PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "J. MAFI (PPI), 1998-05-18"
RECORD_TYPE = STREAM
OBJECT = INSTRUMENT
INSTRUMENT_HOST_ID = "VG1"
INSTRUMENT_ID = "MAG"
OBJECT = INSTRUMENT_INFORMATION
INSTRUMENT_NAME = "FLUXGATE MAGNETOMETER"
INSTRUMENT_TYPE = "MAGNETOMETER"
INSTRUMENT_DESC = "
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."
END_OBJECT = INSTRUMENT_INFORMATION
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "ACUNAETAL1981A"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "BEHANNONETAL1977"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "CONNERNEYETAL1982A"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "CRARY&BAGENAL1996"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "DESSLER1983"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "NESSETAL1971"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "NESSETAL1979"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "SANDEL&DESSLER1989"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
END_OBJECT = INSTRUMENT
END
|