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The driving force – ATV’s propulsion sub-system

During the docked phase, the ATV acts as a propulsion ‘service pack’ for the ISS

The Station’s onboard computers instigate initiation of the ATV’s thrusters to carry out the reboost manoeuvre. The reboost operation is performed with the same propulsion system used to manoeuvre the ATV itself.

The ATV’s Propulsion and Reboost Sub-System (PRSS) comprises:

  • Four main thrusters each delivering 505 N thrust, referred to as the OCS (Orbit Control System) and used for boosting the ISS orbit
  • 28 thrusters each delivering 220 N thrust, referred to as the ACS (Attitude Control System), only 12 of which are used by the ISS itself. These thrusters execute roll, pitch and yaw attitude control operations. The other 16, used solely for the ATV’s own operations during the orbital phase, are not activated during the docked phase to avoid any pollution or contamination of the ISS

The 32 thrusters are arranged in four physical and functional chains, each of which is connected to a digital data bus (enabling, in particular, control of the thrusters). In case of a thruster failure, the affected thruster group is disabled, and full propulsion system functionality is maintained by the other three thruster groups.

The PRSS is a bipropellant system consisting of the propellant (MMH) and the oxidiser (MON). Each of these components is stored separately in four surface-tension titanium tanks. The tanks have a total capacity of nearly seven metric tonnes. The Propellant Management Device (PMD) in the tanks ensures a bubble-free flow of propellant to the thrusters in all circumstances foreseen in the ATV’s mission profile. In addition, propellant acquisition valves (PAV) in the tanks help to prevent any acceleration from being transferred from moving fuel masses to the orbit control system.

Two high-pressure carbon fibre composite tanks (with an initial pressure of 310 bar) contain helium for separate pressurisation of the MON and MMH tanks. The pressure is regulated in each case by a pressure control unit that adjusts the operating pressure to 18 bar.

The distribution system located beneath the propellant tanks, consisting of fuel lines, pressure sensors and shut-off valves, then carries the propellant to the 28 attitude control thrusters and four main thrusters.

The shut-off valves and thruster valves are controlled via the Propulsion Drive Electronics control unit, which is in turn connected to the Fault Tolerant Computer and Monitoring and Safing Unit onboard computers.

The ISS is reboosted with two main thrusters that each delivers a thrust of 505 N. If these thrusters fail, the manoeuvre can be continued with the other two thrusters (simple redundancy). The main thrusters are designed for 2,500 seconds of uninterrupted firing. However, the re-boost manoeuvre on 25 April 2008 took only 740 seconds, raising the orbit of the space station by 4.7 km.


Find out more! A special dossier full of informative articles and videos has been created about the ATV ‘Johannes Kepler’.