of space exploration had a solid basis in the Russian Empire before the First World War with the writings of the Russian and Soviet rocket scientist Konstantin Tsiolkovsky (1857–1935), who published pioneering papers in the late 19th and early 20th centuries on astronautic theory, including calculating the Rocket equation and in 1929 introduced the concept of the multistaged rocket. Additional astronautic and spaceflight theory was also provided by the Ukrainian and Soviet engineer and mathematician Yuri Kondratyuk who developed the first known lunar orbit rendezvous (LOR), a key concept for landing and return spaceflight from Earth to the Moon. The LOR was later used for the plotting of the first actual human spaceflight to the Moon. Many other aspects of spaceflight and space exploration are covered in his works. Both theoretical and practical aspects of spaceflight was also provided by the Latvian pioneer of rocketry and spaceflight Friedrich Zander, including suggesting in a 1925 paper that a spacecraft traveling between two planets could be accelerated at the beginning of its trajectory and decelerated at the end of its trajectory by using the gravity of the two planets' moons — a method known as gravity assist. Gas Dynamics Laboratory (GDL) The first Soviet development of rockets was in 1921 when the Soviet military sanctioned the commencement of a small research laboratory to explore solid fuel rockets, led by Nikolai Tikhomirov, a chemical engineer and supported by Vladimir Artemyev a Soviet engineer. Tikhomirov had commenced studying solid and Liquid-fueled rockets in 1894, and in 1915 he lodged a patent for "self-propelled aerial and water-surface mines." In 1928 the laboratory was renamed the Gas Dynamics Laboratory (GDL). The First test-firing of a solid fuel rocket was carried out in March 1928, which flew for about 1,300 meters Further developments in the early 1930s were led by Georgy Langemak. and 1932 in-air test firings of RS-82 missiles from an Tupolev I-4 aircraft armed with six launchers successfully took place. Sergey Korolev A key contributor to early soviet efforts came from a young Russian aircraft engineer Sergey Korolev, who would later become the de facto head of the Soviet space programme. In 1926 as an advanced student Korolev was mentored by the famous Soviet aircraft designer Andrey Tupolev, who was a professor at his University. In 1930 while working as a lead engineer on the Tupolev TB-3 heavy bomber he became interested in the possibilities