To connect the two modules together, engineers used a crane to lower the 800-kilogram payload module onto the service module via six attachment points. The team took great care to make sure that these points matched up very well, as a poor contact could induce stresses that damage the structure or deform Euclid’s 1.2-metre telescope mirror.

“We had to make sure that the flatness of the service module closely matched the flatness of the payload module at the connection points to reduce the loads on the telescope as much as possible,” explains Hans. “We were targeting a difference of less than 50 microns at every point. It’s not like a piece of Ikea furniture that you can hammer into place – this task required extreme precision!”

To put this into perspective, 50 microns – or 0.05 mm – is the diameter of a thin human hair. Before attaching the two modules together, the assembly team checked the smoothness of the connection points with a laser and used very thin spacers called shims to even out the surfaces where needed.

Hans continues: “After the modules were joined mechanically, we added connector brackets and plugged in the electrical connectors. Then we checked that everything was working properly. Finally, we covered the connector brackets and any tiny remaining gaps between the two modules with thermal insulation to really seal up the spacecraft.”