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Selective Soldering

Completely released – ROSE-L mission in space

Airbus Immenstaad is supported by Ersa in satellite construction

With an endless pioneering spirit, Airbus has been driving sustainable innovation in the aerospace industry for decades. Time and again, the Airbus team has succeeded in pushing the boundaries of what is possible in aerospace. As part of a highly complex project of the European Copernicus space program, Ersa GmbH was called in to develop a sophisticated application based on an ECOSELECT 2 selective soldering system together with the engineers from Airbus Defence and Space.

Soldered ring segments on the groundsheet
Soldered ring segments on the groundsheet

On December 3, 2020, the contract for the development of the environmental monitoring mission “Radar Observing System for Europe in L-band” (ROSE-L) was signed. ROSE-L is an important part of the Copernicus program of the European Union (EU) and is co-financed by the European Space Agency (ESA). Thales Alenia Space is the prime contractor for the mission, while Airbus Defense and Space is supplying the highly-sophisticated radar instrument. Scheduled for launch in 2028, ROSE-L will provide continuous day-and-night monitoring of the land, oceans and land ice, frequently delivering high spatial resolution images from an altitude of 690 km. During its 7.5-year lifetime, the ROSE-L mission will provide important information on forests and land cover, contributing to improved monitoring of the terrestrial carbon cycle. The mission will improve the detection of even the smallest surface shifts and potential geohazards. Designed for the 1.25 GHz range, the two satellites (No. 2 will follow in 2030) of the ROSE-L mission will usefully complement the Sentinel-1 satellites (5 GHz) already active in space with their new functions and capabilities. ROSE-L will automatically map soil moisture and monitor sea and land ice, which will benefit climate change research and mitigation. It will also be possible to measure soil moisture as well as plant and species identification (good support for agriculture, for example) and could also be used in the event of natural disasters – with completely open data access for users.

Airbus Defense and Space builds radar antenna for ROSE-L

Fully assembled subarray with 24 ring structures
Fully assembled subarray with 24 ring structures

Shortly after the contract was signed, the project wheels also started turning at Airbus Defense and Space in Immenstaad at the end of 2020, where production of the radar antenna is based. This is not just any radar antenna – at 11 m x 3.6 m, it is the largest SAR planar antenna ever built. The challenge was to develop a new, innovative radar antenna concept consisting of 60 individual boards measuring 2.2 x 0.3 m using lightweight materials. The antenna surface is three times larger than that of the previous flagship satellite Sentinel-1, whereby the weight of the antenna must not exceed 700 kg as before. A classic case of a sandwich structure with high rigidity and low weight – the centerpiece in the middle: the high-frequency distribution network with a wafer-thin circuit board. Five segments with a total of 60 individual boards, each weighing 2.5 kg, are required per satellite – with a certain reserve (for demonstration and measurement purposes), production amounts to a total of around 135 assemblies with almost 39,000 individual soldered joints.

2.4 m long product carrier, milled from a single piece and fitted with an assembly group
2.4 m long product carrier, milled from a single piece and fitted with an assembly group
Deployment test of the Sentinel IC antenna
Deployment test of the Sentinel IC antenna

Disclaimer: The views and opinions expressed are solely those of the author and the European Commission and/or ESA cannot be held responsible for any use that may be made of the information contained herein.

 

Functioning lightweight solution

Christian Lausch, the responsible development engineer in the Airbus Mechanic & Mechatronic Development Engineering department, and his colleague Harald Arlt, who has been with Airbus for 14 years, put all their expertise into developing a functioning lightweight construction solution. The original idea was to use vapor phase soldering – in principle, this would have been possible. The disadvantage was that the 2.2 m long board would have had to be segmented, which would have resulted in a loss of strength. However, it was also clear that the later application would “see” space and therefore be exposed to considerable temperature fluctuations and external influences. Unlike satellite electronics packed “on board”, for example, which are still surrounded by a protective shell even in space. The Airbus experts therefore decided against the vapor phase soldering process, as the application they were looking for had to offer the greatest possible resistance. The search continued – and they found what they were looking for in the existing machinery in the company´s own clean room production facility, which had been used until recently to produce flight electronics (circuit boards and onboard systems). After this production was relocated internally, the machines were returned to Development Engineering. Among them was an ECOSELECT 2 mini-wave selective soldering system – after a brief analysis it was clear: width fits, height fits, perhaps Airbus could use it to produce the required assemblies measuring 2.2 m x 0.3 m and only 0.4 mm thick in conjunction with a low-temperature solder?

Working together for the ROSE-L mission (from right to left): Harald Arlt and Christian Lausch from Airbus and Ersa colleagues Jürgen Friedrich, Lothar Rodemers and Mark Birl
Working together for the ROSE-L mission (from right to left): Harald Arlt and Christian Lausch from Airbus and Ersa colleagues Jürgen Friedrich, Lothar Rodemers and Mark Birl

This was the time to get in touch with the soldering machine manufacturer Ersa – and to obtain an assessment of whether the planned project was feasible. Things quickly got rolling, and in January 2021, work began on the specification of a test setup for a feasibility study, with an initial series of tests taking place at Ersa from March onwards, including slots and strips, solder joint geometry, workpiece carrier plus hold-down device, solder selection, soldering parameters and motion sequence. In September, a second series of tests started at Airbus – with a new test board with four rings in the original design, a new product carrier for the ring design including hold-down device and ring slots in different geometries. At the beginning of January 2022, the final soldering tests were carried out in Wertheim using a tin-bismuth solder. These were successful, paving the way for Ersa to be commissioned to convert the ECOSELECT 2 system, including the design and construction of a suitable 2.4 m long product carrier. “The challenge was enormous, as we were not dealing with a classic through-hole plated PCB, but a 0.4 mm thin high-tech CFRP substrate, fully copper-coated, without solder resist. The length of the slots at 20 mm raised a number of questions as to whether this could actually be soldered in a single process. We have already soldered a wide variety of geometries. But this project was also new territory for us. We knew from other projects that the solder tends to flow anywhere with large copper surfaces – just not to the planned location. But we actually managed to do it in close cooperation with the Airbus team,” says Jürgen Friedrich, Head of Application Technology at Ersa, who has been with the company for over 25 years. In July 2022, Ersa finally completed the plant conversion at Lake Constance, which included switching from tin-lead to tin-bismuth. One of the major challenges here was adapting the system control for processing the 2.4 m long product carrier in a single pass. Ersa thus supplied a complete system for an unusual application and successfully commissioned it on site.

Complete scan of the earth every six days

60 soldered ring segment assemblies are required for the five-segment radar antenna of a ROSE-L satellite and are produced on the Ersa ECOSELECT 2. Each satellite requires 1,440 individual rings, each with twelve soldered slots. When both satellites – offset by 180° – orbit the earth at an altitude of 690 km from 2030, they will provide a complete scan of the earth every six days – and valuable data to react promptly to short-term changes. “Looking back, it is quite remarkable how quickly we have come to a solution. We are now close to completing the qualification phase and will be starting flight part production in spring, which will take place over a period of around two years – thanks again to the Ersa team, in particular Jürgen Friedrich and the sales and process engineers Mark Birl and Lothar Rodemers, who contributed to the implementation of this application,” says Christian Lausch during the final visit to cleanroom production. From the grandstand, the view wanders down to the production area, where the two-tonne satellites to be completed hang like bats from the cargo crane – with folded solar cell wings to generate energy, which they later unfold in the vastness of space to send important information back to the blue planet …

 

Airbus site in Friedrichshafen
 
 

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