1. ABSTRACTIn the field of the Meteosat Second Generation program, the deep cold space had to be simulated at CSL. The two main constraints were first to keep a temperature lower than 20 [K] under 50 [W] heat load, or lower than 50 [K] under 300 [W] heat load, and secondly, to provide a total hemispherical emittance better than 0.95. Several different coatings have been measured from 5 to 90 [K]. After coating selection, to increase the emittance, the geometrical factor has been adapted. The result is a large opened honeycomb panel, black coated, cooled down by a Helium refrigerator, and with an emittance better than 0.98. Such a panel of 1.6 [m] diameter had to be fitted to the passive cooler of the MSG satellite SEVIRI experiment with a gap of 3 [mm] maximum. As it is used close to infrared optics, special care had also been taken to fit the cleanliness standard class 100, and to avoid degradation after more than twenty thermal cycles from 300 to 5 [K]. In the development of the panel, measurements and tests have been done on samples. Now, as a few payloads have been tested, real size results are available.