This paper gives a survey of the Mars Express orbit design, as it evolved from before launch to arrival at Mars. The orbit selection for Mars Express has major scientific impacts, as the orbit is elliptical, with continuous changes of the latitude and local hour of the pericentre. A first target orbit was defined in 1999 by combining scientific and engineering constraints.
As a very favourable launch date was achieved and the launcher injection error was ‘better than nominal’ (the error removed part of the planned re-targeting), propellant reserves turned out to be available after launch. Part of this was used to improve the target orbit. The plane turn manoeuvre was increased to start with the pericentre near the equator rather… than at 20°S latitude, with the objective of increasing the early observation phase with good day-side viewing conditions.
A few weeks after launch, an anomaly in the spacecraft power system was detected, with a loss of up to 40% in terms of available power. This led to a series of studies on back-up orbits, to the extreme of Sun-synchronous eclipse free orbits. Luckily the problem could be solved at the spacecraft engineering level and the orbit with the best science return could be reached in early February 2004.
A map that shows the necessary condition for avoiding the generation of low-frequency stick-slip of a creep groan is introduced. The map is obtained as a result of comprehensive investigation employing a novel caliper-slider experimental model.
According to the map, creep groan generation is controlled by two dimensionless parameters, designated as stiffness ratio, Sr, and low-frequency stick-slip index, Ls. Stiffness ratio, Sr, is the ratio of structure stiffness to the stiffness at contact interface and Ls is an index formed by various parameters such as normal force, sliding velocity, and difference between static and kinetic coefficients of friction.
On the experimental model, creep groan generation can be avoided if one or both of the following conditions is fulfilled: (a) stiffness… 400). It is expected that the map can be used as a useful guideline for avoiding the generation of similar phenomenon on a real brake system. [PUBLICATION ABSTRACT]
We consider the inverse problem in classification systems described as follows. Given a set of prototype cases representing a set of categories, a similarity function, and a new case classified in some category, we find the cost-minimizing changes to the attribute values such that the case is reclassified as a member of a (different) preferred category. The problem is “inverse” because the usual mapping is from a case to its unknown category.
The increased application of classification systems in business suggests that this inverse problem can be of significant benefit to decision makers as a form of sensitivity analysis. Analytic approaches to this inverse problem are difficult to formulate as the constraints are either not available or difficult to determine. To investigate this inverse… problem, we develop several genetic algorithms and study their performance as problem difficulty increases.
We develop a real genetic algorithm with feasibility control, a traditional binary genetic algorithm, and a steepest ascent hill climbing algorithm. In a series of simulation experiments, we compare the performance of these algorithms to the optimal solution as the problem difficulty increases (more attributes and classes). In addition, we analyze certain algorithm effects (level of feasibility control, operator design, and fitness function) to determine the best approach. Our results indicate the viability of the real genetic algorithm and the importance of feasibility control as the problem difficulty increases.