Showing papers by "William Whittaker published in 2011"

Autonomous Surface Exploration for Mobile Robots

Abstract: Exploration gathers information about the unknown. This information can come in many forms, from knowledge of new terrain, to rock geology, to lifeforms. The value of these different information forms to an explorer is determined by a set of information metrics, one for each form of information, that depend on the goal of the exploration task. As explorations become more complex, increasing numbers of information metrics must be considered in order to succeed. These multiple information metrics must be considered simultaneously during exploration and often conflict with each other to compete for the finite resources of the explorer. Exploration also involves making decisions, based on the collected information, to test hypotheses and collect more information in an efficient manner. This thesis introduces a new exploration technique which actively considers how much information can be gained from taking sensor readings as well as the cost of collecting this information. The methodology can consider multiple metrics of information simultaneously — such as finding new terrain and identifying rock type — as it explores and these information metrics can be easily changed to perform new and different exploration tasks. The method considers the costs, such as driving, sensing and planning times, associated with collecting the information. Exploration plans are produced which maximize the utility, information gain minus exploration costs, to the exploring robot. The multiple information metric exploration planner is used to solve two exploration problems: creating traversability maps and exploring cliffs. These tasks are performed in simulation and the information gain and exploration path lengths are compared as the information metrics are changed. The multiple information metric exploration planner is further demonstrated in a field experiment to explore a cliff, starting at the cliff top the planner found a route to the bottom and collected sensor information from the face of the cliff. ii iii Acknowledgements

The determinants of regional migration in Great Britain: a duration approach

Abstract: Summary. Using the British Household Panel Survey 1990–2007, we estimate a discrete duration model of interregional migration in Great Britain. By exploiting retrospective information on residency we control for late entry as well as unobserved heterogeneity. We find considerable duration dependence in region of residence in the raw data, much of which disappears when controlling for observable and unobservable differences between individuals. We illustrate that the usual way of modelling the effect of regional variables on the propensity to migrate gives insignificant and unrobust results and we introduce a new competing risks technique.

Advantageous bucket-wheel configuration for lightweight planetary excavators

Abstract: Robotic regolith excavation on the Moon and Mars enables outposts, fuel depots, and sustained space exploration. In any space mission, mass is always at a premium because it is the main driver behind launch costs. Low mass and reduced gravity (1/6 of Earth gravity on the Moon, 1/3 on Mars) results in machines with limited weight available to produce traction or plunge tools into regolith. Bucket-wheel excavators have been shown to produce low resistance forces that enable lightweight operation, but in the past have had difficulty transferring regolith from bucket-wheel to collection bin. Exposed conveyors and chains fare poorly in harsh lunar regolith and vacuum. A novel excavator configuration, with bucket-wheel mounted centrally and transverse to driving direction, achieves direct transfer into a collection bin. Experiments with a bucket-wheel digging in lunar simulant show that transverse bucket-wheel orientation does not increase resistance significantly. Excavation resistance is shown to depend mostly on the ratio of bucket-wheel rotation rate to forward advance rate.

Enabling Long-Duration Lunar Equatorial Operations with Thermal Wadi Infrastructure

Abstract: Long duration missions on the Moon s equator must survive lunar nights. With 350 hr of cryogenic temperatures, lunar nights present a challenge to robotic survival. Insulation is imperfect, so it is not possible to passively contain enough heat to stay warm through the night. Components that enable mobility, environmental sensing and solar power generation must be exposed, and they leak heat. Small, lightweight rovers cannot store enough energy to warm components throughout the night without some external source of heat or power. Thermal wadis, however, can act as external heat sources to keep robots warm through the lunar night. Electrical power can also be provided to rovers during the night from batteries stored in the ground beside wadis. Buried batteries can be warmed by the wadi s heat. Results from analysis of the interaction between a rover and a wadi are presented. A detailed three-dimensional (3D) thermal model and an easily configurable two-dimensional (2D) thermal model are used for analysis.

A long-duration propulsive lunar landing testbed

Abstract: Affordable test articles for descent and landing are crucial for developing commercial lunar landing capability. To ensure successful lunar landing, flight software must be tested over mission-length durations on hardware exhibiting dynamics analogous to those of true flight articles. Energetic and structural constraints typically preclude affordable long-duration lander tests.