The last U.S. space shuttle departed the International Space Station on Tuesday, ending a 12-year program to build and service the orbital outpost, the primary legacy of NASA's shuttle fleet.

Shuttle Atlantis commander Chris Ferguson and pilot Doug Hurley gently pulsed their spaceship's steering jets at 2:28 a.m. EDT to pull away from the station as they sailed about 250 miles over the Pacific Ocean.

"Thanks so much for hosting us," Ferguson radioed to the station crew. "It's been an absolute pleasure."

"We'll miss you guys," replied station flight engineer Ron Garan. "See you back on Earth."

Flight controllers at NASA's Mission Control Center sat in reverent silence as they watched the last shuttle pulling away from the station, a $100 billion project of 16 countries that has been assembled and serviced during 37 of NASA's 135 shuttle missions.

During their nine-day visit to the station, Ferguson and his crew delivered more than 5 tons of food, clothing, equipment and science experiments, a stockpile intended to bridge a potential year-long gap in U.S. cargo runs to the station.

Atlantis' return to Earth, scheduled for Thursday, will conclude the 30-year-old U.S. space shuttle program, with no replacement U.S. spaceships ready to fly.

NASA has hired two private firms, Space Exploration Technologies and Orbital Sciences Corp., to resupply the station beginning next year. Russia, Europe and Japan also fly freighters to the station.

Astronauts will fly aboard Russian Soyuz capsules at a cost of more than $50 million per person, until and unless U.S. companies are able to offer similar transportation services. Several firms, including Boeing, Space Exploration Technologies and Sierra Nevada Corp. are developing passenger spaceships, but none are expected to be ready until about 2015.

The first U.S. space taxi to reach the station will return home with a prize. In an emotional farewell ceremony Monday, Ferguson presented the station crew with a small American flag that flew during the April 1981 debut flight of sistership Columbia.

The flag was mounted on the vestibule wall of the compartment that leads to the shuttle's now-obsolete docking port. It is promised to the first U.S. company that flies astronauts to the station.

NASA wants to refly the flag aboard the first of its planned spaceships that are designed to carry astronauts to asteroids, the moon and other destinations beyond the station, where the shuttles cannot go.

Before leaving the station's orbit, Hurley slowly circled halfway around the outpost, which had been repositioned to give the shuttle crew an unprecedented sideways perspective, showing four attached Russian ships, a string of laboratory modules and an edge-on view of the station's golden solar panel wings that span the length of a football field.

After about 90 minutes, the Atlantis crew broke formation and slipped off into an orbital sunset east of Australia to begin the two-day trip back to Earth.

"Get her home safely and enjoy the last couple of days in space shuttle Atlantis," astronaut Dan Tani radioed to the crew from Mission Control.

Atlantis is due back at the Kennedy Space Center at 5:57 a.m. EDT Thursday.