patrick.levacher@oamp.fr

1. PLATO kick-off meeting 09-Nov-2010 PLATO Payload overall architecture patrick.levacher@oamp.fr

2. Main photometric chain • photometry of faint stars (mv > 8), in the visible • made by 32 normal cameras • continuous observation, detector readout every 25.0 s • 1 Data Processing Unit (DPU) for 2 cameras • output: light curve and spot barycentre time series (up to 1 sample / 50s) • 2 “fast” photometric chains • pointing error information for the satellite (AOCS) • high rate and low delay for delivery to AOCS • imperative redundancy of the information • photometry of bright stars (mv < 8), • with a chromatic information: 1 “red” camera and 1 “blue” camera • continuous observation, detector readout every 2.5 s, • outputs: • pointing error at a rate of 1 sample / 2.5 s • light curve and spot barycentre time series (1 sample / 50s) Functional chains P. L. PLATO kick-off meeting– CNES, 09 Nov. 2010

3. Optics • fully centred refractive concept, 6 lenses + a front window, • bandwidth : 500 – 1050 nm • pupil diameter 120.0 mm, f/2.1 • PSF size: 90% of photo-electrons in a diameter of 36 µm (30 arcsec on the sky), • very wide field of view ~1100 dg² • Focal Plane Assembly • 4 detectors assembled in a square area of ~16 x 16 cm² • each detector: • 4510² x 18 µm square pixels (~20 Mpx) • back thinned, back illuminated • 2 outputs • 2 different modes: FF (Normal camera) or FT (Fast camera) • Video Electronics: N-FEE et F-FEE • readout @ 4 Mpx/s, • conversion on 16 bits • 25.0 s fixed cycle time for Normal cameras • 2.5 s fixed cycle time for Fast cameras • Powered and synchronised by: N-AEU or F-AEU The Camera P. L. PLATO KO meeting – CNES, 09 Nov. 2010

4. The overlapping field of view • the 32 cameras are organised in 4 sub-groups, mounted on an optical bench • each sub-group has then 8 cameras with the same line of sight (LoS) • the 4 LoS are tilted by 9.2° from the satellite axis, in four perpendicular directions • offers: • an overall FoV of 2200 deg² in 4 different zones, with an equivalent pupil diameter going • from675 mm (32 cameras) on 300 deg² • … to 340 mm (8 cameras) on 950 deg² • ( fast camera LoS are aligned on ZPLM axis ) Accommodation of the cameras and then optimizes simultaneously the number and the brightness of cool dwarfs and subgiants. In addition, allows us to re-observe during the Step&Stare phase, some stars for which interesting planets where detected during the previous long monitoring phases. P. L. PLATO KO meeting – CNES, 09 Nov. 2010

5. Snapshot of the payload presented at the end of the assessment phase, very similar to the current accommodation presented by the satellite contractors (except 32 + 2 cameras now) Accommodation on the optical bench P. L. PLATO KO meeting – CNES, 09 Nov. 2010

6. Thermal needs • focal plane temperature lower than -65°C (dark current, radiations) • on a design where: • the front window sees the sky and then, is cold, • the last lens is close to the focal plane and then is cold, • axial gradients shall be minimized for optical performance • then: a cold optics • More: in this concept with several cameras the only way to evacuate the power dissipated inside the detectors is the direction of the line of sight • Thermal design of the camera is then based on a FPA power evacuation through the telescope structure and then by the baffle, leading to: • a highly conductive telescope structure • a FPA thermally connected to it • a baffle, used as a radiator • This sub-system is isolated from its environment by use of: • low conductivity bipods for the telescope • low conductivity flexi-cables between detectors and their video electronics • use of MLI on each critical surfaces Thermal of the cameras P. L. PLATO KO meeting – CNES, 09 Nov. 2010

7. Thermal stability • Photometric performances are highly linked to thermal stability of the camera. This stability is ensured by: • a highly isolation from the environment (as said before), • a stable thermal environment given by the orbit (light variation during the 3 months exposure) • a constant power dissipation in the detectors on timescales higher than 25 s • a power dissipation by the baffle on a stable source (sky) • Added to these favourable conditions, a temperature control ensured by the satellite service module allows : • a compensation of the thermal environment difference between various camera locations • an adjustment of the structure mean temperature in a small range around the nominal temperature for a slight re-focus of each camera in flight • And finally, a temperature monitoring on several points of the camera allows possible corrections of the photometry (on ground) P. L. PLATO KO meeting – CNES, 09 Nov. 2010

8. Mechanical design • Need a design able to • accommodate the dimensional changes between integration (~20°C) and operation (~ -80°C) without stress in the materials (in particular lenses) • preserve the optics centring in this large temperature change • fulfil the thermal requirements • telescope structure in Albemet (CTE + highly conductive) • 3 bipods in titanium (good stiffness + poor thermal conductivity) • lenses barrels (Albemet or titanium) under form of several flexible blades • Focal Plane Assembly: positioning adjustment by 3 shims • At any interface (lens/barrel, baffle/structure…): • flexible or quasi-isostatic mounts, • three-points attachment, spherical washers … P. L. PLATO KO meeting – CNES, 09 Nov. 2010

9. Data Processing System P. L. PLATO KO meeting – CNES, 09 Nov. 2010

10. Electrical design P. L. PLATO KO meeting – CNES, 09 Nov. 2010

11. More information in the PLATO Payload Description Document (PPDD) Ref.: PLATO.LAM.INS.REP.1065 Thank you P. L. PLATO KO meeting – CNES, 09 Nov. 2010