Chris Leger

Rover autonomy for long range navigation and science data acquisition on planetary surfaces

This paper describes recent work undertaken at the Jet Propulsion Laboratory in Pasadena, CA in the area of increased rover autonomy for planetary surface operations. The primary vehicle for this work is the Field Integrated, Design and Operations (FIDO) rover. The FIDO rover is an advanced technology prototype that is a terrestrial analog of the Mars Exploration Rovers (MER) being sent to Mars in 2003. We address the autonomy issue through improved integration of rover based sensing and higher level onboard planning capabilities. The sensors. include an inertial navigation unit (INU) with 3D gyros and accelerometers, a sun sensor, mast and body mounted imagery, and wheel encoders. Multisensor fusion using an Extended Kalman Filter (EKF) approach coupled with pattern recognition and tracking algorithms has enabled the autonomy that is necessary for maximizing science data return while minimizing the number of ground loop interactions. These algorithms are coupled with a long range navigation algorithm called ROAMAN (Road Map Navigation) for an integrated approach to rover autonomy. We also report the results of algorithm validation studies in remote field trials at Black Rock Summit in Central Nevada, Californias Mojave Desert, and the Arroyo Seco at JPL.

Distributed control for a modular, reconfigurable cliff robot

We have developed a cliff robot that is capable of descending a cliff and autonomously navigating to way-points on the cliff wall. This aggressive mobility system consists of an ensemble of three tethered robots, which cooperate under tight coordinated control and collective state estimation. The distributed task is described as a behavior network, which consists of a network of controllers spread across the robots and which interact through communication links to achieve a collective control objective. Fielded experimental results show that the cliff robot is capable of navigating to designated way-points on a cliff wall using the proposed control scheme.

Design Through Operation of an Image-Based Velocity Estimation System for Mars Landing

During the Mars Exploration Rover (MER) landings, the Descent Image Motion Estimation System (DIMES) was used for horizontal velocity estimation. The DIMES algorithm combined measurements from a descent camera, a radar altimeter, and an inertial measurement unit. To deal with large changes in scale and orientation between descent images, the algorithm used altitude and attitude measurements to rectify images to a level ground plane. Feature selection and tracking were employed in the rectified images to compute the horizontal motion between images. Differences of consecutive motion estimates were then compared to inertial measurements to verify correct feature tracking. DIMES combined sensor data from multiple sources in a novel way to create a low-cost, robust, and computationally efficient velocity estimation solution, and DIMES was the first robotics vision system used to control a spacecraft during planetary landing. This paper presents the design and implementation of the DIMES algorithm, the assessment of the algorithm performance using a high fidelity Monte Carlo simulation, validation of performance using field test data and the detailed results from the two landings on Mars.DIMES was used successfully during both MER landings. In the case of Spirit, had DIMES not been used onboard, the total velocity would have been at the limits of the airbag capability. Fortunately, DIMES computed the actual steady state horizontal velocity and it was used by the thruster firing logic to reduce the total velocity prior to landing. For Opportunity, DIMES computed the correct velocity, and the velocity was small enough that the lander performed no action to remove it.

The Best of Both Worlds: Integrating Textual and Visual Command Interfaces for Mars Rover Operations

A Mars rover is a complex system, and driving one is a complex endeavor. Rover drivers must be intimately familiar with the hardware and software of the mobility system and of the robotic arm. They must rapidly assess threats in the terrain, then creatively combine their knowledge of the vehicle and its environment to achieve each days science and engineering objectives. To help the Mars Exploration Rover projects rover drivers meet their goals, the software we developed to drive the rovers - the Rover Sequencing and Visualization Program, or RSVP - combines two representations of command sequences, one textual and one using three-dimensional graphics. Changes to one representation are instantly reflected in the other, and the combinations advantages exceed the mere sum of the parts: the different representations offer different levels of abstraction, engage different areas of the drivers brain, and complement each others strengths. This combination plays a crucial role in simplifying a complex feat of interplanetary exploration

Efficient sensor/model based on-line collision detection for planetary manipulators

Manipulator safeguarding is a critical need for operations on planetary rovers. The computing environment on a Mars rover is extremely limited, which necessitates a highly efficient collision checking algorithm. We present such an algorithm that uses the oriented bounding box (OBB) and a primitive called the oriented bounding prism (OBP) to detect potential self-collisions and collisions with terrain objects sensed with the rovers onboard stereo cameras; the algorithm thus has both model-based and sensor-based components. We have implemented the algorithm on JPLs FIDO rover and have tested it under realistic field conditions. Performance analysis indicates this method is significantly faster than previously reported results in the literature, in addition to incorporating sensed geometry. The method is also being used on board NASAs twin Mars Exploration Rovers, which are scheduled to launch in 2003.

Data Visualization for Effective Rover Sequencing

The Rover Sequencing and Visualization Program is a suite of tools for the commanding of planetary rovers which are subject to significant light time delay and thus are unsuitable for tele-operation. The two main components of the program are the Rover Sequence Editor and HyperDrive. This paper focuses on HyperDrive, the immersive visualization component of the system. HyperDrive fuses multiple data types returned from the vehicle in order to facilitate an operator understanding of the current environment and past rover performance, so that safe effective command sequences for successful future rover activities may be generated on a tight tactical timeline. Multiple display and task specific interaction modalities are provided to most efficiently present relevant spatial and time series data to the sequence builder

Mars Science Laboratory Algorithms and Flight Software for Autonomously Drilling Rocks

One of the goals of the Mars Science Laboratory (MSL) mission is to collect powderized samples from the interior of rocks in order to deliver these samples to onboard science instruments. This paper describes the algorithms and software used to control the drill, which is the component of the sample collection and delivery system that directly interacts with rocks to create and acquire powderized samples from their interior. This is the first time that autonomous drilling of rocks has ever been performed on another planet. One of the most important components of the algorithm used for drilling is a force feedback control system used to regulate the force applied to the rock during drilling. This algorithm and all of the other algorithms and software used to enable the process of robustly, efficiently, and autonomously drilling into rocks with a priori unknown and widely varying properties are described in detail in this paper. Results are shown from drilling rocks using the drill software on testbed hardware on Earth as part of the software development process. Results are also shown from the first holes drilled with the flight vehicle on Mars, thus successfully demonstrating the first extraterrestrial autonomous drilling of a rock.

Physical-based simulation for Mars Exploration Rover tactical sequencing

The Mars Exploration Rover (MER) mission has returned tremendous scientific information on a daily basis, owing to the efficient sequencing capability of the ground system tools. For planning the mobility and instrument deployment device (IDD) sequences, physical-based simulation is applied to achieve fast and effective sequencing of complex rover and IDD maneuvers. The sequence rehearsal tool of the Rover Sequencing and Visualization Program (RSVP) is based on modeling and simulation of the multi-body mechanical systems. Using configuration kinematics (CK) and 3D terrain models, a methodology was developed to support a real-time, interactive graphics mode for the visualization tool. The sequence simulation is carried out using the on-board flight software modules for realistic rover behavior. This enables the scientists and rover planners to effectively develop the command sequences to maximize the science return of the MER mission while maintaining rover safety. This paper describes the innovative numerical algorithms and the command sequence simulation used by the MER mission for planning surface operations.

Mars Science Laboratory CHIMRA/IC/DRT flight software for Sample Acquisition and Processing

The design methodologies of using sequence diagrams, multi-process functional flow diagrams, and hierarchical state machines were successfully applied in designing three MSL (Mars Science Laboratory) flight software modules responsible for handling actuator motions of the CHIMRA (Collection and Handling for In situ Martian Rock Analysis), IC (Inlet Covers), and DRT (Dust Removal Tool) mechanisms. The methodologies were essential to specify complex interactions with other modules, support concurrent foreground and background motions, and handle various fault protections. Studying task scenarios with multi-process functional flow diagrams yielded great insight to overall design perspectives. Since the three modules require three different levels of background motion support, the methodologies presented in this paper provide an excellent comparison. All three modules are fully operational in flight.

Mars science laboratory frame manager for centralized frame tree database and target pointing

The FM (Frame Manager) flight software module is responsible for maintaining the frame tree database containing coordinate transforms between frames. The frame tree is a proper tree structure of directed links, consisting of surface and rover subtrees. Actual frame transforms are updated by their owner. FM updates site and saved frames for the surface tree. As the rover drives to a new area, a new site frame with an incremented site index can be created. Several clients including ARM and RSM (Remote Sensing Mast) update their related rover frames that they own. Through the onboard centralized FM frame tree database, client modules can query transforms between any two frames. Important applications include target image pointing for RSM-mounted cameras and frame-referenced arm moves. The use of frame tree eliminates cumbersome, error-prone calculations of coordinate entries for commands and thus simplifies flight operations significantly.