Context. CoRoT is a space telescope dedicated to stellar seismology and the search for extrasolar planets. The mission is led by the CNES in association 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 PROTEUS low earth orbit (LEO) recurrent platform, commenced in October 2000, and the satellite was launched on December 27, 2006. Aims. The instrument and platform characteristics prior to launch have been described in ESA publication (SP-1306). In the present paper we explain 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 that lasted 146 days. These enable us to give a complete overview of the instrument and platform behaviour for all environmental conditions. The ground based data processing is not described in detail because the most important method has been published elsewhere. Results. We show that the performance specifications are easily satisfied when the environmental conditions are favourable. Most of the perturbations, hence data corrections, are related to 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.

In next generation space instrumentation for Earth and Universe Observation, new instrument concepts include often non planar gratings. Their realization is complex and costly. We propose a new technology for designing and realizing convex blazed gratings for high throughput spectrographs. For this purpose, our requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the Telescopio Nazionale Galileo (TNG) and called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 -800 nm. Convex blazed gratings have been fabricated and coated with protected silver, with a final 5.7° blaze angle over the whole surface. Efficiency close to 90% on the 1st diffraction order at 700nm has been obtained. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions.

High resolution observing systems need bigger and bigger telescopes. The design of such telescopes is a key element for the satellite design. In order to improve the imaging resolution with minimum impact on the satellite, a big step must be made to improve the compactness of the telescope.This paper describes the comparative study of several compact optical designs. Different apertures, from F/5 to F/20, and different concepts, TMA (Three Mirror Anastigmat), Ritchey-Chrétien concept and Korsch concept have been studied. We will point out advantages and disadvantages of each design. We will show how compact a high resolution telescope can be. A diffraction limited telescope can be less than ten times shorter than its focal length. A constraining consequence of this compactness is the huge increase of the sensitivity factors. The impacts on the optics and on the opto-mechanical tolerances have been analysed. The need to implement active optics raises. A first active optics experiment is presented

No abstract

In next generation space instrumentation for Earth and Universe Observation, new instrument concepts include often non planar gratings. Their realization is complex and costly. We propose a new technology for designing and realizing convex blazed gratings for high throughput spectrographs. For this purpose, our requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the Telescopio Nazionale Galileo (TNG) and called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 -800 nm. Such gratings have been fabricated and coated with a silver-based layer, with a final 7° blaze angle over the whole surface. Efficiency close to 90% on the 1st diffraction order at 700nm has been obtained, measured on BATMAN spectroscopic arm. Detailed mapping of the blazed grating showed a very good period uniformity with up to 0.5% deviation. Grating depth and blaze angle have higher deviation, up to 7%. An optimized device with the exact required blaze angle would reach the same efficiency and be centered on the mid of 400-800nm wavelength band: its realization is on-going. The grating brings a significant contribution in the total amount of straylight at instrument level. Their straylight level remains a critical issue, and its reduction by specific and controlled implementation of improvements in manufacturing process is a challenge to tackle. Preliminary straylight measurement has been done and shows a lowest straylight level below 10 -2 sr -1 between the diffraction orders. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions.