have main engine start, four, three, two, one and liftoff, liftoff of the 25th space shuttle mission and it has cleared the tower. >> but we also remember the dangers and sacrifices. apollo 1, the challenger and columbia. president obama unveils the next step. a new focus later this afternoon. we want to talk more about nasa's future and the past. in dallas, maryanne webber. she flew two shuttle missions and she's in arlington, vermont. space historian and journalist. roger hannaberg. let's go ahead, mary ellen and start with you, 297 orbits around the earth. just for a moment tell us all what that feels like. what goes through your mind? what you observe, what you remember the most? >> spaceflight is an incredible, incredible, indescribable experience. it's overwhelming what it takes