Bi-aspheric mirrors improve attitude & orbit control of satellites in space
Size, weight and resistance to temperature fluctuations are the most important challenges of modern star sensors, in addition to the autonomous determination of their position. With the development of ASTRO® XP, Jena-Optronik achieved an important advance in the further development of sensors. The star sensor is not only ten times more accurate than others, thanks to its optical design it is also many times lighter. High-precision bi-aspherical mirrors and a spacer from asphericon, built into the optical head of ASTRO® XP, ensure best imaging quality and withstand even extreme thermal-mechanical loads.
On behalf of the European Space Agency (ESA), Jena-Optronik developed the ASTRO® XP star sensor for autonomous attitude and orbit control of satellites and probes. With a measurement accuracy of 0.1 arc seconds, ASTRO® XP is ten times more accurate than other existing sensors. Due to its optical design based on aspheric mirrors, it is also extremely lightweight. ASTRO® XP consists of an electrical unit and an optical head. asphericon manufactured two complex, bi-aspherical mirror optics for the latter (see picture on the left) and a spacer for the first development models. Use of the star sensor for ESA science missions is planned for the late 2020s.
The purely reflecting mirrors with diameters of 77 and 140 mm are bi-aspherical and have an annular entrance aperture (see image on the right). This innovative and award winning (“Thüringer Innovationspreis 2020”) optical design by Jena-Optronik allows a compact construction and avoids the need for additional optics. The latter has a positive effect on size as well as on the weight of the sensor. To enable missions in space, the mirrors with a PV of < 150 nm have an outstanding surface quality. For suitable handling of temperature fluctuations of up to 60°C, the aspheres were made of fused silica, in perfect material match with the overall imaging system parts. This exclusive material selection ensures that the optical components do not suffer from any thermal-mechanical stress. To be able to process and measure several disjunctive optical surfaces on one component surface, the process strategy and measurement technology were precisely coordinated and further developed. A spacer completes the optical system. This 140 mm wide, fused silica ring has a flatness of less than one micrometer and holds the optical system in position.
Optics for ASTRO® XP at a glance:
Manufacturing of two purely reflecting bi-aspherical mirrors (diameter 77 and 140 mm) with ring-shaped input aperture and a 140 mm wide spacer made of fused silica
Surface quality of the mirrors: PV < 150 nm
Material and quality of the components provide excellent imaging properties and allow the sensor to be used at temperature fluctuations of up to 60°C
For processing and measuring the different disjunctive optical surfaces, asphericon’s process strategy and measurement technology were precisely coordinated and further developed
Disclaimer: The contract was carried out under a programme of and funded by the European Space Agency. The view expressed herein can in no way be taken to reflect the official opinion of the European Space Agency.
