Project overview

The Mexar (Mars EXpress ARchitecture) project represents a successful example of the use of Artificial Intelligence techniques for Planning and Scheduling in real application domains. It is the result of the study "Efficient Planning Algorithms for an Interplanetary Mission" conducted by the ISTC's Planning and Scheduling Team for the European Space Agency in the period November 2000 - July 2002, in the context of the Mars Express mission.

On Jun 2, 2003 The European Mars Express space probe has been placed successfully in a trajectory that will take it beyond the terrestrial environment and on the way to Mars - arriving in late December 2003.

Mars Express is the first ESA probe to head for another planet. It will enter an orbit around Mars, from where it will perform detailed studies of the planet's surface, its subsurface structures and its atmosphere. It will also deploy Beagle 2, a small autonomous station which will land on the planet, studying its surface and looking for possible signs of life, past or present.

From November 2000 to July 2002, PST researchers have studied for ESA-ESOC the problem of data return from Mars Express. It is a particular sub-problem in the complex domain of the Mars Express space mission, consisting of synthesizing the downlink operations that allow Earth-bound transmission of the on-board telemetry (data produced by payload activities and by different on-board devices which monitor the conditions of the spacecraft) during downlink connections. This problem has been named Mars EXpress Memory Dumping Problem (MEX-MDP).

The main aims of the study have been:

To achieve these goals the PST has designed and implemented the Mexar tool: this system integrates several intelligent technologies like problem solving techniques based on the CSP (Constraint Satisfaction Problem) paradigm and interactive techniques from the realm of HCI (Human Computer Interaction).

The tool provides a family of problem solving algorithms and a sophisticated user front-end that allows to understand and manipulate different features of both the current problem and the proposed solution, thus supporting the human mission planner in the decision process. At the same time, it preserves the user's responsibility in taking critical decisions. It provides an environment in which the strength of human reasoning and powerful algorithms are combined to solve a problem as the result of an incremental interactive process. Mexar enhances human solving capabilities by providing facilities for creating different solutions, investigating single critical aspects, optimizing a given solution and allowing a user to guide the search by choosing the solution which is to be carried out.

The Mexar tool has been successfully delivered to ESA-ESOC in May 2002 and is currently subject to advanced experimentation.