no one is more eager for a mission's success than astrophysicist albert ruben. >> if you see the screen behind me, this is one of our most recent observations with hubble. >> reporter: the bird's next nibula, 27,000 years away may hold clues to a fundamental history. four years ago a crucial hubble ultraviolet camera suddenly broke. now over the last few days, astronauts are to install another. >> now, assuming it gets fixed, we have another chance. >> reporter: astronomers can keep looking on the mystery. space walking astronauts spent six hours on their 350-mile today. replacing a camera with a new one, it's 30 times more powerful the first of eight new pieces of research gear for the telescope. after a seven hour space walk today astronauts buttoned up the hubble space telescope. the last time humans will touch it. scientists today were afusive in their praise. >> they are putting their lives on the line to making these instruments work. clearly it's important to them, it's important to the academic community, the scientific community and it's important to every day person. >> report