Feasibility of using platform magnetometers to observe and detect Space Weather events (ESA contract AO-i8735/16/NL/LF) Executive Summary Prepared by: Eelco Doornbos, TU Delft Lotfi Massarweh, TU Delft Alessandra Menicucci, TU Delft Elisabetta Iorfida, TU Delft Claudia Stolle, GFZ Potsdam Martin Rother, GFZ Potsdam Ingo Michaelis, GFZ Potsdam Guram Kervalishvili, GFZ Potsdam Jan Rauberg, GFZ Potsdam August 15, 2018 EUROPEAN SPACE AGENCY CONTRACT REPORT The work described in this report was done under ESA contract. Responsibility for the contents resides in the author or organisation that prepared it. Executive summary Introduction Magnetometers are fundamental instruments used in planetary and space science. Mag- netometers are able to measure the magnetic fields originating in the planet’s interior, past fields encapsulated in rocks in the crust, as well as magnetic fields generated by the mo- tion of charged particles in the plasma environments of ionospheres, magnetospheres and interplanetary space. Currents in space plasma transfer energy over very large distances. The state of the Earth’s magnetosphere is to a large extent dependent on the orientation and strength of the interplanetary magnetic field (IMF) just upstream. A southward orientation of the IMF en- ables magnetic reconnection between the IMF and magnetosphere, triggering geomagnetic storms and substorms. This is why IMF measurements in the Sun-Earth L1 point are essen- tial for space weather modeling and prediction. In the case of the plasma within the Earth’s magnetosphere, currents are able to deposit significant energy in the Earth’s upper atmosphere, causing ionization, heating and expan- sion of the neutral upper atmosphere, which in turn interacts with the charged particle envi- ronment in a complex, highly non-linear way. These processes induce variability in the level of atmospheric drag on satellites, as well as perturbations of radio communications, navi- gation signals and scientific observations relying on radio links. Currents in the ionosphere can also induce currents inside the Earth, affecting and possibly endangering man-made in- frastructure, such as power lines and pipes. For these reasons, magnetometer measurements of ionospheric currents are essential observations in the field of space weather. Due to the geometry and high altitude of magnetospheric and ionospheric current sys- tems, satellite measurements are needed in addition to ground magnetic observatories, in order to reveal their detailed behaviour. Due to the large spatial extent of the currents, the variety of spatial scales of variability, as well as the sometimes very rapid fluctuations, adding simultaneous observations from many satellites will be extremely useful to enhance our understanding of space weather, and to be prepared to adjust our response to space weather in more sophisticated ways than is currently possible. This is where the use of platform magnetometers comes in. On low Earth orbiting (LEO) satellites, magnetometers are often used as part of the attitude control subsystem. Although these instruments are not designed and implemented for space weather observation, they can nevertheless be used for this purpose. In this study, data from the diagnostics magnetometers on LISA Pathfinder and the AOCS magnetometers of the ESA GOCE and Swarm satellites has been used (see Figure1 1 TFM100G4-S FLIGHT MAGNETOMETER BBILLINGSLEY AAEROSPACE & DDEFENSE TFM 100S SPACECRAFT ATTITUDE CONTROL TRIAXIAL FLUXGATE MAGNETOMETER Figure 1 The Billingsley 3-axis fluxgateFEBRUARY magnetometers 2008 TFM100-S SPECIFICATIONS (left) of which 3 each are SPECIFICATIONSused as the ’FGM’ instruments in the AOCS subsystems of Swarm and GOCE, and the TFM100G4-S, that was used as ’MGM’ for magnetic diagnostics on LISA Pathfinder. Radiation Tolerance: > 300 kRADs (with 1.59 mm cover) > 100 kRADs (with 0.79 mm cover) Option MissionAxial Instrument Alignment: dimensionsOrthogonality better than ± 1° ; ± 0.5° massspecial; calibration Axial Alignment: Orthogonalitydata provided better than to ± ±0.1 1°°, Special to ± 0.1° Swarm VFM sensor: 8.2 cm diameter, processing unit: 10×10×6 cm 280 / 750 g Input VoltageSwarm Options:Input TFM100-S Voltage: 3.66×3.58×15.4424-34 cm VDC+ 15 to + 45 VDC 200 g Input Current:GOCE TFM100-S 3.66×3.58×15.44> 50mA cm+ 45 to + 125 VDC Option 200 g Input CUrrent: 20 mA at 28 V Power andLPF SignalIsolation: Lines TFM100G4-S 3.51× 3.23×8.26Galvanically cmbetween Isolated power and signal ground > 200 100MΩ g at 500 VDC Field MeasurementField Range Measurement Options: Range: ± 100 μ± T 100 = ± μ10.0T Volts (Other ranges available) Table 1Accuracy: Some characteristics of selected scientific± 0.5% and of platformfull scale magnetometers. Accuracy: Linearity: ± 0. 5%0.015% of full scale, of full Specialscale to 0.1% Linearity: Sensitivity: ± 0.007%100 of μ Vfull / nTscale, Typical < ±0.0025 and TableScale1), Factor to analyse Temperature the performance Shift: .0075% and limitations full scale of/ °C such instruments, for space Sensitivity: Output Ripple: 100 µV/nT3 mV (or peak user to specified)peak @ 2nd harmonic weather use. Scale Factor TemperatureAnalog Output Shift: @ Zero Field:0.003% ± full 0.025V scale/ ° Celsius TheZero Swarm Shift satellites with Temperature: also each carry ≤ two 1.0 scientific nT /°C magnetometers: the ASM (absolute Noise: scalar magnetometer),Susceptibility to providing Perming: a< highly 40 picoTesla± accurate 25 nT RMS/shift absolute with Hz reference,@1± 5 HzGauss Typical and applied VFM (vector field Output Ripple:magnetometer), Output Impedance: providing very accurate3 millivolt332 3-axis peak Ω ± vector to5% peak measurements. @ 2nd harmonic The satellites were Frequency Response: - 3 dB @ > 150 Hz Analog Outputspecifically @E MZero I: designed Field: for making measurements± 0.020CEO1, Volt CEO3, of the REO2, highest CS01, possible CSO2, accuracy. CSO6, RSO1, This al-RSO2, RS03 Zero Shiftlowed with Temperature: usRandom to assess Vibration: the performance < of± the1 nT/20G platform° Celsius RMS magnetometers(20 Typical Hz to 2 KHz) in an ideal environment, Shock: >230 G Susceptibilityand against to Perming: a highly accurate reference.± 20 nT The shift GOCE with satellite ± 5 Gauss is used applied as a test case of a mission that wasTemperature not designed Range: with magnetic cleanliness- 40° to and +85 space °C weather measurements in mind, Output Impedance:Weight: 332 Ω ±200 5% grams (can drive(1.59 >mm 3500’ cover) of cable) but that can nevertheless contribute to this166 purpose. grams (0.79 mm cover) Option Frequency Response: 3 dB @ ≥ 3.5 kHz Over Load Recovery:Size: ± 5 Gauss3.66 slew cm x < 3.58 2 milliseconds cm x 15.44 cm LISA Pathfinder E M I: Connector: DesignedNON-MAGNETIC to meet CEO1, 9 CEO3, PIN "D"REO2, TYPE CS01, CSO2, CSO6, RSO1, RSO2, RS03 Random Vibration: > 20G RMS 20 Hz to 2 KHz The investigations of LISA pathfinder data starts with the downloading of magnetometer, Temperature Range: - 55° to + 85° Celsius operating orbit and attitude data from the LISA Pathfinder Legacy Archive website. The data from Acceleration:each of the three axes on the four> 60G magnetometers contain considerable biases of several Weight: hundred nT, with respect to the IMF,100 whichgrams normally has a strength of only a few nT. The Size: fact that these biases show similarities3.51 in cm terms x 3.23 of magnitude cm x 8.26 andcm timing of changing magni- Connector:tude, for the four instruments, indicatesChassis that mounted they are 9 pin mainly male due "D" to type; stray mating fields originatingconnector supplied from other equipment on the spacecraft. The timing of bias changes is furthermore closely linked to times of switching between the various experiments. In general, the biases can be considered to be piecewise constant, or at the worst, show a linear drift over time, so that the measurements are easily corrected. A simple removal of a daily mean bias already brings 20936 Theseus Terrace, Germantown, MD 20876 USA the magnetometer readings closewww.magnetometer.com together, and close to [email protected] signal that resembles the IMF. This is shown in Figure2, in which 4-minute301-540-8338 averages of the raw 301-774-7707 data sampled (LAB) at 0.25 Hz are plotted. Only for a period of about 2 hours, a clear discrepancy between the 4 magnetome- ter readings is visible in this Figure, which can be traced back to spacecraft operations. The 2 Outliers analysis for each magnetometers [S/C frame] | 39 Figure 2 Measurements by the 4 individual magnetometers on LISA Pathfinder. For each of the 4 Figure 27: Examplemagnetometer’s as in Figure 326 axes,, where a dailya time mean-variable has local been perturbation removed is fromacting the between measurements. hour 3 and 4. To be observed how the effects along each S/C direction depend mostly upon the location of the instrument responsible for this perturbation. In addition, the magnitude is strongly influenced by its relative distance from each MAG. day of data plotted in this Figure was specifically selected to show this. On most days of our analysis,At this point such, we discrepancies can proceed were with not an present.examination of what have been defined “outliers”, as observationFigure3 shows point a comparison that is distant of the from readings other observations from one of the. (Grubbs LPF magnetometers F.E., 1969). with science data from the NASA ACE mission, which is dedicated to measuring the strength and orientation of the IMF. It is clear that both magnetometers measure the same variations in IMF. An analysis with the help of ACE solar wind speed data has shown that the time shift in5.5 the IMFOutliers measurements analysis between for the each missions magnetometers can be completely attributed[S/C frame] to the different �� positionsIn a very ofsimple LPF andway ACE it is possible in their respective to plot the orbits difference around between the Sun-Earth the Δ���� L1 point.measurement During the LPF mission a total of four magnetometer-carrying���� spacecraft were available of each magnetometer and the mean value computed Δ���� .