This structure has the function of a skeleton: Without the specific platform in which the highly sensitive spectrometer is precisely fitted, Sentinel-4 cannot function in the harsh and inhospitable conditions of space. From 2022 onwards, the “environmental guardian” should circle the earth, thereby measuring changes in the air quality over Europe and northern Africa in the ultraviolet, visible and infrared wavelength range. The spectrometer would not be able to function at an altitude of 36,000 kilometres with extreme temperature fluctuations, vacuum and weightlessness without its precisely designed and manufactured instrument structure.
According to Christoph Tschepe, head of the Space Business Unit and Sentinel-4 project manager at Invent, the core task for the seven-member development team at Invent was:
“to develop this structure with a special focus on its thermos-elastic stability and to manufacture it in true handwork, just like in a traditional factory. The material must be able to withstand temperatures of between +140 and – 165 degrees Celsius, for example. The more than 1000 different individual components of the structure must thereby not lose their relative position to each other, even in this wide temperature range.”
Since 2013, a total of four models – two qualification and two flight models – have been co-developed and manufactured at Invent in Braunschweig. In all models, different carbon fibre-reinforced plastics (CFRP) and metal components have been merged together.
Martin Sauerbrey, Sentinel-4 systems engineer at Invent, explains:
“The measurement setup of the instrument defines the basic geometry of the structure. Ultimately, this design and the temperature range planned for the instrument have a strong influence on the possible construction methods and materials and therefore also on the production processes. We have manufactured the structure from materials which are suitable for high temperatures and which, as a result of complex production processes, provide a very low outgassing rate.”
Project manager Christoph Tschepe explains the background:
“Sentinel-4 carries an optical instrument, which means that the structure which holds it must remain very rigid over a wide temperature range and, particularly in space, no more substances may escape, otherwise the spectrometer’s measurements would be permanently impaired.”
The design of the supporting structure, suitable composite materials and an individual process for the curing and baking of the material as well as the high-precision bonding of the individual components consequently had to be determined. The skeleton for the Sentinel-4 instrument weighs around 50 kilograms and measures approximately 1 meter by 1 meter by 1.20 meters. It also forms the scaffold for all the other assemblies, providing protection and stability, particularly during the launch, but also later during operational service in space. Each of the four identical models is comprised of several CFRP aluminium-sandwich panels, monolithic CFRP components, a so-called baffle structure, a solar-reflector shield, a sun-protection strut framework and countless metal parts. The approximately one-meter-high baffle structure, an optical device for preventing scattered light in the measuring instrument, was completely bonded and coated inside with a light-absorbing paint.
For Invent Managing Director Henning Wichmann, the participation in the Sentinel-4 mission is something very special:
“The project has occupied our time intensively for five years. We are very pleased that OHB System AG has expressed its confidence in us and placed its trust in our many years of expertise in lightweight construction. Space projects are always at the limits of what is technically feasible, which makes such projects and missions incredibly exciting and challenging. There are no simple solutions, and this is precisely where the core of our motivation lies.”
Companies: INVENT GmbH