The present document is based on four lectures given for Master of Space and Application in University of Science and Technology of Hanoi. It consists of four parts. The first devoted to filters, the second to DC/DC converter, the third discusses the phase locked loop and the last the modulation. For convenience of the readers the work is organized so that each part is self-contained and can be read independently. These four electronic systems are chosen because they are representative of critical elements encountered in spacecraft; wether for power supply or for data transmission.