PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " 2016-05-15 JNO:lawton V01" RECORD_TYPE = STREAM OBJECT = DATA_SET /* was dATA_SET_ID = "JNO-SW/J-3-FGM-CALIBRATED-V1.0" */ DATA_SET_ID = "JNO-SW-3-FGM-CAL-V1.0" OBJECT = DATA_SET_INFORMATION /* was dATA_SET_NAME = "JUNO FGM CALIBRATED DATA SW/J V1.0" */ DATA_SET_NAME = "JUNO FGM CALIBRATED DATA SW V1.0" DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_OBJECT_TYPE = TABLE START_TIME = 2011-235T15:06:11 STOP_TIME = 2018-051T23:59:59 DATA_SET_RELEASE_DATE = 2016-11-04 ARCHIVE_STATUS = "PRE PEER REVIEW" PRODUCER_FULL_NAME = "JOHN CONNERNEY" DETAILED_CATALOG_FLAG = "N" CITATION_DESC = "J.E.P. Connerney (GSFC), Juno MAG CALIBRATED DATA SW/J V1.0, NASA Planetary Data System, 2016" DATA_SET_TERSE_DESC = "The Juno Fluxgate Magnetomer (FGM) calibrated observations consist of time and position tagged magnetic field samples in physical units and coordinate systems collected by the FGM instrument during cruise and orbital operations at Jupiter." ABSTRACT_DESC = " Abstract ======== This data set consists of the Juno FGM calibrated observations. The FGM sensor block uses two miniature ring-core fluxgate sensors to measure the magnetic field in three components of the vector field There are multiple FGM data products to accomodate different coordinate systems." DATA_SET_DESC = " Data Set Overview ================= The data set consists of calibrated observations. The MAG measures the vector magnetic field. There are three principal coordinate systems used to represent the data in this archive. The SE coordinate system is a Spacecraft- Solar equatorial system and it will be used for cruise data only. The sun-state (ss) and planetocentric (pc) will be used for Earth Fly By (EFB) and Jupiter orbital data. Cartesian representations are used for all three coordinate systems. These coordinate systems are specified relative to a 'target body' which may be any solar system object (but for this orbital operations will Jupiter). In what follows we will reference Jupiter as the target body, but, for example, if observations near a satellite (such as Io) are desired in Io-centric coordinates, the satellite Io may be specified as the target body. The SE coordinate system is defined using the sun-spacecraft vector as the primary reference vector; sun's rotation axis as the secondary reference vector (z). The x axis lies along the sun-spacecraft vector, the z axis is in the plane defined by the Sun's rotation axis and the spacecraft-sun vector. The y axis completes the system. The ss coordinate system is defined using the instantaneous Jupiter-Sun vector as the primary reference vector (x direction). The X-axis lies along this vector and is taken to be positive toward the Sun. The Jupiter orbital velocity vector is the second vector used to define the coordinate system; the y axis lies in the plane determined by the Jupiter-Sun vector and the velocity vector and is orthogonal to the x axis (very nearly the negative of the velocity vector). The vector cross product of x and y yields a vector z parallel to the northward (upward) normal of the orbit plane of Jupiter. This system is sometimes called a sun-state (ss) coordinate system since its principal vectors are the Sun vector and the Jupiter state vector. The planetocentric (pc) coordinate system is body-fixed and rotates with the body as it spins on its axis. The body rotation axis is the primary vector used to define this coordinate system. Z is taken to lie along the rotation axis and be positive in the direction of positive angular momentum. The X-axis is defined to lie in the equatorial plane of the body, perpendicular to Z, and in the direction of the prime meridian as defined by the IAU. The Y axis completes the right-handed set. Data in the vicinity of the moons of Jupiter (Io, Europa, Ganymede, Callisto) may be provided in separate files in moon centered coordinate systems, if it turns out that the mission plan affords an opportunity to acquire data in the immediate vicinity of any of these bodies The planetocentric and SS data follows the definitions above with the reference body being the moon or target specified via option in the command line All of the archived data files are simple and readable ASCII files with attached documentation in a header that precedes the columns of data. Files using a coordinate system centered on a target body other than Jupiter are identified via the target body listed on the command line which appears in the header along with an audit trail of supplementary engineering (kernel) files. The output from the processing program is in Standard Time Series (STS) format. The Object Description Language (odl) header is included in the STS file. There will also be a detached PDS label file describing the contents of the STS file. Each data file contains the observations collected on a given UTC day. Instrument Overview =================== The MAG Instrument Suite consists of two boom mounted observing platforms (MAG Optical Bench, or MOB) each supporting a vector Fluxgate Magnetometer (FGM) and two non-magnetic Advanced Stellar Compass (ASC) Camera Head Units (CHUs). The ASC determines the attitude of the MOB in inertial space and relative to the JUNO spacecraft's Stellar Reference Units (SRU). The FGM was built at the Goddard Space Flight Center (GSFC); the ASC was built at the Technical University of Denmark (DTU). The Juno FGM is fully redundant, with two identical power converters providing power to one of two identical field programmable gate array (FPGA)-based digital systems. Only one set (power converter and digital system) is powered at a time; the other is a cold back-up. Either set receives commands from, and transmits data to, either side of the spacecraft command and data handling (C&DH) unit through redundant interfaces. Two identical sets of analog electronics, both continuously powered by either power converter, drive the outboard (OB) and inboard (IB) sensors, via separate cables connecting the remote FGM sensors and electronics box, and both are controlled by and communicate with either of the digital systems. No single point failure can result in loss of data from both OB and IB FGM sensors. Each FGM sensor block uses two miniature ring-core fluxgate sensors to measure the magnetic field in three components of the vector field. Each of the two ring-core sensors measures the field in two orthogonal directions in the plane of the ring core. With two such sensors, oriented in planes intersecting at 90 degrees, all three components of the vector field are measured (one component measured, redundantly, by both). The sensor electronics uses negative feedback to null the magnetic field in each core, providing linearity over the full dynamic range of the instrument. The field in each ring core is both sensed and nulled by a pair of nested coils within which the ring core resides. Each coil nulls the field in one of the two perpendicular axes that define the plane of the ring core sensing element. All elements are maintained in precise alignment by a sensor block assembly constructed of a machinable glass ceramic with low thermal expansion (MACOR) and excellent mechanical stability. The FGM sensor block attaches to the optical bench via a three point kinematic mount to maintain accurate alignment over the range or environments experienced. The FGM sensor block is designed to operate at about 0 degrees C, whereas the optical bench and CHUs are designed to operate at about -58 degrees C to minimize noise and radiation effects. The FGM sensor block is thermally isolated from the optical bench via the three point kinematic mount and individual thermal blanketing. The FGM sensor itself is impervious to radiation effects. The two FGM sensors are separated by 2 meters on the MAG boom, one sensor (inboard, or 'IB' sensor) is located 2 m radially outward from the end of the solar array and the other sensor (outboard, or 'OB' sensor) is located at the outer end of the MAG boom. This arrangement ('dual magnetometer') provides the capability to monitor spacecraft- generated magnetic fields in flight. The MAG boom is located on the outermost end of one (+x panel) of three solar panels and is designed to mimic the outermost solar array panel (of the other two solar array structures) in mass and mechanical deployment. The OB and IB sensor packages are identical. The CHUs measure the attitude of the sensor assembly continuously in flight to 20 arcsec and are used to establish, and continuously monitor, the attitude of the sensor assembly with respect to the spacecraft SRUs through cruise, orbit insertion at Jupiter, and initial science orbits. In addition to the extraordinarily accurate attitude reference provided by the MAG investigation's multiple ASC CHUs, the spacecraft provides (reconstructed) knowledge of the FGM sensor assembly attitude to an accuracy of 200 arcsec throughout the mission, using sensors on the body of the spacecraft and knowledge of the attitude transfer between the ASC camera heads and spacecraft SRUs. This provides a redundant attitude determination capability that could be used if ASC attitude solutions are interrupted for any reason (e.g., blinding by a sunlit Jupiter obscuring the field of view for certain geometries, radiation effects). If this redundant capability is required at any time, the stability of the mechanical system (MAG boom, solar array hinges, structure, and articulation strut) linking the body of the spacecraft (SRU reference) to the FGM sensors (and CHUs) is an important element in satisfying the spacecraft requirement. The Juno MAG sensors are remotely mounted (at approximately 10 m and 12 m) along a dedicated MAG boom that extends along the spacecraft +x axis, attached to the outer end of one of the spacecraft's three solar array structures. This design provides the maximum practical separation between MAG sensors and spacecraft to mitigate spacecraft-generated magnetic fields which would otherwise contaminate the measurements. A comprehensive magnetic control program is in place to ensure that the spacecraft magnetic field at the MAG sensors does not exceed 2 nT static or 0.5 nT variable. The separated, dual FGM sensors provide capability to monitor spacecraft-generated magnetic fields in flight. The JUNO sensor design covers the wide dynamic range with six instrument ranges (see below) increasing by factors of four the dynamic range in successive steps. The analog signals are digitized with a 16 bit analog to digital (A/D) converter, which yields a resolution of +/- 32768 steps for each dynamic range. In the table below, resolution, equal to 1/2 the quantization step size for each range, is listed in parentheses. FGM Characteristics Dual Tri-Axial Ring Core Fluxgate Dynamic range (resolution) 16.3840 G (+/-25.0 nT) 4.0960 G (+/-6.25 nT) 1.0240 G (+/-1.56 nT) 0.2560 G (+/-0.391 nT) (1 G = 100,000 nT) 6400 nT (+/-0.10 nT) 1600 nT (+/-0.02 nT) Measurement accuracy: 0.01% absolute vector accuracy Intrinsic noise level <<1 nT (range dependent) Zero level stability <1 nT (calibrated) Intrinsic sample rate 64 vector samples/s The data from each sensor can be in one of eight data formats. The instrument intrinsic sample rate of 64 samples/second is supported in data formats 0 and 1; averages over 2 to the n power samples (n = 1,2,3,4,5,6) are supported in telemetry modes 2 through 7. See the JNO_FGM_INST.CAT file for more information and [CONNERNEYETAL2016] for full details. Parameters ========== The FGM powers up in operational mode and returns telemetry immediately every clock tic (2 seconds). The FGM may be operated in autoranging mode, or manual range commands may be sent to fix the instrument in any of its dynamic ranges. Likewise any telemetry mode may be selected, depending on telemetry resource allocation. In addition, packets of engineering telemetry (in addition to science telemetry packets) are telemetered at a variable rate, from one per 2 seconds to one per 512 seconds, per commanded state. Calibration Overview ==================== The FGMs were calibrated in the Planetary Magnetospheres Laboratory and the GSFC Mario H. Acuna (MHA) Magnetic Test Facility (MTF), a remote facility located near the GSFC campus. These facilities are sufficient to calibrate the FGMs to 100 parts per million (ppm) absolute vector accuracy. An independent measurement of the magnetic field strength in the 0.25, 1, and 4 Gauss ranges was provided by Overhausen Proton Precession magnetometers placed near the FGM. Scale factor calibration is extended to 16 Gauss using a specialized high field coil and measurement techniques (see JUNO Magnetic Field Investigation instrument paper). A nuclear magnetic resonance magnetometer (Virginia Scientific Instruments) provided the absolute field strength measurements in the 16 Gauss range. Two independent methods are used to calibrate the magnetometers. The vector fluxgates are calibrated in the 22' facility using a method ('MAGSAT method') developed by Mario Acuna and others. This technique uses precise 90 degree rotations of the sensing element and a sequence of applied fields to simultaneously determine the magnetometer instrument model response parameters (the 'A matrix') as well as a similar set of parameters (the 'B matrix') that describe the facility coil orthogonality [instrument paper reference]. The second calibration method (called the 'thin shell' and 'thick shell') uses a large set of rotations in a known field (magnitude) to obtain the same instrument parameters, subject to an arbitrary rotation [Merayo 2000 & 2001]. In the 'thin shell' method, the sensor is articulated through all orientations in a fixed, or known field magnitude. This can be done in a facility like the GSFC 22 foot coil system, wherein any fixed field up to about 1.2 Gauss may be utilized, or it may be done in the Earth's field using the ambient field in a gradient-free region and a system to compensate for variations in the ambient field (normally corrected via a secondary reference magnetometer coupled with a Proton Precession total field instrument). Application of this method in a coil facility (with closed loop control for ambient field variations) allows for the 'thin shell' to be performed at many field magnitudes ('thick shell'). The MAGSAT calibration method provides the instrument calibration parameters referenced to the optical cube mounted on the sensor (or MOB) which defines the instrument coordinate system. These parameters include the instrument scale factors, 3 by 3 instrument response matrix (or 'A' matrix), and zero offsets for each instrument dynamic range. The 'thin shell' method provides the same parameters, but since the method conveys no attitude information, only the symmetric part of the instrument response matrix is determined via 'thin shell'. Nevertheless, it provides a useful independent verification of the MAGSAT calibration. Inflight calibration activities are designed to monitor instrument parameters, primarily zero offsets, and to monitor the relative alignment of the magnetic field sensor platforms (the MOBs) and the spacecraft attitude reference (Stellar Reference Units, or SRUs). Spacecraft generated magnetic fields will be monitored using the dual magnetometer technique and a series of magnetic compatibility tests designed to identify the source of any magnetic signals (if any) associated with spacecraft payloads. Since Juno is a spinning spacecraft, spinning at 1 or 2 rpm nominally, any field fixed in the frame of reference of the spacecraft (e.g., fixed spacecraft-generated magnetic fields, sensor offsets, etc.) is easily identified. In practice we apply an algorithm developed independently by several groups (Acuna, Reviews of Scientific Instruments, 2002) to estimate bias offsets using differences in the measured field. This method handily corrects for biases in the spacecraft x and y axes, but since the spacecraft spins about the z axis, biases in z must be estimated using different methods. One technique utilizes the Alfvenic nature of fluctuations in the solar wind, that is, the magnitude preserving nature of variations in the field. Of course, not all fluctuations are Alfvenic (preserving magnitude) so some care is taken in application of this method to select appropriate events. LEFT OFF Coordinate Systems ================== The MAG data are represented in the following coordinate systems: - spacecraft-solar equatorial - payload - planetocentric - sun-state all described above. Data ==== Data products contain the observations collected on a given UTC day. Each coordinate system in a separate file." CONFIDENCE_LEVEL_NOTE = " Confidence Level Overview ========================= Not applicable. Review ====== The FGM data set was reviewed internally by the MAG team prior to release to the PDS. PDS also performed an external review of the MAG data. Limitations =========== The Juno magnetic field investigation was designed to measure fields to 16 Gauss per axis over 6 dynamic ranges of the instrument, the most sensitive of which is +/- 1600 nT with a quantization step size of 0.05 nT (16 bit A/D). Moreover, the spacecraft magnetic requirement was not to exceed 2 nT static and 0.5 nT variable spacecraft-generated magnetic field. In very weak field environments, such as encountered in outer cruise, accuracy may be expected to be limited by sensor offset and spacecraft magnetic field variations. The combined (static) spacecraft-generated magnetic field and sensor offset may be continuously monitored in flight in the spacecraft x and y axis, since the spacecraft spins (nominally at 1 or 2 RPM) about an axis closely aligned with the spacecraft payload z axis. However, offsets in the z axis need be estimated using the Alfvenic properties in the solar wind (ref. Juno Magnetic field investigation paper in Space Science Reviews). Statistical in nature, estimates of z axis zeros are not continuously available and are less accurate than the x and y zeros. Also, variations in spacecraft field over a time span comparable to a spin period will also lead to larger errors." END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_MISSION MISSION_NAME = "JUNO" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_TARGET TARGET_NAME = {"SOLAR WIND", "EARTH", "JUPITER"} END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = JNO INSTRUMENT_ID = "FGM" END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CONNERNEYETAL2016" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END