ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 1 ESA UNCLASSIFIED – For Official Use SWARM QWG Overview of ASM, VFM and STR instruments status and recent events

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 2 ESA UNCLASSIFIED – For Official Use Magnetometers basic principles Vector Field Magnetometer (VFM) Instrument (developed at DTU): linear and highly stable tri-axial flux gate magnetometer scale factors, offsets and non-orthogonalities require calibration (explained later) VFM aligned with highly accurate Star Trackers mounted near VFM, either through the option of using an independent Earth magnetic field model (level 1b option) or through co-estimation approach at level 2 Absolute Scalar Magnetometer (ASM) Instrument (developed at CNES & CEA- LETI): based on Zeeman effect in an optically pumped Helium cell foremost aim: calibration of the magnitude of the magnetic field VFM Instrument measurement continuously operated in Vector mode rather than original Scalar mode owing to high quality vector field measurements (using 3 mutually orthogonal low frequency magnetic fields superimposed onto the He cell)

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 3 ESA UNCLASSIFIED – For Official Use Star Trackers Star Trackers (developed at DTU): 3 Camera Head Units (CHU) with 90° boresight angle between each other STR main electronics unit is the “micro Advanced Stellar Compass” CHUs mounted on a stable optical bench which also supports VFM sensor Photos of ASM sensors and optical bench: Courtesy of DTU Courtesy of CNES

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 4 ESA UNCLASSIFIED – For Official Use Satellite boom Optical bench (which supports STR CHUs & VFM sensor) and ASM sensors mounted on satellite boom:

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 5 ESA UNCLASSIFIED – For Official Use VFM – ASM Residual magnitude (without daily calibration) Courtesy of SWARM ESL

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 6 ESA UNCLASSIFIED – For Official Use VFM calibration principle

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 7 ESA UNCLASSIFIED – For Official Use Start of Residual investigation in Phase E2 Preliminary study by AIRBUS (early April) to identify root source of Residual: investigating possible Residual correlations with various satellite signals & parameters using two different sets of VFM calibration parameters (different Residuals)  inconclusive Task Force convened 23 April to identify Disturbance field variables: local time spacecraft-to-sun attitude orbital frequency possibly orbit height possibly short-period time effect others

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 8 ESA UNCLASSIFIED – For Official Use VFM-ASM scalar: F (component of disturbance parallel to ambient magnetic field)  F = b. | Example of disturbance field model (in spacecraft frame):  disturbance field b depends of sun illumination  background field unit vector depends on location (latitude, longitude)  no time component (accounting e.g. for temperature gradients) Disturbance field FF B b B B Courtesy of SWARM ESL

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 9 ESA UNCLASSIFIED – For Official Use Residual characterisation (by mid-year) Sun illumination has appeared as main variable: indeed around eclipses or thermally stable orbit arcs, the Residual can be kept small while VFM calibration parameters remain close to pre-flight values DTU proposed in June to investigate thermal gradients and conductive material near the VFM sensor (for Seebeck thermo-electric effect) mapping the Residual in the VFM coordinate system or the satellite coordinate system to better characterise it special satellite manoeuvres in Phase E2 to support Residual characterisation: Yaw slew manoeuvres (8 to 14 May) MTQ disturbance/datation characterisation (4 to 5 June) ASM confirmed as a reference magnetometer e.g. owing to inter-satellite comparisons, to the use of its Vector mode measurements (see next slides)

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 10 ESA UNCLASSIFIED – For Official Use ASM inter-satellite comparison Courtesy of IPGP

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 11 ESA UNCLASSIFIED – For Official Use ASM-VFM angular displacement Courtesy of IPGP, CEA-LETI, CNES

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 12 ESA UNCLASSIFIED – For Official Use Thermal simulation of optical bench (1/2) Investigation of thermal gradients near VFM: Following suspicion by DTU of electrical current in boom Ti bracket caused by thermal gradients (Seebeck effect), AIRBUS was asked to run thermal simulations (with Sun above STR baffle, or above optical bench, or illuminating an internal part via a hole in MLI junction)  thermal model refined locally at boom Ti bracket but not validated (absence of flight HW) Courtesy of DTU & AIRBUS

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 13 ESA UNCLASSIFIED – For Official Use Thermal simulation of optical bench (2/2) Outcome of simulations (6 October): obtained temperature trends are credible temperature uncertainty on MLI pieces is an order of magnitude higher Conclusions: no high thermal gradient found in boom Ti bracket other thermal sneak paths or current loops to be found Courtesy of AIRBUS

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 14 ESA UNCLASSIFIED – For Official Use Residual characterisation (by October) Disturbance signatures identified by Task Force on 9 October: with Sun at high elevation (i.e. illuminating from the top of VFM) left-right asymmetry with Sun illuminating from VFM sides front-back signature, with differences whether Sun is in front or in back of VFM additional small scale features corresponding to specific Sun positions 3 Residual models: H. Lühr (GFZ), P. Brauer (DTU), V. Lesur (GFZ) Residual model retained for new AIRBUS investigation: V. Lesur’s (GFZ) combination model with assumptions on Instrument behaviour and an external disturbance factor New magnetometers measurement data sets released end October with: pre-flight values of VFM calibration parameters outlier detection application stray field correction

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 15 ESA UNCLASSIFIED – For Official Use On-board Instruments performance VFM: Excellent performance: very low noise as anticipated 2 minor anomalies on electronics attributed to radiation (recovered via re- powering) ASM: Excellent performance: noise level indicator stable trends in life limited items compatible with more than 10-year mission but… 2 ASM models lost on SWARM-C (investigation of last failure is starting) STR: Excellent performance: valid attitude updates CCD ageing very low but… boresight pointing varying with CHU temperature

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 16 ESA UNCLASSIFIED – For Official Use STR inter-boresight angles stability in June DTU suspects crown spherical washers slide with temperature (CHUs are mounted on a crown itself mounted on a SiC cube on the optical bench) in July in a refined FEM analysis AIRBUS denies such sliding possibility Courtesy of DTU & AIRBUS STR inter-boresight angle stability:

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 17 ESA UNCLASSIFIED – For Official Use STR inter-boresight angles stability STR inter-boresight angle stability (cont’d): In August DTU considers local cube surface roughness around the holes DTU performs simulations creating a model from geometric data (no original DTU items)

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 18 ESA UNCLASSIFIED – For Official Use STR inter-boresight angles stability STR inter-boresight angle stability (cont’d): Anomaly Review Board on 6 October 2014 calls for:  AIRBUS to verify the detailed model assumptions with DTU  using the Flight Model surface roughness measurements (received 29 Oct from BOOSTEC for FM3), to refine the IBA variation simulation results Courtesy of DTU

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 19 ESA UNCLASSIFIED – For Official Use ASM failed on SWARM-C Loss of 2 nd ASM on SWARM-C: on 5-Nov while flying over North Pole, Platform detects ASM current consumption of 0,11A which is below nominal value because current level is below 0,16A a Platform automatic on-board procedure switches off ASM attempts to switch on ASM again on 7-Nov, on 11-Nov and on 12-Nov fail to have ASM boot: ASM current consumption remains at 0,11A no tele-command / tele-metering capability with ASM Test of 1 st ASM on SWARM-C: on 13-Nov redundant ASM (failed since launch) was tested: failure remains as observed during Commissioning Investigation management on 2 nd ASM by ESA/CNES: to start upon release of ASM electronics schematics by CEA-LETI / DGA

ESA Presentation | P. Vogel | Potsdam | 02/12/2014 | Slide 20 ESA UNCLASSIFIED – For Official Use Conclusion STR: boresight pointing linear variation with temperature to be corrected on ground VFM: source(s) of disturbance field near VFM to be identified ASM: potential failures in the electronics to be investigated thoroughly calibration of VFM on SWARM-C without ASM to be addressed (using a comparison of the Sun-dependent correction functions and VFM parameters between SWARM-A and SWARM-C over the past year ?)