 It was the twenty-first Hubble servicing spacewalk, and Grunsfeld's seventh EVA, moving him up to fourth in the record book of spacewalking time.During the previous day's mission status briefing, Dave Leckrone, Hubble Space Telescope Senior Project Scientist, made a prediction, joking that since the first two spacewalks, which were considered to be straightforward, had run into issues, the most difficult EVA – to repair the ACS, would be the smoothest one of the mission.