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 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.