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A bladder tank comprises a rigid vessel containing a flexible bladder and perforated axial stand-pipe. Propellant is contained in the bladder and pressurant gas within the tank occupies the volume between the tank wall and bladder. The pressurant gas 'squeezes' the bladder forcing propellant through the stand-pipe to achieve a positive expulsion of propellant to the thrusters, or engine. The bladder tank may be operated in either blow-down mode, or pressure regulated mode. In blow-down mode, the tank is loaded with propellant and 'locked-up with a specified gas mass. This mode avoids the need for additional gas pressurant vessels thereby reducing mass, volume and propulsion systems complexity. The fixed gas mass does however result in diminishing pressure during operation resulting in reducing thrust from Beginning of mission Life (BOL) to the End of Life (EOL). The reducing thrust level can however be very accurately predicted with guaranteed repeatability. In pressure regulated mode, the tank is pressurised from an independent pressurant vessel, via a pressure regulator, supplying a constant pressure from BOL to EOL. Consequently the propellant supply pressure, hence thrust, is constant throughout operational life. Whether in blow-down, or pressure regulated mode, the bladder tank advantages include:
The 400 N hydrazine AOCS is located in the Vehicle Equipment Bay, which forms a part of Ariane 5's upper stage. The 400 N AOCS is both versatile and multifunctional enabling roll and pitch control of Ariane 5 during its ascent as well as all upper stage manouvres preparatory to the separation of one or more payloads. The 400 N AOCS can also be easily up, or down, graded with alternative numbers of bladder tanks according to mission demands.
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