euclid tas system concept€¦ · euclid iq performance image quality performance analysis: vis iq...

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


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


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)


Mission design: sky survey

Example: Flexi mode performance


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


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.


System configuration


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


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


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


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


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


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


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


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

euclid tas system concept€¦ · euclid iq performance image quality performance analysis: vis iq...

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