'Stiction': Key Enemy for Discovery Space Station Astronauts

HOUSTON, March 20, 2009 — -- "Stiction" is the word of the day in Mission Control. It's an engineering term that describes what happens when something sticks together.

In this case, it's the coated solar array panels just installed on the International Space Station. They were neatly collapsed, accordion-style, in a container for launch onboard the Space Shuttle Discovery.

Unfortunately, solar panels have a history of refusing to neatly unfold during installation. Astronauts have used unconventional methods to solve the problem -- shaking and rattling the panels, for instance. They even did squats inside the space station once, to set up a vibration running through the panels in an effort to shake them loose.

This afternoon, the Discovery astronauts successfully got the giant, gold-tinted panels to open. The operation went smoothly -- much more easily than it did with three previous sets brought up on earlier shuttle flights. It was a two-day process to install the 33,000-pound truss at the panels' base.

"We've had a good day," mission control told the astronauts.

This is the final set of solar panels to be installed on the space station -- and they will finally bring the space station to full power. Each solar array set has two 115-feet wings, making for a total span of 240 feet when one includes the equipment that connects the two halves and allows them to turn as they track the sun. They generate 66 kilowatts of electricity -- enough to power about 30 2,800-square-foot homes.

After previous crews ran into trouble with stiction, Mission Control devised a way to keep the arrays from sticking together. They had the astronauts turn the space station and the shuttle into what's called a solar-inertial attitude.

"What that really means," said Flight director Kwatsi Alibaruho before the deployment, "is that we will maneuver in a manner such that one side of the space station is always pointed at the sun at every point in its orbit. That's particularly important because of what we have to do thermally with the solar arrays."

Mission Control: Keep Panels from Sticking

It was a delicate, complicated process -- using the thrusters on the space station and on the space shuttle, firing to keep the entire complex pointed in the right direction toward the sun so that the solar panels would warm up.

Meanwhile, the crew on the space station will also put their plumbing skills to work -- to install a brand new urine processor to replace the one that never worked after it was installed during shuttle mission STS-126 last year.

The current mission is designated STS-119; shuttle flights often don't run in order.

This processor will recycle urine and sweat and turn it into drinking water. It is a critical life support system that must work before the crew on the space station can be expanded from three to six, scheduled for June.

Discovery's flight has gone smoothly so far. Just watch out for stiction.