Spacewalkers Rex Walheim and Stanley Love floated out of the hatch as the space station passed over the Pacific Ocean west of southern Chile.
Walheim and Love were scheduled to spend about 6½ hours installing the experiments, retrieving an old space station gyroscope and, if there's time, examining a tiny chip on a handrail near the spacewalk hatch and a jammed solar rotary joint.
Station commander Peggy Whitson helped Walheim and Love don their spacesuits, moving so quickly the duo was left with a half-hour break before they could start the final tasks to get them out the door. Whitson suggested they take a nap.
"There's no napping in spaceflight!" Walheim quipped.
The astronauts awoke Friday to a song by German Drafi Deutscher, "Marmor,Stein Und Eisen Bricht," whose title translates to English as "Marble Breaks and Iron Bends." German astronaut Hans Schlegel said the tune, popular in his youth, talks about finding one great love.
"I'm very fortunate that I found that in my wife, Heike," he said.
One of the pieces of equipment that Walheim and Love will install is an observatory to monitor the sun. The SOLAR payload consists of three instruments designed to measure the solar spectral irradiance throughout virtually the entire electromagnetic spectrum, from 17 nm to 100 μm, in which 99% of solar energy is emitted.
The crew will also will use the robotic arm to install the European Technology Exposure Facility, or EuTEF, a facility that will allow scientists to carry out several experiments requiring exposure to the uniquely harsh environment of space.
Once those are attached to Columbus and the gyroscope is stowed in the shuttle's cargo bay, the spacewalkers hope to turn their attention to two trouble spots on the station.
The chip - discovered by Love during Monday's spacewalk and thus dubbed Love Crater - is the apparent result of a micrometeorite strike. It may be where spacewalking astronauts have torn their gloves over the past year or so. To find out, Walheim and Love will run a spare glove over the hole to see if the material snags.
The pair also hopes to have time to inspect the rotary joint, which is needed to turn one of the space station's two sets of huge solar wings. Spacewalkers have peered inside several times since the joint broke last fall, but NASA is still trying to determine what is causing the metal parts to grind, clogging the joint with shavings.
While the spacewalkers are outside, other crew members will continue working inside Columbus to get the lab ready to produce science in the coming days.
Atlantis is scheduled to undock from the space station on Monday and land in Florida on Wednesday.
For more information, visit the STS-122 mission page on the NASA Web site: www.nasa.gov