Space shuttle Columbia and its crew sailed through a clear dawn sky and landed with the heaviest scientific load ever Sunday, clearing the way for NASA’s next mission in just six days.

It was, at 16 days, the second-longest flight in shuttle history, just one-half day short of the record.

Columbia’s laboratory-research mission was all about learning how to use the international space station, once it’s built. The next shuttle flight will focus on station assembly.

Atlantis is scheduled to blast off Saturday on the second docking mission with the Russian space station Mir.

There will be no crew swap this time. Rather, the shuttle will take up a docking tunnel, food, water and other supplies for the cosmonauts; the Atlantis crew will attach the tunnel to Mir for future shuttle dockings. It will be the first time a shuttle has ever performed station-building tasks.