After its successful landing, Phoenix has already started its duty. The lander returned information that it was in good health after its first night on Mars, and the team sent the spacecraft its to-do list for the day.

Mission scientists are eager to move Phoenix's robotic arm, for that arm will deliver samples of icy terrain to their instruments made to study this unexplored Martian environment.

The team sent commands for moving the arm on Tuesday morning, May 27, to NASA's Mars Reconnaissance Orbiter for relay to Phoenix. However, the orbiter did not relay those commands to the lander, so arm movement and other activities are now planned for Wednesday. The orbiter's communication-relay system is in a standby mode.

During its mission, Phoenix will use various tools in order to accomplish its tasks. The Robotic Arm will allow Phoenix to explore vertically and to use instruments on the spacecraft deck to analyze samples of Martian soil and ice. The arm will dig trenches, posi­tion arm-mounted tools for studying the soil in place, and deliver scooped-up samples to other instruments.

The aluminum and titanium arm is 2.35 meters (7.7 feet) long. One end is attached to the lander’s deck. An elbow joint is in the middle. The other end has a scoop with blades for dig­ging into the soil and a powered rasp for breaking up frozen soil. The arm moves like a back­hoe, using four types of motion: up-and-down, side-to-side, back-and-forth and rotating.

The arm can reach far enough to dig about half a meter (20 inches) deep. However, the sub­surface ice layer expected at the landing site may not lie that deep. Researchers anticipate that the icy-soil layer will be about as hard as concrete. Once the excavation by the arm reaches that layer, the powered rasp on the bottom of the scoop will be used to generate enough loose material for a sample. The favored work area for the arm will be on the north side of the lander because the soil on that side will be in the shade of the lander during midday work hours, when the sun is in the southern part of the sky. The advantage of having shade on the work area in mid-day is to minimize vaporization of exposed ice.

The Robotic Arm Camera rides fastened to the arm just above the scoop. It will provide close-up color images of Martian soil at the landing site, of the floor and walls of trenches dug by the arm, and of soil and ice samples before and after they are in the scoop.

With a resolution of 23 microns per pixel at the closest focus, this camera can show details much finer than the width of a human hair. For comparison, the microscopic imager cameras on Mars rovers Spirit and Opportunity resolve features on scale of hundreds of microns.

Following today's commands, its movements will begin with unlatching the wrist, then moving the arm upwards in a stair-step manner.

A covering that had shielded the arm from microbes during its last few months before launch had not fully retracted on landing day, May 25, but it moved farther from the arm during the following day.

"The biobarrier had relaxed more and allows more clearance, but it was not a major concern either way," said Fuk Li, manager of the Mars Exploration Program at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Commands to be sent to the lander Wednesday morning also include taking more pictures of the surroundings.