nd generating oxygen. The Station will also recycle water from the sinks, shower, urine, and condensation for oxygen generation, an in-orbit first.
Modules and nodes
The ISS will eventually grow to include over a dozen modules for living quarters, labs, and storage. They will be connected by airlocks and nodes, all tied to the main truss and its solar arrays.
The first module in the jigsaw-puzzle construction was the 42,600-lb Zarya, designed in the U.S. but built in Russia. It is 41-ft long and 13.5 ft at its widest, and provides power and propulsion while the ISS is being built. On the outside, it is studded with 36 steering jets for adjusting attitude, and it carries two larger main engines for reboosting and changing orbit. There are also 16 fuel tanks with a total capacity of 6 tons and two solar arrays putting out 3 kW of electrical power. Most of Zayra's functions will be carried out by the Zveda module once it is in place, leaving the Zayra as storage space and a fuel depot. Zayra's two side docking ports will accommodate Soyuz and Progress spacecraft.
There should always be enough Soyuz reentry vehicles on the station ready to act as lifeboats for the entire crew. The piloted, three-person Soyuz must always be flown by a Russian cosmonaut, according to the Russian space agency. It could eventually be replaced by spaceplanes based on the X-38, a NASA project which recently had its funding deferred.
Progress cargo rockets will deliver up to 6 tons of reboost propellant and dry cargo to resupply the station every two months. They will also serve as self-incinerating trash cans. ISS personnel will fill the Progress rockets with refuse, launch them toward Earth, and they will burn up on reentry.
The 43-ft long Russian Zveda module connects to one end of Zayra. During construction, Zveda houses the crew and main computers, distributes power, and maintains life support. All these functions will be redistributed once the ISS is completed. But Zveda will remain the heart of the Russian segment of the ISS, which will consist of a series of lab modules and a solar array and mast. The 42,000-lb module is similar in layout to the Mir with three compartments: a small spherical transfer chamber forward, a cylindrical work room in the center, and a cylindrical transfer chamber aft. It can dock with a Soyuz or Progress. Zveda also has power-producing solar arrays and an unpressurized assembly area wrapped around the aft end.
Living spaces on Zveda include personal sleeping quarters for three, each with its own window, a toilet and hygiene facilities, a galley with a refrigerator, freezer, a table for eating meals, and a treadmill and stationary bike for exercise. There is a large 16-in viewing port in Zveda's working compartment and three 9-in. ports in the transfer compartment so the crew can watch docking activities. All together, Zveda boasts 14 windows. Astronauts will live in it until the U.S. Habitation module is delivered in 2005.
At the other end of Zarya is Node One, or Unity Node, connecting it and Zveda, along with future Russian modules, to the rest of the station. It also gives engineers five additional ports for planned expansion. The 22-ft-long, 18-ft-diameter node will provide a passage to the U.S. and European labs and living quarters, and be the main structural connection to the truss. Though seemingly simple, Unity contains more than 50,000 mechanical items, 216 lines for fluids and gases, 121 internal, and external cables using six miles of wiring.
The Joint Airlock Module, which connects to the Unity node, gives astronauts a way to access space without using the Shuttle. Before it is installed, there will only be Russian-built airlocks, which are incompatible with U.S. spacesuit umbilicals. The Joint Airlock will store suits and be used for overnight "camp outs" in preparation for spacewalks. Astronauts will sleep in the lock while pressure drops from the station's normal 14.7 to 10.2 psi. This purges their bloodstreams of nitrogen, increases the oxygen in their blood, and prevents decompression sickness, or