Solar Orbiter

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Solar Orbiter
A High Resolution Mission to the Sun an Inner
Heliosphere
E. Marsch, R. Schwenn, E. Antonucci, P. Bochsler,
J.-L. Bougeret, B. Fleck, R. Harrison, R.
Marsden, J.-C. Vial
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Background

• The Solar Orbiter (SO), developed from
  InterHelios, was presented at A Crossroads for
  European Solar and Heliospheric Physics and was
  endorsed by ESAs Solar Physics Planning Group
  (SPPG).
• ESA conducted a pre-assessment study for SO in
  1999.
• Additional mission scenarios, such as polar
  orbits and/or closer approaches to the Sun, were
  discarded for technical reasons.
• Technical feasibility of SO demonstrated.
• SO was one of about 40 responses to the Call for
  Proposals for the next two flexi-missions (F2
  and F3) within ESAs Scientific Programme.
• On 1 March 2000, ESAs Space Science Advisory
  Committee (SSAC) selected SO, among 5 other
  proposals, for an assessment study.
• Next selection round (for definition phase) in
  September 2000.
• Given the realistic cost estimates, international
  partners (e.g. NASA, ISAS, RSA or other national
  agencies) are needed.

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Solar Physics after SOHO New Goals

• Unravel couplings between all layers of the solar
  atmosphere
• make multi-wavelength simultaneous observations
  at very high spatial resolution!
• Disentangle spatial and temporal variations in
  the solar wind
• choose orbit enabling S/C co-rotation with the
  Sun!
• Uncover missing links for understanding the solar
  dynamo
• observe the Sun from high latitudes!

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Novel Measurements

• Observe all layers of the solar atmosphere at
  high spatial resolution (Sun (45 R? ).
• Separate spatial and temporal variations in the
  solar wind from quasi-corotational orbit (1.3?
  per day).
• Enable first observations of the polar regions of
  the Sun from out-of-ecliptic vantage points (up
  to 38? in heliographic latitude).

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Coverage of Solar and Heliospheric Physics

• Interior
• Dynamo ? image solar poles and determine magnetic
  field
• Photosphere and Chromosphere
• Luminosity ? measure irradiance changes (at high
  latitudes)
• Flux tubes ? resolve small-scale magnetic
  elements (
• Corona
• Loops ? imaging and spectroscopic diagnostics of
  the building blocks of the corona
• Flares ? measure radio emissions, particles, and
  neutrons
• Heliosphere
• Streams ? separate structures from turbulence and
  waves

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Scientific Payload

• Solar Instruments
• Visible-light imager and magnetograph
• EUV / X-ray imager
• EUV spectrometer
• UV and visible-light coronagraph
• Neutron and ?-ray detector
• Radiometer

• Heliospheric Instruments
• Solar wind plasma analyzer
• Plasma wave analyzer
• Magnetometer
• Energetic particle detector
• Neutral particle detector
• Dust detector
• Radio spectrometer
• Coronal radio sounding experiment

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Key Goals for the Near Sun Phase

• solar magnetic field - structure and evolution
  at the fundamental scale of magnetic elements,
  providing new insights into magnetoconvection
• coronal heating processes - in the transition
  region and at the coronal base, at a much finer
  scale (
• coronal and interplanetary disturbances -
  magnetic flux tubes, magnetic activity, flares,
  eruptive prominences and coronal mass ejections
• evolution of solar active regions - sunspots,
  loops, and prominences.
• plasma and electromagnetic fields - coronal
  streamer belt and coronal holes extending to the
  near-ecliptic regions (slow and fast solar wind)
• energetic particles close to the Sun - origin,
  acceleration and transport
• near-Sun dust - origin and spatial distribution
• coronal radio emission - and particles
  originating from the same source

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Key Goals for theOut-of-Ecliptic Phase

• nature and evolution of the solar polar coronal
  holes, as well as their boundaries
• origin of solar wind streams at intermediate and
  high latitudes
• coronal mass ejections their global
  distribution, longitudinal extent, onset and
  propagation
• magnetic field structure and evolution, in
  particular over the poles where it is poorly
  known
• working of the solar dynamo, including the
  reversals of the polar field
• dynamics and rotation of the solar corona near
  the poles
• magnitude and nature of the solar luminosity
  variations
• global coronal waves and their effects over the
  poles
• acceleration of the solar wind over the poles by
  Doppler-velocity measurements.

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Solar Instrumentation
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Heliospheric Instrumentation
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Mission Characteristics

• Orbit
• inclination variable (heliographic) 0 ? i ? 38?
• perihelion down to 45 R?
• S/C platform
• 3-axis stabilized, Sun-pointing, better than 3
  arcsec/15 min
• Launch date 2009, compatible with F2/F3
• Lifetime total ? 7 years
• cruise ? 2 years
• scientific ? 5 years (nominal ? 3 years
  extended ? 2 years)
• Payload solar-remote package in-situ package
• Mass S/C ? 1500 kg, P/L ? 100 kg
• Data rate 70 kbit/s (Ka-band)

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Spacecraft Overview

• Total mass 1510 kg
• Dimensions 3 m x 1.2 m x 1.6 m
• 3-axis stabilized
• pointing stability better than 3 arcsec /
  15 min
• Solar Electric Propulsion (SEP)
• 4 x 0.15 N stationary plasma thrusters
• Deployable and rotatable Cruise solar arrays,
  jettisoned after last SEP thrusting
• Deployable and tiltable Orbit solar
  arrays, 16 GaAs cells, 84 OSR.
• 4 X-band LGAs, omni coverage, for TTC.
• One Ka-band HGA, 1.5 m dia., for telemetry after
  Cruise.

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Trajectory
Perihelion Radius
Solar Latitude wrt Solar Equator
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Modes of Operation
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Telemetry Capabilities
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Programmatics

• Mission managed and financed mainly by ESA, with
  strong international collaboration (e.g. NASA).
• PI-type mission, instruments supplied by
  community.
• Cost estimate (pre-assessment study) 232 Meuro.
• Maximum use of available technology, of-the-shelf
  (in 2004), or from the proposed Mercury Orbiter
  Cornerstone Bepi-Colombo.
• Launcher Soyuz-Fregat type.
• S/C and science operations performed with a
  single ground station, e.g. by ESOC.
• Seeking international partners for second and
  third ground station, in order to increase
  science telemetry.
• Design lifetime compatible with a 7-year mission.

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Summary Solar Orbiter will ...

• explore unknown territory near the Sun
• provide unprecedented high-resolution
  observations of the Sun (? 40 km)
• provide the first images of the solar poles
• correlate in-situ with remote-sensing
  measurements at 45 R? from a quasi-co-rotational
  vantage point
• be technically feasible (using electric
  propulsion)
• be the next logical step and open new grounds in
  solar and heliospheric physics!