Space debris reentry prediction and ground risk estimation using a probabilistic breakup model

International audienceWhile the number of artificial space object re-enter the Earth atmosphere daily, predicting the reentry of a space debris remains an open problem. The reentry prediction is a multi-physics problem involving aerodynamics computations in rarefied and continuum flow, heat transfer calculations and structiral breakup predictions. Additionally, numerous uncertainties coming from unknown initial flight conditions, material properties or uncalibrated model parameters affect oru ability to make acurate predictions. In this wrk, we propose an original reentry prediction framework that associates deterministic physical solvers with a stochastic breakup model and uncertainty quantification tools to make robust reentry predictions and a statistical estimate of the impact location. Our method is able to predic breakup distributions and ground impact locations efficiently using simplified but robust models at reasonable computational cost. This framework is used to predict the reenty of Upper Stage deorbited from a GTO orbit

An optimizing PROLOG front-end to a relational query system

An optimizing translation mechanism for the dynamic interaction between a logic-based expert system written in PROLOG and a re-lational database accessible through SQL is presented. The mechanism makes use of an intermediate language that decomposes the optimization problem and makes the proposed approach target-language independent. It can either facilitate expert system-database interaction, e.g., when integrating expert systems into business systems, or augment existing database with (external) deductive capabilities

Common Subexpression Isolation in Multiple Query Optimization

Abstract: The simultaneous optimization of multiple queries submitted to a database system may lead to substantial savings over the current approach of optimizing each query separately. Isolating common subexpressions in multiple queries and treating their execution as a sharable resource are important prerequisites. This chapter presents techniques for recognizing, supporting, and exploiting common subexpressions in record-oriented, relational algebra, domain relational calculus, and tuple relational calculus query representations, It also investigates preconditions that transaction management mechanisms must satisfy to make multiple query optimization effective. The joint execution of batches of queries and update operations has been a standard technique in the conventional, record-at-a-time file systems of the sixties and early seventies. However, with the introduction of interactive database systems based on direct access to specific subsets of data, th