The coming and going of two Russian unmanned supply ships for the International Space Station has forced NASA to delay the final mission of space shuttle Endeavour by ten days.
On Sunday, insiders from Roscosmos stated that Russia will not delay an incoming craft's arrival to the outpost, and that Endeavour would not be at the station during the craft's arrival.
NASA's shuttle mission management team later officially announced the delay.
Endeavour was due to begin ten days docked operations beginning on April 21.
Russia's Progress M-09M resupply craft is scheduled to undock from the station on April 26, for deorbit and burn-up upon a fiery reentry.
One day later, a new unmanned supply craft is scheduled to be launched to the station, arriving there two days later.
The Progress M-010 planned docking on April 29 is a hazard to Endeavour as the spacecraft's engine exhaust blows over the shuttle and could lay a sheet of blinding film on the forward windows.
However, an April 29 launch by Endeavour could shorten her time at the space station from the planned ten days.
On May 16, Russia will undock a Soyuz TMA20 spacecraft with a crew of three having completed nearly six months aboard and return them home.
If Endeavour docks on May 1, Russia could ask NASA to send Endeavour home early to allow for one American, one Italian and one Russian's Soyuz departure and return to earth.
Lift-off is now scheduled for 3:47 p.m. EDT on Friday, April 29.
NASA will hold a management flight readiness review on April 19 to underscore each detail of Endeavour's flight to ensure the crew, vehicle and ground teams are ready.