WASHINGTON -- A privately-owned unmanned U.S. space capsule docked Sunday at the International Space Station bringing food, scientific materials and crucial equipment to the space outpost.

NASA said that SpaceX's Dragon capsule linked up with the ISS's Harmony module at 8:56 a.m.

The U.S. space agency said a hatch between Dragon and the ISS's Harmony module would be opened Monday as the capsule commenced its three-week-long stay at the orbiting space station.

"It's a critical achievement that we once again have a U.S. capability to transport science to and from the International Space Station," said William Gerstenmaier, NASA's associate administrator for the human exploration and operations directorate.

He added that the experiments "carry the promise of discoveries that benefit Earth and dramatically increase our understanding of how humans adapt to space."

Dragon was captured with the help of a robotic arm by NASA Expedition 34 Commander Kevin Ford and Flight Engineer Tom Marshburn, at 5:31 a.m., when the ISS was over northern Ukraine, U.S. space officials said.

The craft, after being inspected via cameras, was brought to the Earth-facing port of the Harmony module and bolted into place by commands from mission control.

The original plan had been for Dragon to attach to the space station on Saturday, but the capsule ran into troubles with its thrusters shortly after Friday's launch from Cape Canaveral, Fla., triggering the delay.

SpaceX engineers found that only one of the spacecraft's four thruster pods, which help maneuver the capsule in orbit, was working, but the malfunction was fixed.

The snafu has not delayed the capsule's splashdown, which remains scheduled for March 25, NASA said.

Dragon is carrying 1,200 pounds of supplies on SpaceX's second resupply mission to the ISS.

Scientists said the capsule will go home much heavier than it arrived, after the ISS offloads equipment from several experiments. Dragon is scheduled to bring home nearly double the amount of supplies it brought up, about 2,668 pounds.

One of the experiments is designed to study molecular changes to a small flowering plant called thale cress in microgravity. A related study examines how the plants' root hold up in low-oxygen environments.

NASA said that the experiments "will improve efforts aimed at growing food in space -- a crucial component of long-duration missions to Mars or elsewhere in the solar system. It can also inform crop production here on Earth."