Astronomy & Astrophysics manuscript no. article-perfo1˙iwr �c ESO 2009 January 14, 2009 The CoRoT satellite in flight : description and performance. Auvergne M.1, Bodin $.2, Boisnard L.2, Buey J-T.1, Chaintreuil S.1, Epstein G.1, Jouret M.2, Lam-Trong &.2, Levacher $.*, Magnan A.*, Perez R.2, Plasson $.1, Plesseria J.11, Peter G.4, Steller M.10, &iphene- D.1, Baglin A.1, Agogue/ $.2, Appourchaux &.1, Barbet D.1, Beaufort &.9, Bellenger R.1, Berlin R.4, Bernardi $.1, Blouin D.*, Boumier $.,1, Bonneau 3.2, Briet R.2, Butler B.9, Cautain R.*, Chiavassa 3.2, Costes 4.2, Cuvilho J.12, Cunha-Parro 4.1 De Oliveira Fialho 3.1, Decaudin M.1, Defise J-M.11, Djalal S.2, Docclo A.1, Drummond R.,13, Dupuis O.1, Exil G.1, 3aure/ C.2, Gaboriaud A.2, Gamet $.2, Gavalda $.2, Grolleau E.1, Gueguen L.1, Guivarc’h 4.1, Guterman $.*, Hasiba J.10, Huntzinger G.1, Hustaix H.2, Imbert C.2, Jeanville G.1, Johlander B.9, Jorda L.*, Journoud $.1, Karioty 3.1, :erjean L.2, Lafond L.2, Lapeyrere 4.1, Larque/ &.2, Laudet $.2, Le Merrer J.*, Leporati L.*, Leruyet B.1, Levieuge B.1, Llebaria A.*, Martin L.*, Mazy E.11, Mesnager J-M.2, Michel J-P.1, Moalic J-P.1, Monjoin <.1, Naudet D.1, Neukirchner S.10, Nguyen-Kim K.1, Ollivier M.1, Orcesi J-L.1, Ottacher H.10, Oulali A.1, $arisot J.1, Perruchot S.*, Piacentino A.1, Pinheiro da Silva L.1, Platzer J.1, Pontet B.2, Pradines A.2, Quentin C.*, Rohbeck U.A, Rolland G.2, Rollenhagen 3.4, Romagnan R.1, Russ N.4, Samadi R.1, Schmidt R.1, Schwartz N.1, Sebbag I.2, Smit H.9, Sunter <.9, &ello M.2, &oulouse $.2, Ulmer B.B, 4andermarcq O.2, 4ergnault E.2, <allner R.10, <aultier G.*, Zanatta $.1,� (Affiliations can be found after the references) ABSTRACT Context. CoRoT is a space telescope dedicated to stellar seismology and the search for extrasolar planets. The mission is led by CNES in asso- ciation with French laboratories and has a large international participation: the European Space Agency (ESA), Austria, Belgium and Germany contribute to the payload, and Spain and Brazil contribute to the ground segment. Development of the spacecraft, which is based on a $,OTEUS low earth orbit recurrent platform, commenced in October 2000 and the satellite was launched on December 27th 2006 Aims. The instrument and platform characteristics prior to launch have been described in ESA publication (SP-1306) . In the present paper we detail the behaviour in flight, based on raw and corrected data. Methods. Five runs have been completed since January 2007. The data used here are essentially those acquired during the commissioning phase and from a long run which lasted 146 days, these enable us to give a complete overview of the instrument and platform behaviour for all environ- mental conditions. The ground based data processing is not described in detail, the most important method being published elsewhere. Results. It is shown that the performance specifications are easily satisfied when the environmental conditions are favourable. Most of the per- turbations, and consequently data corrections, are related to Low Earth Orbit (LEO) perturbations: high energy particles inside the South Atlantic Anomaly (SAA), eclipses and temperature variations, and line of sight fluctuations due to the attitude control system. Straylight due to the reflected light from the earth, which is controlled by the telescope and baffle design, appears to be negligible. 1. Introduction to 10 mHz, covering both pressure and gravity modes of stars. 3or stochastically excited modes, the frequency measurement $(ysical insight into stellar internal structure depends on our precision depends on the length of the observation window, on ability to compare and adjust models to reproduce the obser- the mode lifetime, on the amplitude and on the signal-to-noise vations. However the number of unknown quantities is larger ratio in the 3ourier spectrum. <e expect mode lifetimes of about than the number of measured quantities and many uncertain- 1 days and amplitudes greater than 2 ppm; the target stars are ties remain, preventing accurate tests of the (ypotheses con- therefore observed for 150 days with a minimum signal-to-noise tained in the modeling process. Asteroseismology, i.e. the de- ratio of 15 (in terms of power spectral density) to yield a preci- tection of eigenmodes of oscillations, provides new observables sion on frequency measurements of 0.1 µHz. The signal-to-noise (frequencies and amplitudes of eigenmodes) with very high ac- ratio should be reached in the frequency interval if the noise level curacy, and increases the number of constraints on models. It remains of the order of 0.G ppm in the 3ourier spectrum in 1 days has already proven to be a powerful tool to probe the interior of of observation for a 1.B 4 magnitude star. the Sun. Observations of other stars are needed to test different physical conditions and discriminate among physical processes. <ith high precision stellar photometry we can detect extra- Seismology measurements are performed in the bandwidth 0.1 solar planets by the transit method, measuring the decrease of the stellar flux when the star, the planet and the instrument are almost aligned. The flux decrease is given by D � The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with contributions from Austria, Belgium, Brazil , ESA, Germany and Spain. 3our French lab- oratories associated with the CNRS (LESIA,LAM, IAS ,OMP) collab- 2 orate with CNES on the satellite development. The authors are grateful ∆F Rp ∝ (1) to Ian Roxbur ( for a careful reading of the manuscript. F � Rs � 2 Auvergne et al.: The CoRoT satellite in flight D description and performance. where Rp is the radius of the planet and Rs the radius of the by the CoRoT Mission Centre in collaboration with participat- parent star. If the impact parameter is equal to 0, the transit du- ing laboratories. A network of CNES ground stations (Kiruna, ration is D Aussaguel, Hartebeesthoek, :ourou), and one mission specific secondary ground station located in Alcantara (Brazil), are used P R tr = s (2) for communication with the satellite and/or reception of techni- π � a � cal and scientific telemetry. where $ is the orbital period of the planet and a the radius of The interfaces for a dedicated mission are at satellite level the orbit supposed to be almost circular. between the platform and the payload, and at ground level be- tween the Control Centre and the specific Mission Centre. In In addition to hundreds of Uranus-like or Jupiter-like plan- the configuration adopted for CoRoT, several sub-systems have ets, several telluric planets should be detected, if our (ypotheses been upgraded D Li-Ion battery, high capacity magneto torquer about accretion models and planets occurrence are correct. &o bars and new star trackers (SED-16). The total weight is 626 reach this goal the required photometric precision is B.10−4 for kg, including 300 > for the payload. A mass memory provides a 4=15.1 magnitude star for one hour integration. Up to 12000 at end of life a storage capacity of 2 Gbits for the payload and target stars, in a field of view of 4 square degrees, are simul- housekeeping data. The power is provided by two solar arrays taneously observed during a 150-day period. <ith at least 5ve which feed directly to the battery giving a non regulated voltage different fields of view, more than 60 000 stars will be followed in the interval 23 − *B 4. and a power of 1 ><. The battery man- during 150 days over the whole mission. Between each 150 days agement is driven by autonomous software. An important func- runs a short run of typically 25 days is performed. tional chain is the Attitude Control System (ACS). At platform The layout of our paper is as follow. In section 2 we recap the level the pointing is provided by star trackers, inertial wheels, mission status and the spacecraft characteristics. Then the envi- magneto-torquers and gyrometers, giving an angular stability of ronmental conditions for a Low Earth Orbit (LEO) and the im- 16 arc seconds. Since CoRoT’s requirement is about 0.1 arcsec pact on the photometric data are recalled in section 3. In addition rms, to reach this value it was necessary to include in the con- some results obtained during the commissioning phase are pre- trol loop ecartometry computations based on the position of two sented. Section 4 briefly describes the payload architecture and stars on the payload focal plane. gives details on the payload and satellite behaviour. <e develop important features of some functional subsystems such as the attitude control system, the temperature control system and the 3. Environmental conditions. detection chain. On board and ground based data processing are summarised in sections 1 and G and photometric performances As the orbit is at an altitude close to 900 km the Earth has an are presented in section B for the AsteroSeismology (AS) and influence on the satellite and introduces perturbations on three Planet Finder E$3F channels. In section A a brief summary closes characteristic time scales; the orbit (and harmonics), the day (and the paper. its first harmonic) and the seasons. The main perturbations are: – Eclipses: the transition light/penumbra/shadow and the re- verse produces temperature variations, vibrations in the solar 2. The satellite.