been in the form of external photography or early airframe designs. NASA Administrator James C. Fletcher stated that Buran was based on a rejected NASA design. See the section above. Key differences between Energia-Buran system and NASA's Space Shuttle Unlike Space Shuttle's boosters, each of Energia's four boosters had their own guidance, navigation, and control system. Known as Zenit-2, they were used as launch vehicles on their own to deliver smaller payloads than those requiring the complete Energia-Buran system. Energia could be configured with four, two or no boosters for payloads other than Buran, and in full configuration was able to put up to 100 metric tons into orbit. The Space Shuttle orbiter was integral to its launch system and was the system's only payload. Energia's four boosters used liquid propellant (kerosene/oxygen). The Space Shuttle's two boosters used solid propellant. The liquid fueled booster rockets were not constructed in segments vulnerable to leakage through O-rings, which caused the destruction of. Energia's four boosters were designed to be recovered after each flight, though they were not recovered during Energia's two operational flights. The Space Shuttle's boosters were recovered and reused. Buran equivalent of the Space Shuttle Orbital Maneuvering System used GOX/LOX/Kerosene propellant, with lower toxicity and higher performance (a specific impulse of using a turbopump system) than the Shuttle's pressure-fed monomethylhydrazine/dinitrogen tetroxide OMS engines. Buran was designed to be capable of both piloted and fully autonomous flight, including landing. The Space Shuttle was later retrofitted with automated landing capability, first flown 18 years after the Buran on STS-121, but the system was intended to be used only in contingencies. The nose landing gear was located much farther back on the fuselage rather than just under the mid-deck as with the NASA Space Shuttle. Buran could lift 30 metric tons into orbit in its standard configuration, comparable to the early Space Shuttle's original 27.8 metric tons Buran could return 20 tons from orbit, vs the Space Shuttle's 15 tons. Buran included a drag chute, the Space Shuttle originally did not, but was later retrofitted to include one. The lift-to-drag ratio of Buran is cited as 5.6, compared to a subsonic L/D of 4.5 for the Space Shuttle. Buran and Energia were moved to the launch pad horizontally on a rail transporter, and then erected and fueled at the launch site. The Space Shuttle was transported vertically on the crawler-transporter with loaded solid