Endeavour commander Mark Kelly, center, leads the way as the shuttle crew floats aboard the International Space Station. Photo Credit/NASA TV

The Endeavour astronauts successfully docked with the International Space Station early Wednesday, uniting 12 NASA, Russian and European Space Agency astronauts aboard the two spacecraft for a marathon session of scientific outfitting, cargo exchanges and spacewalks.

Shuttle commander Mark Kelly maneuvered the shuttle into the station’s docking port at 6:14 a.m., EDT.

Aboard the station, European Space Agency astronaut Paolo Nespoli sounded a ship’s bell and declared, “Endeavour arriving.”

“Welcome, welcome,” station commander Dmitry Kondratyev greeted the visitors, as hatches between the two spacecraft opened more than an hour after the linkup.

The two spacecraft sailed 220 miles over the Eastern Pacific on a northeasterly course off the Chilean coast as they docked.

Endeavour closes for a docking with the space station. Photo Credit/NASA TV

Prior to the linkup, Kelly halted Endeavour’s approach at 600 feet below the station for a slow back flip maneuver that permitted three of the space station’s crew to extensively photograph the shuttle’s underside heat shielding with cameras and telephoto lenses. The photos were transmitted to NASA’s Mission Control Center for examination by imagery analysis experts.

Kelly, Endeavour pilot Greg H. Johnson, Mike Fincke, Drew Feustel, Greg Chamitoff and Roberto Vittori of the European Space Agency lifted off on Monday to begin a 16-day mission. The mission is Endeavour’s 25th and final flight, the 12th to the station.

The shuttle is scheduled to remain docked to the station for 12 days.

The shuttle crew joins Kondratyev, Nespoli, Catherine Coleman, Ron Garan, Andrey Borisenko and Alexander Samokutyaev.

As the first task in the long visit, Vittori, Feustel, Johnson and Chamitoff were to use the shuttle and station robot arms to hoist the Express Logistics Carrier-3 from Endeavour’s cargo bay and attach the platform to the orbiting science laboratory. The ELC-3 holds critical spare parts for the station’s thermal control, communications, electrical and robotic systems.

Endeavour’s primary payload, the Alpha Magnetic Spectrometer, a $2 billion particle physics experiment, will be moved to the station using similar robot operations on Thursday. The AMS is the centerpiece of a decade long effort to search for and characterize primordial antimatter, dark matter and other high energy cosmic particles.

Feustel, Fincke and Chamitoff  will begin a series of four spacewalks early Friday. Working in pairs, the astronauts will retrieve and deploy science experiments and carry out a long list of maintenance tasks.

Endeavour’s return to Earth is scheduled for June 1.