Ideas for Future Magnetic Field Missions

Ideas for Future Magnetic Field Missions André Laurens – CNES, Toulouse, France with contributions of Gauthier Hulot – CNRS/IPGP, Paris, France Jean-Michel Léger – CEA/LETI, Grenoble, France Outline

Earth’s Magnetic Field • Sources, scales, historic observation • Why studying it? Space-based magnetometry • Why from space? • Former space missions - The SWARM mission • Current knowledge The NanoMagSat concept • Mission profile • Space system • Perspectives

A. Laurens - Summer School Alpbach 2019 2 Earth’s Magnetic Field Sources, scales, and observation Why studying it?

A. Laurens - Summer School Alpbach 2019 3 Earth’s Magnetic Field Earth’s Magnetic Field has various sources • The main source is the geodynamo located in the core • This field is causing rocks’ magnetization, which is a secondary source • Other sources are electric currents in the ionosphere, the magnetosphere, the Solid Earth and even in the oceans Earth’s crust rocks are magnetized by the core field

Ionized by the Sun and stirred by thermal tides, electric J. Aubert, IPGP currents flow through the ionosphere In the magnetosphere, the charged In the liquid and conductive core sits particles’ motion induces large scale a self-excited dynamo A. Laurens - Summer School Alpbach 2019 electric currents 4 Earth’s Magnetic Field sources and orders of magnitude Magnetospheric signals at Chambon-la-Forêt

Short-term variations during a magnetic storm

Magnetospheric signal and induced currents  few 100 nT

A. Laurens - Summer School Alpbach 2019 5 Earth’s Magnetic Field sources and orders of magnitude Secular variations at Chambon-la-Forêt

Variations due to geodynamo field long-term evolution  ~20 nT / year on a total field of ~40 000 nT

A. Laurens - Summer School Alpbach 2019 6 Earth’s Magnetic Field sources and orders of magnitude Geomagnetic “jerks” at Chambon-la-Forêt

Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics 153

Fig. 4 Secular variation of the smooth Paris declination curve adjusted at Chambon-la-Forêt observatory (black curve), and the secular variation estimated from gufm model (red curve)

Sudden changes in geodynamo field evolution, so that it is mandatory to monitor its acceleration  few nT/yr2 • associated time resolution < 1 year A. Laurens - Summer School Alpbach 2019 7 Geomagnetic jerks prior to the 20th century Prior to the 20th century the quality of available data is less good, the time resolution of observations is poor, and the detection of such events is difﬁcult because of the external signal and of the noise in the available measurements (Alexandrescu et al. 1996). To extend the analysis of geomagnetic jerks back in time, long series of data are needed. Unfortunately, series with high temporal resolution data are available only for the last decades of the 19th century (see http://www.wdc.bgs.ac.uk/catalog/master.html). Few longer geomagnetic series are available and they consist mainly in annual means for declination. Individual time series of declination and sometimes inclination have been compiled by Malin and Bullard (1981), Cafarella et al. (1992), Barraclough (1995), Alexandrescu et al. (1996), Soare et al. (1998), Korte et al. (2009) for London, Rome, Edinburgh, Paris, Bucharest and Munich, respectively. Analysis of these long declination series has enabled detection of some geomagnetic jerks. The Paris declination curve clearly indicates a number of geomagnetic jerks for the period during which continuous annual means are available, as shown in Fig. 4.Thejerk proposed around 1870 based on data from Paris and four other European locations by Alexan- drescu et al. (1997)has recently beendetected inthe Munichcurve (Korte etal. 2009), although a few years earlier. Going back in time, three jerks suggested by Alexandrescu et al. (1997)from the Paris data over the 18th century (see the changes in the secular variation tendency around 1750, 1730 and 1700) have been also conﬁrmed by Korte et al. (2009), but again with some time offset. From the mid-18th to mid-19th century there is no clear ev- idence for sudden secular variation changes, supported by measurements and models (how- ever, in the declination series some changes can be noted around 1800 and 1820).

Geomagnetic jerks over the 20th century Detailed analyzes of geomagnetic data from worldwide observatories have revealed a number of geomagnetic jerks which have occurred during the 20th century and which have been discussed by a number of authors (see for example Macmillan 1996;De Michelis et al. 1998;Mandeaetal. 2000;Nagao etal. 2001; Olsen and Mandea 2008 and the references therein). Without giving an exhaustive review, we note here that the magnetic records show such events, particularly around 1901, 1913, 1925, 1932, 1949, 1958, 1969, 1978, 1986, 1991 and 1999. Four of them (1969, 1978, 1991, 1999) are deﬁnitely detected in magnetic observatories distributed worldwide, three (1901, 1913, 1925) may have a similar extension, but the data distribution for this begin- ning of century is quite uneven, and ﬁnally the remaining (1932, 1949, 1958, 1986) seem to be regional events (Golovkov et al. 1989;Alexandrescu etal. 1996;Macmillan 1996; Earth’s Magnetic Field historic observation

Measurements since 1840

INTERMAGNET • An international network of 150 ground observatories • Complemented by sea- & airborne measurements

A. Laurens - Summer School Alpbach 2019 8 Why studying Earth’s Magnetic Field ? Science objectives • Main field: • Improve understanding of the geodynamo • needs observations continuity over long-term durations (observatory policy) • with a good spatial resolution (up to degree 20 in spherical harmonics) • with a good temporal resolution (< 1 yr) • to study short-term phenomena (geomagnetic jerks and pulses) • Crustal field: Internal field dominated: - by core field up to degree 13 • Improve crustal field mapping - by lithospheric field for degrees > 13 Crustal field derivative : • Magnetospheric field: - can be observed up to degrees 16-17 thanks to space data • Improve description of magnetospheric field and enhance reconstruction of Earth’s deep conductivity • Ionospheric field and environment: • Study electric currents, coupling between ionosphere and magnetosphere, ionosphere‘s instabilities, waves, and response to magnetic storms

A. Laurens - Summer School Alpbach 2019 9 Why studying Earth’s Magnetic Field ? Applicative and Societal issues • Provide a reference model of main field (IGRF-type) regularly updated (<< 5-year period) for various purposes: • Navigation (smartphones, ships, planes, submarines) • Spacecraft attitude determination and control • Drilling guidance • Radio waves modelling and propagation analysis • Magnetosphere morphology determination (radiation belts) • Predict main field evolution, thus of magnetic field structure, for a mid-term prediction (decennial scale) of magnetic conditions to be experienced by long-life satellites • Monitoring of magnetic activity for the need of Space Weather forecasting: • prevention of power distribution networks hazards • planning of activities requiring magnetic quietness • Monitoring of ionosphere state for the need of Space Weather (input parameters to ionosphere models, perturbations detection) • determine ionosphere perturbed areas, likely to cause GNSS localisation errors, or radio or GNSS signal losses A. Laurens - Summer School Alpbach 2019 10 Space-based Magnetometry Why from space? Former space missions - The SWARM mission Current knowledge

A. Laurens - Summer School Alpbach 2019 11 Why Space-based Magnetometry?

Ground observatories’ geographical coverage is uneven: • Highly linked to human presence, poor on seas • Fixed position: can see only temporal variations Satellites provide even and dense geographical coverage but: • Continuously moving: 1 orbit ≈ 90 mn • Can see spatial and temporal variations, but always combined • Reduced sensitivity  1 / R2 Ground- and space-based measurements are complementary !

A. Laurens - Summer School Alpbach 2019 12 Magnetometry Space Missions Kosmos-49 • 1964-1965 : technology demonstration satellite of Soviet Union’s Dnepropetrovsk Sputnik program • Secondary mission : scientific research on the Earth's magnetosphere POGO (Polar Orbiting Geophysical Observatory) • Polar orbiting satellites of NASA’s OGO program (1964 – 1971) • First global survey by satellite of the earth's magnetic field Magsat (Magnetic Field Satellite) • NASA + USGS (*) LEO satellite (1979 – end of mission after 6 months) part of NASA’s Small Explorers program • Objectives : first global and detailed measurement of Earth’s magnetic field • Payload : vector magnetometer (first measurement of field’s 3 components) + absolute scalar magnetometer + star tracker for field orientation reconstruction (*) United States Geological Survey A. Laurens - Summer School Alpbach 2019 13 Magnetometry Space Missions (cont’d) Oersted • Geomagnetic research microsatellite mission of Denmark (several Danish institutes + NASA/CNES/DLR/ESA contributions) • Objectives : highly accurate and sensitive measurements of the geomagnetic field and global monitoring of the high energy charged particles in the Earth's environment • Launched 1999 (for an initial 14-months mission) on a slowly drifting elliptical polar orbit, altitude = 655/857 km, inclination = 96.5°; regular operations halted 2014 • Payload : • Scalar Magnetometer (OVH for Overhauser Magnetometer) [LETI]: measurement principle: proton magnetic resonance; absolute error < 0.5 nT; range: 16,000 - 64,000 nT; sampling 1 Hz; provides in-flight calibration for the vector magnetometer • Vector Magnetometer [DTU+DSRI]: triaxial fluxgate magnetometer; angular resolution: 1 arcsec; absolute error v 1 nT; range: ±65,536 nT; resolution < 0.25 nT; 100-20 vector samples/s modes; resolution < 0.1 nT • Charged Particle Detector [DMI]: high energy electrons (50 keV - 1 MeV), protons (250 keV - 30 MeV), alpha-particles (1-100 MeV) • ASC (Advanced Stellar Compass) [DTU]: provides an attitude reference, precision: a few arcsecs

• TRSR (TurboRogue Space Receiver) [NASA/JPL] : accurate determination of satellite position, class : microsatellite ionospheric electron content measurement, atmospheric soundings (density, pressure, dimensions : 340 x 450 x 720 mm temperature) mass : 60.7 kg A. Laurens - Summer School Alpbach 2019 14 Magnetometry Space Missions (cont’d) CHAMP (Challenging Minisatellite Payload) • German geophysical minisatellite mission of GFZ (GeoForschungsZentrum), in cooperation with DLR • Objectives: • Global long-to medium-wavelength recovery of the static and time variable Earth gravity field from orbit perturbation analyses • Global Earth magnetic field recovery • Atmosphere/ionosphere sounding by GPS radio occultation • Launched 2000; Initial orbit: 418/474 km (decaying to 300 km after 5 years), inclination 87.275°(near polar but non SSO); end of mission: 2010 (natural deorbitation) class : minisatellite dim.: 4.3 x 0.75 x 1.6 m + boom : 4 m Payload: mass : 522 kg (wet) • BlackJack (dual-frequency GPS receiver) [NASA/JPL]: precise (cm accuracy range) orbit determination and continuous coverage; ionospheric electron content, atmospheric soundings; experimental GPS reflectometry for ocean's surface altimetric measurements • STAR (Space Three-axis Accelerometer for Research mission) [ONERA] ; measures non-gravitational accelerations of the satellite (drag, solar and Earth radiation pressure); determines Earth's gravity field from purely gravitational orbit perturbation • LRR (Laser Retro Reflector) [GFZ]: passive optical device for accurate satellite tracking from ground laser ranging stations of the SLR network • MIAS (Magnetometer Instrument Assembly System): scalar magnetometer (OVH, LETI), 2 fluxgate vector magnetometers (FGM, DTU), 2 star imagers (DTU) to provide attitude information for FGM • ASC (Advanced Stellar Compass) [DTU]: accurate attitude reconstruction • DIDM (Digital Ion Drift Meter) [AFRL]: measures the Earth's electric field parallel to the magnetic field (in-situ measurements of the ion distribution and its moments within the ionosphere) • PLP (Planar Langmuir Probe): in combination with DIDM, gives S/C potential, electron temperature and density A. Laurens - Summer School Alpbach 2019 15 Magnetometry in Space : the SWARM Mission A « constellation » of 3 identical satellites for magnetic field and ionosphere study • proposed by DTU (Copenhagen), GFZ (Potsdam), IPGP (Paris) • selected 2004, as 5th mission of ESA Earth Explorer program • launched November 2013 Payload : • Absolute Scalar Magnetometer (CEA/LETI, CNES), 250/1Hz + 1Hz experimental vector data (3-axes field modulation) • Vector Field Magnetometer and Star Tracker (DTU Space), 50Hz, 1Hz • Accelerometer (VZLU, CZ), 1Hz • Electric Field Inst. : Thermal ion imager (UC); Langmuir Probes (Uppsala), 2Hz mass : 369 kg (dry) 468 kg (wet) • GPSR (Ruag), 0.1 Hz A. Laurens - Summer School Alpbach 2019 16 Magnetometry in Space : the SWARM Mission (cont’d) Orbital configuration • 2 satellites – Alpha and Charlie – fly side-by-side (separation in longitude ~150 km at equator) on a quasi-polar orbit (inclination 87,35°) altitude 460 km BoL, then decaying • 1 satellite – Bravo – on a higher quasi-polar orbit (inclination 87,95°), altitude 530 km BoL,

inducing a relative Local Time drift wrt Alpha and Charlie April 2014 This concept has been shown to be very successful for, e.g., • Improving the recovery of the core, crustal, ionospheric, and ocean tidal fields 3 hrs: April 2016 • Investigating field aligned currents

Willingness (and enough fuel) fo maintain the constellation for at least a full solar cycle (until at least 2024) Swarm Bravo (at higher altitude) could last even far beyond 6 hrs: April 2018

A. Laurens - Summer School Alpbach 2019 17 Current knowledge of Earth’ Magnetic Field

Main field at core surface 1840-2010

Gillet et al, GGG, 2013

Reconstruction from historical data since 1840, and former space missions data : POGO (1965-1970), MAGSAT (1979-1980), DE-2, Oersted (since 1999) and Champ (2000-2010) – units : mT A. Laurens - Summer School Alpbach 2019 18 Current knowledge of Earth’ Magnetic Field (cont’d)

180˚ 225˚ 270˚ 315˚ 0˚ 45˚ 90˚ 135˚ 180˚ 60˚ 60˚

50˚ 50˚ Crustal field at Earth’s 40˚ 40˚ 30˚ 30˚ surface – 2010 20˚ 20˚ 10˚ 10˚ 0˚ 0˚ -10˚ -10˚ -20˚ -20˚ -30˚ -30˚ -40˚ -40˚ -50˚ -50˚

-60˚ -60˚ 180˚ 225˚ 270˚ 315˚ 0˚ 45˚ 90˚ 135˚ 180˚ Z (nT) 180˚ 0˚ 200 150 100 50

˚ ˚

0 0

7 7 0

9 9

2 2 -50

-100 Maus

Reconstruction from CHAMP data (2000-2010) – -150

Model MF7, Model S. initial altitude 450 km, finale 250 km – units : nT -200 0˚ 180˚

A. Laurens - Summer School Alpbach 2019 19 Current knowledge of Earth’ Magnetic Field (cont’d)

Crustal field at Earth’s surface – 2015

Model SIFM+, Reconstruction from 14 months of SWARM data (2014-2015) Olsen et al. – altitudes 450 to 520 km – units : nT

A. Laurens - Summer School Alpbach 2019 20

Current knowledge of Earth’ Magnetic Field (cont’d) ) Towards a near-real time nT monitoring of large scale

magnetic field ( MMA_F

)

MMA_C ( MMA_C

)

nT Difference ( Difference

Processing the ring current signal is possible at orbit timescale – units : nT McMillan et al., 5th Swarm DQW

A. Laurens - Summer School Alpbach 2019 21 Current knowledge of Earth’ Magnetic Field (cont’d)

Reconstruction of Earth’s mantel conductivity from magnetic field data

Processing of the internal signal induced by the ring current signal at low frequencies (periods over 1 day) Velimsky et al., 5th Swarm DQW

A. Laurens - Summer School Alpbach 2019 22 Current knowledge of Earth’ Magnetic Field (cont’d)

Towards a better description of « Solar Quiet » ionospheric field at mid latitudes

Comprehensive Model, Dedicated Model, DTU/NASA NOAA/IPGP

Measurement of ionospheric field, units : nT

A. Laurens - Summer School Alpbach 2019 23 Current knowledge of Earth’ Magnetic Field (cont’d)

Prediction (direct computation)

Detection of M2 ocean tide signals

CI (Swarm) CM5 (CHAMP)

Sabaka et al., 5th Swarm DQW

Sabaka et al., in preparation for GRL Sabaka et al., GJI (2015)

Measurement of |Br| from M2 ocean tide signal, with: • 2 years of SWARM data (left)

• 10 years of CHAMP data (right) - units : nT A. Laurens - Summer School Alpbach 2019 24 The NanoMagSat concept Mission profile Space system Perspectives

A. Laurens - Summer School Alpbach 2019 25 The NanoMagSat concept

A brief history • 2014 : first idea of a smallsat dedicated to magnetometry (G. Hulot, IPGP and J.-M. Léger, CEA-LETI) • 2015 : CNES selects for a phase 0 study the NanoMagSat concept proposed by G. Hulot and J.-M. Léger • Based on a miniaturized new generation of SWARM’s ASM • Taking advantage of nanosatellite emergence for designing a low-cost mission • Aiming to complement the SWARM constellation • 2015-2016 : conduct of NanoMagSat phase 0

A. Laurens - Summer School Alpbach 2019 26 NanoMagSat : mission profile at end of phase 0 study To complement and extend SWARM constellation, which has limitations • Polar orbits do not allow crossing points, and North-South tracks introduce North-South artefacts • Local time coverage is slow (~4 months for full coverage) and thus prevents fast recovery of global scale signals a limitation for the recovery of “fast” changes in e.g., the core and planetary ionospheric fields

Improvement is possible with help of at least one additional satellite at ~60° inclination • Crosses both SWARM’s orbits and its own orbit at (almost) all latitudes • Provides an East-West measurement component, to mitigate North-South anisotropies • Faster local time coverage (~1 month for full coverage)

A. Laurens - Summer School Alpbach 2019 27 NanoMagSat : mission profile (cont’d) NanoMagSat’s core ambition • To build and launch this additional (Delta) satellite to complete the Swarm constellation, before Swarm’s demise • To demonstrate the possibility of building a LEO nanosatellite for monitoring the magnetic field and ionospheric environment at a much lower cost than the Swarm satellites • To set the standards for expending the INTERMAGNET network of ground observatories to space by relying on a fleet of cheap nanosatellites (beyond Swarm)

A. Laurens - Summer School Alpbach 2019 28 NanoMagSat : mission analysis Orbit altitude : a compromise between lifetime and sensitivity to the magnetic field • Estimated S/m = 0,025 (average LEO satellite S/m = 0,01) • No impact of orbit inclination

Local time drift due to J2 effect Local time drift along the orbit

A. Laurens - Summer School Alpbach 2019 29 NanoMagSat : mission analysis (cont’d)

Station visibility slots • Typical values for Toulouse and Kourou • 550 km, 5° minimum elevation, 6 months simulation

Visibility passes: Station: Toulouse Duration: min/max/moy (mn): 1.045 / 10.307 / 7.879 Average frequency (#/day): 7.056 Total average duration (mn/day): 55.593

Station: Kourou Duration: min/max/moy (mn): 1.214 / 10.276 / 8.038 Average frequency (#/day): 3.483 Total average duration (mn/day): 27.998

A. Laurens - Summer School Alpbach 2019 30 NanoMagSat : payload configuration A focused instrumental suite • Miniaturized ASM : 250 Hz scalar mode, 1 Hz vector mode • Star tracker for precise attitude determination • High frequency vector magnetometer : TMR(*) as a candidate • Total Electron Content measurement via bi-frequency GPS

ASM new generation probe : outside (left) and inside (right)

(*) Tunnel Magneto Resistance A. Laurens - Summer School Alpbach 2019 31 NanoMagSat : spacecraft concept at end of phase 0 study

All in a 12U-CubeSat • Gravity gradient (passive) stabilisation • Innovative boom (MA2C, CNES patent) : deporting the magnetometer + gravity gradient • Avionics suite : OBC and S-Band TM/TC (CubeSat form factor) developed by CNES R&D program • Budgets : • Mass : 17,6 kg with margins • Power : 16,4 W worst case

A. Laurens - Summer School Alpbach 2019 32 NanoMagSat perpectives

Short-term objective : flying NanoMagSat • As “Swarm Delta” : a complement to SWARM constellation • As a forerunner of a future extension in space of INTERMAGNET observatories Long-term objectives • Space-based monitoring of main field long-term evolution • Study of the geodynamo, IGRF-like model permanently updated for applicative or societal uses, • Long-term monitoring of ionospheric et magnetospheric fields New space architectures allowing new programmatic schemes • Incremental deployment of a constellation by successive satellite batches • Achieving a progressive local time coverage • Taking advantage of opportunistic programmatic conditions • Allowing long-term constellation maintenance and replenishment • Possible partnerships involving countries already contributing to ground-based observation of magnetic field • Towards a collaborative structure, “InterMagSat”, as a natural counterpart of Intermagnet ground observatories network

A. Laurens - Summer School Alpbach 2019 33 Thanks for your attention ! Any question ?

A. Laurens - Summer School Alpbach 2019 34 Short bibliography Science • Measuring the Earth’s Magnetic Field from Space: Concepts of Past, Present and Future Missions – N. Olsen, G. Hulot, T.J. Sabaka – Space Sci Rev (2010) DOI 10.1007/s11214-010-9676-5 • The Present and Future Geomagnetic Field – Hulot G., Sabaka T.J., Olsen N. and Fournier A. – in: Treatise on Geophysics, 2nd edition, Vol 5, 2015 Mission & Instrumentation • The NanoMagSat (Swarm Delta) nanosatellite high-precision magnetic project – G. Hulot1, J.-M. Léger2, P. Vigneron1, T. Jäger2, F. Bertrand2, P. Coïsson1, A. Laurens3, B. Faure3 – 1IPGP, 2CEA/LETI, 3CNES – IUGG, 2019 • Swarm Absolute Scalar and Vector Magnetometer Based on Helium 4 Optical Pumping – J.-M. Leger1, F. Bertrand1, T. Jäger1, M. Le Prado1, I. Fratter2, J.-C. Lalaurie2 – 1CEA-LETI, 2CNES – 2009

A. Laurens - Summer School Alpbach 2019 35