[sarex] Shuttle Mission STS-116: A Hard Wire Job

[Arthur Rowe]

SUBMITTED BY ARTHUR N1ORC - AMSAT AC #31468

Shuttle Mission STS-116: A Hard Wire Job

10.12.06

NASA has said it over and over again: The coming missions to finish the 
International Space Station are among the hardest and most complex ever.

But if you ask the astronauts and engineers which of the final 14 
assembly flights may be the most complex, many would point to 
Discovery's next mission, set to launch in December.

JSC2006-E-23034 : Mark Polansky and William Oefelein"What makes this one 
singularly unique is the fact that we're going to rewire the space 
station," Mark Polansky, Discovery's commander, said.

Image to right: STS-116 Commander Mark Polansky (left) and Pilot William 
Oefelein participate in a training session in the fixed-base shuttle 
mission simulator at Johnson Space Center, Houston. Image credit: NASA

Since it went into orbit in 1998, the space station has been running on 
a temporary electrical system. Lead Space Station Flight Director John 
Curry compared it to the way you might build a house on the ground – 
until your electricity is hooked up, you probably plug your saws into a 
generator. That's basically what the astronauts building and living on 
the station have been doing for the past eight years.

But with the installation of two new electricity-generating solar array 
panels in September, all the pieces are now in place to switch to the 
permanent system. At your house, it would just be a matter of unplugging 
the saw from the generator and plugging it back into the wall. But in 
space, it's not that easy.

"Everything will be fine – if nothing breaks," Curry said.

The plan is to send astronauts out on two spacewalks, each devoted to 
rewiring half of the station. Though it sounds complicated, that part 
shouldn't be too difficult. Spacewalks are inherently dangerous and 
should only be done if there is no alternative, Polansky said, but as 
spacewalks go, these are pretty straightforward. The astronauts will 
head outside, wait for the team on the ground to send commands to switch 
off the power, and then unplug the power cables and plug them in new 
places. There might be the occasional stiff cable to deal with – that 
can happen in the minus 200 degrees Fahrenheit of space – and the 
process will likely be slow, but not especially complex.

The real pressure, Polansky said, will be on those back in Houston.

"I hold my breath every time we do spacewalks because you never know 
what can happen," he said. "So I'll definitely be watching. But I don't 
think I'll be as worried as the guys in Mission Control and the folks 
who have been working on the hardware will be. I think I'll have a lot 
of company in the worry department."

Curry confirmed that suspicion. He's been training for this mission for 
six years, and he said his team couldn't be any more prepared. But when 
asked what about the mission keeps him awake at night, he had no trouble 
coming up with a list.

"My team is the one that has to turn everything back on and get it 
running," he said.

JSC2003-00016 : Robert Curbeam and Christer Fuglesang participate in 
spacewalk training Image above: Mission Specialists Robert Curbeam and 
Christer Fuglesang, wearing training versions of the Extravehicular 
Mobility Unit spacesuit, participate in an underwater simulation of 
extravehicular activity scheduled for the STS-116 shuttle mission to the 
International Space Station. Image credit: NASA

Theoretically, everything should go fine. But there are a few things 
that could cause some big hitches. Several of them have to do with the 
unpredictability of equipment that's been in space for years. For 
instance, before any of the rewiring can be done, half of the solar 
array that's been providing the temporary electricity must be folded up 
to make room for the new solar arrays to rotate. That's never been tried 
before, and it may not be as easy as it sounds.

"It's been sitting out there taking thermal cycles (moving from minus 
200 degrees Fahrenheit to plus 200 degrees Fahrenheit every 45 minutes) 
since November 2000," Curry said. "It's like a map – if you keep a map 
out in your car for six years and then you decide to fold it up again, 
you may get some waves in it or it may not fold back the same way at all."

Many of the main components of the electrical system have been flying 
that long and could cause similar large headaches. It's impossible to 
know for sure if the equipment will work until the power has been turned 
off, rewired and turned back on. And if it doesn't work, the astronauts 
can't leave it like that – the essential systems on the station would be 
running on whichever half of the station has power, but without both 
halves they won't have any backup.

That's not a position anyone wants to leave the station in for any 
longer than necessary. So, if Mission Control flips the switch and the 
lights don't all come on, the astronauts will have to try and fix 
whatever the problem is before they run out of time. If they can't, then 
it's back to square one.

"Then I have to tell the crew, stop what you're doing and undo 
everything," Curry said.

To avoid that, plans addressing possible problems are made well in advance.

"You put all your energy into being successful and doing it safely, 
while making sure you do it efficiently," Lead Shuttle Flight Director 
Tony Ceccacci said. "And then you step back after you get that completed 
and say, ‘What if?'"

JSC2006-E-33306 : Robert Curbeam with virtual reality hardware Polansky 
said the crew spends a lot of time training for those what ifs.

"They run through scenario after scenario," Polansky said. "Today we're 
going to do a main bus switching unit checkout, tomorrow we're going to 
do a pump module remove and replace. The next day we're going to a 
replace a direct current-to-direct current converter unit box. None of 
which we ever plan to do on orbit."

Image to left: STS-116 Mission Specialist Robert Curbeam uses virtual 
reality hardware to rehearse some of his duties on the upcoming mission 
to the International Space Station. Image credit: GO 
TO:http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts116/mission_overview.html

But, Ceccacci said, as much as you would like to, you can't plan for 
every contingency. You look at the most probable failure, impact to 
mission, complexity of recovering, then determine if you should spend 
the resources to develop the fix.

If the old solar array won't fold up, the astronauts won't be able to do 
any of their rewiring spacewalks until they either fold it up manually 
or jettison it. If the pump that keeps the electrical system cool 
doesn't work, there would only be enough time to rewire half of the 
station after replacing it. But he believes NASA is up to the challenge.

"Everyone has stepped up, is prepared, and is confident that this 
mission will be very successful," Ceccacci said. "As with all complex 
assembly flights, it's going to be interesting."