1.   If the two cylinders do not fit together precisely, hydraulic fluid can leak within the mechanism.

2.   That means there are self-adjusting valves -- three for each of the four cylinders -- and an electronic ignition to minimize maintenance.

3.   Then, two astronauts will perform three spacewalks to hook up all the electrical connections and cables between the two cylinders.

4.   Then, two spacewalkers will hook up all the electrical connections and cables between the two cylinders, and attach handrails and tools for future crews.