Re-inventing the wheel for the next generation of planetary rovers

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 84-85).Experiences with Spirit and Opportunity, the twin Mars Exploration Rovers, showed that one of the major issues that needs to be addressed in order to expand the exploration capabilities of planetary rovers is that of wheel traction. The relationships governing how much traction a wheel can produce are highly dependent on both the shape of the wheel and terrain properties. These relationships are complex and not yet fully understood. The amount of power required to drive a wheel is also dependent on its shape and the terrain properties. Wheel sizes that tend to maximize traction also tend to require more power. In the past, it has always been a challenge to find the right balance between designing a rover wheel with high traction capabilities and low power requirements. More recently, researchers invented the idea of a reconfigurable wheel which would have the ability to change its shape to adapt to the type of terrain it was on. In challenging terrain environments, the wheel could configure to a size that would maximize traction. In less challenging terrain environments, the wheel could configure to a size that would minimize power. Theoretical simulation showed that the use of reconfigurable wheels could improve tractive performance and some initial prototyping and experimental testing corroborated those findings. The purpose of this project was to extend that prototyping and experimenting. Four reconfigurable wheels were designed, built, and integrated onto an actual rover platform. A control methodology whereby the wheels could autonomously reconfigure was also designed, implemented, and demonstrated. The rover was then tested in a simulated Martian environment to assess the effectiveness of the reconfigurable wheels. During the tests, the power consumption and the distance traveled by the rover were both measured and recorded. In all tests, the wheels were able to successfully reconfigure and the rover continued to advance forward; but as was expected, the reconfigurable wheel system consumed more power than a non-reconfigurable wheel system. In the end, the results showed that if maximizing vehicle traction was weighed more heavily than minimizing power consumption, the use of reconfigurable wheels yielded a net gain in performance.by Brittany Baker.S.M

Concept evaluation of Mars drilling and sampling instrument

The search for possible extinct or existing life is the goal of the exobiology investigations to be undertaken during future Mars missions. As it has been learnt from the NASA Viking, Pathfinder and Mars Exploration Rover mission, sampling of surface soil and rocks can gain only limited scientific information. In fact, possible organic signatures tend to be erased by surface processes (weathering, oxidation and exposure to UV radiation from the Sun). The challenge of the missions have mostly been getting there; only roughly one third of all Mars missions have reached their goal, either an orbit around the planet, or landing to the surface. The two Viking landers in the 1970's were the first to touch down the soil of Mars in working order and performing scientific studies there. After that there was a long gap, until 1997 the Pathfinder landed safely on the surface and released a little rover, the Sojourner. In 2004 other rovers came: the Mars Exploration Rover Spirit and a while after that, the sister rover Opportunity. These five successful landings are less than half of all attempts to land on Mars. Russia, Europe and the United States have all had their landers, but Mars is challenging. Even Mars orbit has been tough to reach by many nation's orbiters. It is then understandable that of these five successful landings, performed by National Aeronautics and Space Administration (NASA), there have not yet been very complicated mechanical deep-drilling instruments onboard. The risks to get there are great, and the risk of malfunctioning of a complicated instrument there is also high. Another reason to avoid a deep-driller from the lander payload is simply the mass constrains. A drill is a heavy piece of payload, and the mass allocations for scientific instruments are small. In the launch window of 2009, both European Space Agency (ESA) and NASA have their plans to send a rover to Mars. Both of them will include some means to analyse the subsurface material. ESA's rover, called the ExoMars rover, will carry a deep-driller onboard in its Pasteur payload. At the time of writing this thesis, an exact definition of the Pasteur drill has not yet been defined. The author of this thesis has studied the driller instruments in his past work projects and in his doctoral studies. The main focus of this thesis is to analyse the feasibility of different drill configurations to fit to the requirements of the ExoMars' Pasteur payload drill by using the information gathered from the past projects. In this thesis, the author introduces a new concept of a robotic driller, called the MASA drill. The MASA drill fulfils the needs for the drill instrument onboard the Pasteur payload. The main study in this thesis concentrates on design work of the MASA drill, as well as analysis of its operation and performance capabilities in the difficult task of drilling and sampling.reviewe