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Sentinel-5 is an Earth atmospheric monitoring mission developed within the Copernicus program. The mission objective is to monitor the composition of the Earth's atmosphere on a daily basis. TNO is developing the UV1 spectrometer subsystem as well as the two telescope subsystems. In this paper, the design of the UV1 spectrometer is described and its major design and verification challenges are discussed. The UV1 optical design is based on a classical Offner-type spectrometer which has been adapted to employ freeform optics and an aspheric off-axis grating. It generates a magnification of 0.4. A structural, monolithic housing has been designed that is optimized for stability, accessibility and integration of optical components. To realize a thermo-mechanically stable construction, both housing and mirror bodies are built from aluminum. Four out of five mirrors have a dedicated black coating for absorbing out-of-band light. For further stray light suppression, a graded short-pass filter is employed on the last optical element just in front of the detector. Performance verification of a standalone spectrometer without telescope, entrance slit, limiting aperture stop and flight detector is a major challenge. For this verification TNO developed dedicated ground support equipment that will be used under both ambient and vacuum conditions; a dedicated optical stimulus that mimics the illumination from the telescope in terms of pointing and NA, a Slit Assembly that mimics the homogenizer entrance slit and a Test Detector to determine the image plane and to measure the optical performance with high accuracy. At the time of writing this article, the first (proto-flight) model has been aligned and performance verification is about to start.

The DARWIN mission aims to detect weak infra-red emission lines from distant orbiting earth-like planets using nulling interferometry. This requires filtering of wavefront errors using single mode waveguides operating at a wavelength range of 6.5-20 μm. This article describes the optical design of the fibers, the manufacturing protocol, the packaging for operating at cryogenic environment and various optical characterisations performed. The latter includes investigation on the effect of gold and silver absorption coatings, anti-reflection coating, fiber length on higher order mode suppression and attenuation of the fibers.

Sinds enkele maanden draait de Ga¡a-satel]¡et van Esa op anderhalf miljoen kilometer van de aarde. Doel is om een zeer nauwkeurige driedimensionale kaart te maken van ongeveer een miljard sterren in ons Melkwegstetsel. Aan boord zijn twee meetsystemen, door TNO ontwikketd en gebouwd, verantwoordelijk voor de nauwkeurigheid waarmee de exacte positie en beweging van deze sterren worden waargenomen en vastgelegd. Een revolutie in astrometrie.

TNO Science and Industry has designed and is currently developing the Basic Angle Monitoring Opto-Mechanical Assembly (BAM OMA) [1], which is part of the GAIA spacecraft. In GAIA two telescopes mounted on a slowly spinning satellite will measure the position of the stars with an accuracy much higher as ever done before. Crucial in the system is that the relative angle between the two telescopes should remain stable in the μrad range. The GAIA BAM-OMA system is equipped with two off-axis parabolic mirrors that have to be polished to a high shape accuracy.