PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 1977-12-01 NOTE = "INST.TXT contains the instrument description." END_OBJECT = TEXT END INSTRUMENT: FLUXGATE MAGNETOMETER SPACECRAFT: VOYAGER 1 Instrument Information ====================== Instrument Id : MAG Instrument Host Id : VG1 Pi Pds User Id : NNESS Principal Investigator : NORMAN F. NESS Instrument Name : FLUXGATE MAGNETOMETER Instrument Type : MAGNETOMETER Build Date : 1977-09-05 Instrument Mass : 5.600000 Instrument Length : 13.000000 Instrument Width : UNK Instrument Height : UNK Instrument Serial Number : UNK Instrument Description ====================== The magnetic field experiment carried out on the Voyager 1 mission consists of dual low field (LFM) and high field magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFM's, permit the separation of the spacecraft magnetic fields from the ambient fields. Additional reliability is achieved through electronics redundancy. The wide dynamic ranges of +/- 0.002 G for the LFM's and +/- 20 G for the HFM's, low quantization uncertainty (+/- 12.4, 488 nanoTesla respectively), low sensor RMS noise level (0.006 nanoTesla), and the use of data compaction schemes to optimize the experiment information rate all combine to permit the study of a broad spectrum of phenomena during the mission. Science Objectives ================== The investigations of the magnetic fields and magnetospheres of the major planetary systems in the outer Solar System and their interactions with the solar wind are primary objectives of the space exploration program to be conducted during the Voyager 1 mission. In addition, the investigation of the interplanetary magnetic field phenomena during the flights is of fundamental importance both to the understanding of the magnetospheric observations and to a number of outstanding questions in basic plasma physics and in the general dynamics of the solar wind. If the Heliospheric boundary is penetrated, accurate measurement of the interstellar magnetic field is also an important objective. Operational Considerations ========================== There are no special operational considerations for the magnetometer described in [BEHANNONETAL1977]. All magnetometer data are calibrated. Three types of in-flight calibrations are performed: 1) sensitivity calibrations, 2) zero-level calibrations, based on rolls of the spacecraft, and 3) boom- alignment calibrations based on the activation of on-board coils and resulting data (especially important when dual magnetometers are used and in strong fields for any magnetometer). Sensitivity calibrations (for 8 ranges) are done approximately once every two months (early in the mission they were done more frequently). The magnetometer team generally use one or two axis rolls (cruise maneuvers, CRSMR's) of the spacecraft for zero level calibrations as often as they are provided which is variable this is about three times per year for the so-called mini-CRSMR's, which are two axis rolls. Full CRSMR's and z-axis (only) roll-maneuvers have not occurred within the last few years (full CRSMR's and mini's differ only in the number of rolls in each). The magnetometer team usually succeeds in arguing for a series of rolls near each planetary encounter. Boom-alignment calibrations were done once after launch and around the time of the Jupiter encounter. Others have been executed, but it has been determined that the inter- sensor misalignment is small and constant. Measured Parameters =================== The following LFM and HFM values are derived from Table 1 in [BEHANNONETAL1977]. LFM Dynamic ranges and quantization uncertainty: Range (nT) Quantization (nT) ---------------------------------------------- 1. +/- 8.8 +/- .0022 2. +/- 26 +/- .0063 3. +/- 79 +/- .019 4. +/- 240 +/- .059 5. +/- 710 +/- .173 6. +/- 2100 +/- .513 7. +/- 6400 +/- 1.56 8. +/- 50,000 +/- 12.2 HFM Dynamic ranges and quantization uncertainty: Range (nT) Quantization (nT) ---------------------------------------------- 1. +/- 5E+4 +/- 12.3 2. +/- 2E+6 +/- 488 Calibration Description ======================= The 13 meter Astromast booms have proved in extensive pre-flight testing to be highly rigid with respect to bending motions but soft to torsional or twisting motion. Deployment repeatability test have shown as much as +/- 7 degrees uncertainty in the knowledge of the boom twist angle (about the boom axis) at the magnetometer sensor positions, compared with +/- 0.5 uncertainty in bend angles (rotation about axes orthogonal to the boom axis). In order to minimize sensor alignment uncertainties, a method to estimate an angular correction matrix was developed that eliminates most of the twist uncertainty and some of the bend uncertainty. A special calibration coil has been wound around the periphery of the spacecraft's high gain antenna to generate, upon command, a known magnetic field at both LFM magnetometer sensors. The difference between measurements taken when the coil is turned on and off is the coil field, independent of all external fields. Using a 20 turn coil of 1/2 amp yields nominal field intensities 0f 33.4 and 6.1 nanoTesla at the inboard and outboard sensors, respectively. All magnetometer data are calibrated. Three types of in-flight calibrations are performed: 1) sensitivity calibrations, 2) zero-level calibrations, based on rolls of the spacecraft, and 3) boom-alignment calibrations based on the activation of on-board coils and resulting data (especially important when dual magnetometers are used and in strong fields for any magnetometer). Sensitivity calibrations (for 8 ranges) are done approximately once every two months (early in the mission they were done more frequently). The magnetometer team generally use one or two axis rolls (cruise maneuvers, CRSMR's) of the spacecraft for zero level calibrations as often as they are provided which is variable this is about three times per year for the so-called mini-CRSMR's, which are two axis rolls. Full CRSMR's and z-axis (only) roll-maneuvers have not occurred within the last few years (full CRSMR's and mini's differ only in the number of rolls in each). The magnetometer team usually succeeds in arguing for a series of rolls near each planetary encounter. Boom-alignment calibrations were done once after launch and around the time of the Jupiter encounter. Others have been executed, but it has been determined that the inter-sensor misalignment is small and constant. For more information, consult [BEHANNONETAL1977]. LFM and HFM Detectors ===================== Detector Type : RING CORE Detector Aspect Ratio : 0.000000 Nominal Operating Temperature : 273.000000 Total Fovs : 1 Data Rate : UNK Sample Bits : 12 The magnetometer consists of 6 ring core detectors. These are designated as low field magnetometers (LFM) 1-3 and high field magnetometers (HFM) 1-3. The basic sampling rate is .06 +/- .006 seconds. Sampling rate for the high field system is .6 seconds. The detectors measure in the interval of +/- 2.0E+6 nT for HFM, and +/- 5.0E+4 for LFM. Nominal operating temperature for all detectors is 273 K, though the sensors were tested over a range of +/- 60 degrees about the nominal temperature. Both high and low field magnetometer sensors utilize a ring core geometry and thus have lower drive power requirements and better zero level stability than other types of fluxgates and are smaller in size [ACUNA1974]. The cores consist of an advanced molybdenum alloy, especially developed in cooperation with the Naval Surface Weapons Center, White Oak, Maryland, which exhibits extremely low noise and high stability characteristics. The use of this alloy and the ring core sensor geometry thus allows the realization of compact, low power, ultrastable fluxgate sensors with a noise performance that is improved almost an order of magnitude over the best previously flown fluxgate sensors. The HFM's use specially processed miniature ring cores (1 cm diameter) which minimize the power required to measure large fields. This description is taken directly from [BEHANNONETAL1977]. Vector Components ----------------- The LFM1 detector and the HFM1 detector are designated as the detectors which measure the i component of the vector (i,j,k). The LFM2 detector and the HFM2 detector are designated as the detectors which measure the j component of the vector (i,j,k). The LFM3 detector and the HFM3 detector are designated as the detectors which measure the k component of the vector (i,j,k). 'HFM' Section Parameter 'MAGNETIC FIELD COMPONENT' -------------------------------------------------- Instrument Parameter Name : MAGNETIC FIELD COMPONENT Sampling Parameter Name : TIME Instrument Parameter Unit : NANOTESLA Minimum Instrument Parameter : -2000000.000000 Maximum Instrument Parameter : 2000000.000000 Minimum Sampling Parameter : 0.600000 Maximum Sampling Parameter : 0.600000 Noise Level : 0.006000 Sampling Parameter Interval : 0.600000 Sampling Parameter Resolution : 0.600000 Sampling Parameter Unit : SECOND A measured parameter equaling the magnetic field strength (e.g. in nanoTeslas) along a particular axis direction. Usually the three orthogonal axis components are measured by three different sensors. 'LFM' Section Parameter 'MAGNETIC FIELD COMPONENT' -------------------------------------------------- Instrument Parameter Name : MAGNETIC FIELD COMPONENT Sampling Parameter Name : TIME Instrument Parameter Unit : NANOTESLA Minimum Instrument Parameter : -50000.000000 Maximum Instrument Parameter : 50000.000000 Minimum Sampling Parameter : 0.060000 Maximum Sampling Parameter : 0.060000 Noise Level : 0.006000 Sampling Parameter Interval : 0.060000 Sampling Parameter Resolution : 0.060000 Sampling Parameter Unit : SECOND A measured parameter equaling the magnetic field strength (e.g. in nanoTeslas) along a particular axis direction. Usually the three orthogonal axis components are measured by three different sensors. Electronics =========== The instrument is composed of two completely redundant systems: the 'P' or primary system and the 'S' or secondary system. The experiment electronics instrumentation consists of the flux-gate magnetometer electronics and associated controls, and the calibration and data processing electronics. Complete redundancy is provided for the analog to digital converters, data and status readout buffers, command decoders and power converters. Thus not only can the two magnetometers of a system be interchanged, but considerable cross-strapping within the electronics permits interchange of critical internal functions as well. This significantly reduces the impact of single-component failure on the ability of the experiment to continue successful operation during the mission duration of > 4 years. This description is directly transposed from [BEHANNONETAL1977] page 249. Operational Modes ================= Data Path Type : REALTIME Instrument Power Consumption : 2.200000 In the CRUISE mode, only the LFM subsystem is operating. The basic sample rate in this mode is 50/3 vectors/second. In the ENCOUNTER mode, both LFM and HFM subsystems are operating. The basic sample rate in this mode is 50/3 vectors/second for the LFM system and 5/3 vectors/second for the HFM system. Instrument Mounting =================== The LFM is located near the tip of the magnetometer boom and the HFM is located near the spacecraft body. See [BEHANNONETAL1977] for a picture of the actual magnetometer mounting positions and a complete description.