Astronaut Doug Wheelock discusses his experiences while living on the International Space Station during a tweetup at NASA Headquarters in Washington, Wednesday, March 16, 2011. Wheelock, who has accumulated a total of 178 days in space, assumed command of the International Space Station and the Expedition 25 crew. During Expedition 25, there were more than 120 microgravity experiments in human research; biology and biotechnology; physical and materials sciences; technology development; and Earth and space sciences. Wheelock also responded to an emergency shutdown of half of the station's external cooling system and supported three unplanned spacewalks to replace the faulty pump module that caused the shutdown. His efforts restored the station's critical cooling system to full function. The mission duration was 163 days.