Astronauts 'tweet' from space

Astronauts are giving a behind the scenes look at the space shuttle Atlantis's high-risk mission to service the Hubble telescope, thanks to micro-blogging sensation Twitter.

Mike Massimino, 47, blasted off into space on Monday with six other crew members. But thanks to Twitter, the space veteran is keeping his promise to stay posted, even from space.

"Next stop, Earth Orbit!!" Mr Massimino - whose Twitter account is Astro_Mike and can be found at Twitter.com/Astro_Mike - wrote in his most recent tweet, posted just hours before takeoff.

Mr Massimino, one of the mission's specialists, already has 221,119 followers and had given Twitter updates during training last month in Houston.

The current mission, STS-125, is Mr Massimino's second space flight. He had previously participated in a Hubble maintenance mission in 2002 (STS-109) during which he performed two spacewalks.

The other Atlantis crew members are commander Scott Altman, pilot Gregory Johnson and mission specialists Andrew Feustel, Michael Good, John Grunsfeld and Megan McArthur.

Mark Polansky, who will be the commander of the next planned space shuttle mission to the International Space Station (ISS), is giving updates on Twitter about his training for the scheduled June launch.

He has invited his followers, who currently number 6,051 on Twitter, to submit questions on video website YouTube that he will answer from orbit, according to Nasa.

Polansky's Twitter account is Astro_127 and can be found at Twitter.com/Astro_127.

The Hubble mission is the fifth and last maintenance operation to the telescope before the shuttle fleet is retired. If successful, Nasa has said the fix-up would extend the stargazer's already lengthy life by another five years or longer.

It would be the most audacious rescue in space flight history. The US space agency is preparing a second intrepid shuttle mission it hopes never to launch.

If the Hubble trip turns from scheduled service to orbiting calamity, there will be no escape to the relative safety of the International Space Station, so Nasa plans to send a second shuttle - the Endeavour - and a four-strong crew blasting off to save their Atlantis colleagues.

In this scenario, Endeavour - primed to go with just three-days notice on a launch pad at the Kennedy Space Centre in Cape Canaveral, Florida - races to catch up with Atlantis and recover its stranded crew of seven astronauts.

Nasa fears in a powerless shuttle, astronauts would only last for 25 days before they ran out of air, and so, if difficulty strikes the two vessels would rendezvous at an altitude of some 600 kilometres above the Earth.

After parking their payload bays face to face, like a robotic yoga display, Endeavour would delicately maneuver its 15-metre robotic arm to secure the spacecraft together.

Over the course of two days, with Endeavour astronauts stringing a line between the two shuttles, the Atlantis crew would have to spacewalk from their weakened ship to safety.

Such a scenario, however outlandish, has been planned extensively, insists the National Aeronautics and Space Administration.

"It's safety first, as ever," said Nasa spokesman William Jeffs at Houston's Johnson Space Centre in Texas.

Since Nasa's 2003 disaster that saw the shuttle Columbia disintegrate as it re-entered Earth's atmosphere, killing all seven crew members, the agency has worked on elaborate rescue contingencies.

But all shuttle flights since then have been to the ISS - a secure enough haven where crew members would be able to await passage home.

The daunting journey to the 11-ton Hubble carries considerably more risk of being hit by space debris or micrometeorites than a flight to the ISS, because the telescope orbits at almost twice the height of the ISS.

That is much closer to the largest galactic trash fields that threaten all space visits.

After analysis, Nasa said the risk of catastrophic damage arising from space debris around Hubble to be about a 1-in-229 chance.

And beside space junk, numerous liftoff dangers could still await Atlantis, including thermal tiles on the outer skin being damaged at launch.

Astronauts will make a safety assessment of their vessel before heading to Hubble in the coming days, after which Nasa may deem re-entry too risky.

Endeavour Commander Christopher Ferguson said he and his crew were ready to tackle a rescue if called upon.

"I feel as confident about our ability to pull this off, if need be, as I would any other mission," he told CNN television.

It is the first time a rescue shuttle has been on standby on the launch pad, with its crew idling at the ready.

Mr Ferguson said he understands how every hour can be key, when colleagues are running out of air to breath.

"Consumables like food and oxygen would run out quickly. So the reason we've gotten this crew trained and spooled up and ready to go on literally a moment's notice is because they (the Atlantis crew) have no place comfortable to go stay for a long period of time," he said.