Power payload to be handed from shuttle to station today
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 18, 2009
The Discovery astronauts get down to business today, kicking off a two-day procedure to install a $300 million solar array truss segment on the international space station. The crew was awakened at 8:43 a.m. by a recording of Johnny Cash's "Walk the Line" beamed up from mission control.
Before the astronauts went to bed just after midnight, mission control gave them a brief update on work to assess photos shot during Discovery's approach to the space station Tuesday. Only one area of presumably minor damage was noted on one of the shuttle's wing flaps, or elevons.
"A quick look of the RPM imagery is showing there is a tile on the left-inboard elevon that has some substraight exposed," Greg Johnson radioed from Houston. "That's the only item that the team is scrutinizing at this point. There is no decision regarding any focused inspection, but we will continue to analyze that spot overnight."
"Ah, thank you very much," commander Lee Archambault replied. "We appreciate the good words and we'll anxiously await what you find. But thanks for that heads up."
The space station's U.S. power system currently consists of three sets of solar arrays, the port 4 and 6 - P4 and P6 - arrays on the left end of the lab's integrated power truss and the starboard 4, or S4, array on the right end. The 31,000 pound starboard 6, or S6, truss segment carried aloft by Discovery will be mounted on the far right side of the integrated truss during a spacewalk Thursday by astronauts Steven Swanson and Richard Arnold.
"The real fundamental payload that we're carrying is called the S6 truss and it's the final piece of the American electrical power generating truss assembly and it's been a long time coming," astronaut John Phillips said in a NASA interview. "When you look at pictures of the station now, it looks very asymmetric. Well, we're going to complete the symmetry.
"This is almost 16 tons. It fills up the entire payload bay of the shuttle. We're going to deliver that and install it and deploy it, that is, unfold the solar arrays and complete the power generation part of the U.S. segment of the space station which will enable all these brand new labs, the Japanese lab and the European lab, to have the power they need to do the experiments they're going to do."
According to NASA, the addition of the S6 arrays "will nearly double the amount of power available to perform scientific experiments on the station - from 15 kilowatts to 30 kilowatts."
With its arrays stowed for launch, the S6 element measures 16.3 feet by 14.7 feet by 45.4 feet long. It weighs 31,060 pounds.
Getting S6 from Discovery's cargo bay to its attachment point on the right end of the station's power truss is a complex, multi-step procedure. Because of interference issues, the shuttle's robot arm cannot pull S6 from the payload bay. Instead, the station's mobile crane will first pull S6 from its mounting point in the shuttle's cargo bay just before noon and then hand it off to the shuttle arm about two hours later.
The station arm's mobile base then will move down rails on the front face of the power truss to a work site at the far right end. After a break for lunch at 3:18 p.m., the shuttle arm will be positioned to hand S6 back to the station arm around 6 p.m. The station arm will hold the new truss segment in an overnight park position near its eventual attachment point. During the spacewalk Thursday, S6 will be bolted in place and electrically tied into the station's power system.
"I'm sort of the lead crane operator for the station, the space station robot arm," Phillips said. "Now, the space shuttle carries a robot arm but that arm by itself cannot pick this truss out of our payload bay and install it. So what we have to do is, Sandy Magnus and I, driving the space station robot arm, will pick the truss up out of the payload bay. Then we will hand it off to the space shuttle robot arm and they will hold it for us while the little railroad car that our robot arm is based on moves out to another position, way out on the starboard side of the station.
"Then we're going to grab it back from them and position this new truss for installation way out on the extreme starboard end of the existing truss structure. And then, the next morning, the EVA team is going to go outside and they're going to be standing by right there at the interface between the old truss and the new one that we're bringing, and we're going to bring them together and then they're going to bolt the truss together and do a bunch of other manipulations to allow it to unfold the solar blankets."
While NASA always has contingency plans and alternate procedures in case something goes wrong, the station arm simply has to work to get the new truss segment installed.
"We cannot install this truss without the space station robot arm," Phillips said. "We just can't do it. Fortunately, the space station robot arm has built in redundancy. It has multiple ways to get power to it. It has ways to operate it in a degraded mode if you've lost one particular joint or one particular black box. So we're pretty confident that will keep working.
"Now the shuttle robot arm also plays a key role because we have to hand the truss back to the shuttle robot arm in order to move the railroad car on which the station's arm is based out to where it needs to be. If we had a shuttle robot arm problem there are ways we can work around it. It's pretty complicated and would involve a lot of real-time analysis by folks on the ground. You could perhaps temporarily park this truss on a part of the station. If that happened, it will be a bad day. It would be a day that would require a lot of work from a lot of people to come up with a new plan. In the end I think we'd still get it installed."
While the S6 unberthing and repositioning work is going on, Swanson and Arnold will be checking out the tools and equipment they will use Thursday to connect the arrays. They will spend 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 pre-spacewalk procedure to ensure spacewalkers don't get the bends after working in NASA's 5-psi spacesuits.
The astronauts also will take time later today to troubleshoot the shuttle's exercise bike, or ergometer. When the device was set up earlier, the astronauts reported the pedals were jammed. Alternative bungee cord-type exercises are available, as well as exercise equipment aboard the space station.
The astronauts will participate in a media interview today at 2:58 p.m. and NASA mission managers will hold their daily briefing at 6:30 p.m.
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 08:43 AM...02...13...00...STS/ISS crew wakeup 10:18 AM...02...14...35...ISS daily planning conference 11:08 AM...02...15...25...Shuttle arm (SRMS) powerup 11:38 AM...02...15...55...Station arm (SSRMS) S6 grapple/unberth 12:53 PM...02...17...10...SSRMS moves S6 to handoff position 01:13 PM...02...17...30...Equipment lock preps 01:43 PM...02...18...00...SRMS grapples S6 01:58 PM...02...18...15...EVA-1: Tools configured 02:03 PM...02...18...20...SSRMS ungrapples S6 02:18 PM...02...18...35...SSRMS transporter moves to worksite 1 02:43 PM...02...19...00...SOKOL suit leak check/dry 02:58 PM...02...19...15...PAO event with Channel One News 03:18 PM...02...19...35...Crew meals begin 04:18 PM...02...20...35...EVA-1: Tool audit 04:43 PM...02...21...00...SRMS moves S6 to handoff position 05:58 PM...02...22...15...SSRMS grapples S6 05:58 PM...02...22...15...Ergometer maintenance/repair 06:28 PM...02...22...45...SRMS ungrapples S6 06:30 PM...02...22...47...Mission status/MMT briefing 06:43 PM...02...23...00...SSRMS to overnight park position 08:28 PM...03...00...45...ISS evening planning conference 08:43 PM...03...01...00...EVA-1: Procedures review 10:28 PM...03...02...45...Crew choice downlink 10:38 PM...03...02...55...EVA-1: Mask pre-breathe 11:23 PM...03...03...40...EVA-1: Airlock depress to 10.2 psi 11:43 PM...03...04...00...ISS crew sleep begins 03/19/09 12:13 AM...03...04...30...STS crew sleep begins 01:00 AM...03...05...17...Daily highlights reel 08:13 AM...03...12...30...Crew wakeupDiscovery docked with the space station Tuesday and Japanese astronaut Koichi Wakata officially joined the station crew at 9 p.m. when his custom Soyuz seatliner was installed in the station's Russian re-entry craft. Wakata replaced Magnus on the Expedition 18 crew and she will take his place aboard Discovery when the shuttle undocks next week.