As NASA prepares for Curiosity rover landing on Mars, William Shatner shares this thrilling story of NASA's hardest planetary science mission to date. The video titled, "Grand Entrance," guides viewers from entry through descent, and after landing.Watch Curiosity's Landing!Aug 5, 2012 10:31 p.m. PacificAug 6, 2012 1:31 a.m. EasternAug 6, 2012 5:31 a.m. UniversalAs of this post:Countdown to landing:3 days : 8 hrs : 59 mins : 19 secsWatch NASA TV Show OnlineBegins Aug 5: 20128:30 p.m. Pacific11:30 p.m. Eastern