magnetic field instrument for the bepicolombo planetary orbiter magnetic cleanliness and data...
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![Page 1: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/1.jpg)
Magnetic Field Instrument for the
BepiColombo Planetary Orbiter
Magnetic Cleanliness and Data Processing Methods
Chris Carr & André Balogh
U. Auster (IGeP), M. Delva (IWF)
February 2005
![Page 2: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/2.jpg)
BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 2
The Problem
1. Short boom– Minimum 1.5m– Maximum 3m– Due to mass and thermal/mechanical stability considerations
2. Magnetically ‘dirty’ spacecraft– Magnetics shall not be a design or cost driver for the spacecraft
3. Planetary magnetic field determination requires high accuracy magnetometer measurements
Q: How do we meet the science goals?
![Page 3: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/3.jpg)
BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 3
1. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets
2. MERMAG Consortium – Previous Experience
3. Dual Magnetometer MethodsExamples: The Double Star Mission
The Venus Express Mission
4. MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan
![Page 4: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/4.jpg)
BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 4
1. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets
2. MERMAG Consortium – Previous Experience
3. Dual Magnetometer MethodsExamples: The Double Star Mission
The Venus Express Mission
4. MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan
![Page 5: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/5.jpg)
BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 5
Instrument Performance
• The DC part of the spacecraft field shall be low enough to allow operation of the magnetometer in its most sensitive operating range
• The stability of the spacecraft magnetic field is the most critical parameter
Meeting the science goals: The magnetometer shall have an accuracy of 1nT
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 6
Magnetic Cleanliness• Magnetic cleanliness objective:
To provide an acceptable magnetic environment without major cost / schedule / mass impact at system level
Parameter Performance Goal
Residual DC Magnetic Field measured at MAG OB sensor
< 100nT (TBC)
Stability of Residual DC Magnetic Field measured at MAG OB sensor
< 2nT variation (TBC)
Determination of the variable part of the spacecraft field by in-flight (dual-magnetometer) measurements
5%
MERMAG Proposed Accuracy(including all instrument & spacecraft error sources)
0.5 nT
• MERMAG accuracy includes ALL error sources:– Sensor calibration (knowledge), including stability w.r.t. temperature
– Determination of spacecraft contributions, both DC and AC
– Sensor position / attitude knowledge, and timing accuracy
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 7
1. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets
2. MERMAG Consortium – Previous Experience
3. Dual Magnetometer MethodExamples: The Double Star Mission
The Venus Express Mission
4. MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan
![Page 8: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/8.jpg)
BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 8
Team Experience
InstituteImperial
College
London
IGEP
TU-Braunschweig
IWF
Graz
ISAS
JAXA
ExpertiseSpecification
Coordination
DC & AC Magnetic Analysis
‘MAGNET’ Software
DC & AC Magnetic Analysis
DC & AC Magnetic Analysis
Missions
(PI)
Ulysses, Cassini,
Cluster, Double Star
Cassini, Cluster, Double Star,
Rosetta, Venus Express, Themis
Cassini, Cluster, Double Star,
Rosetta, Venus Express, Themis
Nozomi, Selene
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 9
Magnetically ‘Clean’ Spacecraft
• Ulysses
• Cassini
• Cluster
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 10
Magnetically ‘Dirty’ Spacecraft
• Rosetta– No magnetic control– Units measured (DC)– System model performed– Result: BAD
• Double Star– Supposed to be clean– Solar Panels not tested before launch– Result: BAD
• Venus Express– NO magnetic control– NO measurement– NO System model– Result: ???
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 11
1. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets
2. MERMAG Consortium – Previous Experience
3. Dual Magnetometer MethodsExamples: The Double Star Mission
The Venus Express Mission
4. MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan
![Page 12: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/12.jpg)
BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 12
The Dual Magnetometer Method
…for determination of spacecraft fields
Principle
• Two radially separated magnetometers
plus
• Knowledge of location on the spacecraft of the disturbing source
allows
• Estimate strength of the disturbing field
• Original technique Ness et al. (1971)
• Successful application to Double Star
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 13
Dual Magnetometer:Application to Double Star
• Magnetic disturbances:– Signals at the spin frequency and harmonics
• Source: solar panels
– Sudden shifts in the DC ‘background’ field from the spacecraft• Source: current loops – power distribution
U. Auster, K.-H. Fornacon, E. Georgescu
IGeP TU-BS
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 14
Eclipse
Field generated by current loop
Field generated by solar arrays
Dual Magnetometer:Application to Double Star
• Approach
1. De-spin the data2. Average data over spin-period
– Result: interference signals are reduced to ‘offsets’
– These offsets are unknown, and change with the spacecraft power modes
3. Remove remaining offsets using weighted differences between sensors– Modified dual-magnetometer method
4. Evaluate any residual offsets using traditional calibration techniques
– Result: Accuracy of this spin-averaged data is comparable to the equivalent Cluster magnetometer data
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 15
Application to Venus Express
– NO magnetic control– NO measurement– NO System model
• Highly applicable to BepiColombo
– 3-axis stabilised– Short (1m) boom
M. Delva et al. IWF GrazIGeP TU-BSUniv Kosice
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 16
VEX MC – MeasurementsExample at Alenia – Aug. 2004
S1S2
S3
S4
Solar Array Dynamic Motor (on SC +y side) switched on resp. modes
Idea: learn to know the SC magnetically
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 17
Automatic Correction with Neural Network
Cooperation with Univ. of Kosice (Slovakia)• Basic idea: Event-pattern recognition & correction by neural network• Two sensors are needed -> use difference of change as indicator for event of SC-origin
Neural network “learns” characteristic pattern of event from measurements at two sensors
e.g. from MC - measurements on Earth from magnetometer measurements during commissioning
phase
bscx1, bobsx2- bobsx1
bscz1, bobsz2- bobsz1
bscy1, bobsy2- bobsy1
bscx1, bobsx2- bobsx1
bscz1, bobsz2- bobsz1
bscy1, bobsy2- bobsy1
time t1 time t2
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 18
Test of method with real in-flight data: Double Star data (TC-1)
Difference in Btotal at 2 sensors
Recognize jumps > 1 nTCorrect data -> difference
disappears
before correction
after correction: diff < 1 nT
Neural Network Tested with Double Star data
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 19
Double Star / Venus Express: Lessons for BepiColombo
• Magnetic cleanliness programme should give equal effort to– DC magnetic– Stray fields from current loops (Double Star experience)– Moving parts (Venus Express)
• Characterise the spacecraft before launch– Sufficient mode information in the housekeeping
• Magnetometer Instrument Design– Optimised dual-sensor modes of operation– Programmable anti-aliasing filters
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 20
Venus Express / Mars Express Experience:Problem sub-systems
SC subsystem Mean dipole mom. [mA m2]
Expected field at VEX-MAG IS
[nT]
Expected field at VEX-MAG OS( 1m) [nT]
GYROS 74 +/- 39 35 - 152 2 - 9
SADM 708 +/- 234 54 - 213 8 - 39
Reaction Wheels 1,2,3 908 +/- 552 19 – 34 6 - 9
Reaction Wheel 4
963 +/- 459 21 – 32 / - 11
Thrusters, different modes
602 +/- 161 16 - 30 5-10
• Similar for Rosetta
• Can identify problem sub-systems early for Bepi
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 21
1. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets
2. MERMAG Consortium – Previous Experience
3. Dual Magnetometer MethodsExamples: The Double Star Mission
The Venus Express Mission
4. MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan
![Page 22: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/22.jpg)
BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 22
MERMAG Support• Expertise, Experience & Modelling s/w
– Available to the BepiColombo mission
InstituteImperial
College
London
IGEP
TU-Braunschweig
IWF
Graz
ISAS
JAXA
ExpertiseSpecification
Coordination
DC & AC Magnetic Analysis
‘MAGNET’ Software
DC & AC Magnetic Analysis
DC & AC Magnetic Analysis
Missions
(PI)
Ulysses, Cassini, Cluster,
Double Star
Cassini, Cluster,
Double Star, Rosetta, Venus
Express, Themis
Cassini, Cluster,
Double Star, Rosetta, Venus
Express, Themis
Nozomi, Selene
![Page 23: Magnetic Field Instrument for the BepiColombo Planetary Orbiter Magnetic Cleanliness and Data Processing Methods Chris Carr & André Balogh U. Auster (IGeP),](https://reader036.vdocuments.us/reader036/viewer/2022062308/56649dd05503460f94ac5811/html5/thumbnails/23.jpg)
BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 23
Magnetic Control for BepiColombo
• Specification for each unit: DC and AC at 1m– Gradiometer– MCF– Extend EMC test specification to LF Magnetic– Critical Unit Identification
• Gyros, SADM, Reaction Wheels etc.
• First Steps– Spacecraft design, boom length– Knowledge of magnetic contamination sources– Establish a ‘Magnetic Control Group’ – ESA, MERMAG and industry– Design Guidelines
• For payload
• For industry / system
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 24
Concluding Remarks
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BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005 25
Outline for ESTEC Magnetometer Workshop
• Team experience– ‘Clean’ spacecraft such as Ulysses, Cassini, Cluster– ‘Dirty’ spacecraft such as Rosetta, Double Star, Venus Express
• The Double Star Experience– Why it is magnetic– Basic principles of the dual-magnetometer technique (Ness et al.)– Application to Double Star (using input from Uli, Edita and Karl-Heinz and others)
• Venus Express (using inputs from Magda)– Background– Techniques– Applicability to BepiColombo– Re-use of techniques
• Selene (using inputs from Masaki)– Applicability of the Selene magnetic cleanliness programme to BepiColombo