Over the next three weeks or so, the station crew will unload a half ton of equipment and supplies, including experiment hardware, a freezer, spare parts, clothing and food. Taking advantage of the freezer, ice cream was included, a rare treat for space crews.

As the capsule is unloaded, the astronauts plan to stow nearly a ton of no-longer needed gear, failed components and experiment samples that, until now, have had no way to get back to Earth. Again using the robot arm, Williams and Hoshide plan to unberth the capsule Oct. 28 for re-entry and splashdown in the Pacific Ocean off the southern coast of California where recovery crews will be standing by.

The Russian Soyuz spacecraft that ferry crews to and from the space station can only carry a few hundred pounds of small items back to Earth. All other station vehicles -- unmanned Russian Progress supply ships and European and Japanese cargo craft -- burn up during re-entry.

"The SpaceX Dragon is a really important vehicle for us because it supports the laboratory use of ISS, both in bringing cargo up to the space station and in bringing research samples home," said Julie Robinson, the space station program scientist at NASA Headquarters.

"It has a great return capability, it essentially replaces that capacity that we lost when the shuttle retired so that now we'll be able to bring home a wide variety of biological samples, physical sciences samples and we'll be able to bring home research equipment that we need to refurbish and then relaunch again."

Scott Smith, a nutritionist at the Johnson Space Center in Houston, will be eagerly awaiting crew urine samples for on-going medical research on how the body adapts to weightlessness.

"We have not brought any samples back since the last shuttle flight," he told reporters Saturday. "When NASA knew the shuttle was going to retire, we actually flew extra freezers to the space station to hold those samples so the crews could continue to collect samples on orbit knowing we would bring them back when we had the chance.

"The novelty at this point of SpaceX is this is the first real return vehicle for these type of samples. Obviously, we can get the crew home on the Soyuz, but the cargo capability of the Soyuz is extremely limited. So this is our first set of samples that will come back."

Anticipating the shuttle's retirement, NASA announced a new program, Commercial Orbital Transportation Services, or COTS, in 2006 that called for development of new unmanned cargo craft that would be procured by the government on a commercial basis. NASA eventually awarded two major contracts.

Orbital Sciences of MacLean, VA, holds a contract valued at $1.9 billion for eight cargo flights to the station. Another $288 million was budgeted for development and at least one test flight. An initial demonstration mission is expected early next year.

SpaceX holds a $1.6 billion contract with NASA to provide 12 cargo flights to the station for delivery of more than 44,000 pounds of equipment and supplies. The company originally planned three test flights under a separate contract valued at up to $396 million.