1.   The astronauts are conducting a series of experiments to learn more about how the body adapts to weightlessness.

2.   American astronauts generally conduct spacewalks within the open bay of the Space Shuttle.

3.   And the astronauts will conduct a six-hour space walk to test suits, tools and tasks for the building of the ambitious international space station.

4.   A second spacewalk was to begin late Friday, this one conducted by astronauts Greg Harbaugh and Joe Tanner.

5.   Meanwhile Thursday, Columbia astronauts conducted a flame propagation experiment in which electrical current was used to ignite small drops of fuel in a protective enclosure.

6.   The astronauts are also conducting experiments in combustion as part of an effort to develop a fire detection system for the planned international space station.

7.   The idea is for Russian astronauts to conduct an internal space walk.

8.   To help the engineers perfect their computer models, the astronauts conducted a series of precise tests early Saturday morning in which jets were fired one at a time.

9.   When American astronauts conduct space walks, they generally do so within the open bay of the space shuttle.

10.   During the mission, the astronauts conducted four spacewalks on four successive days.