First steps in the development of a piston sensor for large aperture space telescopes

in Oschmann, J.; Clampin, M.; MacEwen, H. (Eds.) Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave (2010, July 01)

Nowadays spaceborne missions for astronomy or Earth imaging need high resolution observation which implies the development of large aperture telescopes. This can be achieved by multi-aperture telescopes ... [more ▼]

Nowadays spaceborne missions for astronomy or Earth imaging need high resolution observation which implies the development of large aperture telescopes. This can be achieved by multi-aperture telescopes or large segmented telescopes. One of the major issues is the phasing of the sub-apertures or the segments of such telescopes. A cophasing sensor is therefore mandatory to achieve the ultimate resolution of these telescopes. In this framework, Liège Space Center (CSL) concern is the development of a compact cophasing sensor to phase new large lightweight segmented mirrors for future space telescopes. The sensor concept has its origins in new phase retrieval algorithms which have been recently developed. In this paper, we outline the concept and the experimental validation results of our piston sensor breadboard which is currently under development in our laboratory. Finally, future prospects and further developments of our experiment are presented. [less ▲]

Optical methods for non-contact measurements of membranes

in Acta Astronautica (2009), 65(9-10), 1317-1329

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film ... [more ▼]

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film membranes. Their inherent properties (low mass and small thickness) preclude the use of conventional measurement methods (accelerometers and displacement transducers for example) during on-ground testing. In this context, innovative non-contact measurement methods need to be investigated for these stretched membranes. The object of the present project is to review existing measurement systems capable of measuring characteristics of membrane space-structures such as: dot-projection videogrammetry (static measurements), stereo-correlation (dynamic and static measurements), fringe projection (wrinkles) and 3D laser scanning vibrometry (dynamic measurements). Therefore, minimum requirements were given for the study in order to have representative test articles covering a wide range of applications. We present test results obtained with the different methods on our test articles. [less ▲]

Synthetic aperture co-phasing and co-alignment using an external reference source

in Proceedings of ICSO 2006 (2006, June 27)

A breadboard set-up has demonstrated a concept of co-phasing and co-alignment based on an external reference source for synthetic aperture telescopes applications. These types of systems can be extremely ... [more ▼]

A breadboard set-up has demonstrated a concept of co-phasing and co-alignment based on an external reference source for synthetic aperture telescopes applications. These types of systems can be extremely valuable in order to perform coarse re-alignment of synthetic aperture telescope, following thermo-elastic deformation and deployment effects in space flight environments. [less ▲]

Cryo-optical test of the PLANCK reflectors

Conference (2006, March 20)

Focii determination of an off axis ellipsoid : Theory to practice

in Osten, W.; Novak, E. (Eds.) Proceedings of the Eighth International Conference on Laser and Laser Information Technologies (2004, August 02)

In the frame of cryogenic test on an off axis ellipsoid, it has been required to set-up an unambiguous method to determine and track the foci position during temperature transitions. This procedure was ... [more ▼]

In the frame of cryogenic test on an off axis ellipsoid, it has been required to set-up an unambiguous method to determine and track the foci position during temperature transitions. This procedure was mandatory to avoid: (1) impact of the operator skills working on triple shift scheme to assure continuously monitoring of the ellipsoid shape during cool down. (2) correctly dissociate the impact of the thermal deformation on the mirror shape with respect to alignment errors. This paper will demonstrate the process, starting from ideal ellipsoid shape, then introducing 3D metrology data in a model, and finally presents the results in a practical situation. [less ▲]

Development of optical ground verification method for mu m to sub-mm reflectors

in Warmbein, B. (Ed.) Proceedings of the 5th International Conference on Space Optics (ICSO) (2004, April 02)

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. The ... [more ▼]

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. The challenging tasks of on-ground testing are to achieve the required accuracy in the measurement of the reflector shapes and antenna structures and to verify their performance under simulated space conditions (vacuum, low temperatures). A small number of infrared interferometers have been commercially developed over the last 10 years but their applications have also been limited due to poor dynamic range and the restricted spatial resolution of their detectors. It has therefore been considered essential, from the viewpoint of supporting future ESA exploration missions, to develop and realise suitable verification tools based on infrared interferometry and other optical techniques for testing large reflector structures, telescope configurations and their performances under simulated space conditions. Two methods and techniques are developed at CSL. The first one is an IR-phase shifting interferometer with high spatial resolution. This interferometer shall be used specifically for the verification of high precision IR, FIR and sub-mm reflector surfaces and telescopes under both ambient and thermal vacuum conditions. The second one presented hereafter is a holographic method for relative shape measurement. The holographic solution proposed makes use of a home built vacuum compatible holographic camera that allows displacement measurements from typically 20 nanometres to 25 microns in one shot. An iterative process allows the measurement of a total of up to several mm of deformation. Uniquely the system is designed to measure both specular and diffuse surfaces [less ▲]

Design of the cryo-optical test of the PLANCK reflectors

Conference (2003, March 18)

PLANCK is the third Medium size mission of the ESA long-term scientific plan Horizon 2000. This paper present the current design status of the design of the cryo-optical test for the Planck primary ... [more ▼]

PLANCK is the third Medium size mission of the ESA long-term scientific plan Horizon 2000. This paper present the current design status of the design of the cryo-optical test for the Planck primary reflector and Planck secondary reflector [less ▲]

Applications de l'optique diffractive dans le domaine du traitement de l'information

Scientific conference (1996, October 10)

Après une introduction résumant l'historique du mariage entre l'optique diffractive et le traitement de l'information, la synthèse d'optiques diffractives sera discuté, suivie par des exemples d ... [more ▼]

Après une introduction résumant l'historique du mariage entre l'optique diffractive et le traitement de l'information, la synthèse d'optiques diffractives sera discuté, suivie par des exemples d'applications d'optique diffractive dans le domaine du traitement de l'information. [less ▲]

Algorithm for scalar near-field calculations of computer generated holograms

Conference (1995, October 23)

Design for polarizing holographic optical elements

in Applied Optics (1995), 34(19), 3595-3602

We present results of the application of a three-dimensional rigorous-vector coupled-wave theory to the design of polarizing holographic optical elements. Two different cases have been selected giving ... [more ▼]

We present results of the application of a three-dimensional rigorous-vector coupled-wave theory to the design of polarizing holographic optical elements. Two different cases have been selected giving rise to two types of element, one of which is completely original. Experimental realizations were performed. The recording material was dichromated gelatin because of its outstanding performance related to diffraction efficiency. A fair agreement between the theoretical previsions and the experimental results was achieved. [less ▲]