By Jonathan Amos
Science reporter, BBC News, Kennedy Space Center
Nasa is continuing with preparations to launch the Atlantis shuttle despite concerns about the weather.
The shuttle seems to be past its recent technical woes
The orbiter is due to loft Europe's Columbus laboratory to the International Space Station (ISS).
Low cloud and showers are likely to force a delay but mission managers say they only need conditions to lift for a few minutes to make a launch possible.
The good news for Nasa is that the technical problems the shuttle has had of late appear to have been fixed.
In a number of recent launch attempts, the engine cut-off, or Eco, sensors have sporadically given out readings indicating orbiter fuel tanks are dry even when they have just been topped off with propellant.
Mission managers ordered that the problems be resolved after the glitch reappeared during December's aborted attempts to get Columbus away.
The replacement of electrical connections seemed to have worked on Thursday when Atlantis' giant tank was filled in the early morning and the Eco-sensors gave the correct "wet" readings.
The seven-man crew was then suited up to take their seats in the orbiter, with the planned lift-off timed for the middle of a 10-minute window running from 1440 to 1450 EST (1940 to 1950 GMT).
Columbus is Europe's main contribution to the scientific endeavours of the space station project.
Once the 1.3bn-euro ($1.8bn; £0.9) module is in place, an intensive programme of research in weightless surroundings will begin.
The scientific studies will impact diverse fields, from crop breeding to the development of advanced alloys.
The experiments will also help researchers better understand the physiological demands of long-duration spaceflight, something that will be important if humans are ever to colonise the Moon or travel to Mars.
Total length - 6.8m
Diameter - 4.5m
Volume - 75 cu m
Launch mass - 12.8t
Operation - 3 crew
Cabin temp - 16-27C
Total power - 20kW
Columbus will be installed on Day Four of the mission.
The 7m-long (24ft), 4.5m-wide (14ft), 12.8-tonne laboratory will be manoeuvred into position by the shuttle's robotic arm, and docked to the station's Harmony Node 2 connector.
Hans Schlegel, the German Esa astronaut on the flight, will play a key role in this process, carrying out two spacewalks to get the job done.
Esa colleague Leopold Eyharts will be staying on the station to commission Columbus, a process that should take a few weeks to complete fully.
Columbus contains a number of science racks. Each is a laboratory in its own right. Experiments in life sciences, physiology and physics can all be carried out within the one structure.
Experimental payloads can also be mounted on the outside of Columbus. On the Atlantis flight, an observatory to study the Sun will be installed, together with a suite of instruments to examine how materials are affected by long exposure to the space environment.
Data from the module will be passed down in real-time through the Columbus control centre, in Oberpfaffenhofen in Germany, to researchers across the globe.
The next few weeks will be among the most significant in the history of the 17-member-state European Space Agency. On 8 March, it will launch its unmanned logistics ship to the space station.
The Automated Transfer Vehicle (ATV) is designed to find its own way to the platform and perform an automatic docking. It can haul up to 7.5 tonnes of supplies to the orbiting outpost.
Eyharts is excited about the coming days. The BBC had a very brief phone conversation with him on Wednesday. He said: "The highlight will be the installation of Columbus and if I'm lucky I will also see the arrival of the French-built ATV. That would be great for me to be present at these two great events for Europe."