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
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