Other
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..466g&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Other
Scientific paper
This paper summarizes a study performed by ten students at the Delft University of Technology on a lunar exploration vehicle suited for competing in the Google Lunar X Prize1. The design philosophy aimed at a quick and simple design process, to comply with the mission constraints. This is achieved by using conventional technology and performing the mission with two identical rovers, increasing reliability and simplicity of systems. Both rovers are however capable of operating independently. The required subsystems have been designed for survival and operation on the lunar surface for an estimated mission lifetime of five days. This preliminary study shows that it is possible for two nano-rovers to perform the basic exploration tasks. The mission has been devised such that after launch the rovers endure a 160 hour voyage to the Moon after which they will land on Sinus Medii with a dedicated lunar transfer/lander vehicle. The mission outline itself has the two nano-rovers travelling in the same direction, moving simultaneously. This mission characteristic allows a quick take-over of the required tasks by the second rover in case of one rover breakdown. The main structure of the rovers will consist of Aluminium 2219 T851, due to its good thermal properties and high hardness. Because of the small dimensions of the rovers, the vehicles will use rigid caterpillar tracks as locomotion system. The track systems are sealed from lunar dust using closed track to prevent interference with the mechanisms. This also prevents any damage to the electronics inside the tracks. For the movement speed a velocity of 0.055 m/s has been determined. This is about 90% of the maximum rover velocity, allowing direct control from Earth. The rovers are operated by a direct control loop, involving the mission control center. In order to direct the rovers safely, a continuous video link with the Earth is necessary to assess its immediate surroundings. Two forward pointing navigational cameras aid the human controller by obtaining stereoscopic images. An additional navigational camera in the rear is used as a contingency to drive rearwards. All navigational cameras have a maximal resolution of 640 by 480 pixels. Each rover has one main High Definition (HD) camera capable of acquiring still images and videos. These cameras have a resolution of 1920 by 1080 pixels and a frame rate of 60 frames per second. Resolution and sampling rates can be modified to accommodate data transmission constraints. To comply with the self portrait requirement imposed by the Google Lunar X Prize, the rovers will take images of each other, capturing 50% of the surface exploration system on the still image. As a contingency, both vehicles are also capable composing self portraits from an assembly of multiple images of its own structure, similar to the panoramic images. The camera is positioned above the rover on a mast providing two degrees of freedom for the camera to be able to rotate 360º horizontally and from -45º to 90º vertically. Both rovers are equipped with an omni-directional antenna. A WiMax system is used for all communication with the lander vehicle. The communication is done via the commonly used TCP/IP, which can be easily integrated in the software systems of the mission. The lander vehicle itself will act as a relay station for the data transfer with the ground station on Earth. The selected Digital Signal Processor (D.S.P.) has been specifically designed for compressing raw HD format using little power. The D.S.P. is capable of compressing the raw video data while at the same time performing remaining tasks such as navigation. Since the D.S.P. is designed for Earth use, it has to be adapted to cope with the lunar environment. This can be achieved by proper implication of radiation shielding. As the primary power source Gallium-Arsenide solar panels are used. These are the most efficient solar panels to date. Additionally, a Lithium-Ion battery is used as the secondary power source. In total at least 45Wh of energy are needed to complete the mission. A passive thermal system has been found to comply with the thermal requirements of the rovers. Therefore white paint and optical solar reflectors are used. These have a high emissivity and low absorption. The most striking characteristic for the rover mission is the miniaturization of components, allowing a small and low-mass rover design. Also, the use of adapted offthe- shelf components would dramatically reduce costs with respect to proven space grade components. The typical short mission lifetime allows this approach. It must be noted however that to ensure correct functionality of these components in space, they have to be customized and adapted to cope with vacuum and high radiation levels. Based on the achieved results, the Delft University of Technology is currently looking for partnerships in further development of a design capable of competing in the Google Lunar X Prize.
Buutfeld A. M. B.
Gill Eberhard
Honfi Camilo L.
Kuystermans P.
Maas S. B. B. A.
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