The Phoenix lander, which arrived on Mars on Sunday, was in excellent shape, said project manager Barry Goldstein. He said the communications glitch was only a blip in the robot's three-month exploration of the planet's northern arctic region.

The glitch happened on Tuesday in one of two Nasa satellites circling Mars when a radio shut off before it could relay commands to the lander to get the 8ft arm moving, Mr Goldstein said.

Arm mechanics

The robotic arm was folded on the lander's science deck to protect it from the vibrations of the launch and landing. Before Phoenix can flex its arm, it must rotate its wrist to release the latches on its forearm and elbow and "move it out in a staircase fashion" to remove its protective sleeve, said robotic arm manager Bob Bonitz of Nasa's Jet Propulsion Laboratory.
Controllers sent the instructions yesterday to begin the two-day process. Mr Goldstein said he hoped photos of the partially unfurled arm would be available today.

Phoenix's arm will eventually dig into the soil surrounding it, seeking ice believed to be within inches to a foot below the surface. It is part of the effort to study whether the site could have supported primitive life.

Four joints

The robotic arm has four joints in all - two at the shoulder to allow it to move side to side as well as up and down, an elbow and a wrist, which allows it to move its crucial scoop and digging device.

Phoenix has delighted scientists with the first-ever peek of the planet's northern arctic region since its landing on Sunday on to relatively flat terrain containing few rocks. Twin rovers have been operating near the Martian equator since 2004.