they successfully completed the mission's main objective, delivering and installing a special particle detector for the international space station. its 600 computer processors will help scientists from 16 countries try to understand the origin of the universe by searching for wild sounding things like anti-matter, dark matter, and cosmic rays. this is shuttle "endeavour's" final mission of course. it will go to a museum when it lands. i spoke to the crew about what for most of them will be their last time in space. >> as you begin to prepare to come home and you look down i am tempted to ask knowing that this is your last shuttle mission, like a vacation to the grand canyon, are you tempted to call down and say can we extend the rental a little bit? >> john, these missions are really complex. there is a lot of risk and we develop a plan way ahead of time. yeah it would be nice to have an additional day in space to look down at our beautiful planet and enjoy zero gravity. but tomorrow is the right time