Astronaut Susan Helms and Cosmonaut Yury Usachev were the first crew members to enter the station as they opened the first of five station hatches at 7:03 p.m. CDT Monday.

Helms and Usachev then opened the hatch into the station's Unity connecting module a half-hour later and were quickly joined by Astronaut Jim Voss. Voss, Helms and Usachev are scheduled to live aboard the station for more than four months next year as the second resident station crew.

Helms and Usachev next entered the Zarya module at 7:53 p.m. CDT and opened the final station hatch, accessing Zarya's main compartment, at 7:58 p.m.

The crew went to work in the modules immediately, placing ducting throughout the station to improve air circulation and prevent problems with stale air that were experienced during a mission last year.

Because of problems reported by the crew of that previous mission, STS-96 in May 1999, the ducting was modified for this flight and Atlantis' crew has reported no problems with air ! circulation.

Maintaining a pace hours ahead of schedule, Helms and Usachev replaced two of six batteries in the Zarya module along with some associated battery-charging electronics. Two additional fresh batteries will be installed on successive days of the mission.

This morning, station controllers in Moscow have begun charging the first of the two newly installed batteries, finding it functioning perfectly thus far. The crew also installed three fresh fire extinguishers in Zarya, replacing three that were nearing the end of their design life.

Inside the Unity module, Pilot Scott Horowitz and Mission Specialist Jim Voss replaced a power distribution box for a United States-built communications system. The crew also inspected the station for signs of condensation or mold, finding all areas clean and dry.

Aboard Atlantis, Mission Specialist Mary Ellen Weber readied more than a ton of supplies -- ranging from sewing kits and trash bags to an exercise treadmill and IMAX film camera -- for transfer to the station beginning this evening.

The crew also began filling several water containers that will be left aboard the station as well to await future resident station astronauts.

The crew will begin a sleep period at 7:41 a.m. CDT and awaken for Day 6 of the mission at 3:41 p.m. CDT. This evening, Commander Jim Halsell will fire Atlantis' steering jets 27 times over an hour to boost the average altitude of the station by about nine statute miles.

A similar process will be repeated twice more later in the mission to increase the station's average altitude by a total of about 27 statute miles before Atlantis departs. The higher altitude will aim the International Space Station toward the optimum orbit for a link up with the Russian Zvezda living quarters module planned for launch in July.

The Atlantis and station complex are now in an orbit with a high point of 208 statute miles and a low point of 204 statute miles, circling Earth each 91 minutes. The next status report will be issued at 7 p.m.