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Low Magnetic Field Technology for Space Exploration E.J Low magnetic field technology for space exploration E.J. Iufer To cite this version: E.J. Iufer. Low magnetic field technology for space exploration. Revue de Physique Appliquée, Société française de physique / EDP, 1970, 5 (1), pp.169-174. 10.1051/rphysap:0197000501016900. jpa-00243354 HAL Id: jpa-00243354 https://hal.archives-ouvertes.fr/jpa-00243354 Submitted on 1 Jan 1970 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. REVUE DE PHYSIQUE APPLIQUÉE TOME 5, FÉVRIER 1970, PAGE 169. LOW MAGNETIC FIELD TECHNOLOGY FOR SPACE EXPLORATION By E. J. IUFER (1), National Aeronautics and Space Administration (Nasa), Ames Research Center, Moffet Field, California (U.S.A.). Résumé. 2014 Une observation définitive de la morphologie du champ magnétique inter- planétaire ne dépend pas seulement de la reproductibilité et de l’intégrité spectrale des magnéto- mètres envoyés dans l’espace, mais aussi de l’existence de véhicules ayant des champs perturbateurs négligeables. Un étalonnage convenable des magnétomètres et la possibilité de faire des mesures magné- tiques dans l’espace sont essentiels pour obtenir un résultat. Étant donné le petit nombre de publications portant directement sur la technique de réalisation, bien des recherches concernant la mise au point de matériel pour des observations magnétiques au cours de missions spatiales n’utilisent qu’une petite partie des connaissances disponibles. En conséquence, il a fallu un temps inutilement long pour faire accepter de nouvelles réalisations dans ce domaine ; elles ont en outre, en ce qui concerne les caractéristiques magnétiques et les essais, été considérées avec réticence, sans nécessité par certains. Le but de cet article est de présenter une revue critique de l’état actuel des connaissances dans les domaines des mesures du vecteur champ magnétique à basse fréquence, de la standar- disation des magnétomètres et de la réalisation de véhicules spatiaux à faible champ magnétique. On décrit les caractéristiques des performances de l’appareillage et les techniques instru- mentales utilisées pour la mesure du vecteur champ magnétique standardisé dans le domaine de 0,05 à 60 000 nT (1 nT = 1 gamma). On établit une comparaison entre des modèles pouvant estimer les propriétés magnétiques des matériaux et montages pour véhicules spatiaux à l’aide de nombreux résultats de laboratoire. On discute de façon détaillée les critères généraux et les considérations permettant de comparer les techniques de blindage magnétique, de compensation active du champ, et d’emploi de constituants non magnétiques. Une revue des principaux points de l’étude qui aboutit à la mesure du champ magnétique de 0,25 nT à partir des véhicules du type Pioneer VI est indiquée ; on présente les caractéristiques des véhicules et de l’appareil- lage pour les missions interplanétaires futures. Abstract. 2014 Definitive observation of interplanetary magnetic fields depends not only upon the development of high sensitivity spaceflight magnetometers but also on the availability of spacecraft having negligible disturbance fields. Test results obtained in the Pioneer VI-IX program have demonstrated that through careful design, spacecraft magnetic fields can be reduced by a factor of 25 so that spacecraft field levels of 10-6 gauss or less can be realized. Since the literature contains little information on the magnetic properties of spacecraft parts and materials, low-magnetism design principles and low-field magnetic testing techniques, those recently concerned with low-magnetism design may be working with only a small fraction of the information currently known. A critical review of the current state-of-the-art for low- magnetism spacecraft design and test is presented. Introduction. - Analysis of data from magnetome- ters used in space exploration has changed the concept of the Earth’s magnetic field from that approximated by a dipole in free space to that of the magnetosphere. The boundary of the Earth’s magnetic field is produced by the solar plasma flow which compresses the Earth’s field to about 15 Earth-radii (15 Re) on the day-time side and extends it to greater than 80 Re on the night- time side. Immediately beyond the magnetosphere, one encounters the interplanetary medium where the ambient magnetic field has a quiescent value of about 5 X 10-5 gauss due predominantly to the Sun. At greater solar distances, as illustrated in figure 1, the interplanetary field becomes weaker and at Jupiter FiG. 1. - Magnetic Fields in the Solar System. its value is thought to be about 5 X 10-6 gauss. The ambient field may not decrease significantly at greater (1) Research Scientist, National Aeronautics and Space ranges because of the galactic magnetic field. Administration, Ames Research Center, Moffett Field, Observation of the and Califomia 94035, Presented at Measurement of Low steady-state, temporal spatial Magnetic Fields of Spatial and Geophysical Interest fluctuations ofsuch weak magnetic fields can be comple- Conference, Paris, France, May 19-25, 1969. tely obscured by the spacecraft’s own magnetic field Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:0197000501016900 170 FLUXGATE MAGNETOMETERS where H is the net magnetizing force acting on thé rod, ELEKTRON 2, 4 Ho is the gross external magnetizing force, N is the rod EXPLORER VI, X, XI, XIV, XV, XVIII, XXI demagnetization factor which depends upon geo- XXVI, XXVIII, XXXIII, XXXIV, XXXV metry, and I is the intensity of magnetization. OGO 1- T7 Because the ratio of H0/H for spacecraft parts is OV 2-6 usually large, one finds that spacecraft induction and residual induction can be considered linear for external SP UT NIK 3 field exposures of 15 gauss or more. The ability of PIONEER VI-IX a magnetized rod to produce an external magnetic field is characterized by its magnetic moment, M. PROTON PRECESSION MAGNETOMETERS For magnetizations along the axis of the rod, the VANGUARD I, III magnetic moment is the product of the volume, V, of the rod and its intensity of magnetization, I. The ALKALI VAPOR MAGNETOMETERS intensity of magnetization is related to the induction, B, the EXPLORER X, XVIII, XXI, XX TlIII, XXXIV demagnetization factor, N, and the applied field, Hn, by : OGO I h 0 v 1-10 HELIUM MAGNETOMETERS This expression is approximate because both the inten- of and are functions MARINER IV, V sity magnetization permeability offlux density which is non-uniform in a rod. the above one calculate the SEARCH COIL MAGNETOMETERS Using expression, may induced moment of a rod from : EXPLORER VI OG0 I h Calculations using this approximate method provide FIG. 2. - Having Magnetic Spacecraft results accurate to an order of magnitude or better. Field Experiments. Although several ways are known to analyse the magnetic fields of bodies in two dimensions, it is only unless strict attention is given to the magnetic design recently that an analysis has been performed which and test of the spacecraft. The design of low-magne- treats magnetic fields in three dimension and accommo- tism spacecraft for magnetic exploration require the dates a field-dependent permeability. This analysis and in application of principles techniques which, by A. Halacsy subdivides a magnetic body into a many cases, may be new to structural and electronic finite number of elemental boxes, each having its designers of space flight hardware. magnetic moment concentrated at its center. Partial As showns in figure 2, a large number of scientific differential equations are written for the scalar magne- spacecraft have flown magnetometers. Of the space- tic potential and the permeability of each box. The to the craft measurements reported date, spacecraft partial differential equations are linearized and solved having the lowest magnetic field is the Pioneer with by matrix inversion. This analysis does not require 2.5 X 10-l gauss at the magnetometer sensor located boundary conditions because by avoiding the use of 2 meters from the spacecraft center. vector potential, no integration is necessary. The In the following sections, the nature of spacecraft accuracy of this method increases as the number of will fields, their reduction and measurement be dis- elemental boxes increase. With this method, one cussed. Facility requirements and high sensitivity requires only the hysteresis curve and geometrical shape will be instrument calibration methods described. of a body to calculate its magnetic field. A FORTRAN computer program which solves of Fields. - The The Calculation Spacecraft mag- these equations has been written and successfully netic field of a is a of the indi- spacecraft composite run on an IBM fields fields of all ofits which contain 360/50 computer. Computed vidual static parts alloys for rods, cubes and spheres have been checked against nickel or cobalt and the active fields of iron, produced laboratory measurement by the author and found to electrical current loops. by have greater accuracy than fields calculated by pre- arise from a of Static fields heterogenous assembly vious methods, figure 3. small bodies which can usually be charac- magnetized The calculation of total spacecraft fields can be terized as rods of small geometrically ferromagnetic linear of the vector ratio. The reluctance accomplished by superposition length to diameter high of space fields of subassemblies. Before these analytical tools to that of the ferromagnetic material causes compared were available, the design oflow-magnetism spacecraft the net force inside the rods to be less than magnetizing was based on frequent and detailed measurements of the field.
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