During last decade, satellite manufacturing business has stopped being only a pioneer high tech area to become a real competitive industry. Considering the cost to set 1 kg into orbit, saving weight on satellites has become an obsession in space industry. To win invitations to tender, designers must then be able to develop innovative lightweight structures within very short times. That's why ASTRIUM Mechanical Design Office (M.D.O) has been developing, testing and comparing, for years, tools that would help to speed up structural mechanical design, to minimize weight and to maximize mechanical performances. These tools do not intend to replace engineering competences, but on the contrary to amplify them and to suppress boring repetitive steps. Indeed, good results can only be obtained if the best strategy has been selected to determine what the real design drivers and the best design parameters are. When properly used, optimization tools can be used for rapid design, to suggest new shapes at the very beginning of conception. They can also be used to have a critic and objective opinion on mechanical specifications and to have a quick idea on how hard it will be to fulfil them. They also can be applied to an existing design, to improve it and to save mass wherever possible. In a nutshell, optimization tools can help to provide attractive technical solutions by saving what is the more precious for space structure mechanical design: time and weight. In forthcoming presentation, we will detail the process of structure optimization that is now generally in use at ASTRIUM Mechanical Design Office, and illustrate this process and the gains obtained with the help of structural concrete examples We will also insist on the importance that, to get the best results, optimization tools have to be used with lot of precautions and verifications. Indeed, the quality and pertinence of obtained results will be directly linked with the way each given mechanical problem has been cautiously defined, and with the pertinence of the strategy that the engineer decided to follow.