The difficulties NASA experienced in the past two weeks due to the failure of a pump module in the space station’s cooling system has illustrated many things about the future of the International Space Station. I’ve already noted how it has shown us what we will lose when the space shuttle is retired in 2011, with nothing to replace it.

The pump module failure also illustrates a more fundamental issue, one that speaks directly to the station’s raison d’etre, and how neither NASA nor the American government gave this issue much thought when they designed and built ISS.

To put it simply, the space station is nothing more than a prototype interplanetary spaceship. As I explained in detail in Leaving Earth, the only reason at this stage in our history that you put human beings into space in a vessel for long periods of time is because you want to test the engineering and medical issues involved in building such a spaceship.

Most NASA engineers understand this. So do the astronauts. Consider astronaut Bill Shepherd’s thoughts during his stay on ISS back during the first expedition in 2001. “Put some more engines on this thing and send up that Mars vector,” he wrote passionately one day in his daily log. He knew the station’s real engineering purpose was to work out the kinks for building an interplanetary spaceship. He also knew that ISS wasn’t fulfilling that purpose very well.

The Russians have also understood this fact, from the very beginning of their space station program back in the late 1960s. Though Breshnev tried to sell the program as a research program for improving life on Earth, his space engineers paid only superficial lip service to this idea. Instead, they focused almost all their energies in trying to figure out how to build a spaceship that humans could not only live in for many years but would be as self-sufficient as possible.

For example, the Russians worked hard to develop closed water and oxygen systems. They also tried to grow plants in space, thereby providing crews with food and air as well as emotional stimulation as they acted as gardeners.

Furthermore, they engineered their stations so that the astronauts on board could easily maintain and repair them, using the material on hand with minimal help from mission control. They realized that if the spaceship was in orbit around Mars rather than the Earth, asking for help from the ground was simply impossible. And even in Earth orbit, they learned that it was often impractical to depend on any Earth-based resources. They found that the best and fastest way to get things fixed was to build their spaceship so that the crew could handle the problem, on their own.

For example, the failure of the coolant loop on the American half of ISS is not the first time a cooling system has failed on a space station. The Russians had their own problems with the cooling system on Mir. When that station was a decade old, corrosion began to appear wherever water condensed at the point of contact between the system’s aluminum pipes and the stainless steel grounding straps that held those pipes in position. Soon the corrosion led to leaks, and before long, Russian astronauts were scrambling continuously to keep the system from spilling its antifreeze coolant everywhere.

In the case of Mir, however, the system was built so that the astronauts could access everything from inside the station during their normal maintenance routines. Over a period of years they made it a routine practice to not only repair the leaks but to reconfigure the entire system so that the corrosion would not reoccur. In the end the problem was completely fixed, and Mir functioned better in its later years because of this.

Unfortunately, the American half of ISS was not designed with this flexibility in mind. Instead, its components are built not to be maintained in space but to be shipped as large units up and down by the shuttle so that they can be refitted on the ground.

The result is that the repair of the American cooling system is far from trivial, as it requires multiple spacewalks to replace the failed pump. Moreover, the pump itself can’t be maintained or repaired in orbit. Instead, it must be removed as a unit and returned to Earth for overhaul. This design means that the American portion of ISS is tied to the Earth and to its ferrying service, rather than being self-sufficient and independent as any interplanetary spaceship must be.

There are other indicators to show how little the American half of the station resembles a useful spaceship. View for example the tour of ISS that I have been posting for the past week and compare the Russian and American sections of ISS. It is no accident that the walls in the Russian section are painted in pleasant oranges, blues, and greens. Many years ago on their early Salyut stations they learned that these colors helped improve the crew’s morale during long stays in this artificial environment.

The American side of the station, however, whether built by the U.S., Europe, or Japan, all have blandly white walls, and look very sterile. If you had to choose between living in either the Russian or American sections, which would you prefer?

What all these facts illustrate about ISS is that its design is not focused on creating a spaceship useful for interplanetary travel, able to function independent of the Earth for long periods. Instead, the station was conceived by politicians as a so-called space laboratory that also serves as a jobs program for their constituents in Texas and Florida. It was then built by NASA as a sophisticated engineering toy that might work wonderfully, but remains entirely a creature of the Earth, even if it is in space, several hundred miles above its surface.

As a result, we will have continuing and chronic problems keeping this station afloat. Even after we replace the shuttle’s ample crew and cargo ferrying capability, we will be forced to spend a great deal of money and time maintaining and supplying the station. Repairs will be complex and require ground assistance. And relatively little will be learned on how to build a spaceship that can safely and effectively fly humans to Mars and back.