Last Updated 3:06 p.m. ET
Spacewalkers Garrett Reisman and Stephen Bowen successfully mounted a 6-foot-wide dish antenna to an 8-foot-tall support boom atop the International Space Station, but they fell well behind schedule locking the dish in place and getting a balky electrical connector plugged in.
The backup Ku-band antenna was carried to the work site by Garrett, riding on the end of the station's robot arm. He and Bowen secured the dish around 11:39 a.m., but it took more than an hour to plug the connecter into its socket and to re-torque bolts holding the antenna to its boom.
An overly-tight fit was resolved by allowing sunlight to heat up the socket while the astronauts shaded the plug. When the connector finally locked in place, the spacewalkers bumped fists in a brief celebration, writes CBS News space analyst Bill Harwood.
Reisman then left the area to begin the crew's next task while Bowen worked to disengage launch locks on the antenna's steering system. While that work was going on, engineers at the Johnson Space Center decided they were not comfortable with a slightly loose fit between the antenna and its support boom.
Bowen was asked to re-engage the gimbal locks and to use a tether to firmly secure the antenna pending additional discussions. By the time the antenna was tethered in place, the spacewalkers had spent five hours on a task that was budgeted for about three.
The next item on the agenda was to install an equipment mounting platform on the Canadian Special Purpose Dexterous Manipulator, a hand-like attachment that can be used by the robot arm to remotely install various components and experiments.
Because of time lost during the antenna, today's spacewalk (which began at 7:54 a.m. EDT) lasted longer than the planned six-and-a-half hours.
Earlier, Reisman was preparing to unbolt the antenna from the cargo carrier when a computer glitch aboard the lab complex knocked out power to several systems, including the video displays being used by the robot arm's operator, mission specialist Piers Sellers.
It took about a half-hour to bring up a different system and restore the displays to normal operation. The antenna work resumed just after 10:30 a.m.
There was some levity amid the slow-downs. Reisman - anchored to the end of the space station's 58-foot-long robotic arm - was carried to a cargo pallet to retrieve the 6-foot-wide dish antenna.
"Wow! I'm way up here now," he said. "I might only be five foot four, but right now I think I'm the highest person around. Whoo!"
If time is available, the astronauts will wrap up today's EVA by loosening bolts holding six solar array batteries in place on a cargo pallet. The batteries will be installed during the crew's second and third spacewalks.
The Atlantis carried up a new space-to-ground antenna system that will serve as a backup high-data-rate antenna, used for space station video and experiment data.
The second objective of the spacewalk is to install an enhanced spare parts storage platform on the Canadian special purpose dexterous manipulator, or DEXTRE, a hand-like robot arm attachment that can be used to install replacement components or service external experiments.
"The current one that's installed on DEXTRE can only handle one spare box," Station flight director Scott Stover said. "This new enhanced version is able to handle multiple boxes, so what Garrett and Steve are going to do is remove the old one, temporarily stow it on the space station, and install the new one."
This is the first of three planned spacewalks by the shuttle Atlantis' crew, the eighth so far this year, and the 144th devoted to station assembly and maintenance since construction began in 1998.
Bowen is making his fourth spacewalk and Reisman is making his second. Bowen (call sign EV-2) is wearing a suit with red stripes around the legs while Reisman (EV-1) is wearing an unmarked suit.
Reisman and Bowen spent the night in the Quest module at a reduced pressure of 10.2 pounds per square inch to help purge nitrogen from their bloodstreams, a routine protocol intended to prevent decompression sickness, or the bends, when working in NASA's 5 psi spacesuits.
The backup antenna dish and its support beam, along with robot arm storage platform and six new solar array batteries, are mounted on the integrated cargo carrier. The carrier was pulled from the shuttle's cargo bay after docking Sunday and mounted on the robot arm transporter on the front side of the station's solar power truss.
After exiting the airlock, Reisman and Bowen will make their way to the cargo pallet and install foot restraints, one on the pallet itself and one of the robot arm. The eight-foot-long boom that will support the spare antenna will be removed from the pallet, and Reisman, riding on the end of the robot arm, will carry it to the Z1 truss atop the station's central Unity module.
The spacewalkers then will secure the boom with two bolts. While Bowen is making electrical connections, Reisman will ride the arm, operated by Piers Sellers from the new multi-window cupola, in a windshield wiper-like trajectory back to the cargo pallet to pick up the six-foot-wide Ku-band antenna.
"The dish is pretty fragile and we're instructed not to bump that into anything," Reisman said. "Piers is going to be operating the big arm, and I'll be standing on the end of it while we bring the dish out. At that point, the dish comes very close to the boom of the arm.
"The worrisome thing for me is I can't really see it because I have a big face full of dish, and the boom is on the other side. So I'll be counting on Piers to talk me through it and give me nice calls. We'll have to coordinate very carefully. It's definitely an area of concern."
Reisman, holding the dish, will follow another windshield wiper trajectory back to the top of the Z1 truss where Bowen will help move it into position before driving four bolts to hold it in place and hooking up two electrical connectors.
After installing insulation around the base of the antenna, Reisman will ride the arm back to the cargo pallet to retrieve an equipment stowage platform that will be attached to the Canadian special purpose dexterous manipulator, or SPDM, robot arm extension. The platform will be used down the road to temporarily hold components that are being replaced by the space crane.
Once the platform is in place the astronauts will turn their attention to a get-ahead task if time is available, loosening the bolts holding new solar array batteries to the cargo pallet.
"While the pallet's based on the truss there, we can actually break all the torque on the bolts with a ratchet wrench instead of using this heavy torque multiplier," Reisman said. "Just like lug nuts on your car, we can do it very quickly."
Bowen said the key to the first spacewalk is "a very intricate choreography."
"Everything has to work," he said. "Any one of these EVAs, a single bolt can put everything behind. So we have to be very efficient and hopefully get through our tasks in a very nominal timeframe so the next piece is ready to go."
Reisman, who carried dirt from the pitcher's mound of Yankee Stadium into space on an earlier mission, is sporting a New York Yankees' logo on his suit during today's EVA (left).
In 2008 Reisman threw a ceremonial opening pitch in space, during a Yankees-Red Sox game. Speed: 17,500 mph.