1/28/2024 0 Comments Gaia astrometry mission![]() M2 and M3 are 0.65 by 0.275 meters in size. Following polishing, the mirrors were coated with enhanced silver reflective coating.Īfter being reflected by the primary mirrors, the light is bounced back and forth between the M2 and M3 mirrors to create a total focal length of 35 meters. Each mirror was polished to an accuracy of 10 nanometers. The mirror blanks were coated with a layer of silicon carbide via vapor deposition. ![]() The mirrors were shaped using computer-guided milling and polishing machines. Like all the other mirrors, the primary mirrors are rectangular in shape and have been fabricated from blanks made of sintered silicon carbide – the same material used for the optics bench, chosen because of its favorable thermal properties. The primary mirrors are 1.45 by 0.5 meters in size. Light passes through the apertures and onto the two primary mirrors opposite to the respective aperture (designated M1 and M’1). The two telescopes of Gaia’s instruments are identical in construction sharing an optical bench and common focal plane assembly. ![]() Telescope Design Image: ESA/Astrium Image: ESA/Astrium Radial Velocity is determined by the Radial Velocity Spectrometer using doppler shift technique. Data processing on the ground derives the actual star parameters via sphere reduction. To gain astrometric data (two angular positions & corresponding proper motions as well as parallax), the relative separations of thousands of stars are cataloged and the repeated measurements of each star build a network in which the star is connected to a wealth of others in every direction. For all these observations, the basic angle between the two fields of view has to be constant. The constant solar angle for Gaia is 45 degrees.Ī fundamental aspect of astrometric measurements is the repetition of measurements – covering the entire celestial sphere a large number of times over an extended period of time.Īt a precession cycle of about 63 days, Gaia will map each star 70 times on average during its primary mission. To achieve an all-sky survey, the satellite is put through a slow precession on the Satellite-Sun-Axis which produces a continuous drift of the great circle on the sky. Due to the spinning, the instruments see the stars crossing each field of view in a regular motion. Gaia operates at a spin rate of 4 revolutions per day. The scanning law developed for Gaia requires the satellite to be spinning perpendicular to the two lines of sight so that the two lines of sight describe a ‘great cycle’ within a single spin period. The angular distance between the two fields of view is referred to as the basic angle, 106.5 degrees in Gaia’s case. Global astrometry requires the simultaneous observation of two fields of view in which the star positions are measured and constantly correlated. The viewing directions are 1.7 by 0.6 degrees in size and are separated by a highly stable basic angle of 106.5 degrees. The two telescopes are looking through two apertures on the Thermal Tent. ![]() Gaia’s science payload consists of two telescopes that are mounted on the hexagonal optical bench and share common focal plane equipment. Scanning Law Overview Image: EADS AstriumĪlthough Gaia theoretically carries three instruments that complete three separate tasks, the entire payload has to be seen as a single integrated assembly as most equipment is shared by the three instruments.
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