178 sensors were already used on the Mars Exploration Rovers Mission to control numerous motors on  “Spirit” and “Opportunity”.    All these sensors were designed and manufactured by Sensitec GmbH, located in Lahnau, near Wetzlar,  Germany. MR sensors from Sensitec will also be used for the precise positioning of a miniaturized low - mass optical shutter for the MERTIS thermal infra- red imaging spectrometer within the BepiColombo  mission to Mercury. Furthermore,  MR-based current sensors are likely to be part of the power electronics  driving the Thrust Vector Actuators of the Ariane 6 launcher.    Until now the growth in MR applications in space has been opportunistic, with the result that there has  been considerable du plication of effort when developing sensor solutions specifically for use in space.  In  order to focus the effort and to fully exploit the benefits of MR technology for European space  mechanisms and applications , HTS GmbH  and Sensitec GmbH initiated a close collaboration, leading to  dedicated activities for the design and qualification of MR -based angular sensors for space applications.   HTS GmbH is  located in Coswig, Germany specializing in the development and manufacturing of  mechanisms for spacecraft s.  

Magneto -Resistive Effects and S ensor Application  

The magneto- resistive effect has been known for more than 150 years. The British physicist William  Thomson, later known as Lord Kelvin, discovered that the electrical resistance of a conductor changes   under  the influence of a magnetic field. This effect would first be used industr ially more than 120 years  later during the late 1970s  in combination with thin- film technologies derived from the semiconductor  industry. The intelligent arrangement of thin- film st ructures within a sensor enabled the development of  many sensor types for measuring the angle, strength or gradient of a magnetic field. The effect discovered by Thomson was named the “anisotropic magneto- resistive effect” (AMR) and resulted in a  resistanc e change of just a few percent. Nevertheless , this effect was used million- fold in the production  of read- heads for hard discs. At the end of the 1980s , the “giant magneto- resistive effect” (GMR) was  discovered independently by Prof. Grünberg at the Forschungszentrum Jülich in Germany and by Prof. Fert at the University of Paris in France. Here the resistance change was more than 50%, which opened up even more applications for MR sensors. This discovery was awarded the Nobel Prize for Physics in 2007.    Sens itec manufactures AMR - and GMR -based sensors for industrial and automotive applications and  specific terrestrial applications in very harsh environments.  The anisotropic magneto- resistive effect may  be considered the most obvious and simple effect. It can be observed in ferromagnetic materials  such as  iron, nickel and cobalt. The specific resistivity R of these materials is depend ent on the angle α between  the current I and the magnetization vector M. If the directions of the current and magnetization are i n  parallel, the resistivity is at its  maximum, whereas if the directions are perpendicular, then the resistivity is  at its minimum. Base d on this relation, illustrated in  Figure 1, the resistances R considering the AMR - effect can be described by the follow ing equation:  

)2cos(2)( α αRR Rm∆+=        The function R(α) for 0° < =  α  < = 3 6 0 ° is shown in Figure 1(b). It can be seen from Figure 1 that the  resistance R varies around the mean resistance R m as a function of the double angle 2α.