The astronauts were on schedule to wrap up by day's end Friday after replacing batteries in one of the Hubble Space Telescope's bays. STS-125 mission specialists Mike Good and Mike Massimino began the nearly 7-hour spacewalk just before 9 a.m. Massimino and six other astronauts launched Monday on an 11-day mission to service and repair the Hubble so it can work through 2014 or longer.
They spent Friday disconnecting and reconnecting electrical parts, unscrewing and screwing bolts, and swapping batteries -- all while recharging their oxygen levels and maneuvering in a zero-gravity environment. Each of the two battery modules weighs 460 pounds.
Each module contains three batteries that power the Hubble's night operations. NASA said that the second battery module will be installed during the fifth and final spacewalk.
For their first spacewalk, the two astronauts replaced the Hubble's three rate sensing units, which allow a rate gyro assembly to sense vehicle motion and provide data that enables the telescope to make science observations.
Massimo said in posts earlier this week that he was enjoying the magnificent views in space. Massimo's message appeared on NASA's Twitter feed. When he was training, Massimino began "tweeting" in early April. He now has a following of more than 247,000 people on Twitter.
While in space, Massimino e-mails the Johnson Space Center, which then posts the notes to Twitter. The astronauts can send e-mail once or twice a day, but they don't have Internet access.
Massimino's first tweet from orbit read, "Launch was awesome!! I am feeling great, working hard, & enjoying the magnificent views, the adventure of a lifetime has begun!"
Mark Polansky, who will command the next shuttle flight, also has begun tweeting while he and his crew prepare for the STS-127 mission to the International Space Station in June.
InformationWeek will be highlighting innovative government IT organizations in an upcoming issue. Nominate your agency by submitting an essay on your most innovative IT initiative completed in the last year. Find out more, and nominate your organization -- deadline extended to May 15.