Call him @Astro_Mike. That's the latest digital moniker of NASA astronaut Michael Massimino, who has invited the world to tag along via the Twitter micro-blogging Web site as he trains for a May space shuttle mission to overhaul the Hubble Space Telescope.

Massimino, a veteran spacewalker and Hubble repairman, is set to make his second trip to the iconic orbital observatory when he and six other astronauts launch toward Hubble on May 12 aboard NASA's space shuttle Atlantis. The risky 11-day mission will include five spacewalks and expected to extend Hubble's lifetime through at least 2014.

Twitter allows users to post 140-character notes about their current thoughts and actions and to track the posts of others who do the same. NASA has been using the social networking site to reach out to a Web-savvy public and promote various space science and mission efforts.

According to Massimino's latest "tweet," he is currently embroiled "in a simulator practicing for the first spacewalk on my mission."

"He just started on Friday," NASA spokesperson James Hartsfield told SPACE.com from the Johnson Space Center in Houston. "He has always been looking for good ways of connecting with the public and telling the stories of what they're doing."

Massimino is a veteran of two spacewalks, both of which he performed during his first flight to Hubble during a 2002 service call. He will perform two of the five planned spacewalks during the upcoming STS-125 shuttle flight to add new instruments, replace batteries and gyroscopes, attach a docking ring for future robotic vehicles and make unprecedented repairs to systems that were never designed to be fixed in space.

The mission is riskier than recent NASA shuttle missions because it is not bound for the International Space Station, where astronauts can take refuge if their orbiter suffers critical damage. Because Hubble flies in a higher orbit and different inclination than the station, Atlantis will not be able to reach the orbiting laboratory to ferry its crew to a safe haven. Instead, NASA will have a second space shuttle on a Florida launch pad ready to launch a rescue mission, if required.

Massimino is using a mobile device to update his Twitter messages and is currently the only NASA astronaut to use the online tool for official space agency business, Hartsfield said. The space agency has a general, agency-wide NASA Twitter account and uses the tool to spread updates for many ongoing missions and other probes that have not yet launched into space.

"Social media is a large and growing sector of communications," Hartsfield said. "So this is a very neat thing and it offers Mike a chance to connect with the public."

Hartsfield cautioned Massimino's Twitter followers to be patient, especially as his mission's launch date draws near.

"Of course, training keeps him very busy," Hartsfield said. "So we'll see how much he can update."

Click here to follow Massimino's Twitter updates.

Copyright © 2009 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.