Experimental evaluation of the stability and mechanical behavior of contacts in Silicon Carbide for the design of the basic angle monitoring system of GAIA

The satellite GAIA will be launched in ca. 2010 to make a 3-D map of our Galaxy. The payload module of the satellite will carry two astrometric telescopes amongst other instrumentation. The optical bench and astrometric telescopes will be constructed for a large part in Silicon Carbide (SiC). A truss structure concept design was developed, which could serve as optical bench for the scientific instrumentation of GAIA. It is lightweight and has a first eigenfrequency of 80 Hz. Also a concept design has been developed for the Basic Angle Monitoring (BAM) system of GAIA, which will measure 1 micro-arcsecond (ƒÝas) variations of the angle between the lines-of-sight of the two telescopes. For the design of these systems, contact mechanics is an important issue and therefore experiments have been conducted to obtain practical experience of the contact behaviour of SiC. This knowledge will be used in our project for a design of the BAM system. These experiments consist of friction experiments and experiments in which SiC tubes are bonded with several techniques like bolting, brazing and gluing

Metrology concept design of the GAIA basic angle monitoring system

The GAIA satellite, scheduled for launch in 2010, will make a highly accurate map of our Galaxy. It will measure the position of stars with an accuracy of 50 prad using two telescopes, which are positioned under a 'basic' angle between the the lines-of-sight of the telescopes of 106°. With a Basic Angle Monitoring system, variations of this angle will be measured with 5 prad accuracy, to correct for these variations on the measured position of stars. A conceptual design of the Basic Angle Monitoring system is presented. Two pairs of parallel laser bundles are sent to the telescopes, which create two interference patterns. If the basic angle varies, the interference patterns will shift. The optical design is such that the rotation of one pair of beams with respect to the other pair, does not affect the measured basic angle. The position stability requirement of the mirrors is a maximum shift of 1 pm in 6 hours. For material stability and good thermal and mechanical properties, Silicon Carbide has been chosen. The structural design is such that the design is as much monolithic as possible. The alignment is performed along the horizontal plane with external and removable alignment mechanisms. The components are locked by adhesives

Experimental evaluation of the stability and mechanical behavior of contacts in Silicon Carbide for the design of the basic angle monitoring system of GAIA

The satellite GAIA will be launched in ca. 2010 to make a 3-D map of our Galaxy. The payload module of the satellite will carry two astrometric telescopes amongst other instrumentation. The optical bench and astrometric telescopes will be constructed for a large part in Silicon Carbide (SiC). A truss structure concept design was developed, which could serve as optical bench for the scientific instrumentation of GAIA. It is lightweight and has a first eigenfrequency of 80 Hz. Also a concept design has been developed for the Basic Angle Monitoring (BAM) system of GAIA, which will measure 1 micro-arcsecond (ƒÝas) variations of the angle between the lines-of-sight of the two telescopes. For the design of these systems, contact mechanics is an important issue and therefore experiments have been conducted to obtain practical experience of the contact behaviour of SiC. This knowledge will be used in our project for a design of the BAM system. These experiments consist of friction experiments and experiments in which SiC tubes are bonded with several techniques like bolting, brazing and gluing

Experimental set-up for testing alignments and measurement stability of a metrology system in Silicon Carbide for GAIA

The GAIA satellite will make a 3-D map of our Galaxy with measurement accuracy of 10 microarcseconds using two astrometric telescopes. The angle between the lines-of-sight of the two telescopes will be monitored using the Basic Angle Monitoring system with 1 microarcsecond accuracy. This system will be an interferometer consisting of a number of small mirrors and beam splitters in Silicon Carbide. Silicon Carbide has very high specific stiffness and very good thermal properties (low CTE and high conductivity). It also is a very stable material. A possible concept design for this Basic Angle Monitoring system is subject of a PhD study performed at the Technische Universiteit Eindhoven and TNO Science and Industry (The Netherlands). To prove that this concept design meets the alignment and measurement stability requirements, the GAIA extreme stability optical bench is developed. It will consist of a fourfold Michelson interferometer with four separate optical paths, which will measure the stability of the optical bench and the individual optical components. Also thermal cycling experiments and vibrations tests will be performed. ‘Absolute’ position measurements of the optical components with respect to the optical bench after the vibrations test will be performed using markers. The GAIA extreme stability optical bench will be placed in a vibration damped vacuum tank in order to imitate the highly stable L2 space environment. The goal is to obtain the first results early 2006

Metrology concept design of the GAIA basic angle monitoring system

The GAIA satellite, scheduled for launch in 2010, will make a highly accurate map of our Galaxy. It will measure the position of stars with an accuracy of 50 prad using two telescopes, which are positioned under a 'basic' angle between the the lines-of-sight of the telescopes of 106°. With a Basic Angle Monitoring system, variations of this angle will be measured with 5 prad accuracy, to correct for these variations on the measured position of stars. A conceptual design of the Basic Angle Monitoring system is presented. Two pairs of parallel laser bundles are sent to the telescopes, which create two interference patterns. If the basic angle varies, the interference patterns will shift. The optical design is such that the rotation of one pair of beams with respect to the other pair, does not affect the measured basic angle. The position stability requirement of the mirrors is a maximum shift of 1 pm in 6 hours. For material stability and good thermal and mechanical properties, Silicon Carbide has been chosen. The structural design is such that the design is as much monolithic as possible. The alignment is performed along the horizontal plane with external and removable alignment mechanisms. The components are locked by adhesives

Absolute distance metrology for space interferometers

Future space missions, among which the Darwin Space Interferometer, will consist of several free flying satellites. A complex metrology system is required to have all the components fly accurately in formation and have it operate as a single instrument. Our work focuses on a possible implementation of the sub-system that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy is on the order of 70 micrometer over a distance of 250 meter. We are exploring a technique called frequency sweeping interferometry, which involves interferometrically measuring a phase difference while sweeping the wavelength of a tunable laser. This phase difference is directly proportional to the absolute distance. A very high finesse Fabry-P´erot cavity is used as a reference standard, to which the laser is locked end-points of the sweep. We will discuss the control system that drives the setup and show some first experimental results.Optics Research GroepApplied Science

Experimental set-up for testing alignment and measurement stability of a metrology system in silicon carbide for GAIA

The GAI A satellite will make a 3-D map of our Galaxy with measurement accuracy of 10 microarcseconds using two astrometric telescopes. The angle between the lines-of-sight of the two telescopes will be monitored using the Basic Angle Monitoring system with 1 microarcsecond accuracy. This system will be an interferometer consisting of a number of small mirrors and beam splitters in Silicon Carbide. Silicon Carbide has very high specific stiffness and very good thermal properties (low CTE and high conductivity). It also is a very stable material. A possible concept design for this Basic Angle Monitoring system is subject of a PhD study performed at the Technische Universiteit Eindhoven and TNO Science and Industry (The Netherlands). To prove that this concept design meets the alignment and measurement stability requirements, the GAIA extreme stability optical bench is developed. It will consist of a fourfold Michelson interferometer with four separate optical paths, which will measure the stability of the optical bench and the individual optical components. Also thermal cycling experiments and vibrations tests will be performed. 'Absolute' position measurements of the optical components with respect to the optical bench after the vibrations test will be performed using markers. The GAIA extreme stability optical bench will be placed in a vibration damped vacuum tank in order to imitate the highly stable L2 space environment. The goal is to obtain the first results early 2006

Absolute distance metrology for space interferometers

Space interferometers consisting of several free flying telescopes, such as the planned Darwin mission, require a complex metrology system to make all the components operate as a single instrument. Our research focuses on one of its sub-systems that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy would be in the order of 10 ?m over 250 meter. To measure this absolute distance, we are currently exploring the frequency sweeping interferometry technique. Its measurement principle is to first measure a phase in the interferometer, sweep a tunable laser over a known frequency interval and finally measure a second phase. By also counting the number of fringes during the sweep it is possible to determine the absolute path length difference without ambiguities. The wavelength at the endpoints of the sweep is stabilized on a Fabry-Perot cavity. In this way the unknown distance is directly referenced to the length of the Fabry-Perot cavity.Optics Research GroepApplied Science