The International Space Station's first three-man crew moved in on Nov. 2, 2000, 15 years ago Monday, the first of 45 expeditions to date that have logged a decade and a half of continuous human presence in low-Earth orbit.

Some 220 individuals have visited or lived aboard the sprawling laboratory complex to date, building the outpost piece by piece, working through complex research, enduring tragedies on Earth and celebrating hard-earned triumphs, all in the vacuum of space at an altitude of 250 miles and a velocity of 5 miles -- more than 80 football fields -- per second.

The numbers boggle the mind.

Doing the math

Building the station required 37 dedicated space shuttle flights to deliver the lab's solar arrays and truss segments, nine U.S., Japanese and European pressurized modules, the station's Canadian-built robot arm, science racks, experiment hardware, spare parts and myriad other components.

Russia launched two heavy-lift Proton rockets to deliver the Russian-built, NASA-financed Zarya storage and propulsion module and the Zvezda command module, launched a pair of airlock/docking modules aboard Soyuz boosters and built a third that was delivered aboard a space shuttle.

The International Space Station

NASA

The steady stream of Soyuz spacecraft provided the transportation backbone that kept the outpost operational when the shuttle was grounded after the 2003 Columbia disaster. And in the wake of the shuttle fleet's retirement in 2011, the Soyuz is the only vehicle currently able to carry crew members to and from the station, serving as a lifeboat between dockings and departures.

A cadre of 122 astronauts and cosmonauts representing nine nations has carried out 189 spacewalks to build and maintain the space station, logging 1,184 hours -- 49.3 days -- of EVA time. Another spacewalk, the 190th, is on tap Nov. 6. All told, station spacewalkers have logged seven times more than the 166 hours of spacewalk/moonwalk time spent by the Apollo astronauts during orbital test flights and moon missions.

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To deliver the supplies, equipment and research gear needed to support station operations, Russia has launched 61 robotic Progress supply ships to date, including two launch failures. Japan has launched five of its large HTV supply ships and two U.S. companies, SpaceX and Orbital Sciences Corp., have launched 12 supply spacecraft, including two failures.

The European Space Agency contributed five Automated Transfer Vehicle -- ATV -- cargo ships before the program was phased out last year.

The resulting space station, after a final shuttle visit in 2011, has a mass of nearly 925,000 pounds, roughly equivalent to 320 automobiles, a spine of pressurized modules stretching 167 feet and a huge solar array truss mounted at right angles that extends 375 feet, longer than a U.S. football field.

The NASA-supplied solar arrays have a surface area of 38,400 square feet, enough to cover eight basketball courts, generate 84 kilowatts of power and are tied into more than 8 miles of wiring threaded throughout the complex. More than 350,000 sensors feed data to scores of computers running millions of lines of code.

The station has a total pressurized volume equal to a 747 jumbo jet and a useable volume roughly equal to a five-bedroom house.

Depending on how one does the math, the International Space Station cost U.S. taxpayers more than $100 billion over three decades, including shuttle assembly flights, making it one of the most expensive engineering and science projects in human history.

The space station compared to a football field

NASA

Has it been worth the extraordinary price tag?

To Bill Shepherd, a three-flight shuttle veteran who served as NASA's first space station program manager and then commander of the lab's first crew, the tools and techniques that were used to build and operate the outpost provide a roadmap for how future deep space missions to Mars and beyond will be managed.

"I always had in the back of my mind, what would this mean to space efforts 20, 30, 50 years in the future? What were we doing that would affect these future outcomes?" he said in an interview.

Multiple trips to low-Earth orbit will be required, he said, along with "substantial EVA, very complex, very well choreographed, we'd have to have a multi-national effort that brought together the best things the different countries could offer in terms of resources and capabilities."

"If you look at space station, it's a blueprint for the future," he added. "All of those questions are behind us. Space station is just that, and that's why it's important."

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Astronaut Terry Virts, who returned to Earth in June after 200 days aboard the station, agreed, saying the lab will be remembered for centuries to come for laying the groundwork for future exploration.

"I think from an international relations point of view, the space station has been the most successful American foreign policy initiative since the Marshall Plan," he said. "I think 500 years from now, people are going to remember that this was our first step into space."

But John Logsdon, a noted author and space historian, said the jury's still out on the project's ultimate value. Learning how to build a large space vehicle may, indeed, inform plans for future missions. But if that's the only objective, it's already been accomplished.

The question now, with the space station essentially complete, is whether it will generate the science needed to justify continued operations.

"I think we don't know yet," Logsdon said in an interview. "After all, the research really started in earnest only after assembly complete (in 2011), and the nature of research is it takes some time before you can get a sense of the quality of the results. There haven't been any spectacular research breakthroughs that I'm aware of."

But, he added, there has been "a lot of peer-reviewed published papers coming out of space station research so there's good quality science being done."

"But I think its a fair question whether good quality science is worth the annual cost of getting it," he said. "It probably makes sense to give that test the 10-plus years to 2024. But by that time ... somebody else should either assume the major responsibility or it's time to quit."

A Russian Soyuz ferry craft approaches the International Space Station carrying a crew of three.

NASA

From a purely technical standpoint, the space station should remain viable at least through 2024, the U.S. government's current goal, as long as NASA has the resources to build spare parts, pay for cargo launches and provide transportation for U.S. and partner astronauts, either aboard U.S. commercial spacecraft or Russian Soyuz capsules.

The station's long-term survival also assumes Russia stays the course, continuing to supply a steady stream of Soyuz spacecraft and crews, along with Progress cargo ships.

And it's important to remember that neither nation can operate the station on its own. Russian modules and cargo ships provide the propellant and rocket power needed to maintain the lab's orbit while stabilizing gyroscopes provided by NASA, along with most of the station's electrical generation capability, are operated by the United States.

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Michael Suffredini, who retired as NASA's space station program manager in September, said a recent analysis by Boeing, NASA's prime contractor, shows the complex is structurally sound and, barring a catastrophic failure of some sort, should remain so through 2028, the 30th anniversary of the Zarya module's launch.

In an interview before he stepped down, he said the space station "is designed in a modular fashion meant for repair. So as long as you have spares for all the things that can break, you can last as long as the structure will let you last. Within reason."

Getting to 2024, the currently approved objective, should be relatively straight forward. Getting to 2028 or beyond, even with political support, will be more problematic.

"When we get to 2028, the solar arrays are going to be struggling, I'm probably going to have a handful of radiator (coolant) lines that have been isolated," Suffredini said. "2028 might be possible, but it also might be very challenging because then you're talking about the cost of replacing big things that may be prohibitive.

"All our analysis kind of says we think we can get to 2028. As we start getting beyond 2028, if it makes sense, and things aren't failing at a rate that makes it difficult for us to keep up, and the country thinks it's the right thing to do, then we can look at going beyond that.

"But 2028's kind of where we're drawing our line today based on the original design of the structure."

Next: A Long and Tortured History

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