ATV docking process – from ‘first contact’ to electrical and data hook-ups
The ‘magical moment’ in the ATV 3 docking process is scheduled to take place at 00:33 CEST; the docking probe of ‘Edoardo Amaldi’ will make contact with the docking cone in the aft port of the Russian Zvezda module on the International Space Station (ISS). This is just the first stage in a process lasting about 25 minutes.
Once contact has been established, ATV 3 will fire its thrusters for up to 10 seconds to push the docking probe into the socket at the inner end of the docking cone. Upon successful capture, the ISS will go into ‘free drift’. At this point, its attitude and orbit control system will stop making corrections to the Station’s attitude for the remaining duration of the docking process. ‘Edoardo Amaldi’ will then retract its docking probe to draw itself the last few centimetres to the ISS while correcting any remaining misalignments; this can take from six to 10 minutes.
ATV-3 ‘Edoardo Amaldi’ on its launcher, just prior to the installation of the fairing, showing the active docking mechanism.
Once the docking probe is fully retracted and the interface surfaces of ‘Edoardo Amaldi’ and Zvezda are aligned, ATV will close the hooks that lock it to the ISS. At this point, the docking probe will re-extend to enable the latching mechanism at its tip to be retracted. The probe itself will then retract into the ATV hatch, allowing it to be opened once docking is completed. The docking mechanism on Zvezda will then close its hooks, to further secure ‘Edoardo Amaldi’ to the Space Station.
With mechanical docking completed, the power connections between ATV and the ISS will be tested and ‘Edoardo Amaldi’ will begin to draw the power required for its systems from the Space Station; systems that were required only for navigation and docking will have been progressively turned off during the docking process. With electrical connections established, it is the turn of the signalling lines and data bus that allow ‘Edoardo Amaldi’ to become a fully functional part of the ISS for the duration of its stay. In addition to power and data connections, ATV also makes connections to enable it to transfer propellant and oxidiser to the storage tanks on the ISS.