PPLC/ESA meeting, Feb 27th 2009 Gérad Epstein Patrick Levacher. OVERALL PAYLOAD CONCEPT TRADE-OFFS AT SYSTEM LEVEL PLATO

PPLC/ESA meeting, Feb 27th 2009 GE + PL PLATO Overall concept (1) Heritage from CDF design: –Mission: Launcher, orbit, operations unchanged Design life time unchanged –Instrument: Concepts optimised for better performances with respect of the available ressources of the SVM (PDD data). Overall diameter, Sun shield size and shape…

PPLC/ESA meeting, Feb 27th 2009 PLATO Overall concept (2) Performances to optimize –Number of observed cool dwarfs with the required signal to noise ratio, in each pointing phase (samples P1, P3, P5) –With respect of the required signal to noise ratio, prioritize a star distribution favouring low magnitudes –Optimization of the step&stare phases : find stars with detected « exoplanets » (sample P2, P4), which can be re-observed during these phases with a S/N of 27ppm in 1 hour. GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Overall concept (3) Design drivers: –Try to conserve an instrument limited by its photon noise: each other noise shall be dimensionned at 1/3 of the photon noise –Avoid (reduce) any periodic perturbation in the seismic observation range: [100 sec – 4 days] GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Overall concept (4) As in the CDF design, concept of several telescopes (like in the CDF design), –better pupil size to mass ratio, better protons effects management, natural redundancy…  Maximize the number of telescopes in the instrument Overlapping FoV concept –Optimize the number of observed cool dwarfs with the required S/N in each observation phase Fully dioptric design –Trade-off at the PDR –Dioptric solution selected for compactness, baffling possibility, low distortion, but temperature sensitivity GE + PL

G E. + P.L. PLATO Enhanced FOV : 4x10 normal telescopes Global FOV 1800 sqr degrees in 9 zones –Corners: 10 telescopes 800 sqr degrees –Cross: 20 telescopes 800 sqr degrees –Center: 40 telescopes 200 sqr degrees and 2 fast telescopes 400 sqr degrees

PPLC/ESA meeting, Feb 27th 2009 PLATO Overall concept (5) Pupil size –Dimensionned by photometry requirements (first evaluation with photon noise only), for a G0 star, at magnitudes close to 11 Field of view –Compromise between number of cool dwarfs in the FoV and confusion. –Overlapping FoV concept needs a large FoV of each telescope which shall inscribe the FPA, with a good quality of PSF up to the edge –Limited by the feasability of the optics (~ f/2) GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Optics dimensionning (1) Signal budget with the following assumptions to evaluate the pupil size needed –back-thinned CCD with a red enhanced coating (commercial data + margin of 2%) –6 lenses optics, transmission value based on the Corot OD (+ margin of 2%) –90% of phote- inside the PSF effectively used –smearing losses (23s of exposure and 2s of readout time) –reference star: G0, magnitude close to 11 GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Optics dimensionning (2) Pupil diameter needed to reach the S/N of 27 ppm in 1 hour as a function of the magnitude Number of telescopes needed to reach the S/N of 27 ppm in 1 hour as a function of the magnitude and for different pupil diameter Considered with photon noise only  40 normal telescopes, pupil dia of 115mm, goal 120mm GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Optics dimensionning (3) Field of view needed evaluation –Statistic number of star / square degree, function of magnitude, –Percentage of cool dwarfs, function of magnitude –Evaluation of confusion, function of magnitude  Need of a FoV close to 800 square degrees for each telescope to reach the required number of observed cool dwarfs (plate scale ~ 14.3 arcsec /px) % of cool dwarfs function of magnitude GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Instrument optimization Overlapping factor selection (k=0, adjacent FoVs; k=1, same FoV) k factor Sample P1-4 %nominal+4 % Sample P2+14 %nominal-14 % Sample P5-3.2 %nominal+3.2 % Effect on lower magnitudes + nominal - Mechanical accomodation - nominal + Total FoV2048 °²1800 °²1568 °² Supposed: same PSF quality in the entire FoV, FoV distortion effects are negligible Temporary conclusion: k=0.5 seems a good compromise and is our baseline GE + PL

PLATO Electronics architecture GE + PL PPLC/ESA meeting, Feb 27th 2009 Homogeneous with 40 telescopes in 4 groups Failure tolerant architecture Fully redundant on ICU

40 normal + 2 fast telescopes Two fast telescopes in the middle of the instrument Four sub-sets of 10 normal telescopes Each sub-set is tilted of 10° to realize the overlapping FoV (k = 0.5) X Z X Y PLATO Mechanical accomodation GE + PL PPLC/ESA meeting, Feb 27th 2009

PLATO Mechanical accomodation GE + PLPPLC/ESA meeting, Feb 27th 2009

PLATO Thermal needs FPA and their detectors –Detectors shall be at a temperature lower than -80°C (TBC), their mean temperatures are not critical (few degrees) –FPA power dissipation is stable, around 1 watt per telescope –Only very slow detectors temperature fluctuations are acceptable, but few degrees drift within a 3 month observation period may be foreseen. Electronics boxes –FEE and MEU shall be at temperature higher than - 40°C (electronics components), –FEE power dissipation is stable, around 4 watt per telescope –FEE short term stability is the only constraint –MEU are less sensitive to temporal variations, Telescopes –Need an in-flight focus control, 40 mechanisms are inconceivable, but thermal adjustment of the focus (in one way) seems possible, –Temperature close to room temperature prefered Stay alive during OFF phases Heaters to be controlled by SVM GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Thermal concept (1) Derived from the CDF proposed architecture: –Cold and stable « optical » zone The FPA, which needs to be connected to a highly stable cold well, is cooled through the optics structure and by the optical baffle (and the front lens) Power injected in the telescope to adjust the focussing is finally dissipated by the baffle (and the front lens), and consecutively limits the detectors temperature. –Warmer Electronics zone Electronics boxes are mounted on a thermal plate ’’under’’ the OB, cooled by lateral radiators (CDF design) GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Thermal concept (2) Thermal dimensionning of the telescope –Need to reduce the temperature axial gradient (acceptable value is still TBD). –Low thermal fluxes, high thermal conductivity of structures: FPA : ~1 or 1.5W, parasitic flux coming from the fixation on the OB shall be reduced with low conduction legs (titanium ?). Value is TBD with the OB temperature (Thermal I/F). Power injected in the telescope to adjust the focussing is located close the internal pupil plane and participate very slightly to a axial gradient. Low exchanges of radiative power between telescopes in the middle of the instrument (~ same temperature), but sahll be evaluated for those on the edge (Thermal I/F) High conductive structure of the optics (material, section…) –Dimensionning of the baffle, thermally coupled to the telescope structure, for the evacuation of the power at the temperature where the optical study is made. GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Thermal concept (3) Thermal concepts for the electronics boxes –Working temperature: -40°C to +40°C measured at TRP of the boxes. –Long term temporal gradient are acceptable for FEE boxes, value is still TBD (Thermal I/F), –The electronics boxes are mounted on a thermal plate connected to lateral radiators –Thermal fluxes to evacuate: Boxes: 40 FEE + 8 MEU + 1 ICU + 2 fast FEE + 2 fast DPU, Total flux: 564 W without margin (Thermal I/F). Heaters needed on this thermal plate to maintain the storage temperature of the boxes when they are off. GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Sources of noise (1) Photon noise Background ‘’light’’ noise due to: –Zodiacal light, –Light coming from (out of the FoV) (baffling system inefficiency) –Light coming from the FoV: optics self contamination (diffusion, parasitic reflexions), –Smearing effect –Thermal background of the CCD, –Hot pixels (irradiation effects) Electronics noise –Readout noise (CCD, cables, analog electronics, ADC) < 18 e- rms Jitter noise –Displacements following a normal distribution with a standard deviation of 0.2 arcsec (first approach) GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Sources of noise (2) 1/3 of photon noise (27ppm in 1 hour), for a PSF of 9 pixels  background < 120 e-/s/px in the zone observed with 40 telescopes, 240 e-/s/px with 20 telescopes, 480 e-/s/px with 10 telescopes. Zodiacal light –evaluated at 25 e-/s/px,with a plate scale of 14.3 arcsec/px Baffling system inefficiency –for a first approach, specified at 20 e-/s/px, value TBC with the baffle design and performance evaluation Optics self contamination (diffusion, parasitic reflexions) –considered negligible for a first approach, TBC with the optical detailed design, the molecular and particular contamination of the optics… Smearing effects –evaluation based on a mean value of 30 e-/px (3 stars of mv=9 affect one column of the spot) Thermal background of the CCD –considered negligible compared to the zodiacal light value, at the considered temperature for the detectors (CCD t° < -80°C) Hot pixels in the PSF –in term of noise, acceptable hot pixel value, before rejection of the image: order of magnitude ~ 45 e-/px/s on each pixel of the PSF, or one hot pixel impacted by a proton delivering ~ 400 e-/s GE + PL

PPLC/ESA meeting, Feb 27th 2009 PLATO Photometric noise (1) Noise evolution with magnitude Photon noise =1 Background noise includes zodiacal noise Jitter noise is TBC Made with the nominal pupil dia of 115 mm GE + PL Noise sources compared to photon noise, as a function of magnitude

PPLC/ESA meeting, Feb 27th 2009 PLATO Photometric noise (2) Limit of magnitude for stars observed at 27ppm in 1 hour  Limit for the zone observed by 40 telescopes is mv = 11.1  Limit for the zone observed by 20 telescopes is mv = 10.3  Limit for the zone observed by 10 telescopes is mv = 9.6 Limit of magnitude for stars observed at 80ppm in 1 hour  Limit for the zone observed by 40 telescopes is mv = 13.1  Limit for the zone observed by 20 telescopes is mv = 12.6  Limit for the zone observed by 10 telescopes is mv = 11.9 With the nominal pupil diameter of 115mm GE + PL

Performances (in ppm), evolution with magnitude for the 3 zones: 40 telescopes 20 telescopes 10 telescopes (nominal pupil dia = 115 mm) PLATO Photometric performances GE + PL

GE + PL PLATO Photometric performances

PPLC/ESA meeting, Feb 27th 2009 Sample P1 (27ppm in 1 hour, > 2, goal 3 years) –P1 = ~ cool dwarfs / 2 pointings ( required) Sample P2 (80ppm in 1 hour, could be re-observed with a larger pupil to reach 27ppm in 1 hour, > 5 months) –P2 = ~ cool dwarfs / 2 pointings ( required) Sample P3 (27ppm in 1 hour, mv 2, goal 3 years) –Photometry on saturated stars (normal telescopes) 5 < mv < 8, P31= ~300 –Photometry with fast telescopes, stars 5 < mv < 7, P32= ~65 –P3 = 365 cool dwarfs / 2 pointings (1 000 required) Sample P4 (27ppm in 1 hour, mv 5 months) –Photometry on saturated stars (normal telescopes) 5 < mv < 8, P31= ~300 –Photometry with fast telescopes, stars 5 < mv < 7, P32= ~65 –P4 = 365 cool dwarfs / 2 pointings (3 000 required) Sample P5 (80ppm in 1 hour, > 2, goal 3 years) –P5 = ~ cool dwarfs / 2 pointings ( required) PLATO Photometric performances GE + PL

20 telescopes Fast telescopes 40 telescopes GE + PL PPLC/ESA meeting, Feb 27th 2009 PLATO Photometric performances

PPLC/ESA meeting, Feb 27th 2009 GE + PL Limitation for the number of telescopes PLATO Design critical points Telescope sizeDioptric compact designSeems ok Baffle sizeCompromise between straylight needs, thermal needs vs baffle size Not yet completely studied Number of CCDsTotal number to manufacture, possible yield…TBC with E2V Electrical powerTotal power (FPA, DPU, thermal) increases as the number of telescopes, and thermal control added on the telescope High increase in the budget, possible ? Telecope dissipation The telescope and FPA power is dissipated by the baffleSeems ok Electronics dissipation The electronics power is dissipated by lateral radiators, like in the CDF design. Even the power has increase, seems possible Seems ok MassTotal mass has increase as the number of telescopes, budget not completely consolidated. High increase in the budget, possible ?

PPLC/ESA meeting, Feb 27th 2009 GE + PL CCD –Selection of the working temperature, Thermal dark current is lower than zodiacal light for T<-50°C Degradation due to radiation effects in L2 has to be considered, CTE degradation seems acceptable for photometry (under investigation by simulation) Hot pixels : Corot feedback is not pessimistic  CCD working temperature selected at < -100°C in November could be increased to < -70°C (TBC at the end of on-going studies)  Consecutively, telescope temperature could increase by 30°C, which would be cost saving in development and qualification –Increase of the FWC: development of a new component, needs prototypes… to be consolidated –Increase of the total number: yield / planning to be consolidated PLATO Design critical points

PLATO Main characteristics GE + PL PPLC/ESA meeting, Feb 27th 2009 Number of telescopes 40 normal dioptric telescopes 2 fast dioptric telescopes Field of viewIndividual : 800 °² (28.3° x 28.3°) Global : overlapping FoV, overlapping factor=0.5, 1800 °² (42.5° x 42.5°) Pupil diameterIndividual, nominal : 115 mm, goal : 120 mm Global, depends of the zone: dia 727 mm (40 tel.), dia 514 mm (20 tel.), dia 363 mm (10 tel.) Detectors160 full frame transfer 3584 x 3584 pixels CCD (normal) 8 frame transfer 3584 x 3584 pixels CCD (fast) Working temperature < -70°C (TBC) FEE40 FEE (1 per normal telescope), each controls 4 CCDs 2 fast FEE (1 per fast telescope), each controls 4 CCDs DPU40 DPU (1 per normal telescope), in 8 groups of 5 DPU, 2 fast DPU (1 per fast telescope), put together with the fast FEE ICU2 ICUs (1 main, 1 redundant), put together in the same box