# Presentation: 241209

## Solar Orbiter 

**A high-resolution mission to the Sun and inner heliosphere**

## 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

## 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**

##                 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**

**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**

## 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*

## 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°**

## Novel orbital design

**Projected trajectory**

**-  ***closer to the Sun*
*- out of the ecliptic*

## 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**

## 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*

## 	Co-rotation observations:         linking corona and heliosphere

** ****Global solar corona and solar wind**

**SOHO**

**Ulysses**

*Solar Orbiter will discriminate spatial from temporal variations*

## 	 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*

## 	 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)**

## 	 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.*

## 	 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)*

##     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)*

##  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*

##    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?**

##  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                                 *

##   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.**

##    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.**

## 	Heliospheric in-situ package

##  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**

## Remote-sensing instruments

**	****	**

##  Visible-light Imager and Magnetograph (VIM)

** ****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**

##    	    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)**

##    	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**

##    	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**

## 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)

## 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**	**

## 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)

## 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

##    Schematic presentation of the orbit

**	**

## Mission phases

**	**

**Earth departure**

**Subsequent Venus swing-by’s**

**First Venus swing-by**

**X-Y-plane trajectory plot including extended mission**

##        S/C heliographic latitude 

**  **

##    S/C perihelion distance

**  **

##     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)**

##     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**

## 	   Launch configuration

## 		Spacecraft in cruise phase

## 		Spacecraft in observation mode

## 		Spacecraft in data-dump mode

##     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**

##     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**** ****	****	****	**

## Spacecraft budgets

** **

***  Including 50 kg for L/V adapter;   **  System margins included**

## Cost at completion

** **

**Current (year 2000) flexible mission budget envelope  =  181.7  M Euro**

## 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.**

##         Conclusions: Solar Orbiter...

**will explore ****unknown territory**** near the Sun**
**will deliver the first images of the ****solar poles**** **
**will provide unprecedented ****high-resolution****       ****observations of the Sun ****(> 35 km)**** **
**will correlate in-situ & remote-sensing measurements at ****45 Rs**** from a ****co-rotational**** vantage point **
**is ****technically feasible**** (using electric propulsion)**
**will maintain ESA’s position at the ****forefront**** of solar and heliospheric physics**

**...is the next logical step towards understanding our star, the Sun.**