Composite sandwich structures are widely employed in various applications, due to their high specific stiffness and specific bending strength compared to solid panels. Lately, for that reason, the advanced composite sandwich structures are employed in satellite structures: materials should be as light as possible with the highest attainable performance. This study is majorly focused on inserts employed to the composite sandwich satellite structures. A new insert design was developed to reduce the mass of the sandwich structure since the mass of the satellite structure is related to high launching cost. Carbon composite reinforcing method was developed to increase the maximum pull-out load of the new insert without increasing its mass. Also new co-curing method was developed to reduce the fabricating steps and time of the composite sandwich structures with inserts. Finite element analysis was performed to verify the capability of the new insert design, moreover, to investigate the mechanical behavior of the new insert on the structural reliability of the composite panels. The load capability and the behavior of the composite sandwich structures with the inserts were investigated via insert pull-out and shear tests. Also, in the developed reinforcing method, the reinforcing effect of the carbon composite web formed around the insert was investigated and compared with the non-reinforced insert via static pull-out and shear tests. To investigate the effect of boundary conditions, the new static test methods were developed which improved the accuracy of the test results. Lastly, the thermal characteristics and behavior of the new insert with carbon composite reinforcing web and the conventional partial insert were numerically investigated.