It's not just the Discovery shuttle's six human astronauts who face an extra three-week wait to get into orbit. Their mechanical passenger is clenching his fists in frustration, also

Nasa has big plans for R2 but first the humanoid robot has to "earn its stripes"

Packed in a box in the back of the orbiter is R2, the first human-like robot to be sent into space.

The robonaut is the product of 15 years' research in Nasa and General Motors.

In his current guise, he is just a head, arms, and a torso mounted on a pedestal. But the plan eventually is to give R2 some legs to let him move around the station. And in a couple of years, he'll also get a body upgrade that should significantly advance his capabilities.

The expectation is that before the decade is out, this robot will be clambering about on the outside of the space station, assisting astronauts on a spacewalk.

How realistic the computer graphics of this prospect really are, I don't know. The video artist clearly was a fan of the Boba Fett bounty-hunter from Star Wars. The visors are uncannily similar.

But, anyway - first things first. In R2's initial year in orbit, he will be confined to the station's Destiny lab, working away at a taskboard placed in front of him.

He has to demonstrate the full range of his dextrous capabilities, picking up and moving items, throwing latches and switches, and handling soft materials like cloth that have traditionally been problematic for robotic systems.

R2 also has to prove he is safe to have around. Rob Ambrose is the acting chief of the automation, simulation and robotics division in the engineering department at Nasa's Johnson Space Center:

"Superficially R2 is soft, padded and safe. Mechanically it is soft as well with springs. But deeper than that, it has three levels of electrical sensors and software, which can in each of the three levels identify forces that are being felt by the robot and decide if those forces are safe or not and stop the robot, if necessary. Those three levels of safety were essential in convincing our payload safety review panel that this robot would be safe to work adjacent to astronauts inside the space station."

You've probably seen pictures of astronauts in the weightless surroundings of the station picking up fridge-sized metal boxes and moving them around as if they're made of cardboard.

They're not, of course; and a 100kg of box can do a quite a bit of harm if it's not handled properly. R2's behaviour has to be predictable but sufficiently reactive that he doesn't persist with a task where to do so might result in the robot damaging equipment or, worse still, crushing an astronaut.

On the ground, you see this reactive behaviour when someone walks into the robot's path. If his arms collide with an unexpected object, they immediately pause - they don't keep pushing regardless of the obstruction. But that's on Earth; how will these types of systems really work in space where the gravity loads are so different?

R2 will help engineers understand this sort of thing.

Certainly, the future looks bright for human-like robots. They will not only work alongside astronauts as humans push out across the Solar System, it is highly likely they will lead the way.

Who'd like to bet the first thing with two legs to walk on Mars will be mechanical, not human?

And, surely, that's particularly true of the more hostile locations one would eventually want to visit, like those fascinating moons of Jupiter and Saturn.

We wouldn't risk sending a human down to the surface of Europa with its unbelievably harsh radiation environment; we'd send a robot with legs to climb over the ice boulders and to use its dextrous hands to pick objects of interest. Rob Ambrose again:

"There are really three phases of exploration. The first phase is where the robots are really out ahead of the humans. The second phase is when the humans are at the same site as the robots, working alongside them. Typically these two phases will be short - of the order of weeks or months. And then, in between human crews going back to that site or never going back to that site, the robots would be left behind as caretakers, to run longer-term experiments."

Feel free to recall you favourite sci-fi robots. I still have a major soft spot for Huey, Dewey and Louie from Silent Running. I think that's because I have dogs and those little guys were like Bruce Dern's pets. Humans project personalities on to animals and objects. That's what we do. It will be no different for robots in space.

"At this point we have no plans for R2 to come back to Earth. I can't say what the future will hold. It may ride the station into the Pacific, but we don't know where station might go someday. That chapter in robonaut's life has not been written yet. We might take R2 beyond low-Earth. It's got to earn its stripes first."

R2 is currently discovering the frustration all humans have got used to with shuttle launches - delays due to technical glitches. Clive Simpson, the editor of Spaceflight magazine, is one of many who've been waiting around at Kennedy this week for Discovery to get off the ground.

He found R2's "brother" trying to pass the time and sent me a picture.