The crew of the Space Shuttle Endeavour is carrying some special cargo during its two-week mission at the international space station.

When the space shuttle launched from the Kennedy Space Center Nov. 14, it included signatures from the students at Knox Elementary. The school participated in the Student Signatures in Space (S3) program, jointly sponsored by NASA and Lockheed Martin.

Last May, students at Knox joined more than 500,000 other students from around the world in signing giant Space Day posters. Those signatures were downloaded onto a disc and given to the crew to fly onboard the shuttle this week.

“From an educational standpoint, we are very pleased that STS-126 is the mission that will be carrying our students’ signatures,” said Barbara Reinike, Space Day program manager for Lockheed Martin. “It’s an exciting mission that is sure to pique students’ interest as they follow the travels of their signatures.”

Throughout the 15-day mission, Knox students have been learning about mission activities and the space program in general and will demonstrate how learning science and math can help them prepare for future roles in America’s space program.

Astronauts at the international space station prepared to work on a urine-recycling contraption and re-fire the space shuttle’s thrusters Friday before enjoying a half-day off to reboost their own energy.

Endeavour’s extra push will elevate the docked space shuttle and space station complex about a mile (1.6 kilometers). Endeavour starts heading back to Earth on Thanksgiving. The space station generally stays in the range of 200 to 220 miles (321 to 354 kilometers) 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.

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.

“These are the growing pains we expect to see,” said flight director Ginger Kerrick. “These are very complicated pieces of equipment with very complicated software to control them.”

The astronauts were going to delay the urine test until flight controllers figure out what’s wrong, but they planned to test another part of the system that purifies water. Samples from the recycling system will need to be analyzed on Earth before station crew members can use the machine 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.

“The (carbon dioxide) level never got to a level that we would have been concerned that it would cause him any problems,” said John Ray, lead spacewalk officer. “We were just managing it to make sure we got him inside before it got to that level, and we did.”