PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " 2016-05-06 JNO:lawton V01; 2016-05-06 PDS:mafi; 2016-08-18 JNO:lawton; 2016-11-07 JNO:lawton" RECORD_TYPE = STREAM OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "JNO" INSTRUMENT_ID = "FGM" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "MAGNETOMETER" INSTRUMENT_TYPE = "MAGNETOMETER" INSTRUMENT_DESC = " The Juno Magnetometer (MAG) Investigation is a principal science investigation on the Juno New Frontier Mission to Jupiter. MAG will conduct the first global magnetic mapping of Jupiter and contribute to studies of Jupiter's polar magnetosphere. The Juno MAG investigation is designed to acquire highly accurate measurements of the magnetic field in Jupiter's environment, mapping the planetary magnetic field with extraordinary accuracy and spatial resolution (orders of magnitude better than current knowledge). 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 FGM uses two miniature ring-core fluxgate sensors to measure the magnetic field in three components of the vector field. 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 half 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. The MAG instrument suite is described in full detail in [CONNERNEYETAL2016]." END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "CONNERNEYETAL2016" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END