Cover: Illustration of the MetOp-SG A spacecraft carrying the SENTINEL-5/UVNS instrument (Credits: ESA)
The Liège-based company AMOS has just delivered to TNO the last set of 5 mirrors for the UV-1 spectrometers of the Sentinel-5 instrument.
SENTINEL-5 is a European Earth observation mission developed in support of the Copernicus program of the European Commission. This mission includes a single instrument: a broadband spectrometer (UV-VIS-NIR-SWIR) observing the Earth in nadir mode. It will fly on board the MetOp-SG A satellite operated by EUMETSAT as part of the EPS-SG system (EUMETSAT Polar System Second Generation).
The main objective of the SENTINEL-5 mission is to carry out atmospheric measurements, at high spatio-temporal resolution, relating to air quality, the climate system, ozone and UV radiation, while ensuring a daily global coverage.
The instrument’s prime contractor, the Dutch TNO, chose AMOS following the success of a previous contract for the TROPOMI instrument, the precursor of Sentinel 5 currently in orbit, for which AMOS had already supplied the aluminum mirrors.
This time, AMOS ‘contribution was to manufacture and polish 5 sets of four different mirrors, as well as some spare mirrors, for the spectrometers of the Sentinel-5 mission.
The two main challenges of this project were that some of these mirrors had complex shapes (also called “free form”), very different from classic geomtries such as a sphere or a parabola, and that the requested surface finish was even more demanding. Special figuring and polishing techniques were therefore required to achieve a surface accuracy of 5 nm (5 billionths of a meter) and a residual average roughness of 0.5 nm (half a billionth of a meter). When we know that the diameter of an atom on the mirror surface is around 0.3nm, it gives an idea of the extreme precision of the polishing process.
This success once again underlines AMOS ‘ability to meet the technological challenges imposed by the most ambitious space missions.