In the second volume of the collected works of the distinguished Russian scientist, Academician V. A. Kotelnikov (1908-2005), prepared for the centenary of his birth, you will find his groundbreaking research that laid the foundation for new scientific fields in space exploration—cosmic radio physics and planetary radar. The results of these studies are of paramount importance for understanding the Solar System and have shaped the trajectory of all subsequent space programs. Additionally, the volume includes Kotelnikov's last unfinished work, "Non-relativistic Quantum Mechanics," the drafts of which were published in 2008, after his passing. A specialist's commentary on this work is also included. This volume is essential for scientists, specialists, and students, as well as anyone interested in the history and achievements of domestic science in the realms of space exploration and radio astronomy.