Astronauts have made the third and final spacewalk for the observation dome, christened the Tranquility Node on the International Space Station. The astronauts made the final walk to add the windows to the Space Station. The observation dome features seven windows that offer breathtaking views of the earth below,with electrical connections and cooling systems being added in a series of spacewalks over the weekend. This extension to the space station has cost a whopping $27million, making it by far the most expensive piece of glass ever fabricated.