With the advance on technology field, aerospace systems have been evolving during the years. Tendency on reducing size, mass and cost by increasing the efficiency on different elements has opened a wide range of possibilities. In this project is presented the design of the bus for a very small solar sail including the electric power subsystem, communication subsystems, on-board computer as well as the description of the mission. Few years ago, the elaboration of any spacecraft involved high economical costs leaving this possibility only to big companies, with the appearance from nanosatellites to fentosatellites, this possibility has been open to small companies or university research groups, allowing at the same time, scientific advance on space exploration. In this project is presented the design of the bus for a very small solar sail, which includes the electrical power subsystem, communication subsystem and the on-board computer. The main difficulty on this project resides on the mass requirements, limiting with a maximum weight of 50 grams for all those subsystems listed before.