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Robbie Ashley, ISS payload manager
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You're listening to NASA Direct.

GEORGE DILLER: From the Kennedy Space Center in Florida, I'm George Diller.

NASA is about to embark on mission STS-115, a mission to resume construction of the International Space Station.

Right now, Space Shuttle Atlantis is at Launch Pad 39B, ready to fly.

Tucked safely inside its cargo bay: an important piece of hardware to be installed during the shuttle and crew's 11-day trip into space.

Here to tell us more about Atlantis' payload is the STS-115 payload manager, Robbie Ashley.

Robbie, thank you so much for taking time to talk with NASA Direct about the P3/P4 segment.

ROBBIE ASHLEY: Well, it's my pleasure, George. I'm glad to come over and talk about this payload that we've worked on for so long, as we look forward to a successful launch on Sunday and a successful mission next week.

DILLER: Now, before we get into all the specifics about what the payload will do once it's installed, tell us what the P3/P4 truss segment is and what it will be used for.

ASHLEY: OK. Well, the P3/P4 truss is actually two separate segments: P3 and P4, as you might suppose. They were delivered individually to Kennedy Space Center back in 1999 and 2000, respectively, and then they were later joined together here using a series of interconnecting struts, referred to as the Alpha Joint Interface Structure, or AJIS. The P3 segment is a hexagonal-shaped truss that includes the solar alpha rotary joint and two unpressurized cargo carrier attach system platforms, which are external sites that can be used as logistics pallets for storing replacement station parts on orbit. The P4 segment is a power module like the one on P6, which has been on orbit since November of 2002 and is serving as the primary power source for the International Space Station.

DILLER: Now, it's a remarkably heavy piece of hardware, isn't it?

ASHLEY: P3/P4 weighs around 34,885 pounds and it's one of the heaviest payloads that will be launched to station. P6 launched on STS-97 in November 20002, as I just mentioned, was slightly heavier, weighing in at 34,918 pounds. So we've already got a good experience base working with payloads of this size on station. But let me also add that P6 won't be the heaviest that we'll have to contend with, either. The heavyweight title goes to the S3/S4 truss, scheduled to launch in February of next year. It is estimated to weigh about 35,580 pounds at time of launch.

DILLER: After the installation of this new part of the International Space Station, how much is still left to be installed?

ASHLEY: For station completion as a whole, after this mission, there are 14 more shuttle flights planned to get the station assembly complete, plus potentially two contingency flights that could become available if necessary before the shuttle program winds down in 2010.

DILLER: How will you and your team know that the payload has made it safely into space?

ASHLEY: Well, actually, there's a couple of ways. First, after, immediately following the launch, we'll be tying in to the mission management team daily status meetings and following the progress of the mission through the mission management team. In addition, we've got engineers that are going to be going out to Houston and supporting in the mission evaluation room out there and tied in around the clock throughout the duration of the mission. So we'll, we'll also be hearing through them how things are performing on orbit.

DILLER: So, how will the P3/P4 get installed?

ASHLEY: Well, it's actually going to be quite complex and, and interesting to watch. Both the shuttle and the station robotic arms will be used during the shuttle mission, and both are absolutely critical to connecting the P3/P4 truss segment to the International Space Station.

Astronauts Chris Ferguson and Dan Burbank will use the shuttle robot arm to lift the P3/P4 truss out of orbiter Atlantis' payload bay and maneuver it into a position where it will be handed off to the station robot arm. Astronaut Steve MacLean from the Canadian Space Agency, along with station crew member Jeff Williams working from the station's robotic work station in the U.S. Laboratory module, will position the station's robot arm to receive the P3/P4 truss from the shuttle robot arm.

Once the handoff is complete, the truss will remain grappled to the station arm overnight in a parked position while the crew sleeps. The next day, MacLean and Williams will slowly and carefully position the P3/P4 truss at the edge of the P1 truss and, using television cameras to properly orient and position the two truss components into ready-for-mated condition. Once in position, the segment-to-segment attach system will be used to complete the mating of the two segments.

DILLER: Robbie, thank you very much for stopping by NASA Direct.

ASHLEY: Well, it has been my pleasure, George. I'm always glad to come and talk about the P3/P4 truss element that I've worked on for over seven years now, especially as we're approaching the launch coming up on Sunday. It's quite exciting for us and, and, you know, the entire team that has been working on this element.

DILLER: For more on STS-115, go to From the Kennedy Space Center in Florida, I'm George Diller.

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