander to an arbitrary selected measurement site, position the instruments and communicate the measurement data to the lander. The following additional constraints also apply:
To identify and develop the critical electromechanical components necessary for a planetary micro-rover, a preliminary system concept was studied. This consisted of a rigid chassis with four driving wheels and two actuated lever arms used to disembark it from the lander and to accurately locate the payload. Cables installed in a tether were used to supply electrical power to the rover and to transmit data to and from the lander. The payload, the vehicle drives and the drive and telecommand electronics were housed in a thermally controlled box. A prototype is shown in Figure 1.
Figure 1. Prototype mobile instrument deployment device (MIDD) (Courtesy of DLR).
The wheel drive and front wheel levers, the dynamic dust seals and the tether link have been identified as critical electromechanical components and these have been designed and manufactured. They are now undergoing a series of functional tests, thermal vacuum tests and environmental tests to simulate the Martian sand storms. A detailed mechanical analysis has demonstrated the adequacy of these components to withstand the landing loads.
A more detailed investigation of viable system concepts, including various wheeled, tracked and legged vehicles is ongoing. These approaches will be compared and two concepts will be selected for the definition of conceptual designs of all major functions and subsystems. Prototypes will be manufactured and tested under ambient laboratory conditions. Figure 2 shows one of the concepts, the 'Nanokhod', which has already been extensively analysed and tested by the Max-Planck-Institut für Chemie.
Figure 2. A model of the 'Nanokhod' (Courtesy of Max-Planck-Institut für Chemie)
In addition, other completely different concepts are also under evaluation elsewhere.
Planetary rovers have been identified by the scientific community as necessary elements for extending the reach of measurements around the planetary landing stations. To maximize the resources available to the scientific payload, to contain the development cost and schedule and to optimize the chances of a flight opportunity, only micro-rovers, with a mass below 4 kg, are being investigated by ESA at the moment. The mobility and performance of these vehicles are driven by the need to accomplish the scientific mission with a maximum of simplicity and robustness.
Preparing for the Future Vol. 7 No. 2