text: There he acquired a copy of Die Rakete zu den PlanetenrÃ umen ( 1929 ) ( By Rocket into Interplanetary Space ) ( in German ) by rocket pioneer Hermann Oberth .
simplified: He bought with his extra money the book Die Rakete zu den PlanetenrÃ umen ( English : The Rocket Into Interplanetary Space ) , which is the basis of the modern rocket research .