SOLAR ORBITER A Mission Overview Joachim Woch MPS, Katlenburg-Lindau

1. SOLAR ORBITER A Mission OverviewJoachim WochMPS, Katlenburg-Lindau • Scientific Goals • Baseline Mission Profile • Scientific Reference Payload • Schedule

2. What is unique about this mission? Not a single feature rather a combination of specials • orbit → closest to Sun ever, with corotation periods and out of ecliptic • suite of remote sensing instruments working as an ensemble doing coordinated measurements • combined with a comprehensive in situ package • allows to trace solar processes from the photosphere through the corona into the interplanetary medium close to the Sun

3. Top level scientific goals With Solar Orbiter we will, for the first time: • Determine the properties, dynamics and interactions of plasma, fields and particles in the near-Sun heliosphere • Investigate the links between the solar surface, corona and inner heliosphere • Explore, at all latitudes, the energetics, dynamics and fine-scale structure of the Sun’s magnetized atmosphere • Probe the solar dynamo by observing the Sun’s high-latitude field, flows and seismic waves Combination of Remote Sensing + In-Situ science

4. Solar Orbiter Solar Orbiter Firsts: • Study the Sun from close-up (48 solar radii or 0.22 AU) at high resolution • Explore the uncharted innermost regions of our solar system • Fly by the Sun and examine the solar surface and the space above from a nearly co-rotating vantage point • Provide images of the Sun’s polar regions from heliographic latitudes as high as 35° Solar Orbiter will open a new research chapter, because: the payload suite and the orbit are unique No solar imaging mission has yet come close to the Sun or climbed out of the ecliptic  unprecedented views  exploration and potential discoveries

5. Comparison with solar missions In the Solar Orbiter time-frame (with launch in 2015): • SOHO, TRACE, Ulysses missions will be over • STEREO, Solar-B missions likely to be complete • Solar Dynamics Observatory (SDO) should still be operational • Kuafu possibly operational • ground based observation facilities certainly operational → opportunities for `stereoscopic` observations

6. Measuring polar magnetic field • Solar Orbiter will allow us to study the: • magnetic structure and evolution of the polar regions, • detailed flow patterns in the polar regions, • development of magnetic structures, using local-area helioseismology at high latitudes. Model magnetogram of the simulated solar cycle. The sun viewed from a latitude of 30° north of the ecliptic (courtesy Schrijver)

7. Resolving fundamental scales SOHO/EITTRACE Solar Orbiter 1850 km pixels350 km pixels75 km pixels Due to proximity, Solar Orbiter will resolve scales such as the photon mean free path, barometric scale height and flux tube diameter in the photosphere ( ~ 150 km)

8. Baseline mission profile • Launch date (current baseline): May 2015 • (backup opportunity in Jan 2017) • Launch by Soyuz-Fregat 2-1b • Cruise phase (3.4 yrs) • Chemical Propulsion • Gravity Assist Manoeuvres (Venus, Earth) • Science phase • 3:2 resonant orbit with Venus (period 149.8 days) • Total mission duration, incl. extended phase (2015): 10 yrs • Minimum perihelion distance: 48 solar radii (0.22 AU) • Maximum solar latitude: 34° (in extended phase)

9. SEP vs. Chemical (Ballistic) mission • Science phase orbits can be reached using either high specific impulse (solar electric) or low specific impulse (chemical) propulsion • Solar Electric Propulsion • Short cruise phase (1.8 yrs) • Commonality with BepiColombo • Increased complexity (SEP module to be jettisoned) • Development risk • Chemical Propulsion • Lower development risk • Longer cruise phase (3.4 yrs) • Chemical propulsion (ballistic) mission launched has better mass margins • Science operations possible during cruise phase

10. CP Profile – launch opportunities • Ballistic transfers: • 3.4 yr - Oct 2013 • 3.4 yr - May 2015 • 4.1 yr - Jan 2017 • 3.4 yr - Aug 2018 • Inclination raising phase almost identical for all launch dates. • 2017different from 2013-2015-2018: 4:3 resonance initial orbit  3:2, orbit reached only 3 month before 2018 scenario longer mission duration

11. Baseline (chemical) mission - 2015 launch

12. Baseline (chemical) mission - 2015 launch

13. Baseline (chemical) mission - 2015 launch

14. Baseline (chemical) mission - 2015 launch Transfer Phase Science Phase Extended Mission

15. Mission profilevs. solar cycle

16. Science payload / SO status • Instruments to be selected via a competetive process based on an AO open to the international scientific community • Philosophy: • Resource-efficient instrumentation (e.g., remote-sensing instruments to be "1 metre, 1 arcsec resolution" class) • Science Management Plan calls for proposals to be submitted via relevant funding agencies • ESA Solar Orbiter Instrument AO: • Foreseen for release end of 2007 / beginning 2008 after final decision by SPC on SO implementation (Nov 2007) • Letters of Intent to Propose were due Sept 15th, 2006 • → Consolidation - Heat Shield / System Study Phase • Project – Instr. Teams Iterations on technical (thermal) issues • SO Mission Consolidation

17. Reference payload

18. Visible-light Imager and Magnetograph (VIM) High-resolution images (75 km pixels), Dopplergrams (helioseismology) and magnetograms of the photosphere Vector magnetograph consisting of: - 125 mm diameter Gregorian telescope - 15 mm diameter full disc telescope (refractor) - Filtergraph optics (two 50 mm Fabry-Perot etalons)

19. Visible-light Imager and Magnetograph (VIM)Overview • Measurement of: • velocity fields using Doppler effect • magnetic fields using Zeeman effect • Magnetograph : imagery in narrow (5 pm FWHM ) spectral bands around a visible spectral line at different polarisation states line of sight (LOS) velocity magnetic field vector • Time resolution : 1 minute (5  x 4 polarisations) • Spatial resolution : • 1 arc-sec with 0.5 arc-sec sampling :  125 mm (@ 500nm) • Field : 2.7° (angular diameter of sun at 0.22 AU) • Split in 2 instruments : HRT for resolution and FDT for field • Stringent LOS stability: 0.02 arc-sec over 10 s (differential photometry)  internal Image Stabilisation System

20. Extreme UV Spectrometer (EUS) Principle scientific goal: determine the plasma density, temperature, element/ion abundances, flow speeds and structure of the solar atmosphere using spectroscopic observations of emission lines in the UV/EUV. High-res. plasma diagnostics

21. Extreme UV Spectrometer (EUS) Instrument Concept: - off-axis normal incidence system (NIS) - Single paraboloid primary mirror reflects portion of solar image \\\into a spectrometer - Spectrometer utilises toroidal variable line spaced (TVLS) grating (normal incidence configuration) - The solar image is scanned across the spectrometer slit by motions of the primary mirror. - The wavelength selections are geared to the bright solar lines in the extreme ultraviolet (EUV) emitted by a broad range of plasma temperatures within the solar atmosphere. - Wavelength bands under consideration: 170-220 Å, 580-630 Å and >912 Å, to obtain spectral information from the corona, transition region and chromosphere,

22. Extreme UV Imager (EUI) Principal scientific goals: • provide EUV images with at least a factor 2 higher spatial resolution than currently available, in order to reveal the fine-scale structure of coronal features; • provide full-disc EUV images of the Sun in order to reveal the global structure and irradiance of inaccessible regions such as the "far side" of the Sun and the polar regions; • study the connection between in-situ and remote-sensing observations. High-resolution imaging of the corona.

23. Extreme UV Imager (EUI) Instrument Concept: - High Resolution Imager (HRI) and a Full Sun Imager (FSI)) - HRI comprises up to three telescopes in different wavelength bands (resources permitting). - Both the quiet Sun network regions and the coronal loops will be observed.. • The wavelength choices for the reference design were 30.4, 17.1 and 13.3 nm covering temperatures from 5 × 104 K to 1.6 × 107 K. • FSI is based on a single telescope concept. This will provide a global insight into changes in the solar atmosphere and in addition will provide context information for other instruments. The operating wavelength for the reference design is TBD in the range 13.3 - 30.4 nm.

24. Coronagraph (COR) Principal scientific goals: • Investigate the evolution of the magnetic configuration of streamers in order to test the hypothesis of magnetic reconnection as one of the main processes leading to the formation of the slow solar wind during the quasi helio-synchronous phases of the orbit; • Measure the longitudinal extent of coronal streamers and coronal mass ejections from an out-of ecliptic vantage point. These data are essential to determine the magnetic flux carried by plasmoids and coronal mass ejections in the heliosphere; • Investigate the large-scale structure of the F-corona (the dust) and the cometary sources of the dust near the Sun. This will provide important information for the in-situ instruments in the payload that measure plasma and dust.

25. Coronagraph (COR) Instrument Concept: - COR is an externally occulted telescope for broad-band polarisation imaging of the visible K-corona and for narrow-band imaging of the UV corona in the H I Lyman-α, 121.6 nm, line • annular field of view between 1.2 and 3.5 solar radii, when the Solar Orbiter perihelion is 0.22 AU. • off-axis Gregorian telescope • The UV Lyman- α line is separated with multilayer mirror coatings and (optionally) EUV transmission filters (optimized for 30.4 nm) • The visible light channel includes an achromatic polarimeter, based on electro-optically modulated liquid crystals.

26. Solar Wind Plasma Analyser (SWA) Principal scientific goals: • provide observational constraints on kinetic plasma properties for a fundamental and detailed theoretical treatment of all aspects of coronal heating; • investigate charge- and mass-dependent fractionation processes of the solar wind acceleration process in the inner corona; • correlate comprehensive in-situ plasma analysis and compositional tracer diagnostics with spacebased and ground-based optical observations of individual stream elements.

27. Solar Wind Plasma Analyser (SWA) Instrument Concept: • A Proton/α-particle Sensor (PAS) with the principal aim to investigate the velocity distribution of the major ionic species at a time resolution equivalent to the ambient proton cyclotron frequency. The sensor is Sun pointing. • An Electron Analyser System (EAS) consisting of two (three optional if resources allow) sensors to cover nearly 4π ster of viewing space and to allow the determination of the primary moments of the electron velocity distribution with high temporal resolution. • A Heavy Ion Sensor (HIS) which allows the independent determination of the major charge states of oxygen and iron and a coarse mapping of the three-dimensional velocity distribution of some prominent minor species. Also, pick-up ions of various origins, such as Si+, etc.) should be measured. The sensor is Sun pointing.

28. Radio and Plasma Wave Analyser (RPW) Principal scientific goals: • Provide measurements of both the electric field and magnetic field in a broad frequency band (typically from a fraction of a Hertz up to several tens of MHz) covering characteristic frequencies in the solar corona and interplanetary medium. • Measurements of both electrostatic and electromagnetic waves provide different diagnostics: - Electrostatic waves provide in-situ information in the vicinity of the spacecraft; - Electromagnetic waves provide extensive remote-sensing of energetic phenomena in the solar corona and interplanetary medium.

29. Magnetometer (MAG) Principal scientific goals: • Provide vector measurements of the solar wind magnetic field with high resolution (better than 1 nT) at sub-second sampling. • The MAG instrument will enable the investigation of: - The link between coronal structures and their signatures in the solar wind; - Kinetic effects in the solar wind plasma; - Large-scale structures in the solar wind, e.g., coronal mass ejections; - MHD waves and turbulence.

30. Energetic Particle Detector (EPD) Principal scientific goals: • Determine in-situ the generation, storage, release and propagation of different species of solar energetic particles in the inner heliosphere; • Identify the links between magnetic activity and acceleration on the Sun of energetic particles, by virtue of combined remote-sensing of their source regions and in-situ measurements of their properties; • Characterize gradual (typically CME-related) and impulsive (typically flare-related) particle events and trace their spatial and temporal evolution near the Sun. • Measure energetic pick-up particles originating from the interaction of the Solar Wind with near-Sun dust. In order to achieve these goals, measurements should be acquired at high time resolution (capable of up to 1 s, during high flux situations), with as complete an angular coverage as possible in order to resolve particle pitch-angle distributions.

31. Observational Strategies • Prime Science Periods: ~ 10 days around perihelion and/or highest latitudes highest data rates dumped to onboard memory instruments run autonomous in pre-defined mode sequences pointing by pre-defined s/c orientation maneuvers burst mode triggering, re-orientation triggering under consideration • Cruise Phase: CP allows for science observations during the transfer period possibilities (data rates, length of observation intervals...) TBD • `Aphelion Segments` during Science and Extended Phase: TBD so far, only observation opportunities for in situ instruments at low data rates are foreseen → we have to strongly push to open opportunities for remote sensing instruments and define reasonable low data rate modes

32. Schedule - Planning assumptions • Sept 2006 Letters of Intent to Propose • to Nov 2007 `Mission Consolidation` Phase • Nov 2007 SPC Decision • thereafter AO release • 2008 SPC approval of payload • 2008 Start of definition phase (18 months) • 2010 Start of implementation phase (tbc) • May 2015 Launch