Spacewalkers hang experiments on Alpha

Dan Barry, with the red bands on his spacesuit legs, hands a MISSE suitcase to fellow spacewalker Pat Forrester.

(CNN) -- Two astronauts on Thursday went on the first spacewalk of shuttle Discovery's mission to the international space station, adding equipment and experiments to the exterior of Alpha.

"We had a very successful spacewalk today," said Scott Bleisath, the lead shuttle extravehicular activity, or EVA, officer.

"As soon as the crew got started -- once they got outside -- they immediately got ahead on the timeline," he said at a post spacewalk briefing.

Mission specialists Dan Barry and Pat Forrester started their spacewalk at 9:58 a.m. EDT. The spacewalk was scheduled to last 6 1/2 hours, but the pair finished in 6 hours and 16 minutes.

Experiments, equipment for Alpha

VIDEO Watch a NASA animation of the installation of the Early Ammonia Servicer on space station Alpha. Play video (QuickTime, Real or Windows Media)   RESOURCES Message Board: Space Exploration   Mission Guide: STS-105

Discovery's robot arm was used to help lift a device called the Early Ammonia Servicer from the shuttle's cargo bay so that it could be bolted to the station by Barry and Forrester. The unit contains spare ammonia for the station's cooling system.

Next, Barry and Forrester snapped on two packages of experiments to the station's Quest module. Called the Materials International Space Station Experiments, or MISSE, the suitcase-like containers were the first experiments to be mounted on the outside of Alpha.

"That went flawlessly, just as we practiced," said shuttle flight director Kelly Beck.

The MISSE containers hold a total of 750 samples of spores, seeds, coatings and other items, including some that were originally flown on the Russian Mir space station. They will be retrieved and returned to Earth in about 18 months, according to William Kinard, a senior research scientist at NASA's Langley Research Center which manages the project.

MISSE samples will be exposed to space for more than a year.

Researchers are flying the samples to get a better understanding of how the items hold up in the harsh space environment.

"These are materials that are planned for use on future spacecraft," Kinard said. "We're getting an opportunity now using the space station as a host to expose these experiments to the space environment and see how they survive and how they perform."

A second set of MISSE samples later will replace the set deployed on Thursday, according to Kinard.

Second spacewalk up in the air

Barry and Forrester are scheduled to take a second spacewalk on Saturday to install handrails and hook up cables for equipment that will be delivered to the station next year. But mission managers may cancel the spacewalk if the crew needs more time to transfer trash and used equipment from the station to the Leonardo cargo module for return to Earth.

"There is still some assessment. Things look promising so far with respect to transfer," said Beck. "We will be getting the final numbers tonight."

She said mission managers would make a decision Friday morning.

A thousand days for Alpha

Alpha commander Frank Culbertson, center, and Russian crewmates Michael Tyurin, left, and Vladimir Dezhurov, float in the Zarya module.

Earlier Thursday, new Alpha commander Frank Culbertson and Russian flight engineers Vladimir Dezhurov and Mikhail Tyurin beamed down a message marking the one-thousandth day in space for the first component of the space station, the Russian-built Zarya module.

"We're here today to wish the international space station some greetings itself because today is the one-thousandth day that the first component of the station has been on orbit ," Culbertson said as he floated in Zarya with Dezhurov and Tyurin.

Zarya was launched on November 20, 1998 on a Proton rocket.

Next month, a new Russian docking module will become the latest addition to Alpha. Russian flight controllers reloaded a software upgrade into the computers of the Zvezda module to prepare for the arrival of the docking port.

The Russians also are preparing to launch a Progress supply ship to the space station on Tuesday. The ship is slated to dock with Alpha on August 23.

Discovery, meanwhile, is scheduled to undock from Alpha on August 20 and land at Kennedy Space Center on August 22 at 12:48 p.m. EDT.