'Discovery' finally enjoys a day of good news

Two of Discovery's astronauts replaced one of the space station's four control moment gyroscopes, or CMGs, which are used to orient the station yesterday. The ISS can run on two gyroscopes, but using all four will permit the addition of new modules and trusses in the future. The broken gyroscope failed in 2002, just a few months before Columbia's mission.

The astronauts are expected to conduct another space walk tomorrow, to fix a new problem on the surface of the space shuttle itself. Two small pieces of material have poked out in between the thermal tiles that protect the craft from the intense heat of re-entry into the Earth's atmosphere.

A decision must be made whether to cut these pieces of material, yank them out or try to poke them back inside, a bit like repairing a hernia. This new problem follows reports of tile damage at take-off. The tile problems, along with other hitches that delayed Discovery's lift-off, prompted Nasa to suspend future shuttle flights indefinitely.