Eric Ruch, Safran Reosc
Eric Ruch, CTO, Safran Reosc
Safran Reosc has developed the SEEING imagers, a family of instruments for earth observation. This family includes several payloads from medium resolution with a wide field of view, to very high resolution with a ground sampling distance below 1 meter.
The first imager of the family, the SEEING 130 a wide field of view and medium resolution instrument, has been delivered to the Norwegian Research Defense Establishment and is part of the NorSat-4 satellite, that will be launched in early 2025.
This imager has been specifically developed to provide a high signal to noise ratio (SNR) in low light observing conditions. This requires the use of a very fast imager (F-number below 1,5) resulting in several challenges that will be presented in the paper. Another driver for the design of the Seeing 130 is the requirement to cover a swath of 60km. The combination of a large field of view with the low F-number is rather unique for this type of imager.
We will report optical performances achieved during the qualification phase of the imager. This includes optical wave front measurement after the final alignment of the optical elements, modulation transfer function (MTF) after integration and alignment of the camera module. The image quality has been measured before tests and compared to the image quality measured after tests: this demonstrates the very high stability of the imager after the tests that simulates the launch conditions. It has also demonstrated the high stability that is achieved during the operating conditions (especially the stability of the image quality with the operating temperature range).
This paper will then present an innovative optical and mechanical design for a 27 U optical imager intended to provide a 1 meter ground sampling distance from à 500km altitude and a 10 km field of view. The optical design is a five elements all mirror telescope made in low expansion material as well as the metering structure of the telescope housing. In order to achieve a very small volume, it has been required to introduce very fast aspherical mirror in the optical design. The error budget that will be presented result in very challenging mirror to be manufactured.
We will first present the main drivers of the design and the optical and mechanical performances of the imager. We will then report on the manufacturing and the assembly of the imager and the first results of the imager qualification that have been achieved. We will present optical measurements of the imager (FTM) after environmental tests including vibration and thermal vacuum tests.
The last section of the presentation will present the development of the Seeing VHR, an instrument for high optical resolution aiming at achieving a ground sampling distance comprised between 0,7 meter and 0,5 meter. The optical combination is based on a three mirrors design with a short primary to secondary mirror distance and an off-axis tertiary mirror. All three mirrors are highly aspherical mirrors. The paper will present the main characteristics of this very high resolution imager.
The Seeing family covers the full range of medium resolution to high resolution imagers.