Hermann Oberth (1894–1989) was born in Transylvania, in what is modern-day Romania, and built his first rocket as a teenager. He obtained his higher education in Germany; for his doctoral dissertation, he wrote about the mathematical theories of rocketry and practical considerations of space flight. This work, By Rocket into Planetary Space, was rejected by his German academic advisors, but later revised and expanded into the book Ways to Spaceflight, which was published in 1929. Over his career, Oberth worked on solid propellant rockets and on vehicles to go to the Moon.