The ESA GAIA mission

1. The ESA GAIA mission G.Santin*, P.Nieminen Space environments and effects analysis section ESTEC * RHEA System SA Geant4 Collaboration Workshop 2003 TRIUMF, 5 September 2003

2. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 2 The GAIA mission Multi-epoch survey of the central regions of galaxies with high spatial resolution and multicolor photometry Successor to ESA�s Hipparcos satellite (1989-�93) a factor of more than 100 improvement in accuracy a factor 1000 improvement in limiting magnitude, and a factor of 10000 in the number of stars observed Target for the launch: 2010 L2 orbit http://sci.esa.int/hipparcos HIPPARCOS: LAUNCH DATE:08-Aug-1989 23:25 UT MISSION END:Aug-1993 LAUNCH VEHICLE:Ariane LAUNCH MASS:500 kg MISSION PHASE:Completed ORBIT:highly elliptical ACHIEVEMENTS: Hipparcos is the first space mission dedicated to measuring the positions of the stars Hipparcos helped to predict the impacts of Comet Shoemaker-Levy 9 on Jupiter; identified stars that will pass close to the Sun; THE MISSION:Unique to Europe was the very first space mission for measuring the positions, distances, motions, brightness and colours of stars - for astrometry, as the experts call it. ESA's Hipparcos satellite pinpointed more than 100 000 stars, 200 times more accurately than ever before. As astrometry has been the bedrock of the study of the Universe since ancient times, this leap forward has affected every branch of astronomy. The primary product from this pioneering and successful mission was a set of stellar catalogues, The Hipparcos and Tycho Catalogues, published by ESA in 1997. http://sci.esa.int/hipparcos HIPPARCOS: LAUNCH DATE:08-Aug-1989 23:25 UT MISSION END:Aug-1993 LAUNCH VEHICLE:Ariane LAUNCH MASS:500 kg MISSION PHASE:Completed ORBIT:highly elliptical ACHIEVEMENTS: Hipparcos is the first space mission dedicated to measuring the positions of the stars Hipparcos helped to predict the impacts of Comet Shoemaker-Levy 9 on Jupiter; identified stars that will pass close to the Sun; THE MISSION:Unique to Europe was the very first space mission for measuring the positions, distances, motions, brightness and colours of stars - for astrometry, as the experts call it. ESA's Hipparcos satellite pinpointed more than 100 000 stars, 200 times more accurately than ever before. As astrometry has been the bedrock of the study of the Universe since ancient times, this leap forward has affected every branch of astronomy. The primary product from this pioneering and successful mission was a set of stellar catalogues, The Hipparcos and Tycho Catalogues, published by ESA in 1997.

3. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 3 The GAIA spacecraft Service Module (SVM) Electronics, propellant, antenna,� Payload Module (PLM) Optical bench Mirrors Focal Plane Sun shield

4. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 4 Measurement technique

5. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 5 Radiation environment and effects Solar radiation Protons, heavy ions, electrons, neutrons, gamma rays, X-rays� Event driven � occasional high fluxes over short periods. Cosmic rays Continuous low intensity (~4/(cm2 s)) Heavy ions Trapped radiation (not relevant here) Continuous with variable intensity source of radiation Electrons ~< 10 MeV Protons ~ <102 MeV TOS-EES web page: Surviving the Space Environment Quite apart from the problems caused to spacecraft by the ultra-high vacuum and extremes of hot and cold in space, spacecraft have to survive an array of hostile environments which can severely limit space missions. The clickable diagram below summarizes these. Radiation in Space Surrounding the Earth are belts of energetic charged particles - the Van Allen belts. The sun also creates streams of very energetic particles. High energy heavy particles also reach near to Earth from outside the solar system. All these natural radiation sources are a serious problem to the survivability and operation of satellites. The Radiation Environment� Radiation in the space environment comes from the trapped particle belts, solar particle events and cosmic rays. Trapped Particle Belts The radiation belts consist principally of electrons of up to a few MeV energy and protons of up to several hundred MeV energy. These are trapped in the Earth's magnetic field; their motions in the field consist of a gyration about field lines, a bouncing motion between the magnetic mirrors found near the Earth's poles, and a drift motion around the Earth [Hess] (Fig. 1). Solar Particle Events During solar events (Fig. 5), large fluxes of energetic protons are produced which reach the earth. The August 1972 event produced a peak flux in excess of 1E+06 protons/cm�/sec above 10 MeV energy. Such events are unpredictable in their time of occurrence, magnitude, duration or composition. The earth's magnetic field shields a region of near-earth space from these particles (geomagnetic shielding) but they easily reach polar regions and high altitudes such as the geostationary orbit. Cosmic Rays Cosmic Rays originate outside the solar system. Fluxes of these particles are low but, because they include heavy, energetic ("HZE") ions of elements such as iron, they cause intense ionisation as they pass through matter, are difficult to shield against, and therefore constitute a significant hazard. They give rise to single-event processes (SEU, latch-up) in large-scale integrated electronic components, as well as interference and an uncertain radiobiological effect. Other Radiation Other aspects of the radiation environment include induced radioactivity, planetary environments (Jupiter and Saturn have particularly hostile radiation environments), trapped ions and spacecraft nuclear generator systems. TOS-EES web page: Surviving the Space Environment Quite apart from the problems caused to spacecraft by the ultra-high vacuum and extremes of hot and cold in space, spacecraft have to survive an array of hostile environments which can severely limit space missions. The clickable diagram below summarizes these. Radiation in Space Surrounding the Earth are belts of energetic charged particles - the Van Allen belts. The sun also creates streams of very energetic particles. High energy heavy particles also reach near to Earth from outside the solar system. All these natural radiation sources are a serious problem to the survivability and operation of satellites. The Radiation Environment� Radiation in the space environment comes from the trapped particle belts, solar particle events and cosmic rays. Trapped Particle Belts The radiation belts consist principally of electrons of up to a few MeV energy and protons of up to several hundred MeV energy. These are trapped in the Earth's magnetic field; their motions in the field consist of a gyration about field lines, a bouncing motion between the magnetic mirrors found near the Earth's poles, and a drift motion around the Earth [Hess] (Fig. 1). Solar Particle Events During solar events (Fig. 5), large fluxes of energetic protons are produced which reach the earth. The August 1972 event produced a peak flux in excess of 1E+06 protons/cm�/sec above 10 MeV energy. Such events are unpredictable in their time of occurrence, magnitude, duration or composition. The earth's magnetic field shields a region of near-earth space from these particles (geomagnetic shielding) but they easily reach polar regions and high altitudes such as the geostationary orbit. Cosmic Rays Cosmic Rays originate outside the solar system. Fluxes of these particles are low but, because they include heavy, energetic ("HZE") ions of elements such as iron, they cause intense ionisation as they pass through matter, are difficult to shield against, and therefore constitute a significant hazard. They give rise to single-event processes (SEU, latch-up) in large-scale integrated electronic components, as well as interference and an uncertain radiobiological effect. Other Radiation Other aspects of the radiation environment include induced radioactivity, planetary environments (Jupiter and Saturn have particularly hostile radiation environments), trapped ions and spacecraft nuclear generator systems.

6. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 6 GAIA in a L2 orbit Orbit choice: L2 orbit 1.5 million km in the anti-Sun direction uninterrupted observations Earth, Moon and Sun remain behind the spacecraft viewing direction chosen for other astronomy missions, like Eddington, Herschel-Planck and JWST http://tonno.tesre.bo.cnr.it/Report/420.htm Operational Orbit The operational orbit for PLANCK been selected to maximize the scientific return within the technical constraints, and is a Lissajous orbit around the L2 point of the Earth/Sun system. The L2 libration point (also known as the L2 Lagrangian point) is a point collinear with the Sun and the Earth-Moon barycentre, at a distance of about 1.5 million km from the Earth, and in opposite direction to the Sun in relation to the Earth (see Figure 3.9). This orbit offers the best possibilities to satisfy the stringent requirements imposed by the scientific instruments on stray light suppression, and on low and stable heat input to achieve the required low temperature in the focal plane assembly (see Section 3.7.3). In addition, the sky coverage of the telescope is maximized without disturbances by the Earth, Moon or Sun. Image from http://imagine.gsfc.nasa.gov/Images/news/map_L2_large.jpg imagine.gsfc.nasa.gov/docs/ features/news/03jul01.html. http://tonno.tesre.bo.cnr.it/Report/420.htm Operational Orbit The operational orbit for PLANCK been selected to maximize the scientific return within the technical constraints, and is a Lissajous orbit around the L2 point of the Earth/Sun system. The L2 libration point (also known as the L2 Lagrangian point) is a point collinear with the Sun and the Earth-Moon barycentre, at a distance of about 1.5 million km from the Earth, and in opposite direction to the Sun in relation to the Earth (see Figure 3.9). This orbit offers the best possibilities to satisfy the stringent requirements imposed by the scientific instruments on stray light suppression, and on low and stable heat input to achieve the required low temperature in the focal plane assembly (see Section 3.7.3). In addition, the sky coverage of the telescope is maximized without disturbances by the Earth, Moon or Sun. Image from http://imagine.gsfc.nasa.gov/Images/news/map_L2_large.jpg imagine.gsfc.nasa.gov/docs/ features/news/03jul01.html.

7. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 7 L2 orbit and radiation environment Very stable thermal and radiation environment, compared to other considered orbit hypotheses Not affected by the trapped particle belts Cosmic rays and solar event particles outside the geomagnetic shielding Effects from the magnetotail dynamics caused by variations of the solar wind density and velocity

8. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 8 GAIA Geant4 simulation: geometry model Selection from CAD engineering model volumes STEP interface not complete for GAIA Even simple CATIA elements cannot be imported Accurate description of the materials

9. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 9 Source description Protons spectra relevant for the L2 radiation environment �Flare� model environment CR�ME�96 (worst week/day, peak 5 min) Quiet time environment CR�ME�96 model (2010-2016) 6 year mission total proton fluence JPL�91, 90% confidence level Individual solar events Examples of real data spectra NOAA database Bastille day event

10. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 10 Physics description LHEP_PRECO_HP standard G4 physics list: Geant4 standard electromagnetic processes LHEP_PRECO_HP for the hadronic physics pre-equilibrium decay model for modeling the inelastic interaction nucleons LEP and HEP parameterized models for the other inelastic interactions Point-wise evaluated cross section data to model neutron interactions from thermal neutron energies up to ~20 MeV (capture, elastic scattering, fission and inelastic scattering) Fission fragments not available Data base used: G4NDL version 3.7. Secondary e+/- and gamma production cut: global 10 micron Thin multi-layer insulating foils (< 100 micron) Analysis of damage on the CCD, thin protecting and active layers Difference wrt standard cut 0.7 mm ~ 10-50 % Moved recently to cuts per region (to avoid low cuts in SVM) Moving to Binary Cascade (PRECO?BIC) model For low energy hadronic interactions, better secondary description + HP models for low energy neutrons UR: standard list BIC_HP ? Problems with g4.5.1 (seg faults) seem to be solved with g4.5.2

11. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 11 Flux on the CCD surface Counts of different particle species on the CCD surface (from front or back) Mono-energetic proton source Energies from 1 MeV to 50 GeV Each energy point normalized to # incident protons Spherical source Cosine-law emission Limited solid angle Convolved with environment spectra Integrated over the energy Total results on rates Flux results are interesting for background estimates and NIEL analysis

12. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 12 NIEL analysis NIEL based on flux information and CERN coefficients MULASSIS macroscopic approach GAIA NIEL simulation data convoluted with input spectra

13. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 13 Total Ionising Dose TID analysis Total Ionising Dose Same approach as flux and NIEL analysis Mono-energetic simulations Results convoluted with input spectra Contribution to the TID VS primary proton energy 2D distribution of doses No significant effect observed

14. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 14 Estimates for various geometry configurations TID and NIEL as a function of Tent thickness CCD shielding side panels Front/Back � ill. CCD CCD surface shield (glass) Results: ESTEC Technical Note, v1r1 Effect: modify the spectrum of the particles impinging on the CCD

15. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 15 Comparisons with other tools: CCD Glass shield option, thermal tent thickness Tent: 0.12 mm eq. Al Front-ill. CCD Quartz cover Thickness between 0.1 and 5 mm (overlapping the Alenia study)

16. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 16 SSAT � Sector Shielding Analysis Tool Shielding sectorial analysis Ray tracing: from a user-defined point within a Geant4 geometry ? shielding levels (fraction of solid angle for which the shielding is within a defined interval) and shielding distribution (the mean shielding level as a function of look direction). It utilizes geantinos Provides both global shielding and shielding from single materials GAIA: view from the CCD surface

17. G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003 17 Conclusions Complete model of the GAIA mission developed All relevant volumes Fair level of geometry complexity Ionising and NIEL dose estimates have been obtained Results in agreement with other estimates Help in the spacecraft design phase Geant4 capabilities appreciated by the GAIA mission team Analysis detail, geometry model flexibility, dose prediction power