Installing the S1 truss
Posted: September 26, 2002

The day after docking - flight day four - the combined crews will face the busiest day of Atlantis' mission: Installation of the S1 truss and, during a planned six-and-a-half-hour spacewalk by Wolf and Sellers, initial connection of the electrical cables and data lines needed to bring the truss to life.

Three spacewalks will be required to complete the job.

The massive S1 truss is moved by overhead crane during final launch processing at Kennedy Space Center. Photo: NASA
"We're going to go out three times and in rough order of importance what we're going to try and do is to make all the electrical connections between the new piece of the station we're putting on there, the truss, and the existing station," said Sellers. "And this is to keep all the heaters alive and the brains of the new components alive, the electrical power.

"The next thing we're going to do is put a new comm device on there, which will be used for communications between the crew and the station," he said. "Next important is fluid connections, we want to make the coolant loops that exist on station connect with the cooling radiators that are on the S1 truss. And the fourth thing that, I think, is going to be fun is to activate the CETA cart, which is this little railway cart that trundles up and down the front face of S1."

The truss completely fills Atlantis' cargo bay and it is a marvel of complexity.

"The electrical utilities consist of 22 different types of wire, totaling 79,241 feet, or 15 miles of wire," said Ronald Torcivia, STS-112 launch package manager. "Another way to look at it is to say that for every foot of the 45-foot-long truss there is a third of a mile of wire. The electrical system has 103 separate harnesses with 8,020 contacts housed in 718 connections.

"In addition, there is over a third of a mile of fiber optic cable used to carry video information. The fluid system provides all the utilities needed to transfer ammonia and nitrogen within the thermal control system as well as transferring it to the adjoining structures.

"The fluid system consists of 426 feet of rigid stainless steel tubing terminating in 59 EVA-operable connections, or QDs (quick-disconnect fittings)," Torcivia said. "Fifty six of these QDs are used to transfer ammonia while three are used to transfer nitrogen. The ammonia lines are used for cooling and the nitrogen lines are used to maintain pressure within the ammonia system at 3,000 psi.

Throw in the complex rotary joint that allows the radiators to be properly oriented, the S-band antenna system, the CETA cart and the segment's computer system and even the casual observer begins to realize the truss is more than a simple, if massive, structural element.

"S1 is essentially a full spacecraft," said Gerstenmaier. "The only thing it's lacking is propulsion and some attitude control determination. It has computers on board, multiplexers and de-multiplexers, it has a communications antenna system, it has integral thermal control system, it has radiators, a very large ammonia tank, a crew translation aid. It's a very, very complex spacecraft."

While Wolf and Sellers, assisted by Melroy, begin preparations for their first spacewalk, Whitson and Magnus will use the station's robot arm to slowly lift S1 from Atlantis' cargo bay. Ashby will assist by positioning the shuttle's robot arm to provide different television views of the operation.

Animation shows the robotic arm beginning to lift S1 truss out of the shuttle's payload bay. Photo: NASA TV/Spaceflight Now
"This is a major transition in the assembly sequence of the station," said Melroy. "At the beginning, the work area was all very close to the shuttle. It was a pretty small station. We were attached to it. We could use the shuttle robotic arm, which, by the way, we have a lot of experience on and feel very comfortable using. We could do all of our assembly tasks very close to the shuttle.

"Well, we're moving into a situation now, and the S1 truss is a classic example of it, it's way too far out there! It's on the other side of the shuttle from the robotic arm. There's just no way you can get it over there. So, we've transitioned to using the station arm for the assembly task. Reaching into the payload bay, pulling the S1 truss out, and putting it into position."

The truss will be pulled straight up from the payload bay and then maneuvered over the starboard side of the orbiter until it is roughly lined up with S0. Canadarm2 will carefully position S1 so that its capture bar is within reach of the motorized claw at the end of S0.

Animation shows the S1 truss being maneuvered by the station's robotic arm. Photo: NASA TV/Spaceflight Now
"When we bring S1 into the proper area of that claw, we have sensors around the truss that tell the system that we're in the proper position to begin latching," Torcivia said. "This claw begins to close and it pulls the two trusses together. Once they're together, we have a system called a bus bolt controller and they're located at the four corners of the truss. They are electrically driven screws that drive the structure together. And they can exert anywhere from 8,000 to 16,000 pounds of force on each corner."

Wolf and Sellers will be cleared to exit the Quest airlock module once the initial attachment procedure is complete. But they could exit early if there are problems getting S0 and S1 connected.

"If there's a problem lining things up, Dave and I will go out there and help guide things in," Sellers said. "Then, if the motorized bolts don't work that tie the new truss to the station, Dave and I have a pocket full of bolts to manually put in there and tie the two together."

In a worst case scenario, Wolf and Sellers could use retention straps to ratchet the two truss segments together.

"We're trying to make sure if everything else fails, we still have a way to do the primary objective, which is installing this thing," Ashby said. "Providing the station arm is working well enough to at least get it up close, then we can install this thing."

Animation shows the S1 attached to the S0 truss. Photo: NASA TV/Spaceflight Now
But assuming no such problems develop, Wolf and Sellers will begin their excursion after S1 has been bolted to S0. The primary goal of the first spacewalk is to hook up electrical connectors between S1 and S0 to route power into the new truss segment.

The connectors are located in two utility trays, one on the upward, or zenith, side of S1 and the other on the nadir side. One tray has seven connectors and the other, eight. The astronauts will begin with the zenith tray.

"The crew starts out by connecting up the first set of power and data umbilicals to the S1 truss segment," said Algate. "After that's complete, they'll be getting the S-band antenna from its stowed location and installing it on the truss and hooking up its power and data cables. Once this system is up and connected, a little later in the mission we'll be testing out this second string of communications gear."

While Wolf and Sellers are working through their initial tasks, ground controllers will begin powering up internal truss systems, activating its computers and turning on critical heaters. The spacewalkers then will unlatch launch locks that held the CETA cart firmly in place during Atlantis' climb to space.

CETA is NASA-ese for "crew EVA translation aid."

"We know that there are going to be times when things break down," Melroy said in a NASA interview. "They do, just like they do in your house. So, you have to go out and you have to replace parts. And to do that, you have to do spacewalks. ... The designers of the station took this into consideration, and what's neat is there's this little railroad cart that runs along the bottom of the truss. And, it goes all the way out, in both directions.

"(It) kind of makes me think of one of those little railroad carts that you kind of see them in TV and cartoons. But in fact what the crew will do is they pull themselves along hand-over-hand with their feet stuck in the cart, and that's how they move it from place to place. So, this cart will be a part of the, we're taking up one of these carts on the S1 truss, and we'll be basically getting it ready.

A view of a CETA cart. Photo: NASA
"It's cinched down, bolted down very tightly for launch," Melroy said. "You don't want this thing wiggling around or moving. So, the EVA crew will go outside. They will take all these bolts out. They will set the parking brake. They're going to practice moving it back and forth. It's the first time we've used it. We're very excited about it!"

After releasing launch locks holding the rotating radiator array framework in place, Wolf and Sellers plan to close out the first spacewalk by hooking up the second set of power and data umbilicals located in the nadir utility tray. Until both sets are connected, the truss is not considered in a safe configuration.

The spacewalkers also will mount a video camera on one of the keel assemblies that held S1 in the shuttle's cargo bay.

"There are two levels of difficulty to consider," Sellers said before launch. "One is the complexity of the task, the thing you're trying to do, and that's where Pam keeps us straight. She has the checklist, she knows where we're going and exactly what connects to what.

"The other level of difficulty has to do with can I get my arm, which is incased in this thick, heavy (spacesuit), into a place to do a connection or to throw a lever on a bale or something like that? Those things we've practiced in the pool, endlessly, and I think we're very well prepared for those, too. So in both cases, after a lot of effort by our training team and the people who supported us, I think we're ready."

The next day, flight day five, the astronauts will enjoy a bit of time off and begin transferring supplies and equipment from the shuttle's middeck to the station. Along the way, they'll review plans for the second spacewalk the next day.


Pre-launch briefing
Mission overview - Atlantis to launch outward extension of station truss.

A trying summer for NASA - Small cracks in fuel flow liners grounded shuttle fleet.

Rendezvous and docking - Description of Atlantis' trek to catch the station.

Installing the S1 truss - The day after docking the Starboard 1 truss will be attached to the station with help of spacewalkers.

Plugging potential leaks - The second spacewalk will ready the S1 ammonia cooling system.

Odds and ends - The remaining highlights of the mission include a radiator deploy, treadmill repair and a final spacewalk.

Undocking, re-entry and landing - A look at the conclusion of Atlantis' 11-day voyage.

STS-112 index - A full directory of our mission coverage.

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