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ATV SM

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Status: Study 1985. Gross mass: 8,363 kg (18,437 lb). Unfuelled mass: 5,500 kg (12,100 lb). Height: 3.28 m (10.76 ft). Diameter: 4.40 m (14.40 ft). Span: 22.30 m (73.10 ft).

With its own flight-control and propulsion systems, the ATV had a high level of autonomy which allowed it to stay in free flight for long periods of time, as well as to dock even if the Station was totally dormant and unmanned. After docking, these systems were used to perform ISS attitude control, debris avoidance maneuvers and to raise the Station's orbit to overcome the effects of atmospheric drag. On completion of the resupply mission the systems would de-orbit the spacecraft, carrying up to 6.4 metric tons of used equipment and general ISS waste in a controlled destructive reentry high above the Pacific Ocean. The SM consisted of the following subsystems:

• Avionics System: These were housed in a cylindrical ring, 1.36 m high, located in the upper part of the Service Module. It accommodated computers, gyroscopes, navigation and control systems and communications equipment. These were mounted on ten equipment carrier trays and protected from temperature variations by heat pipes. The ATV Service Module's architecture was designed to keep the ATV functioning in case of hardware failure or main malfunction.
• Electrical System: The Service Module had four solar arrays, which were deployed 100 minutes after lift-off. These reached a total span of 22.3 m and provided electrical power to rechargeable batteries, which powered ATV systems during eclipse periods in orbit. The solar arrays were comprised of silicon solar cells, spread on 4 carbon fiber reinforced plastic sandwich panels per array, with a total surface area of 33.6 m² (4 x 8,4m²) and produced an average of 4800 watts. Mounted on the ATV Service Module, the four sun tracking arrays were totally independent and obtained the best orientation to the sun through rotating mechanisms.
• Propulsion System: The ATV propulsion system provided the capability to transport the ATV to the ISS, navigating as a fully automatic spaceship with four main engines (providing 490 N thrust) plus 28 smaller thrusters (providing 220 N) for attitude control. All valves and thrusters were controlled by four control units connected to the main ATV computers. Once docked to the Station, the ATV's propulsion capabilities was used for ISS attitude control, debris avoidance maneuvers and reboosting the Station. In order to perform this reboost the ATV could use up to 4.7 metric tons of its own propellant at intervals of 10 to 45 days. At the end of the mission the ATV Service Module thrusters used their remaining fuel to de-orbit the spacecraft. All the propellant tanks were located in the ATV Service Module, between the main engines and the avionics bay. There were eight titanium propellant tanks and two high pressure carbon-fiber helium tanks for propellant tank pressurization. The propellant tanks held up to seven metric tons of monomethylhydrazine (MMH) and nitrogen tetroxide (N2O4), part of which could be used for the station attitude and orbit control.