After almost 10 years of construction, the International Space Station (ISS) will complete its power grid by deploying the last set of solar arrays today. The solar wings were installed during a space walk yesterday, March 19, and astronauts started unfurling them at 10:58 A.M. (EST). The entire process will last five hours (you can follow NASA updates on the deployment).

The 35-meter-long solar arrays, which extend 73 meters, tip to tip, will boost the power system on the ISS by 25 percent. Altogether, the station has four sets of solar wings that produce enough electricity to power 42 houses back on Earth. For the space station, though, the ramped-up energy supply will allow the crew to double in size, from three to six, and increase the capacity for science experiments.

But deploying the $298 million solar arrays does not come without concern. A previous set of wings snagged on a guide wire and ripped during deployment. An emergency space walk stitched the tear back together, and since then, the solar wings have worked flawlessly.

The new solar arrays are folded up in a set of boxes on the edge of the backbone-like main truss (S6) and unfurl like a map. It is common for the folds of the solar arrays to stick together since they have been stored in boxes for years. To avoid this phenomenon, known as stiction, the astronauts will deploy them in stages, giving each wing ample time to warm up.

As the solar wings deploy, the station must fly at an orientation that leaves it susceptible to communication failures. It also exposes some parts of the ISS to the extreme cold and puts other parts in danger of overheating. Thus, the astronauts have only five hours to unfurl the wings. Luckily, they have set aside extra time on Sunday in case things go awry.

The installation of the S6 truss, which holds the solar wings, increased the station to 102 meters in length from the left end of the truss backbone to the right. It is 14 meters high and weighs 303,585 kilograms. The $100 billion station is now, by mass, 81 percent complete. (View NASA’s animated assembly sequence of the ISS.)