The astronaut is sending messages to the social-networking site from 350 miles (563 kilometres) above Earth on the space shuttle Atlantis - and what's cramping his 'tweets' is time, not the character limit.

On Earth, Massimino tweeted about having dinner, eating lunch, working out in the gym and watching a movie. In space, he just doesn't have the time to tweet the routine, if you consider anything on orbit routine.

He averaged about four tweets a day before launch. Now that he's in orbit, it's down to one a day.

Still, Astro_Mike, which is Massimino's Twitter name, did make history.

He's the first person to tweet from space: "From orbit: Launch was awesome!! I am feeling great, working hard, and enjoying the magnificent views, the adventure of a lifetime has begun!"

Massimino's messages, promoted by NASA, are part of the space agency's full-throttle embrace of new social media. There are 36 NASA Twitter accounts, including Massimino's. NASA also has 24 Facebook accounts, 13 YouTube channels, eight Flickr photo accounts, and five MySpace sites.

The Astro_Mike tweets come to Earth indirectly. He sends them in emails to Johnson Space Center in Houston and officials there post them. More than 270,000 people have signed up to follow his tweets.