Atlantis, which will carry the European space laboratory Columbus to the International Space Station, had been set for takeoff December 6 but was eventually delayed until indefinitely after several scrapped launches blamed on the failing fuel sensors.

Known as Engine Cut-Off (ECO) sensors, the instruments sit on the bottom of Atlantis' 15-story external tank and serve as liquid hydrogen fuel gauges that ensure a shuttle's three main engines shut down before their hydrogen supply runs dry after liftoff.

Last week, John Shannon, deputy manager for the Space Shuttle Program, said that the launch schedule depends on test results and modifications to a fuel sensor system connector on the external fuel tank Atlantis will use for launch on its STS-122 mission.

Atlantis will carry the European-developed Columbus laboratory and attach it to the International Space Station.

Columbus is about 23 feet long and 15 feet wide, allowing it to hold 10 "racks" of experiments, each approximately the size of a phone booth. Five NASA racks will be added to the laboratory once it is in orbit. Each rack provides independent controls for power and cooling, as well as communication links to earthbound controllers and researchers. These links will allow scientists all over Europe to participate in their own experiments in space from several user centers and, in some cases, even from their own work locations.

The reschedule of Atlantis’s mission will affect also the launch of STS-123. Initially the mission STS-123 on space shuttle Endeavour should deliver the pressurized section of the Kibo (Hope) Japanese Experiment Logistics Module (ELM-PS) was scheduled for February. But now, on NASA website STS123’s launch date is listed as “Under Review”