HOUSTON -- NASA astronaut Mike Massimino is using Twitter to provide a unique, behind the scenes peek at the last weeks of his training for the fifth and final shuttle servicing mission to NASA's Hubble Space Telescope.

Massimino, whose Twitter username is Astro_Mike (@Astro_Mike), will fly aboard space shuttle Atlantis as a mission specialist and spacewalker during the STS-125 mission, targeted to launch May 12. Atlantis' 11-day flight will include five spacewalks to refurbish and upgrade Hubble with state-of-the-art science instruments. After the astronaut's visit, Hubble's capabilities will be expanded and its lifetime extended through at least 2014.

This will be Massimino's second trip to space. He first flew on the STS-109 mission to Hubble in 2002. During that flight, he performed two spacewalks.

Along with Massimino, the crew of Atlantis includes Commander Scott Altman, Pilot Gregory C. Johnson and Mission Specialists Andrew Feustel, Michael Good, John Grunsfeld and Megan McArthur.

To follow Massimino's Twitter, visit: http://twitter.com/Astro_Mike

Follow NASA mission activities on Twitter @NASA, and for a complete list of all agency missions on Twitter, visit: http://www.nasa.gov/collaborate

For information about the STS-125 mission and its crew, visit: http://www.nasa.gov/shuttle