Complex sentence: Scott Kelly will serve as commander of Expedition 26 which is scheduled to begin in November 2010, when half of the crew of Expedition 25 returns to Earth on board of Soyuz TMA-19.
Split into simpler sentences: Scott Kelly will serve as commander of Expedition 26. The mission is scheduled to begin in November 2010, when half of the crew of Expedition 25 returns to Earth on board of Soyuz TMA-19.