This book is an introduction to Cubesats, those popular and relatively inexpensive modular spacecraft that are upending the aerospace world. They have been built and deployed by colleges and Universities around the world, as well as high schools and elementary schools, even individuals. This is because Cubesats are modular, standard, and relatively low cost. The expensive part is the launch, but that is addressed by launch fixtures compatible with essentially every launch vehicle on the planet. Although you may not have much of a choice in the orbit. Cubesats are also flown on high altitude balloons.