Magnetometers for space measurements over a wide range of field intensities

2014 The exploration of the earth’s magnetic field out to interplanetary regions has required magnetometers capable of measuring a wide range of field intensities. The past decade has witnessed considerable development of such instruments. Representative of these are the rubidium vapor magnetometer and fluxgates flown on OGO-5 by the Goddard Space Flight Center. For scalar measurements the rubidium vapor magnetometer, with a range of three gammas to fifty thousand gammas, has an error which reaches a maximum of 1.5 gamma at fifty thousand gammas. Present development is directed towards reducing the electronic phase shifts and the experiment weight. For vector measurements, the fluxgate system covers a range ± 4,000 gammas in each of three components with an error of of 0.1 % at the top of the range, and a resolution of ± 1/8 gamma. A fluxgate system is being developed to achieve an accuracy of .01 % up to 60,000 gammas. The current source which has been developed for this system has an accuracy of better than ± .005 % over a temperature range of ± 25°. REVUE DE PHYSIQUE APPLIQUÉE TOME 5, FÉVRIER 1970, PAGE Introduction. One of the many by-products of space research has been the rapid development of magnetometry in the past decade. Many spacecraft explore both magnetospheric and interplanetary regions ; this has emphasized the development of magnetometers capable of measuring over a wide range of field intensities. This paper will discuss some of the wide range magnetometers developed by the Goddard Space Flight Center. The Center’s magnetic field experiment flown on the fifth Orbiting Geophysical Observatory (OGO-5) contains both a rubidium vapor magnetometer and a triaxial fluxgate with a digitally controlled field compensation system. These magnetometers and current development at Goddard Space Flight Center (GSFC) of these two types of magnetometers are described below. Rubidium vapor magnetometer. 1. INTRODUCTION. The development of optical pumping techniques arose from the suggestions in 1949 of F. Bitter [1] and of J. Brossel and A. Kastler [2] for a double resonance technique to detect the radiofrequency resonances of optically excited states of atoms. Observations of the orientation of atoms by optical pumping, both in atomic beams and saturated vapor, followed [3]. In 1957, H. G. Dehmelt [4] pointed out that atomic precession could be observed by the resulting modulation of the transmitted light beam. He also proposed a self-oscillating device. In the same year, W. E. Bell and A. L. Bloom [5] developed a model of double resonance phenomena and they suggested the application of optical pumping methods to the measurement of weak magnetic fields. In 1958, the first optical pumping magnetometer was constructed [6] and in 1961 the space probe Explorer 10 carried a self-oscillating rubidium magnetometer [7]. Experiments using optical pumping magnetometers have also been carried on the first three Interplanetary Monitoring Platforms (IMP 1, 2 and 3) [8]. Mariners 4 and 5 carried "low-field" Helium magnetometers [9]. The Orbiting Geophysical Observatories (OGO 1, 2, 3, 4 and 5) have all included rubidium vapor magnetometers [10, 11]. W. H. Farthing and W. C. Folz [ll] have published a detailed description of the rubidium vapor magnetometer experiments carried on the Polar Orbiting Geophysical Observatories (OGO 2 and 4). Those two experiments and the spacecrafts involved had many similarities to their OGO-5 counterparts. The discussion below is not a complete description of the OGO-5 experiment; rather it is a description of some of the features peculiar to the OGO-5 magnetometers. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:0197000501016400