An illustration shows the current makeup of the international space station. Photo: NASA

President Reagan first proposed building an international space station during his 1984 State of the Union address. At that time, NASA hoped to have the station in orbit by 1992 at a cost of $8 billion, not counting shuttle transportation.

They were a bit off on the launch date and the cost.

The Government Accounting Office estimated in a 1998 report that NASA will spend more than $50 billion on the station through assembly complete in 2006.

The European Space Agency, Japan and Canada will contribute another $12 billion. There are no reliable cost estimates for Russian hardware and services.

Despite the soaring costs and numerous delays and redesigns, space station assembly finally began Nov. 20, 1998, with launch of the NASA-financed, Russian-built Zarya module atop a Russian Proton rocket.

NASA launched the Unity node the following month, on Dec. 4, and a shuttle supply and outfitting mission on May 27, 1999.

But, as expected, assembly came to a halt because of Russian funding problems that delayed completion of the all-important Zvezda command module for more than two years.

The Russian built-and-financed Zvezda provides crew quarters, life support systems, propulsion and the computer control needed to operate the station in its early stages. The module was not ready for launch until July 12.

As the Russians were putting the finishing touches on Zvezda, another shuttle crew delivered fresh supplies to the station on May 19, 2000, and replaced ailing batteries in the Zarya module.

Zvezda then was launched and an unmanned Progress supply ship docked with Zvezda's aft port in early August. It was unloaded by the crew of shuttle Atlantis in mid September.

The station as seen by Discovery during undocking earlier this month. Photo: NASA TV/Spaceflight Now

Melroy, McArthur and five crewmates aboard the shuttle Discovery delivered a $273 million structural truss one month later that was attached to Unity's upward-facing, or zenith, hatch. The astronauts also mounted a new $20 million shuttle docking port on Unity's Earth-facing, or nadir, hatch.

The 18,300-pound Z1 truss will serve as the mounting point for the so-called P6 solar arrays scheduled for delivery in December.

The largest power system ever deployed in space, the P6 arrays will stretch 240 feet from tip to tip, providing nearly 31 kilowatts of power. The array truss also features radiators to dissipate heat generated by the Destiny module's electronic systems.

Once in place, the P6 arrays will make the space station the third brightest object in the night sky when it passes overhead at dawn or dusk. And the huge arrays make up just one quarter of the station's eventual complement of solar panels.

The Z1 truss also houses the station's main communications antennas and four massive gyroscopes that will keep the station stable and properly oriented without rocket firings that would use up valuable fuel and jar sensitive microgravity experiments.

The satellite communications system and the gyros cannot be activated until after the laboratory module Destiny - and its computer system - is attached in late January.

Until then, normal television from the station will only be possible when shuttles are docked and during infrequent passes over Russian ground stations.

But that is the least of Shepherd's worries.

"One of the biggest challenges we've got is finding everything," he said. "Right now, we have the (Zarya module) basically filled to the gills with bags of gear. We also have a fair amount of equipment in the node. Much of this stuff is to be installed in (the Zvezda module)."

So much "stuff," in fact, the station features a computer barcode system to keep track of what's on board and where it's located.

Continue to Part 3