KPL/IK J-MAG Instrument Kernel =============================================================================== This instrument kernel (I-kernel) contains the Magnetometer Instrument (JMAG) sensors' parameters. Version and Date ------------------------------------------------------------------------------- Version 0.1 -- July 13, 2022 -- Marc Costa Sitja, ESAC/ESA Updated description values. Removed Platform ID section. Version 0.0 -- July 12, 2016 -- Marc Costa Sitja, ESAC/ESA Initial Release. Pending review by the J-MAG instrument and JUICE Science Operations Working Group teams. References ------------------------------------------------------------------------------- 1. ``Kernel Pool Required Reading'' 2. ``C-kernel Required Reading'' 3. JUICE Frames Definition Kernel (FK), latest version. 4. ``JUICE - Jupiter Icy Moons Explorer. Exploring the emergence of habitable worlds around gas giants. Definition Study report,'' ESA/SRE(2014)1, September 2014 (JUICE Red book v1.0) 5. ``JUICE - JUpiter Icy Moons Explorer MAG (Magnetometer) Experiment Interface Document - Part B,'' JUICE-ICL-MAG-EID-B, Issue 2.4, 07 April 2016 Contact Information ------------------------------------------------------------------------------- If you have any questions regarding this file contact the ESA SPICE Service (ESS) at ESAC: Alfredo Escalante Lopez (+34) 91-8131-429 spice@sciops.esa.int or the JUICE Science Operations Center at ESAC: Marc Costa Sitja (+34) 91-8131-236 Marc.Costa@ext.esa.int Implementation Notes ------------------------------------------------------------------------------- Applications that need SPICE I-kernel data must ``load'' the I-kernel file, normally during program initialization. The SPICE routine FURNSH loads a kernel file into the pool as shown below. CALL FURNSH ( 'frame_kernel_name' ) -- FORTRAN furnsh_c ( "frame_kernel_name" ); -- C cspice_furnsh, frame_kernel_name -- IDL cspice_furnsh( 'frame_kernel_name' ) -- MATLAB Loading the kernel using the SPICELIB routine FURNSH causes the data items and their associated values present in the kernel to become associated with a data structure called the ``kernel pool''. Once the file has been loaded, the SPICE routine GETFOV (getfov_c in C, cspice_getfov in IDL and MATLAB) can be used to retrieve FOV parameters for a given instrument or structure. The application program may obtain the value(s) for any other IK data item using the SPICELIB routines GDPOOL, GIPOOL, GCPOOL (gdpool_c, gipool_c, gcpool_c in C, cspice_gdpool, cspice_gipool, cspice_gcpool in IDL and MATLAB). See [1] for details. This file was created with, and can be updated with a text editor or word processor. Naming Conventions and Conventions for Specifying Data ------------------------------------------------------------------------------- All names referencing values in this IK file start with the characters `INS' followed by the NAIF JUICE spacecraft ID number (-28) followed by a NAIF three digit ID code for the JMAG sensors. This is the full list of names and IDs for the RPWI instrument described by this IK file: Name NAIF ID --------------------- --------- JUICE_JMAG_MAGIBS -28300 JUICE_JMAG_MAGOBS -28310 JUICE_JMAG_MAGSCA -28320 JUICE_JMAG_JACS-X -28330 JUICE_JMAG_JACS-Y -28331 The upper bound on the length of the name of any data item is 32 characters. If the same item is included in more than one file, or if the same item appears more than once within a single file, the latest value supersedes any earlier values. Instrument Description and Overview ------------------------------------------------------------------------------- The magnetometer will measure the three components of the local magnetic field vector in the vicinity of the spacecraft in the bandwidth DC up to a maximum of 64Hz. The instrument design is composed of two fluxgate sensors (identified as MAGOBS and MAGIBS) and a Coupled Dark State Magnetometer (CDSM) scalar sensor (identified as MAGSCA). Each sensor will be attached via an IEH, by the Prime, to a single platform mounted electronics box. Each fluxgate is a tri-axial design measuring the three field components Bx, By, Bz and the scalar sensor measures the absolute field |B|. All three sensors should be mounted externally to the spacecraft platform with the MAGSCA sensor positioned at the furthest extremity. The boom should be of appropriate length in order to meet the required magnetic cleanliness requirements of J-MAG. (see [5]). The dual fluxgate solution ensures that the sometimes very small science signal (calibrated relative accuracy better than 0.2 nT will be needed to meet induction-related science requirements) can be separated from the disturbing spacecraft field signature through use of the gradiometer technique. The addition of the scalar sensor enables in-flight calibration of the fluxgates sensors during the operational mission phase without the need for frequent roll manoeuvres. The main characteristics of the J-MAG instrument are provided in the following table: -------------------------------------------------------------------- PARAMETER VALUE ------------------------------ ----------------------------------- Instrument noise performance <10 pT/sqrt(Hz) (at 1 Hz) Fluxgate sensor orthogonality <0.01 deg (calibrated) Offset stability <0.5 nT/100 hours (fluxgate sensor) Absolute accuracy <0.2 nT (scalar sensor) Linearity <0.05 % Operating temperature range -150 to +60 deg (MAGOBS/IBS) for MAGOBS/IBS/SCA sensors -150 to +50 deg (MAGSCA) Performance temperature range -75 to +60 deg (MAGOBS/IBS) for MAGOBS/IBS/SCA sensors -150 to +50 deg (MAGSCA) (calibrated data) Survival temperature rage for -150 to +80 deg MABOBS/IBS/SCA (measured at the MAG Temperature sensor) Normal mode data rate 2292.0 bps (32 & 1 & 1 measurements/s) Gradiometer mode data rate 2232.0 bps (16 & 16 & 1 measurements/s) Burst mode data rate 8952.0 bps (128 & 16 & 1 measurements/s) Fluxgate Measurement range +/-8400 nT, +/-61000 nT MAGOBS Fluxgate Measurement range +/-1000 nT, +/-2000 nT, +/-4000 nT MAGIBS +/-8000 nT, +/-16000 nT Scalar Measurement range 100 - 149588 nT (n=2 mode) Bits per sampled field 20 MAGOBS/MAGIBS component 24 MAGSCA Fluxgate Resolution 16.1 pT (OBS), 15.3 pt (IBS) (in +/8000 nt range) Scalar Resolution 0.58 pT / 0.37 pT (1) -------------------------------------------------------------------- (1) MAGOBS sensor ADC data acquisition uses 24 bits, of which the most significant 20 bits are transmitted to ground. MAGIBS has physically only one range (+/-16,000nT) with 24 bit resolution, 20 bit of the 24 bits can be freely selected for transmission. For both fluxgate sensors, this then corresponds to approximately 16 pT digital resolution in the +/-8000 nT range The scalar sensor resolution depends on the resonance mode used. For the n=2 mode the range is 100 - 149,588 nT corresponding to a digital resolution of 0.557 pT, for the n=3 mode the range is 100 - 99,791 nT and digital resolution of 0.371 pT. The MAGOBS Fluxgate sensor bears heritage from those flown on the Cassini and Double Star spacecraft. It is very similar in design to the model currently under development for Solar Orbiter. The sensor features two orthogonally-mounted low noise Permalloy ring-cores each of which senses the magnetic field in two axes in the plane of the sensor. The cores are mounted to a Macor glass-ceramic structure which is in turn mounted to a GFRP insulating support which is fastened to a Titanium baseplate. Each ring-core has associated with it a small PCB which makes the electrical connections between the wiring harness and the ring-core, and also a tuning capacitor, thermistors and sensor heaters. The MAGIBS fluxgate sensor consists of two single ring-core elements measuring the magnetic field in X- and Y-direction. The magnetic field in Z-direction is measured by a coil surrounding both single sensors. The sensor core (ring-cores, pick-up and feedback coils) is identical to the ones used for Rosetta Lander, Venus Express, THEMIS and BepiColombo. The sensor electronics generates an excitation AC current (fundamental frequency of approx. 9.6 kHz), which drives the soft magnetic core material in the sensor deep into positive and negative saturation. According to the fluxgate principle, the external magnetic field distorts the symmetry of the magnetic flux and generates field proportional to even harmonics of the excitation frequency in the sense coils. Sensor accommodation and thermal control of the MAGIBS sensor is ensured via an insulting base plate and standoff made from PEEK which provides both sufficient mechanical robustness and thermal isolation. The baseplate is manufactured with a reference edge machined with high precision, this is required to reduce the aignment error introduced from sensor mounting to the boom to below the required value allowed in the instrument alignment budget. The MAGSCA sensor uses the energy from a light source (e.g. laser diode) for exciting electrons in an atom for measuring the magnitude of the surrounding magnetic field. In the MAGSCA the light source is a multi-modulated laser which optically excites rubidium atoms in a glass cell according to the atomic level. When the spectral components of the laser light exactly match the energy differences between the atomic levels special quantum-mechanical mechanism called Coherent Population Trapping (CPT) is taking place in the rubidium atoms. As a result, the atoms inside the sensor cell are transferred into a so called dark state where the atoms are decoupled from the light field. In this state the cell gets more transparent (less laser light absorption) which can be detected by a photo diode. The MAGSCA comprises five subunits a Low Frequency (LF) block, High Frequency (HF) block, Vertical Cavity Surface Emitting Laser (VCSEL) with housing and fibre coupler, sensor unit and sensor harness. The LF and HF blocks as well as the laser are mounted in the J-MAG electronics box inside the spacecraft whereas the sensor unit is designed for boom mounting. Mounting Alignment ------------------------------------------------------------------------------- J-MAG is accommodated in the spacecraft boom (JUICE_MAG_BOOM). When deployed the boom will be 10.6m long. The length of the boom has been chosen to enable the system to satisfy the stringent maximum allowed spacecraft magnetic field requirements imposed by J-MAG on the spacecraft. MAGSCA is located at the tip of the boom to be farthest away from any influence of the spacecraft, MAGOBS is close to MAGSCA and MAGIBS further down the boom towards the spacecraft. The spacing between MAGOBS and MAGIBS is optimised to allow them to operate together in a Gradiometer mode to make estimations of the spacecraft magnetic field. MAGSCA does not require aligment but MAGOBS and MAGIBS have their own Unit Alignment Reference Frames. Refer to the latest version of the JUICE Frames Definition Kernel (FK) [3] for the J-MAG reference frame definitions and mounting alignment information. End of IK file.