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. This metrology system consists of various sub-systems to monitor distances, angles and speeds. Our research focuses on one of these 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 μm over 250 meter.
To measure this absolute distance, we are currently building a frequency sweeping interferometer. It is operated by first measuring a phase in the interferometer, sweeping a tunable laser over a known frequency interval and finally measuring 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. We plan on actively stabilizing the wavelength at the endpoints of the sweep on a Fabry-Perot cavity using the Pound-Drever-Hall technique. In this way the unknown distance is directly referenced to the length of the Fabry-Perot cavity.
The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a collaborative science mission between ESA and the Chinese Academy of Sciences (CAS). SMILE is a novel self-standing mission to observe the coupling of the solar wind and Earth's magnetosphere via X-Ray imaging of the solar wind -- magnetosphere interaction zones, UV imaging of global auroral distributions and simultaneous in-situ solar wind, magnetosheath plasma and magnetic field measurements. The SMILE mission proposal was submitted by a consortium of European, Chinese and Canadian scientists following a joint call for mission by ESA and CAS. It was formally selected by ESA's Science Programme Committee (SPC) as an element of the ESA Science Program in November 2015, with the goal of a launch at the end of 2021.
In order to achieve its scientific objectives, the SMILE payload will comprise four instruments: the Soft X-ray Imager (SXI), which will spectrally map the Earth's magnetopause, magnetosheath and magnetospheric cusps; the UltraViolet Imager (UVI), dedicated to imaging the auroral regions; the Light Ion Analyser (LIA) and the MAGnetometer (MAG), which will establish the solar wind properties simultaneously with the imaging instruments. We report on the status of the mission and payload developments and the findings of a design study carried out in parallel at the concurrent design facilities (CDF) of ESA and CAS in October/November 2015.
Moon4You is a project led by the Dutch Organisation for Applied Scientific Research TNO, with partners from industry
and universities in the Netherlands that aims to provide a combined Raman / LIBS instrument as scientific payload for
lunar exploration missions. It is the first time that Raman spectroscopy and LIBS (Laser Induced Breakdown
Spectroscopy) are combined into one miniaturised instrument with minimum mass, volume and use of resources and can
deliver data-products almost instantly. These characteristics make it the next-generation instrument for mineralogical and
elemental (atomic) characterisation of lunar soil and rock samples, as well as for a host of other planetary exploration
and terrestrial applications.
Large stellar telescope is indispensable for astronomy. Aperture synthesis is a well-known technique to simulate a large space telescope by an array of small telescopes. Condition for aperture synthesis is that the light of the telescopes have to be combined coherently. Therefore, an interferometric Fringe Sensor (FS) to detect and stabilize the Optical Path Difference (OPD) between light from the different telescopes is required. Conventional Fringe Sensor for Space Interferometer utilizes either Quadrature Stabilization or Double Synchronous Detection to find and control OPD=0. OPD demodulation based on Quadrature Stabilization is sensitive to change in the visibility V of the interferometric signal, while Double Synchronous Detection requires an active modulation of the OPD to generate the required carrier signal. To overcome these problems, TNO develops a Fringe Sensor based on a 3x3 Fiber Optic (FO) coupler. A breadboard demonstrator operating around 830 nm is built. A piezo stretcher and a translation stage are used to generate the OPD. High-speed OPD measurement down to 0.15 nm is demonstrated. The influence of the visibility V of the interferometric signal is also investigated. Even for V=0.2, an OPD modulation of 0.4 nm can still be detected.
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.
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-Perot cavity is used as a reference standard, to which the laser is locked at the end-points of the sweep. We will discuss our measurement scheme, our set-up and some first measurements.
KEYWORDS: Interferometers, Signal processing, Digital signal processing, Interferometry, Distance measurement, Metrology, Satellites, Phase measurement, Control systems, Semiconductor lasers
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-Perot 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.
Large stellar telescope is indispensable for astronomy. Aperture synthesis is a well-known technique to simulate a large space telescope by an array of small telescopes. Condition for aperture synthesis is that the light of the telescopes have to be combined coherently. Therefore, an interferometric Fringe Sensor (FS) to detect and stabilize the Optical Path Difference (OPD) between light from the different telescopes is required. TNO TPD develops a Fringe Sensor based on a 3x3 Fiber Optic (FO) coupler. A breadboard demonstrator operating around 830 nm is built. A piezo stretcher and a translation stage is used to generate the OPD. High-speed sub-nm OPD measurement is demonstrated. The influence of the visibility V of the interferometric signal is also investigated. Even for V=0.2, an OPD modulation of 0.4 nm can still be detected.
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 μm 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.
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.
The mineralogy of the surface material of Mars is the key to disclose its present and past life and climates. Clay mineral species, carbonates, and ice (water and CO2) are and/or contain their witnesses. X-ray powder diffraction (XRPD) is the most powerful analytical method to identify and quantitatively characterize minerals in complex mixtures.
This paper discusses the development of a working model of an instrument consisting of a reflection mode diffractometer and a transmission mode CCD-XRPD instrument, combined with an XRF module. The CCD-XRD/XRF instrument is analogous to the instrument for Mars missions developed by Sarrazin et al. (1998). This part of the tandem instrument enables "quick and dirty" analysis of powdered (!) matter to monitor semi-quantitatively the presence of clay minerals as a group, carbonates, and ices and yields semi-quantitative chemical information from X-ray fluorescence (XRF). The reflection mode instrument (i) enables in-situ measurements of rocks and soils and quantitative information on the compounds identified, (ii) has a high resolution and reveals large spacings for accurate identification, in particular of clay mineral species, and (iii) the shape of the line profiles observed reveals the kind and approximate amounts of lattice imperfections present. It will be shown that the information obtained with the reflection mode diffractometer is crucial for finding signs of life and changes in the climate on Mars. Obviously this instrument can also be used for other extra-terrestrial research.
In preparation for the planet-finding missions DARWIN (ESA) and the Terrestrial Planet Finder (NASA) a range of precursor missions are being defined, aimed at testing and validating the technology needed to make the planet-finder missions feasible from a technology point of view. In Europe the SMART-2 mission is meant to test high critical technologies for the DARWIN and the gravitation wave mission LISA (ESA/NASA). The mission SMART-2 consists of two spacecraft. These two spacecraft will demonstrate the feasibility of formation flying related to the DARWIN mission. Furthermore SMART-2 will simulate a stellar interferometer by combining white light from the two spacecraft in an interferometric focus. Two fringe-tracking modes of operations will be tested. In the standard fringe-tracking mode an onboard optical delay line is commanded to keep the optical path difference within the coherence length of the combined light. In the second mode the optical path difference is equalised by commanding the FEEPS (Field Emission Electric Propulsion) thrusters. In both modes a range of metrology systems are needed to measure deviations from the nominal configuration of the two spacecraft. Here we report on the work related to metrology systems for the SMART-2 mission needed to measure the longitudinal distance with nanometer accuracy and the lateral position of one spacecraft with respect to the second spacecraft with 5 mm accuracy. We discuss the present concepts for the metrology systems for SMART-2 and we will elaborate on the possibility to integrate the different optical metrology systems into a single system reducing complexity, risks and mass.
KEYWORDS: Control systems, Metrology, Telecommunications, Actuators, Space operations, Space robots, Fourier transforms, Data communications, Amplifiers, Atmospheric modeling
The VLTI Delay Line verification program has been performed in the first quarter of the year 2000. This paper will present results from the measurements done at Fokker Space premises, supported by results from Matlab simulations. Key requirements are addressed, except for those which deal with the opto-mechanical verification. Jitter on the mechanical velocity and the OPD, as well as pupil stability and heat dissipation in the tunnel, have been driving requirements for the design and construction of the Delay Lines. The results which are presented below will demonstrate that these requirements are met with the `Two-Stage' concept chosen for the control of the commanded optical path trajectory.
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