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Magnetic Field Instrument for the BepiColombo Planetary Orbiter

Magnetic Field Instrument for the BepiColombo Planetary Orbiter. Magnetic Cleanliness and Data Processing Methods Chris Carr & Andr é Balogh U. Auster (IGeP), M. Delva (IWF) February 2005. The Problem. Short boom Minimum 1.5m Maximum 3m

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Magnetic Field Instrument for the BepiColombo Planetary Orbiter

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  1. 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

  2. The Problem • Short boom • Minimum 1.5m • Maximum 3m • Due to mass and thermal/mechanical stability considerations • Magnetically ‘dirty’ spacecraft • Magnetics shall not be a design or cost driver for the spacecraft • Planetary magnetic field determination requires high accuracy magnetometer measurements Q: How do we meet the science goals? BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  3. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets • MERMAG Consortium – Previous Experience • Dual Magnetometer MethodsExamples: The Double Star Mission The Venus Express Mission • MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  4. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets • MERMAG Consortium – Previous Experience • Dual Magnetometer MethodsExamples: The Double Star Mission The Venus Express Mission • MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan 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 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 • 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 BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  7. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets • MERMAG Consortium – Previous Experience • Dual Magnetometer MethodExamples: The Double Star Mission The Venus Express Mission • MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  8. Team Experience BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  9. Magnetically ‘Clean’ Spacecraft • Ulysses • Cassini • Cluster 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: ??? BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  11. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets • MERMAG Consortium – Previous Experience • Dual Magnetometer MethodsExamples: The Double Star Mission The Venus Express Mission • MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan 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 BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  13. Dual Magnetometer:Application to Double Star U. Auster, K.-H. Fornacon, E. Georgescu IGeP TU-BS • 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 BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  14. Field generated by current loop Eclipse Field generated by solar arrays Dual Magnetometer:Application to Double Star • Approach • De-spin the data • Average data over spin-period • Result: interference signals are reduced to ‘offsets’ • These offsets are unknown, and change with the spacecraft power modes • Remove remaining offsets using weighted differences between sensors • Modified dual-magnetometer method • Evaluate any residual offsets using traditional calibration techniques • Result: Accuracy of this spin-averaged data is comparable to the equivalent Cluster magnetometer data BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  15. M. Delva et al. IWF GrazIGeP TU-BSUniv Kosice Application to Venus Express • NO magnetic control • NO measurement • NO System model • Highly applicable to BepiColombo • 3-axis stabilised • Short (1m) boom BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  16. VEX MC – MeasurementsExample at Alenia – Aug. 2004 Idea:learn to know the SC magnetically S4 S3 S2 S1 Solar Array Dynamic Motor (on SC +y side) switched on resp. modes BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  17. bscz1, bobsz2- bobsz1 bscz1, bobsz2- bobsz1 bscx1, bobsx2- bobsx1 bscx1, bobsx2- bobsx1 bscy1, bobsy2- bobsy1 bscy1, bobsy2- bobsy1 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 time t1 time t2 • 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 BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  18. Neural Network Tested with Double Star data Test of method with real in-flight data: Double Star data (TC-1) before correction Recognize jumps > 1 nT Correct data -> difference disappears after correction: diff < 1 nT Difference in Btotal at 2 sensors 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 BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  20. Venus Express / Mars Express Experience:Problem sub-systems • Similar for Rosetta • Can identify problem sub-systems early for Bepi BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  21. Magnetometer Performance Requirements vs. Spacecraft Magnetic Cleanliness Targets • MERMAG Consortium – Previous Experience • Dual Magnetometer MethodsExamples: The Double Star Mission The Venus Express Mission • MERMAG Support to the BepiColombo Project & Outline Magnetic Control Plan BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  22. MERMAG Support • Expertise, Experience & Modelling s/w • Available to the BepiColombo mission 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 BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

  24. Concluding Remarks 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 BepiColombo MPO Magnetic Cleanliness C. Carr & A. Balogh. February 2005

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