ATV Johannes Kepler is set to undock from the ISS on 20 June 2011, giving the resupply vessel a longer docked phase than originally foreseen. We spoke with ESA's Nico Dettmann by email earlier today, who told us:
"Our new undock date is mainly due to the change in launch date for NASA's Shuttle mission STS-134, now set for lift-off on 29 April. That launch in turn had been shifted to 29 April from the initially planned 19 April due to the requirement to launch the Russian Progress M-10M cargo vessel on 27 April. Also, the later-than-expected arrival of Shuttle STS-134 affected later planned Russian arrivals, meaning that Soyuz TMA-02M/27S will now arrive a bit later, so ATV can stay attached until the 20th."
Nico said the extension to the ATV attached phase means the European resupply vessel will provide additional reboost capacity to the ISS, with four reboosts now planned from end-May to early June. "It's not a big change in the mission plan - we had extensions also on the first ATV mission in 2008," he added.
At ATV-CC in Toulouse, the extension will mean that mission controllers will shift dates for the undocking readiness review and rearrange some shift plans. The extension will also not substantially affect plans for deorbiting ATV, with reentry now also happening within just a day or two of undocking.