On Wednesday, the Obama administration announced that it wanted to extend the life of the International Space Station until at least 2024 — four years past the existing deadline.

That could postpone the day when the space laboratory needs to be brought down into the Pacific Ocean. But the decision will still have to go through Congress, which has the final say over NASA's budget. The U.S. currently spends around $3 billion per year to help maintain the space station with other countries.

So it's worth taking a step back and asking, why do we have the International Space Station in the first place? What's it for? And what does it matter if we extend its lifespan or not? Below is a basic primer:

What is the International Space Station?

It's a large space station orbiting at 250 miles above Earth, with living space for up to six crew members, laboratories, and solar arrays to generate electricity.

The program began in 1993 as a joint effort between the United States, Russia, Europe, Japan, and Canada. Construction began in 1998 — four years behind schedule — and the first crew members got there in November 2000. Since then, the space station has been continuously occupied by rotating crews that typically stay four to six months. The station was finally completed in 2011.

The U.S., Russia, Europe, and Japan have all sent spacecraft up to the station. But in 2011, NASA ended its space shuttle program, which means that, currently, the only way for crew members to get to the station is via Russian Soyuz spacecraft. Some private U.S. companies are developing their own spacecraft to get to the station — Space X launched the first successful resupply mission in 2012 — but that's still in the early stages.

To date, the International Space Station has cost as much as $160 billion, with the United States providing the bulk of the money — nearly $100 billion (although it depends how you include the price of the space shuttle program). Russia, Europe, Canada, and Japan chipped in for the rest. It's arguably the most expensive single object ever built.

What's the point of the space station?

Scientific research, mainly — from studying drug-resistant bacteria to preparing for future space exploration. But the goals have shifted over time.



Japanese astronaut Takuya Onishi is helped with entry into his Extra Vehicular Activity suit by EVA tech James Lemon on the pool deck inside the Neutral Buoyancy Laboratory at the Lyndon B. Johnson Space Center in Houston. Astronauts training for service on the international space station train underwater at the laboratory, which has a mock-up of the space station. Ricky Carioti / The Washington Post

The project was originally conceived as NASA's next step after the Apollo moon missions, but sat on the drawing board for decades. Then in the early 1990s, after the fall of the Soviet Union, U.S. officials worried that Russian rocket scientists might "work for rogue nations, spreading missile technology." An international space station was one way to keep those scientists busy (though that wasn't the only rationale).

In 2001, NASA outlined three official goals for the station: Conducting research, establishing a continuous human presence in space, and fostering international cooperation. Later, when NASA began setting its sights on sending people to Mars, the station emphasized more research related to exploration, such as the effects of zero-gravity on human biology.

As my colleague Joel Achenbach reports, the space station's zero-gravity environment makes it useful for certain types of research that simply can't be done on Earth: "Dust has no urge to settle down, and so it clogs air filters faster than engineers had once anticipated. Bacteria grow in odd corners and crannies. ... Mundane problems such as clogged filters and mold formation provide lessons for an eventual human mission to Mars. On a Mars voyage there would be no way to turn back halfway, so engineers have to understand in advance what could go disastrously wrong."

NASA is currently planning to send humans to an asteroid by 2025 and to Mars by the 2030s. The agency has identified 32 different potential health risks that astronauts could face on long flights through outer space. And, the agency has found, research on the space station is indispensable for mitigating at least 21 of those risks. So that's one big area of focus.

Is all that research worth the $100 billion price tag?

There's no easy answer to this, since we don't yet know how all that research will pan out. And a lot depends on how much value you place on human space exploration. But here are a few numbers to consider:

As Indiana University's William Bianco points out, after a slow start, at least 278 research projects have since been carried out on the International Space Station. More than 90 percent of projects on the station are expected to lead to published articles — an encouraging sign of research quality.

Advocates claim that some of this research has already proven extremely promising, with benefits for us Earth dwellers: "Medical examples include potential vaccines for Salmonella and antibiotic-resistant strains of bacteria, and a microencapsulation technique for delivering cancer treatment drugs to tumors without affecting healthy cells. Additionally, technologies advanced by the ISS have led to robotic surgical techniques that are opening the door to successful removal of tumors that were previously considered inoperable."

That said, a full accounting would also have to factor in the opportunity costs. NASA doesn't have an infinite budget, and there are experts who think human space exploration is less cost-effective than other types of space research.

What's the argument for funding the space station another four years until 2024?

The alternative is to let it crash into the ocean in 2020. The space station can't just stay up in orbit on its own — its too bulky, and would create too much space junk. So if the world cut off funding, the station would need to brought down in a controlled "de-orbit" — eventually splashing into the Pacific Ocean.

Giving the station a four-year reprieve would allow further research that could prove crucial to future human space exploration, officials have argued. "We want to push out beyond low-Earth orbit," said William H. Gerstenmaier, the head of NASA’s human spaceflight program. "We are going to have to use this small foothold called the International Space Station to go do that. This is our only opportunity."

NASA and the White House offered a bit more detail here: "A related critical function of [the International Space Station] is testing the technologies and spacecraft systems necessary for humans to safely and productively operate in deep space. Extending ISS until 2024 will give us the necessary time to bring these systems to maturity."

Another possible side effect: Keeping the space station will help NASA nurture a private U.S. space industry. There are currently two companies — SpaceX and Orbital Science Corp. — with contracts to resupply the space station until 2017. And several firms, including SpaceX and Sierra Nevada, are developing their own capacity to launch crews to the station by 2017. If the space station is sticking around until 2024, more companies could get into the business — which could, in theory, help drive down the cost of private spaceflight.

What's the downside of extending the space station's lifespan?



In 2012, the SpaceX Dragon capsule successfully attached to the international space station--the first private company to launch its own craft for successful rendezvous with the station. (NASA)

It's not cheap. As mentioned, the station currently costs NASA about $3 billion per year. And that's just NASA's contribution. If other nations don't get on board with the extension, it's possible that the United States could pick up more of the tab. "We are prepared to do what we have to do in case the partners need to take a different path," NASA's Gerstenmaier said on Wednesday.

That's a hefty chunk of NASA's budget, which will clock in around $17 billion in 2014. The space station could well eat into NASA's other missions. Here's Achenbach: "Space policy experts warn that, without a significant boost in budget, NASA will not be able to keep running the station and simultaneously carry out new, costly deep-space missions."

There are also technical challenges in maintaining the station, as laid out in a Congressional Research report. Until 2011, NASA's space shuttles could transport broken space-station parts down to Earth for repair. But the shuttle program has ended, and it's not clear that the next generation of private spacecraft are versatile enough for repair work. "Instead, new parts will need to be manufactured and sent up, but even this may be impossible in a few cases, as some ISS parts are too large for any of the planned post-shuttle cargo alternatives."

Is 2024 the final date? How long can the space station last?

In his press conference on Wednesday, Gerstenmaier mentioned that the space station would stay up until "at least" 2024. Right now, NASA and its contractors are working on certifying that the station's components can hold up until at least 2028.

What does Congress think?



A Falcon 9 SpaceX rocket lifts off Dec. 3 from Cape Canaveral Air Force Station in Florida. The rocket is carrying its first commercial payload, a communications satellite. John Raoux / AP

The space station has plenty of supporters — not least because of the economic angle. In 2011, NASA bought goods and services in 396 of the 435 congressional districts.

One example: Florida's space industry took a big hit after the end of the space shuttle program in 2011. So it's no surprise that Florida Sen. Bill Nelson is in favor of keeping the space station aloft: "This means more jobs at the Kennedy Space Center as we rebuild our entire space program.”

But there are other arguments, too. Rep. John Culberson (R-Tex.), a member of the House appropriations committee in charge of NASA funding, applauded the move on national-interest grounds. "“It’s inevitable and I’m delighted that NASA understands the value of ensuring that America continues to hold the high ground.”

Still, the budget crunch could prove difficult, as NASA expert Keith Cowing detailed here. The House wants to set NASA's budget at $16.6 billion in 2014, which will make it tough to fully fund both the space station and deep-space missions like the SLS/Orion Exploration program. "As such," Cowing notes, "death for both of them is a likely through financial neglect" — unless Congress plans to boost NASA's budget significantly.

Further reading: My colleague Joel Achenbach has written a terrific series on the station, and NASA more generally, that's worth reading in full.