Spacewalkers to install station's final truss today
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 19, 2009
Astronauts Steven Swanson and Richard Arnold are gearing up for a planned six-and-a-half-hour spacewalk today to attach a 31,000-pound solar array truss unit to the international space station. The $300 million starboard 6, or S6, truss segment was pulled from the shuttle Discovery's cargo bay Wednesday and parked overnight near its attachment point on the far right side of the lab's main power truss. The station's robot arm will move it into place for installation starting around 11:08 a.m. and if all goes well, Swanson and Arnold, floating in the Quest airlock module, will switch their suits to battery power at 1:13 p.m. to officially begin their spacewalk.
This will be the 121st spacewalk devoted to station assembly and maintenance since construction began in 1998, the second so far this year and the first of three planned for Discovery's crew. For identification, Swanson will be wearing a suit with red stripes and use the call sign EV-1. Arnold's suit has no strips and he will use the call sign EV-2. Joseph Acaba will serve as the spacewalk director, or IVA, inside the shuttle.
Assuming S6 is successfully attached and connected, the arrays likely will be extended Friday. They originally were scheduled for deployment Sunday, but with the decision Wednesday to forego additional docked heat shield inspections - work that would have been carried out Friday - the astronauts likely will get the green light to extend the arrays Friday, ahead of schedule.
If that scenario plays out, mission managers may look into the possibility of bringing Discovery back to Earth one day earlier than currently planned to ensure that time-critical experiment samples make it down safely even if the shuttle crew runs into multiple weather delays. Discovery currently is scheduled to land March 28, but by re-arranging off-duty time and other activities, sources say it may be possible to shave a day off the mission without impacting any mission objectives or off-duty time, giving the experiment samples additional cushion. But at this point, no such decisions have been made.
The installation of the S6 truss segment is the primary objective of the 125h shuttle mission. Measuring 45.4 feet long and 16.3 feet wide in its stowed configuration, the 31,060-pound S6 is the fourth and final set of solar arrays to be attached to the lab complex and the final heavyweight payload scheduled for launch aboard a shuttle. According to Boeing, the prime contractor, S6 cost $297,918,471.
Originally built as a structural test article and then delayed by the 2003 Columbia disaster, S6 has endured a long wait for launch. It will join the S4 arrays on the right side of the station and match the port 4 and 6 arrays on the left end of the power truss. All four sets of arrays, each set stretching 240 feet from tip to tip, are designed to rotate like giant paddle wheels as the station orbits the Earth to stay face on to the sun.
The S6 arrays will provide an additional 30 kilowatts of power for science experiments above and beyond what they generates for station systems.
"Once the S6 is installed on the space station, the entire space station's power generation capability, at least from the U.S. provided hardware, will be right around 264 kilowatts," said Kwatsi Alibaruho, the station's lead flight director. "So it's very impressive. We're excited about having that much power available to support not only core space station systems operations, but also all of the science that's going to be performed."
Swanson and Arnold spent the night in the station's Quest airlock at a reduced pressure of 10 pounds per square inch to help purge nitrogen from their bloodstreams. This is a standard procedure to ensure the spacewalkers don't get the bends working in NASA's 5-psi spacesuits.
While they are preparing to leave the airlock, John Phillips and Japanese astronaut Koichi Wakata, operating the station arm from a work station inside the Destiny laboratory module, will move S6 into position for installation. The arm is anchored at a work site on the far right side of the power truss. Even so, it will still have to be fully extended across the S4 arrays and the S5 spacer segment to get S6 into position.
"There's quite a bit of choreography going on there because John and Koichi are going to be getting S6 into position," Arnold told reporters before launch. "When they have it in position, Swanee and I will go out the door and make our way to the interface where we're going to mate the S6 truss.
"From there, we have four attachment points to bolt the two pieces of truss together. Basically, it's like backing your car in the garage. We'll be telling John, 'a little bit closer, a little bit to the left, little bit to the right,' and they will fly it into position where we can then drive the bolts."
As S6 is moved toward contact with the S5 spacer truss, Phillips and Wakata will pause at one foot and six inches to make sure the alignment is precise. Initial capture will be accomplished using a central "capture claw" that will engage to hold S6 and S5 together while four attachment bolts at each corner are driven in.
"While Swanee's going around driving the bolts, we're going to attach some grounding straps, we're going to go ahead and make sure the two truss interfaces are mated," Arnold said. "Once that's all done, we then have to make some electrical connections and some data connections and then head on out to get the solar array blanket boxes deployed. The blanket boxes are in a launch configuration now."
Four electrical connections are required between S5 and S6: two for power and two for data. At this point, S6 will be structurally and electrically mated to the station. But the boxes holding the folded array blankets, and the canisters housing the collapsed masts that will be used later to pull them out, must be rotated out of their stowed positions and locked in place. The mast canisters and their associated beta gimbal assemblies - used to move the arrays from side to side once extended - will be deployed first, followed by the blanket boxes. A folding set of radiator panels will be deployed toward the end of the spacewalk.
"Swanee's going to be doing some stuff to get the mast canisters ready and while he's doing that, I'm going to be removing some launch locks that are holding the blanket boxes containing the solar arrays. I have four of those launch locks in total that I have to remove. Once the launch locks are removed, the arrays are able to move away from the truss and ... we're expecting they're going to largely go out on their own, deploy on their own. But we'll probably have to give them a little bit of a shove to get them into position."
Once the mast canisters are deployed and locked in place, "we're going to make our way up onto the mast canisters and then we have to pull the blanket boxes out into the deployed position," Arnold said. "It's a pretty complex EVA, we've got a lot of robotics going on. We have a lot of different kinds of work to do. But we're hoping when we're all done, we'll come back inside and if we don't need a focused inspection the next day, we're going to be able to go ahead and deploy the arrays."
Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision C of the NASA television schedule):
EDT........DD...HH...MM...EVENT 08:13 AM...03...12...30...Crew wakeup 08:48 AM...03...13...05...EVA-1: 14.7 psi repress/hygiene break 09:38 AM...03...13...55...EVA-1: Airlock depress to 10.2 psi 09:58 AM...03...14...15...ISS daily planning conference 09:58 AM...03...14...15...EVA-1: Campout EVA preps 11:08 AM...03...15...25...Station arm (SSRMS) moves S6 to pre-install 11:28 AM...03...15...45...EVA-1: Spacesuit purge 11:43 AM...03...16...00...EVA-1: Spacesuit prebreathe 12:43 PM...03...17...00...EVA-1: Crew lock depressurization 01:13 PM...03...17...30...EVA-1: Spacesuits to battery power 01:18 PM...03...17...35...EVA-1: Airlock egress 01:48 PM...03...18...05...EVA-1: Setup 02:03 PM...03...18...20...EVA-1: S6 attachment operations 03:08 PM...03...19...25...EVA-1: S6 umbilical connections 03:08 PM...03...19...25...SSRMS releases S6 04:03 PM...03...20...20...EVA-1/EV-2: Blanket box launch lock release 04:03 PM...03...20...20...EVA-1/EV-1: Radiator cinch/winch release 04:28 PM...03...20...45...SSRMS solar array viewing maneuver 04:48 PM...03...21...05...EVA-1/EV-1: Keel pin stow 05:03 PM...03...21...20...EVA-1/EV-1: Beta gimbal joint release 05:18 PM...03...21...35...Ergometer repair 05:33 PM...03...21...50...EVA-1: Unstow blanket boxes 06:33 PM...03...22...50...EVA-1: SSU/ECU cover removal 06:43 PM...03...23...00...EVA-1: Cleanup and ingress 07:43 PM...04...00...00...EVA-1: Airlock pressurization 07:58 PM...04...00...15...Spacesuit servicing 08:30 PM...04...00...47...Mission status briefing 08:58 PM...04...01...15...ISS evening planning conference 09:38 PM...04...01...55...Crew choice downlink 11:13 PM...04...03...30...ISS crew sleep begins 11:43 PM...04...04...00...STS crew sleep begins 03/20/09 12:00 AM...04...04...17...Daily highlights reel 07:00 AM...04...11...17...HD highlights 07:43 AM...04...12...00...Crew wakeup