Ella M. Atkins

Information consensus in multivehicle cooperative control

The purpose of this article is to provide a tutorial overview of information consensus in multivehicle cooperative control. Theoretical results regarding consensus-seeking under both time invariant and dynamically changing communication topologies are summarized. Several specific applications of consensus algorithms to multivehicle coordination are described

A survey of consensus problems in multi-agent coordination

As a distributed solution to multi-agent coordination, consensus or agreement problems have been studied extensively in the literature. This paper provides a survey of consensus problems in multi-agent cooperative control with the goal of promoting research in this area. Theoretical results regarding consensus seeking under both time-invariant and dynamically changing information exchange topologies are summarized. Applications of consensus protocols to multiagent coordination are investigated. Future research directions and open problems are also proposed.

Second-order Consensus Protocols in Multiple Vehicle Systems with Local Interactions

In this paper, a distributed coordination scheme with local interactions is studied for multiple vehicle systems. We introduce a second-order consensus protocol and derive necessary and/or su‐cient conditions under which consensus can be reached in the context of uni-directional interaction topologies. The consensus protocol is then applied to achieve altitude alignment among a team of micro air vehicles as an illustrative example.

Emergency Flight Planning Applied to Total Loss of Thrust

Autopilot systems are capable of reliably following flight plans under normal circumstances, but even the most advanced flight-management systems cannot provide robust response to most anomalous events including in-flight failures. This paper describes an emergency flight-management architecture that can be applied to piloted or autonomous aircraft, with focus on the design and implementation of an adaptive flight planner (AFP) that dynamically adjusts its model to compute feasible flight plans in response to events that degrade aircraft performance. A two-step landing-site selection/trajectory generation process defines safe emergency plans in real time for situations that require landing at an alternate airport. A constraint-based search algorithm selects and prioritizes feasible emergency landing sites, then the AFP synthesizes a segmented trajectory to the best site based on postfailure flight dynamics. The AFP architecture is general for any failure situation; however, operational success is guaranteed only with accurate postfailure performance characterization and a trajectory generation strategy that respects degraded flight envelope boundaries. A real-time segmented trajectory planning algorithm and case study results are presented for total loss of thrust failure scenarios. This emergency is surprisingly common and necessitates an immediate approach and landing without a go-around option.

Planning and resource allocation for hard real-time, fault-tolerant plan execution

We describe the interface between a real-time resource allocation system with an AI planner in order to create fault-tolerant plans that are guaranteed to execute in hard real-time. The planner specifies the task set and all execution deadlines required to ensure system safety, then the resource utilization. A new interface module combines information from planning and resource allocation to enforce development of plans feasible for execution during a variety of internal system faults. Plans that over-utilize any system resource trigger feedback to the planner, which then searches for an alternate plan. A valid plan for each specified fault, including the nominal no-fault situation, is stored in a plan cache for subsequent real-time execution. We situate this work in the context of CIRCA, the Cooperative Intelligent Real-time Control Architecture, which focuses on developing and scheduling plans that make hard real-time safety guarantees, and provide an example of an autonomous aircraft agent to illustrate how our planner-resource allocation interface improves CIRCA performance.

Solus: an autonomous aircraft for flight control and trajectory planning research

The University of Michigan has developed a fixed-wing model aircraft (Solus) with an embedded control system to develop and demonstrate UAV technology. The analytical objective of this project is the development of intelligent flight control and trajectory planning techniques, focusing on automated fault detection and recovery. Our experimental objective is to implement and evaluate these techniques on Solus for a variety of mission and fault scenarios.

X-HALE: A Very Flexible Unmanned Aerial Vehicle for Nonlinear Aeroelastic Tests

The University of Michigan has designed and built an unmanned aerial vehicle denoted X-HALE, which is aeroelastically representative of very flexible aircraft. The objective of this test bed is to collect unique data of the geometrically nonlinear aeroelastic response coupled with the flight dynamics to be used for future code validation. The aircraft presents specific aeroelastic features (e.g., coupled rigid/elastic body instability, large wing deflection during gust) that can be measured in flight. Moreover, the airframe construction choice is such that the elastic, inertial, and geometric properties can be well characterized. These are requirements driven by the need of the collected data to be used to support validation of coupled nonlinear aeroelastic/flight dynamics codes.

Incorporating Resource Safety Verification to Executable Model-based Development for Embedded Systems

This paper formulates and illustrates the integration of resource safety verification into a design methodology for development of verified and robust real-time embedded systems. Resource-related concerns are not closely linked with current xUML model-based software development although they are critical for embedded systems. We describe how to integrate resource analysis techniques into the early phase of an xUML-based development cycle. Our hybrid framework for resource safety verification combines static resource analysis and runtime monitoring. A case study based on an embedded controller for satellite simulation, TableSat, illustrates the benefits obtained by incorporating resource verification into design and combining static analysis and runtime monitoring.

Optimization of a Tetrahedral Satellite Formation

Two fundamental approaches can be applied to satellite-formation mission design: active control, where satellites exert forces with their thrusters to maintain a constant or periodic geometry for all or part of each orbit, and natural, where satellite orbits are designed to naturally assemble a geometry for all or part of each orbit to within a tolerance defined from scientific requirements. An actively controlled formation can be labeled virtual rigid body (VRB) because geometry is precisely maintained as if the satellites were rigidly connected. This work describes a hierarchical optimization method for minimizing mission design computational complexity and applies this method to the design of VRB, natural-orbit, and multi-impulse solutions for a tetrahedron formation applicable to the proposed magnetospheric multiscale mission. Cost is defined in terms of total fuel per second of observation and tetrahedron geometric quality factor. Although both natural-orbit and active solutions are feasible, the active solutions substantially increase average data quality and observation time per orbit at minimum fuel cost, and the multi-impulse solution does not require thruster use during data collection periods.

The Ranger robotic satellite servicer and its autonomous software-based safety system

We describe the Ranger robotic system and its autonomous hazard control system, which is designed to meet the stringent criteria imposed on space shuttle payloads. Mature Ranger systems have enabled evaluation of telerobotic servicing tasks in a variety of 1-g and neutral buoyancy environments. These evaluations have included rigorous testing with operators that ranged from experienced system designers to small children who frequently activate the safety system as they operate manipulators without skill or caution. Originally developed to demonstrate space-based robotic servicing as a shuttle payload, Ranger has subsequently evolved into an Earth-based test bed for robotic servicing tasks.