The upcoming deployment of two wing-like solar arrays outside the space station has been the focus of astronauts and flight controllers, but there is one more power-producing array on-board Atlantis that lies hidden - for now - from the public's view.

This third array is stowed inside a shuttle middeck locker, along with thousands of other items flown on behalf of, for and with the STS-115 crew when they launched Saturday.

"We're taking a little mini-solar array up there," pilot Chris Ferguson told collectSPACE during a pre-flight interview. "We're taking it [among] our personal items. We're going to make a video - all below the radar-scope - for education purposes."

The hidden payload is a much smaller, but still functional version of the arrays attached to the 17.5 ton, 45 foot-long P3/P4 integrated truss segment that Atlantis delivered to the International Space Station earlier today and which the STS-115 astronauts used both shuttle and station robotic arms to hand-off between spacecraft.

Once installed and switched on during a later mission, the new arrays will double the electricity available to the ISS.

The mini-array, one of several, was put together by the crew using spare solar cells donated by the company that built the full-size versions.

"What we've done is made several little packages that we've wired four cells together and distributed them to schools throughout the country," said Ferguson. "We'll be doing some work up there, just a demonstration-type thing, to show the kids what you really can do with solar power."

In a separate interview with a newspaper, Ferguson said they would be powering a CD player with the mini-array.

"I figured it was really quite fitting considering what it was we were doing," said Ferguson, relating the demo to the STS-115 mission objectives.

Though Ferguson will access the mini-array during flight, most of the crew's personal items will remain untouched until Atlantis lands, now scheduled for September 20.

"We're allowed to fly some personal items, they have to be very small and they have to basically fit inside a small zip lock bag. And then of course, we don't even have access to those items during the mission. They're put away safely and then returned [post-flight]," commander Brent Jett told collectSPACE.

"What I decided to do, as this was my fourth flight, I offered most of those slots to our training team. I asked them if they had anything personal that they would like me to fly for them," said Jett. "I don't want to get into details as to what those items are but they are basically small trinkets and jewelry, that type of things. For me, those folks put so much into our space flight, those... who run the mission from the ground or train us to get ready to go, it's a small thing for us to do that for them."

Others on Jett's crew chose to fly items for their families.

"I'm taking two items - I'm allowed two - one of them is the gear-shift knob off of my son's 1969 Camaro that he and I did as a restoration project," said mission specialist Joe Tanner. "So, I am taking that as a tribute to the work that he and I did together. And the other item is a key fob for my other son's car - he's got a Subaru WRX - and I gave him this key fob for Christmas."

"I think most of what I am taking up is pictures," said Heidemarie Stefanyshyn-Piper, also a mission specialist, about what she was flying for family. "They can't come with me but I figure if I have their likenesses, they're there with me."

"I am taking something for Eric, my one brother who won't be at the launch because [in August] he deployed with the Marine Corps. And so I am taking something up for him," Piper said.

For Dan Burbank, who with Ferguson performs in the all astronaut band Max Q, one of the personal items he might have taken is already on-board the station.

"I'm certainly bringing up some music with me. There's a guitar up there, or that's what I hear. I am looking forward to a chance to play it. But I am not looking forward to the chance to play it on the downlink, so you may have to look hard to see me do that," joked Burbank. "But it will be really neat to do."

"And we don't have a drum set [on-board] unfortunately. Chris Ferguson is our Max Q drummer and a dynamite one at that. I'm not sure if we have drumsticks up, but he may be able to make due with some [thing]."

That he may.

"Unfortunately, we are limited in the number of personal items we can take, and I had one more left and they said that a 'pair of drumsticks' is two items. So I had to leave the drumsticks back," said Ferguson.

In addition to their items stowed in "personal preference kits," the STS-115 astronauts are also flying thousands of items for presentation to their co-workers and supporters, both professional and personal.

"I have a couple of items for my high school. I went to Derham Hall High School in St. Paul, Minnesota, which is now part of Cretin-Derham Hall, and I'm taking some stuff up for them. I've got a banner for my ROTC unit that I am [taking] up," said Piper.

Canadian Space Agency astronaut Steven MacLean had packed aboard several items he thought were "neat".

"A friend of mine has climbed all seven mountains, the highest mountains on all seven continents, so I have a small stone off of Mount Everest that I am carrying in what is called an Official Flight Kit."

"Also we have some apple seeds that are unique - you know Sir Isaac Newton 'found' gravity with an apple falling on his head, well the university in Europe kept that tree going over the generations. And York University up in Canada recently got a sapling, a cutting off of that tree and planted that tree in Toronto. And I have the first seeds from that tree," MacLean told collectSPACE.

"I don't know if that's really important but its kind of neat."

View the full manifest of the STS-115 Official Flight Kit.

VIDEO: First Tasks of NASA's STS-115 Mission

Gallery: Prepping Atlantis

Complete Space Shuttle Mission Coverage

NASA's STS-115: Shuttle Atlantis to Jump Start ISS Construction

The Great Space Quiz: Space Shuttle Countdown

Complete Coverage: ISS Expedition 13

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