Yuri Vasilievich Kondratyuk (real name Aleksandr Ignatyevich Shargei, Russian: Алекса́ндр Игна́тьевич Шарге́й, Ukrainian: Олександр Гнатович Шаргей) (21 June 1897 – February 1942) was a Ukrainian and Soviet engineer and mathematician. He was a pioneer of astronautics and spaceflight, a theoretician and a visionary who, in the early 20th century, developed the first known lunar orbit rendezvous (LOR), a key concept for landing and return spaceflight from Earth to the Moon.[1][2] The LOR was later used for the plotting of the first actual human spaceflight to the Moon.