Diapositive 1

1
THE PICARD MISSION OBJECTIVES, MEASUREMENTS
and PLANS Gérard Thuillier1, Judit Pap2, and
Sabatino Sofia3 1 Service dAéronomie du CNRS,
France 2 GSFC 3 Yale University PICARD
mission - scientific objectives -
measurements - instruments - international
context Launch October 2008
CNES microsatellite
2
PICARD MISSION MAIN SCIENTIFIC OBJECTIVES
(1) Measure the variability of several global
solar properties. In particular, the solar
diameter with a metrological instrument. (2)
Modelling of the solar machine Role of the
magnetic field, on surface or deeper in the
convective zone. (3) Contribution to solar
luminosity reconstruction (4) Long term
trend (5) Understanding of the ground based
measurements
3
Key constraints for validating Physical processes
of the solar models are simultaneously measured
by PICARD - solar diameter, limb shape,
asphericity in the photosphere - total solar
irradiance - oscillation modes - Temperature
variations in the photosphere ? HMI and
PICARD have a strong synergy
4
UNCERTAINTIES OF CURRENT MEASUREMENTS OF SOLAR
DIAMETER VARIATIONS Definition of the solar
diameter not unique Instruments psf and their
stability in time? What is the role of the
atmosphere for ground measurements? What is the
role of the spectral domain of measurement?
5
RESULTS FROM GROUND OBSERVATIONS There are
several optical methods (Mercury transits,
eclipses, astrolabes, imaging telescope) showing
- in phase, or anti phase with the 11-year
solar cycle, or no variation. ? Contradictory
results
Photospheric Diameter Variations from
Measurements Made outside the Atmosphere -
MDI/SoHO images are used to determine the radius
variation as a function of time. The recent
results show a maximum change of 15 mas per year
(Kuhn et al., 2004). MDI has no internal means
to control the instrument angular scale.
Corrections by models were made.
6
DIAMETER VARIATION FROM STRATOSPHERIC BALLOON
OBSERVATIONS Sofia et al. (1994) have built the
Solar Disk Sextant (SDS) using an angular
reference. Operated on board a stratospheric
balloon, four flights were carried
out. Results of four stratospheric
balloons flights carrying SDS (Egidi et al.,
2006) showing a diameter increase of 0.2 while
the solar activity decreases.
Calern ? SDS
7
Sofia et al, 2005
Avec turbulence, diamètre et activité sont en
antiphase
Sans turbulence, diamètre et activité sont en
phase
Sofia et al., 2005
No turbulence
With turbulence
2 4
6 Depth (Mm)
8
INSTRUMENTS ON BOARD PICARD Two radiometers
of different type allow to discriminate between
variations of instrumental origin and of solar
origin. PICARD will be in the same configuration
as SoHO with the DIARAD instrument (IRMB) and the
PMO6 instrument (PMOD-WRC). SOVAP (radiometer,
IRMB) PREMOS (radiometer and 4 sunphotometers,
PMOD) SODISM (imaging telescope, CNRS)
9
Themes Measurements Instruments
Solar Physics Variability diameter/luminosity, activity, luminosity SODISM I, SOVAP, PREMOS
Asphericity, limb shape SODISM I
Differential rotation SODISM I
Diameter/ stellar reference SODISM I
Helioseismology SODISM I, PREMOS
Climate Diameter/luminosity SODISM I, SOVAP, PREMOS
Luminosity SOVAP, PREMOS
UV Variability PREMOS, SODISM I
Atmospheric Physics Diameter and limb shape at ground Ozone Ground-based instruments (SODISM II, MISOLFA, ) SODISM I, PREMOS
Space Weather Images _at_ 215 and 393 nm (Ca II) SODISM I
SODISM I diameter measurement in orbit. SODISM
II, on ground SOVAP and PREMOS measurement of
the Total Solar Irradiance (TSI) PREMOS
measurement in 5 spectral domains
10
SODISM PRINCIPLES OF DESIGN 1) Use of stable
materials ZERODUR for mirrors INVAR and C-C
for structure 2) The whole instrument is kept at
20C within 0.3 C 3) the 2k x 2K CCD is kept at
- 40C within 0.1C 4) Spectral domains selected
by interference filters 5) a four-prism system
measures the internal geometrical instrument
scale 6) Internal scale checked by use of
stellar angular distances
11
Interference filters
12
Location of the Imaging Telescope
Two Interference Filters Wheels
Main door
Guiding Telescope
Foot to compensate the platform thermal expansion
Shutter
13
(No Transcript)
14
STATE OF DEVELOPMENT AND SCHEDULE Stabilization
of the primary mirror achieved with 0.1 
precision Electronics QM CCD,
DSP,TM-TC Optics made Flight components
provided Flight unit to start end of
February Delivery for integration end
2007 Launch October 2008
15
The 4 prisms generate 4 solar images in each
corner of the CCD. Their intensity is lower than
the main image given the ratio of the pupils. The
CCD size Is approximately indicated.