It’s just 1 week until the 5th and final Automated Transfer Vehicle built by Airbus Defence and Space, undocks from the ISS.
ATV 5, named Georges Lemaître, provided the ISS with a rare de-boost last week, bring the orbit down by approximately 1km.
A lower orbit slightly increases the (already tiny) drag exerted by the wisps of atmosphere on the ISS and, therefore, also increases the decay of the ISS orbit. This allows the visiting vehicles (Progress, SpaceX, Cygnus, &etc.) to bring up a heavier load.
It is the first time that an ATV has been used to decrease the altitude; usually, on the contrary, ATV propulsive support is used to lift the orbit due to the regular decay (around 1 or 2 km per month). To allow this manoeuvre, the ISS has been turned 180 degrees so that the ATV, docked to the rear, is in front of the other modules with its thrusters directed opposite to the Station’s velocity vector.
(EDIT: ATV-1 did conduct a similar ‘retro’ burn in 2008, as part of a debris avoidance manoeuvre)
ATV 5 will undock carrying solid and liquid waste from the ISS, and burn up in the atmosphere two weeks later.
And don’t forget, the ATV platform is the basis for the new Service Module on NASA’s Orion Spacecraft!