1. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Solar Orbiter A high-resolution mission to the Sun and inner heliosphere

2. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Study team E. Marsch Max-Planck-Institut für Aeronomie, Germany E. Antonucci Osservatorio Astronomico di Torino, Italy P. Bochsler University of Bern, Switzerland J.-L. Bougeret Observatoire de Paris, France R. Harrison Rutherford Appleton Laboratory, UK R. Schwenn Max-Planck-Institut für Aeronomie, Germany J.-C. Vial Institut d’Astrophysique Spatiale, France ESA: Study Scientists: B. Fleck, ESA/GSFC and R. Marsden, ESA/ESTEC Study Manager: O. Pace, ESA/ESTEC Solar System Mission Coordinator: M. Coradini, ESA/HQ

3. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Solar Orbiter rationale  The Sun's atmosphere and heliosphere are - uniquely accessible domains of space, - excellent laboratories for studying in detail fundamental processes common to astrophysics, solar and plasma physics  Remote sensing and in-situ measurements, - much closer to the Sun than ever before, - combined with an out-of-ecliptic perspective, promise to bring about major breakthroughs in solar and heliospheric physics

4. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Close-up observations of the Sun  Imaging and spectroscopy, due to proximity, with an order of magnitude improvement over past missions SOHO/EIT TRACE Solar Orbiter 1850 km pixels 350 km pixels 35 km pixels

5. Solar Orbiter F2/F3 Presentations, 12 Sep 2000  Sources of solar wind and magnetic network Solar wind emanates from supergranular cell boundaries in coronal hole. The Solar Orbiter line- of-sight allows detailed analysis of the polar outflows Co-rotation will enable steady magnetic linkage Linking corona and heliosphere

6. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Basic questions  Why does the Sun vary and how does the solar dynamo work?  What are the fundamental processes at work in the solar atmosphere and heliosphere?  What are the links between the magnetic field dominated regime in the solar corona and the particle dominated regime in the heliosphere? These questions are basic to astrophysics in general

7. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Solar Orbiter firsts  explore the uncharted innermost regions of our solar system  study the Sun from close-up (45 solar radii or 0.21 AU)  fly by the Sun tuned to its rotation and examine the solar surface and the space above from a co-rotating vantage point  provide images of the Sun’s polar regions from heliographic latitudes as high as 38°

8. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Novel orbital design  Projected trajectory - closer to the Sun - out of the ecliptic

9. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Scientific goals  determine in-situ the properties and dynamics of plasma, fields and particles in the near-Sun heliosphere  investigate the fine-scale structure and dynamics of the Sun’s magnetised atmosphere, using close-up, high-resolution remote sensing  identify the links between activity on the Sun’s surface and the resulting evolution of the corona and inner heliosphere, using solar co-rotating passes  observe and fully characterise the Sun’s polar regions and equatorial corona from high latitudes

10. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 New perspectives  Co-rotation remote-sensing observations  In-situ diagnostics of the innermost heliosphere  Close-up high-resolution imaging and spectroscopy  Observations from out of the ecliptic plane These unique scientific perspectives form the basis for our scientific case

11. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Co-rotation observations: linking corona and heliosphere q Global solar corona and solar wind SOHO Ulysses Solar Orbiter will discriminate spatial from temporal variations

12. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Co-rotation observations: linking corona and heliosphere  Boundaries and fine structures Solar Orbiter will determine relationships between coronal and solar wind structures on all scales correlate in-situ particle characteristics with coronal sources identify ion compositional boundaries

13. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 In-situ measurements of the inner heliosphere Plasma microstate Temperature anisotropies Ion beams Plasma instabilities Interplanetary heating Solar Orbiter will make high-resolution plasma measurements (10 ms) Proton velocity distributions (Helios)

14. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 In-situ measurements of the inner heliosphere Magnetohydrodynamic waves and turbulence Spectrum of Alfvénic fluctuations: Steepening and dissipation! Solar Orbiter will show how MHD turbulence varies and evolves spatially, what generates Alfvén waves in the corona, how the turbulence is dissipated.

15. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 In-situ measurements of the inner heliosphere Solar energetic particles Solar Orbiter will provide novel information on shock, flare and CME related particle acceleration, by virtue of proximity to the Sun co-rotating orbit (long- term magnetic linkage)

16. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Close-up observations of the solar atmosphere Solar Orbiter will resolve the highly structured solar atmosphere an order of magnitude better than presently possible (both images and spectra)

17. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Close-up observations of the solar atmosphere An illustration of the multi-thermal nature of the solar atmosphere Solar Orbiter will observe loops and resolve their fine structure and map plasma flows

18. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 The Sun’s polar regions and equatorial corona  The polar magnetic fields and the dynamo What are the detailed flow patterns in the polar regions? What is the magnetic field structure in the polar regions?

19. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 The Sun’s polar regions and equatorial corona  Coronal mass ejection longitudinal extent and global distribution Viewing from out of the ecliptic plane allows the Solar Orbiter to study - CME longitudinal spreads - CME directions - the global distribution of CMEs

20. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 The Sun’s polar regions and equatorial corona  Solar luminosity variations Solar Orbiter will address questions such as: Does luminosity vary globally, or is brightening at the equator balanced by polar darkening? What is the angular distribution of radiance from active regions? The Sun is the only star for which we can determine the 3-D luminosity contribution.

21. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Solar Orbiter payload  The science goals require a sophisticated suite of remote sensing and in-situ instruments.  The mission profile demands that the instruments be low-mass, autonomous and thermally robust.  The thermal aspects have demanded quite mature instrument concepts at this early stage.

22. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Heliospheric in-situ package

23. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Heliospheric in-situ package  First in-situ detection of neutral (hydrogen) atoms from the Sun  First measurement of near-Sun dust (e.g., from grazing comets)  First detection of low-energy solar neutrons from flares

24. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Remote-sensing instruments

25. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Visible-light Imager and Magnetograph (VIM) Vector magnetograph consisting of: - 25 cm diameter Gregorian telescope - 5 cm diameter full disc telescope (refractor) - Filtergraph optics (two 50 mm Fabry- Perot etalons) High-resolution images (35 km pixels), Dopplergrams (helioseismology) and magnetograms of the photosphere

26. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Extreme UV Spectrometer (EUS) - 120 mm Ritchey- Chretien feeding spectrometer - light-weight carbon fibre structure with SiC optics - thermal control includes radiators, light rejection and shield High-resolution plasma diagnostics (75 km pixels)

27. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Extreme UV Imager (EUI) High-resolution imaging (35 km pixels) of the corona - EUV imaging, simultaneously in 3 part-Sun and and one full- Sun Gregorian 20 mm telescopes - long baffle system for thermal control of each telescope - common pointing mechanism

28. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 UV and Visible Light Coronagraph (UVC) Imaging of the visible and UV emission line corona - imaging of visible, H I and He II corona using off-axis Gregorian with external occulter - resolving element down to 1200 km. Stray light <10 -8 (visible) - principal thermal approach through occultation and optical rejection of unwanted light

29. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Main mission features  Orbit : solar orbits achieving high heliographic latitudes (goal over 30°) perihelion inside 0.3 AU co-rotation  Launch windows: as early as 2007, compatible with ESA F 2/3 in principle every ~ 19 months: May 2007, Jan. 2009, Aug. 2010  Mission duration: cruise phase ~1.9 years (3 orbits) nominal mission ~2.9 years (7 orbits) extended mission ~2.3 years (6 orbits)

30. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Main mission features  3-axis stabilised satellite: always Sun-pointing pointing accuracy (rms): - absolute pointing error ± 3 arcmin - relative pointing error ± 0.7 arcsec /15 min  Payload resources: Mass 130 kg Power 127 W Total data rate (in observation) 74.5 kbit/s  Spacecraft: magnetically clean

31. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Programmatic assumptions  Mission financed by ESA  Mars Express programmatic approach (model philosophy, industrial organisation, AIV approach, and launcher type)  Payload, e.g. instruments, booms, antennas, etc. supplied by the scientific community (PI approach), with science operations directed by Project Scientist, supported by the Science Team and Data Centre(s)

32. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Programmatic assumptions  Maximum use of already developed (or to-be-developed) hardware (e.g. technology qualified by 2004) and new technologies planned for BepiColombo considered available  Orbit injection by Soyuz-Fregat, launched from Baikonur  Operations done by ESOC, only one 15m ground station (Perth), single shift of 8 h/day, 7 days/week  Observation during cruise phase possible, consistently with spacecraft operation plan and radio link capability

33. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Schematic presentation of the orbit

34. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Mission phases Earth departure 1.5 Earth swing-by Subsequent Venus swing-by’s First Venus swing-by X-Y-plane trajectory plot including extended mission

35. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 S/C heliographic latitude

36. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 S/C perihelion distance

37. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Spacecraft design approach  Mission lifetime: 4.7 years (extended 7.1 years)  Solar aspect angle: 0° (Sun pointing)  Spacecraft: 3-axis stabilised  Observations: 30 days around each perihelion  Lift-off mass: 1296 kg, with 130 kg payload  Power: 7500 W, on cruise 457 W, on nominal mission  Science data rate: according to data dumping strategy (science data at 74.5 kb/s in observation, stored on 240 Gb on-board memory, dumped through HGA at max 750 kb/s)

38. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Spacecraft design approach  Configuration: Modular concept (SVM, PLM) at structural level  Structure: S/C body: 3 m x 1.2 m x 1.6 m, compatible with Soyuz-Fregat type-S fairing  Stabilisation: 3-axis, pointing accuracy for imaging, thermal, and High Gain Antenna (HGA) Sensors: star sensors, sun sensors, and gyros Actuators: reaction wheels (3+1) and hydrazine thrusters ( 2 x 6, 5 N) as main actuators  Propulsion: Solar Electric Propulsion (SEP) for transfer orbit and cruise phase, with 4 x 0.15 N Stationary Plasma Thrusters (SPT), commercially available in 2003

39. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Launch configuration

40. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Spacecraft in cruise phase

41. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Spacecraft in observation mode

42. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Spacecraft in data-dump mode

43. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Spacecraft design approach  Power supply: 2 solar arrays, 50 V bus regulated, with 2 Li-ion, 200 Wh batteries Cruise solar array (for SEP): - two steerable wings of 4 panels, 14 m 2 each (7500 W at 0.33 AU) - dual junction GaAs solar array, jettisoned at end of cruise phase - standard telecom technology, with edges protection Orbiter solar array (for S/C): - two rotating wings (0° - 90°), 86% OSR, 14% GaAs cells, 10 m 2, (500 W at 0.89 AU) to power orbiter in nominal operation - BepiColombo technology  Data handling: - standard ESA TT&C with centralised control unit for S/C operations, attitude and orbit control, thermal control - 240 Gb on-board mass memory

44. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Spacecraft design approach  Thermal Control: Combination of active and passive devices - Front sunshield (5 Ti foils + 20 Ka/Dacron net and upper Ti foils coated with white paint), covering S/C main body and mechanisms - Use of radiators and heat pipes, also for PLM CCDs cooling - Variable Orbiter solar array/Sun angle (0°-80°) according to Sun-S/C distance  Communications: TT&C: Standard ESA X-band up- and down-links, omni-directional by 4 LGAs, 20 W Science Telemetry: - 20 W, Ka-band, for up to 750 kb/s (at 0.7 AU, turbo code) science data dump rate - Dump strategy as from 0.5 AU (S/C-Sun distance) by 1.5 m, Cassegrain, HGA antenna, mounted on deployable boom and shielded for distance < 0.5 AU - BepiColombo technology for HGA

45. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Spacecraft budgets * Including 50 kg for L/V adapter; ** System margins included

46. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Cost at completion Current (year 2000) flexible mission budget envelope = 181.7 M Euro

47. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Technical summary  The mission design concept meets all the scientific requirements for solar and heliospheric observations close to the Sun (0.21 AU) and at high inclination with respect to the solar equatorial plane (38°).  The spacecraft design concept is feasible with the assumption that all the required technologies would be available off-the shelf or from the BepiColombo programme.

48. Solar Orbiter F2/F3 Presentations, 12 Sep 2000 Conclusions: Solar Orbiter... q will explore unknown territory near the Sun q will deliver the first images of the solar poles q will provide unprecedented high-resolution observations of the Sun (> 35 km) q will correlate in-situ & remote-sensing measurements at 45 Rs from a co-rotational vantage point q is technically feasible (using electric propulsion) q will maintain ESA’s position at the forefront of solar and heliospheric physics...is the next logical step towards understanding our star, the Sun.