Late Thursday, flight director Ginger Kerrick described the hang-ups as "growing pains."
"There are very complicated pieces of equipment with very complicated software to control them," she said.
Endeavour's extra push, meanwhile, elevated the docked space shuttle and space station complex about a mile. That puts the space station at the right altitude to receive a Russian Progress spaceship scheduled to deliver cargo to the orbiting outpost three days after Endeavour starts heading back to Earth on Thanksgiving.
The space station generally stays in the range of 200 to 220 miles above Earth.
Endeavour's seven astronauts and the three space station crew members have been working without a break since the space shuttle launched from Florida a week ago. Mission Control gave them the afternoon off Friday.
Endeavour's astronauts delivered the recycling system to the space station last weekend and, with help from the space station crew, have been trying to get it up and running.
The astronauts had hoped to run a test batch of urine through the contraption Thursday, but a caution alarm usually caused by combustion delayed those plans. Flight controllers believe it was a false alarm because they didn't notice smoke or a combustible odor.
NASA wants samples from the recycling system returned to Earth for analysis before giving the go-ahead for the space station astronauts to drink it. That's not supposed to happen until sometime next year. Once running, the system will help the space station support six residents instead of the current three inhabitants.
Just as the alarm on the urine recycling system went off inside the space station Thursday evening, two spacewalkers wrapped up a nearly seven-hour spacewalk outside.
To everyone's relief, Heidemarie Stefanyshyn-Piper and Shane Kimbrough deftly stepped through their work without any mishaps.
During Tuesday's spacewalk, Stefanyshyn-Piper's tool bag slipped away while she was trying to clean grease leaked from a gun used to lubricate a jammed solar wing joint outside the space station.
There were two small hitches at the very end of Thursday's spacewalk: Kimbrough had trouble communicating with Mission Control and also had elevated levels of carbon dioxide in his spacesuit.
Neither problem put the astronaut in danger. The communication problem was likely caused by a bump to his headset's volume control.
