was initiated at 16:59 UTC, and was one minute and 53 seconds in duration. The deorbit burn is performed while the orbiter is facing opposite its direction of travel, which allows the engines to act as a braking system, slowing its speed by approximately . After the burn, the remaining propellant in the orbiter's maneuvering thrusters was dumped overboard, at 17:13 UTC. Discovery began to feel the effects of gravity around , as it traveled above the North Pacific Ocean at 17:30 UTC. As the orbiter descended, Melroy initiated a series of "rolls", and roll reversals, which serve to create friction and bleed off additional speed. At 17:40 UTC, Discovery entered the United States, flying over Montana. At 17:53, the orbiter entered Florida, flying at a speed of , and an altitude of . Discovery touched down on runway 33 at 13:01:18 EST, the rear landing gear touching down first, the nose gear touching down at 13:01:32 EDT, and the orbiter came to a complete stop at 13:02:13 EDT. Total mission time was 15 days, 2 hours, 23 minutes, 55 seconds, for a distance of 6.25 million miles in 238 orbits. The completion of STS-120 marks the longest duration mission for Discovery. Extra-vehicular activity Four spacewalks were scheduled and completed during STS-120. The cumulative time in extra-vehicular activity during the mission was 27 hours and 14 minutes. ESA Esperia mission In addition to his participation in the ISS assembly mission during the STS-120 flight, Paolo Nespoli conducted science research as part of the Esperia mission for ESA. According to the STS-120 press kit, Nespoli was to carry out a number of experiments on behalf of the European science community. Two of these experiments (Chromosome‐2 and Neocytolysis) were sponsored by ESA. The other three (HPA, FRTL‐5 and SPORE) were sponsored by the Italian Space Agency. Chromosome‐2, Neocytolysis and HPA were experiments in the field of human physiology. FRTL‐5 and SPORE were biology experiments. Wake-up calls NASA began a tradition of playing music to astronauts during the Gemini program, which was first used to wake up a flight crew during Apollo 15. Each track is specially chosen, often by their families, and usually has a special meaning to an individual member of the crew, or is applicable to their daily activities. Contingency mission STS-320''' was the designation given to the Contingency Shuttle Crew Support mission which would have been launched in the