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All rights reserved, 2008, Thales Alenia Space
EUCLID TAS System Concept
Alberto Anselmi (1) and Eric Thomas (2)
(1)Thales Alenia Space, Torino, Italy (2)Thales Alenia Space, Cannes, France
Euclid Mission Meeting 2011Area della Ricerca del CNR, Bologna, September 7-8, 2011
All rights reserved, 2011, Thales Alenia SpacePage 2
Introduction
High-precision survey mission to map the geometry o f the Dark Universe, optimized for two complementary cosmological probes� Full extragalactic sky survey with 1.2m telescope at L2� High precision imaging at visible wavelengths� Photometry/Imaging in the near-infrared� Near Infrared Spectroscopy
Experienced TAS team comprising TAS-I (Prime) and T AS-F (PLM) with support by Deimos Space and Kayser-Threde� 2 industrial design studies performed for ESA in 2008-2009 (Assessment) and 2010-
2011 (Definition)
Evolving design requirements� One NIR array for both photometry and spectroscopy� Improved definition of the performance indices
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Mission design: sky survey
Driven by the WES� 20,000 deg² in 7 years� DS performed in the idle times of the
WES
Sky scan law design drivers� 0.54 deg² FOV� 3000s to 3600s field dwell time� In-built Earth and Moon avoidance� Strategy must follow the sun (~1 deg
gap)� “Basic” mode (LOS orthogonal to
sun) and “Flexi” mode (LOS allowed to deviate from orthogonality at selected epochs)
� If Flexi, solar aspect angle transitions must be smooth
Field dwell time[s] 20,000 deg² 15,000 deg²
3000 Basic 7 53600 Basic 9 5
3000 Flexi5
(no margin) <4
WES Duration Strategy
Derived requirements for spacecraft design
� SAA (90º to 120º) and “Roll” (-3º to +3º) boundaries
� Telescope baffle slant (30º)� Number of field, strip and
hemisphere slews� Upper limits to dithering times
including settling (< 100s)
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Mission design: sky survey
Example: Flexi mode performance
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Sky-scan design tool
� Software tool designed by Deimos Space as part of TAS contract� Available to science team via ESA
� Simulates sky observation strategy, generating a variety of output information (FOV projection, command history, visit count, Earth/Moon aspect angle, X-axis Sun aspect angle, …)
� Fortran-coded simulation engine and MATLAB coded simulation environment � Basic scan: almost completely controlled by
simulator itself� Flexi scan: user-controlled observation schedule
� Graphical User Interface allows user to quickly design flexi mode observations� Direct feedback on how the variation of the
observation schedule control parameters affects the observation strategy
� Potential improvements: � Numerical optimization of observation strategies
with automated implementation of priority constraints
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Spacecraft Design Drivers
Multiple Dark Energy probes� One telescope feeding 2 instruments and 3 channels
Survey speed� Large Field of View (0.5 deg²) / Optimized sky survey strategy / Fast attitude
slews
Survey depth and signal to noise ratios� Baffle / Cold telescope for low background / On board data processing for
noise limitation / Low-T optics and detectors
Size reconstruction and stability of the Point Spre ad Function � High image quality / Large data rates / Fine guidance sensor
� Permanently shaded, temperature-controlled telescope
M-mission cost ceiling and target launch date� Passive cooling
� Telescope aperture limited to 1.2 m
� Limited number of NIR detectors
� Any new technology demonstrated by test by end of Definition Study.
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System configuration
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Spacecraft capabilities and resources
� L2 orbit, <7-year science mission� ~300,000 pointing steps (0.7°slews and
100 arcsec dithers)� Pointing Stability < 15mas @
700seconds, Pointing < 2 arcsec
� K-band telemetry, 74 Mbit/s via steerable K band HGA
� Fine-Guidance Sensor� Cold-gas thruster based pointing control
(GAIA heritage) and slews by small reaction wheels
� Herschel-heritage SVM hosting warm payload electronics
� PLM always in shadow of sunshield
� Sunshield-mounted solar array� 2160 kg launch mass, 1500 W EOL
power
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Euclid Telescope & instruments
� Telescope:
■ 3 mirrors off-axis Korsch design■ 1.2 m diameter primary mirror,
f=24.5 m■ ~110 mm dichroïc in output pupil
separates VIS and NISP beams
� VIS instrument■ FPA + shutter + calibration
■ Optical interface: telescope focus
� NISP instrument
■ Optical interface: telescope output pupil (dichroic)
FPA + FEE Shutter Unit Calibration Unit
Opto-mechanical assembly +
Detection System
Euclid optical layout proposed by ESA
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Euclid Telescope Overview
M2 Frame
Ultra Stable M1M2 truss
Optical Bench
M1
M2 and Focalisation
system
Highly recurrent design
- Mature technologies already flight proven or in implementation phase- Mastered development aspects
240 K telescope temperature- Limited excursion between integration and operational temperature- Limited impact on WFE
Instrument Cavity
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System Performance drivers
Vis :- requirement for high quality optics: wfe is a major contributor to ellipticity. - high sensitivity to defocus- Impact of pointing on ellipticity is found nearly negligible
Vis :- requirement for high quality optics: wfe is a major contributor to ellipticity. - high sensitivity to defocus- Impact of pointing on ellipticity is found nearly negligible
NISP:- Compatible with telescope optics temperature of 24 0 K- Challenging requirement on dichroic
NISP:- Compatible with telescope optics temperature of 24 0 K- Challenging requirement on dichroic
Thermal shields and radiators provided to instruments cold units accommodated in PLM
Thermal shields and radiators provided to instruments cold units accommodated in PLM
PLM instrument cavity architecture and instrument accommodation authorizes a modular instrument integration sequence
PLM instrument cavity architecture and instrument accommodation authorizes a modular instrument integration sequence
PLM design optimized to limit contribution to syste m mass budget
PLM design optimized to limit contribution to syste m mass budget
Proposed PLM architecture based on mature solutions and limited developments- High Resolution / stable architecture telescope he ritage
Proposed PLM architecture based on mature solutions and limited developments- High Resolution / stable architecture telescope he ritage
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Euclid IQ Performance
� Image Quality Performance analysis:■ VIS IQ performance calculation including
� Mirrors WFE• Based on experience
� AIT performance� Misalignments
• Ground to orbit effects• Cool down• Thermo-elastic• Hygro-elastic
� Compensation by M2� AOCS contribution
■ Sensitivity analyses to simulation parameters, comparison with ESA approach� Pupil/PSF sampling effects on results stability, FWHM calculation method
■ Complete telescope system performance calculated including optics+ structure + AOCS
Telescope PSF Line of Sight movement
Ellipticity distribution
FWHMdistribution
Variability of Ellipticity residuals
Variability of FWHM residuals
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Euclid IQ performance
� Complete analyses performed for all requirements■ static and residuals■ Optics + line of sight effects included
� Ellipticity performance driven by mirrors wfe
� Minimum FWHM requirement requires minimum residual LOS movement
� Residuals requirements achieved through fine regulation of telescope cavity
� NISP WFE requirement challenging■ 20 nm wfe for dichroic in transmission
� Straylight■ 240 K telescope compatible with requirement
� PLM proposed concept validated by analyses
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Development Plan
Staggered procurement approach, defined by ESA (Pri me first, level-1 subcontractors after; team in place by end of B2)
Three-model approach at system level: STM – AVM – PFM 6-yr development plan, compliant with 6-month syste m margin,
launch in early 2019Schedule driven by experiments need dates, telescop e primary mirror
manufacturing, PLM PFM structure preparationTelescope performance verification at PLM level wit h selected checks
repeated at integrated system level
2010 - 2011Project Phases Phase A/B1 Project Milestones BDCR PDR CDR QRR FAR �
System Models
2019Phase CPhase B2 Phase D Phase E1
2012 2013 2014
STM
2015 2016 2017 2018
Refurbish
AVM AVM maintenance
Launch
PFM Margin
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Conclusions
� Throughout the Definition Study, remarkable converg ence process of ESA, science, instrument and industrial teams to well de fined missionrequirements and feasible implementations
� Extensive proof of spacecraft performance provided by detailed and meticulous analysis� Telescope optics, thermal, thermoelastic, straylight, AOCS …
� Preliminary Requirements Review Board acknowledged significant progress in the definition of the Euclid space segm ent. No fundamental feasibility or technology readiness issues were fou nd
� Remaining issues identified by PRR board being addr essed now - none is a showstopper