"Last week, NASA sent a response letter to our Russian partners that says we believe this isn't right time to extend International Space Station crew missions from six months to a year.

"We believe the timing is not appropriate, in part, because the Station is currently in a reduced operational state.

"We don't have sufficient countermeasures in place yet to offset the effects that a longer duration space flight would have on the crew. Also, the impacts on planned Station biomedical research still needs to be addressed.

"We know we'll eventually need to extend the amount of time astronauts are in space to prepare for the missions outlined in the new Vision for Space Exploration. In fact, as International Space Station Program Manager Bill Gerstenmaier has said, we have people studying what it would take to implement longer Expedition missions. However, we don't see a way to practically address these concerns in time to support the Expedition 10 mission this October."