Design Concepts for a new Temporal Planning Paradigm

Abstract Throughout the history of space exploration, the complexity of missions has dramatically increased, from Sputnik in 1957 to MSL, a Mars rover mission launched in November 2011 with advanced autonomous capabilities. As a result, the mission plan that governs a spacecraft has also grown in complexity, pushing to the limit the capability of human operators to understand and manage it. However, the effective representation of large plans with multiple goals and constraints still represents a problem. In this paper, a novel approach to address this problem is presented. We propose a new planning paradigm named HTLN, intended to provide a compact and understandable representation of complex plans and goals based on Timeline planning and Hierarchical Temporal Networks. We also present the design of a planner based on HTLN, which enables new planning approaches that can improve the performance of present real-world domains

Problemi di Scheduling con Risorse Consumabili: Risoluzione con Approccio a Vincoli

No English abstract availableQuesto articolo descrive un approccio per la risoluzione dei problemi di scheduling su risorse consumabili. Il lavoro si basa su una modellazione a vincoli del problema; l\u27approccio risolutivo comprende due contributi distinti: il primo ? lo studio di tecniche di deduzione capaci di ridurre lo spazio di ricerca permettendo una convergenza pi? immediata alla soluzione. Il secondo consiste nell\u27analisi dello spazio di ricerca che a seguito della sua complessit? richiede l\u27utilizzo di valutazioni euristich

Abstract

We consider a schedule optimization problem where each activity to be scheduled has a duration-dependent quality profile, and activity durations must be determined that maximize overall quality within given deadline and resource constraints. To solve this quality maximization problem, prior work has proposed a hybrid search scheme, where a linear programming solver for optimally setting the durations of temporally related activities is embedded within a larger search procedure that incrementally posts sequencing constraints to resolve resource conflicts. Under this approach, dual concerns of establishing feasibility and optimizing quality are addressed in an integrated fashion. In this paper, we propose an alternative approach, where feasibility and optimization concerns are treated separately: first, we establish a resource-feasible partial order schedule, assuming minimum durations for all activities; second, these fixed duration constraints are relaxed and quality optimal durations are determined. Experimental results indicate a tradeoff: when resource capacity constraints are loose, the integrated hybrid approach performs comparably to the separated scheme. However, in problems with tighter capacity constraints we find that separation of concerns enables both better solving capability and higher quality results. Following from these results, we discuss potential synergy between problem objectives of maintaining temporal flexibility and maximizing quality

Anatomy of a Scheduling Competition

International audienc

Schedule robustness through Solve-and-Robustify: generating flexible schedules from different fixed-time solutions

In previous works the authors have defined Solve-and-Robustify an original two-step procedure to generate flexible solutions, or partial order schedules, for scheduling problems. The partition in two steps — first find a solution then make it robust — not only represents a way to generate flexible, robust schedules but is also an alternative to achieve good quality solutions. This paper extends the analysis of this paradigm investigating the effects of using different start solutions as a baseline to generate partial order schedules. Two approaches are compared: the first based on the construction of flexible schedules after performing an iterative improvement phase focused on makespan optimization, the second that selects the best partial order schedule considering different fixedtime schedules as starting points. The paper experimentally shows how the characteristics of the fixed-time solutions may lower the robustness of the final partial order schedules and discusses motivations for such behavior

Planning Spacecraft Activities: An Automated Approach

In 2013 the Alphasat spacecraft will be launched: in addition to its main commercial payload, four Technology Demonstration Payloads (TDPs) will fly on-board. The different payloads are provided by different research institutes, which will be able to define in-orbit demonstration tests of these new technologies. To optimize this opportunity, coordination of the different, possibly conflicting, payload operations is required. A software system to support the management of the TDP operations has been developed. While this system is intended to be completely automated (i.e., without any human intervention in the nominal case), it has been designed to keep all the different users (system and TDP operators) in the loop. This paper presents this system and in particular focuses on its core: the planning engine