## 4 Magnetic sensors for space missions. The implementation of magnetic COTS in spacecrafts
Figure  
Figure 2: The graph represents the roadmap for space of AMR and GMR technologies. In the horizontal axis it is represented the time and in the vertical axis the Test Readiness Level. Below the curves some of the on-ground demonstrations are shown; above the curves the in-flight demonstrations are shown. 2 shows the roadmap of AMR and GMR magnetic sensors. AMR technology was already mature in the nineties and its use on Earth was widely spread. GMR effect in contrast, was discovered in 1988 and has experienced a fast industrial development together with the \"VLIS\" techniques. In 2003 several missions with AMR COTS were launched: the American ION-F [63], the Canadian CanX-1 [64, 65], the Danish DTUsat [66] and AAU Cubesat [67], etc. Some of these spacecraft were based on an Off-The Shelf structure, the Cubesat concept [68], developed by Stanford University and Santa Clara University in 2000 and inspired by the FBC concept. ION-F - the Ionospheric Observation Nanosatellite Formation of the three satellites [69]: DawgStar (University of Washington) [70], USUSat (Utah State University) [71] and HokieSat (Virginia Technological University) [72], all of them between 10 and 15 kg, used the HMC2003 three-axis AMR magnetic COTS sensor by Honeywell for the measurement of the Earth magnetic field up to a 2 \({}^{\circ}\) accuracy together with Fuga 15d CCD cameras by Vector International as Earth's horizon sensors (9 \({}^{\circ}\) accuracy), solar arrays by TECSTAR as Sun sensors (10 \({}^{\circ}\) accuracy) and a three solid-state quartz rate sensor by BEI Systron Donner for the measurement of the angular velocity (0.004 \({}^{\circ}\)/s accuracy). The same sensor was used on board CanX-1, devoted to space-testing of key technologies for future missions. In the same line, but with a different approach were the Danish student projects of cubesat-based platforms - DTUsat by the Danish Technical University and AAU Cubesat by Alborg University. DTUsat used four (for redundancy) one-axis HMC1021 magnetic sensors and AAU Cubesat used the one-axis HMC1001 in combination with the two-axis sensor HMC1002 for a vector measurement of higher resolution. Many other missions have successfully used these AMR analog sensors in the following years like the Spanish NANOSAT (2004) [73], the Norwegian NCubes (2005), the Japanese CUTE 1.7 (2005) or the American ION (2005). GMR sensors have not been flown yet but INTA, the Spanish National Institute of Aerospace Technology, is working in the adaptation of a miniaturized GMR three axis sensors for a triple-cubesat called OPTOS (to be launched in 2009) [34]. In this line, INTA is also working in the validation of a MI-based three-axis experimental sensor for a nanosatellite called NANOSAT-1B (to be launched in the end of this year) respectively. Both satellites, OPTOS and NANOSAT-1B will have quasi-polar low Earth orbits (650 km height approximately) with a maximum intensity of the magnetic field of 48.75 \(\mu\)T (at -60\({}^{\circ}\) latitude). NANOSAT program is the technological experimentation platform of INTA. OPTOS is a picosat of 3 kg for the demonstration of a distributed wireless on-board computer. The resolution required for the experimental magnetic sensors on-board NANOSAT-1B and OPTOS is 10 nT. Figure 3 shows the evolution of AMR-based magnetometers developed by INTA. The institute started flying AMR sensors as ACS in the NANOSAT program because they offered a good trade-off between power, mass, volume and performance and the developments have been gradually miniaturized. The actual goal is to develop double AMR vector sensor with an ASIC as front-end for MetNet Precursor mission. With a total envelope of 135 g for three payloads, this magnetometer will allow us to do some preliminary _in situ_ magnetometry even though some of the scientific objectives could be not reached. In the implementation of VLSI techniques some previous work has already been done with fluxgates.