Climate change imposes prerogative tasks to space missions for climate research and weather forecast. ESA, NASA and many other national space agencies push development of mm-wave radiometer technology for Earth Observation. MM-wave Direct Detection Radiometers (DDR) are very promising instruments for Earth Observation space missions on climate research. Several national space agencies in Europe led by ESA push development of European mm-wave DDR technology during last two decades through a number of dedicated R&D activities and studies. All these efforts were targeting at one of the most significant space missions of ESA, called MetOp-SG. DDR technology has considerably advanced and nowadays is standardly employed for an important frequency channel at 89 GHz in several space missions for Earth Observation (EO) not only in Europe but also in the USA, Japan, China, and other countries. This progress could not be realized without great ambition and commitment of ESA and space related companies in Europe. Nowadays ESA and space related European companies push further development towards extension of DDR technology to other important frequency channels for Climate research.