Edward A. LeMaster

Combined CDGPS and vision-based control of a small autonomous helicopter

Recent results in merging carrier-phase differential GPS (CDGPS) sensing with vision-based sensing to control a small autonomous helicopter are presented. The helicopter is a heavily modified yet low-cost kit helicopter that includes a full on-board CDGPS system, stereo video cameras, and sufficient computational capabilities to perform fully autonomous missions. The demonstration mission presented here is a search of a field to find an object followed by the tracking of that object (using the vision system) as it moves around the field. The helicopter system is described and the performance in accomplishing the task is presented.

A Local-Area GPS Pseudolite-Based Navigation System for Mars Rovers

Tasks envisioned for future generation Mars rovers—sample collection, area survey, resource mining, habitat construction, etc.—will require greatly enhanced navigational capabilities over those possessed by the Mars Sojourner rover. Many of these tasks will involve cooperative efforts by multiple rovers and other agents, adding further requirements both for accuracy and commonality between users. This paper presents a new navigation system called a Self-Calibrating Pseudolite Array (SCPA) that can provide centimeter-level, drift-free localization to multiple rovers within a local area by utilizing GPS-based transceivers deployed in a ground-based array. Such a system of localized beacons can replace or augment a system based on orbiting satellite transmitters, and is capable of fully autonomous operations and calibration. This paper describes the basic principles of navigation using an SCPA, focusing on the critical issue of array self-calibration. The new algorithm presented herein—called Quadratic Iterative Least Squares—achieves successful self-calibration 99.80% of the time even under extremely adverse conditions. The paper concludes with a description of the experimental prototype developed to demonstrate these capabilities and presents successful results from field trials which validate both the navigation and self-calibration functions of the SCPA.

Field demonstration of a Mars navigation system utilizing GPS pseudolite transceivers

Tasks envisioned for future generation Mars rovers-sample collection, area survey, resource mining, habitat construction, etc.-will require enhanced navigational capabilities over the Mars Sojourner rover. Many of these tasks will involve cooperative efforts by multiple rovers and other agents, adding further requirements both for accuracy and commonality between users. This paper presents a new navigation system (a self-calibrating pseudolite array) that can provide centimeter-level, drift-free localization to multiple rovers within a local area by utilizing GPS-based transceivers deployed in a ground-based array. Such a system of localized beacons can replace or augment a system based on orbiting satellite transmitters, and is capable of fully autonomous operations and calibration. This paper describes the prototype SCPA that has been developed at Stanford to demonstrate these capabilities and then presents new results from the most recent set of field trials performed at NASA Ames Research Center. These experiments, which utilize the K9 Mars rover research platform, validate both the navigation and self-calibration capabilities of the system.