The reinstallation of both repaired transponders into Gaia was successfully finished at the European launch base in Kourou completing a delicate operation that you can compare with a open heart surgery somehow. The access to the place in the service module of Gaia where the transponders are mounted was not an easy one as you can see in the image above taken during the reinstallation. As the sunshield (DSA) was already in launch configuration covering all the lateral surface of the spacecraft an opening through had to be found. Otherwise the sunshield had to be unfolded again before the retrieval of the transponders and then folded back after their reinstallation. These are complicated processes that need several working days to accomplish. If this route had to be gone for getting access most likely the launch of Gaia would have been delayed to the next launch window starting January 16.
Fortunately, there was a way found avoiding these time-consuming procedures. Two solar panels mounted on top of the MLI needed to be removed first. The blankets of the multi-layer insulation (MLI) mounted on the hard structure of the sunshield were then successfully folded back to get access to the service module with the transponders inside. No cuts into the MLI of the DSA were needed. Unmounting and reinstallation of the transponders itself were relatively quick processes. Testing needed more time. The repair of the transponders is a different story that eventually will never be told.
There was a lot of progress made during the last few days. It was even possible to advance the launch date one day. What an impressive effort! Let us hope that the next critical process – the pressurisation of the fuel tanks – goes well, too.
More details are available at the ESA Gaia blog: http://blogs.esa.int/gaia/2013/11/25/gaia-is-whole-again/.