For 50 years, NASA’s been famous for counting backward from 10 to zero. But a final countdown is now under way that will stand out among them all.

After 126 space shuttle missions, only eight remain before the fleet is scheduled to retire. That’s eight flights remaining to use the unique capabilities of the shuttle to finish construction on the International Space Station and prepare it for life after shuttle. Each flight is unique and extremely complicated. Attention to detail and planning will be needed to be successful. There are no easy flights remaining and there may be pauses in this countdown that will ensure the highest chance of mission success. The shuttle will fly each flight when it’s ready.

Take the time to look and really study the remaining shuttle flights. Here’s a close up look at the countdown of flights:

8: STS-127—A Mission for all Nations

The International Space Station has been growing steadily over the past few years, but the one thing it still doesn’t have is a porch. STS-127 will take care of that.

Space shuttle Endeavour will deliver the external facility for Japan’s Kibo module during that mission, completing the Japanese complex on the space station and providing a science platform outside the station walls.

And if the international flavor of the cargo isn’t enough, it will be the first shuttle mission to visit the station after its expansion to a six-person crew, when the station will have representatives from all five international partners on board.

“It just brings a lot of different nations together,” STS-127 Commander Mark Polansky said. “I look at space and what we’ve done with the International Space Station as a wonderful example of how we can cooperate. We all have a common goal, and we all work together. We all have cultural differences, and somehow we put all that aside and we get the job done.”

The installation of the new external facility will be the perfect opportunity to demonstrate all that.

“You’ll have this truly integrated operation, where you’ve got the Canadian robotic arm holding the new big piece of Japanese hardware, brought up by a United States vehicle,” said Holly Ridings, the lead space station flight director for the mission. “If you think about the integration of all those parts and pieces, it’s really amazing how far we’ve come.”

7: STS-128—Stepping Up Station Science

Astronauts Nicole Stott and European Space Agency's (ESA) Christer Fuglesang, both STS-128 mission specialists, attired in training versions of their shuttle launch and entry suits, participate in a fixed-base shuttle mission simulator (SMS) training session in the Jake Garn Simulation and Training Facility at NASA's Johnson Space Center. Image credit: NASA

With the increasing size of the space station crew comes an increasing amount of crew time available to be spent on science. STS-128 will bring up new projects for them to spend that time on.

Tucked inside the multi-purpose logistics module to be carried up inside Discovery’s cargo bay will be two new experiment racks – the materials science research rack-1 and the fluids integrated rack. The materials rack will allow the crews of the space station to conduct experiments on such diverse materials as metals, glasses, crystals and ceramics. They’ll be able to study how materials mix and solidify or how crystals grow, outside the confines of the Earth’s gravity.

If it’s not covered by the materials rack, there’s a fair chance that it will be by the fluids rack. Colloids, gels, bubbles, boiling and cooling are just a few of the long list of areas astronauts will study using the fluids rack.

Of course, with all the additional science being done on the station, the crews will need more room in which to store the fruits of their labor. So Discovery will also bring up a second Minus Eighty Laboratory Freezer for ISS – or MELFI, as it’s known.

And one other way that the STS-128 (and STS-125 and STS-127) mission will further the cause of science is by taking part in crew seat vibration tests that will help engineers on the ground understand how astronauts experience launch. They’ll then use the information to design the crew seats that will be used in future Constellation launches.

6: STS-129—Spares to Space

There will be lots of reasons to miss the space shuttles when they retire, but one of the most practical ones will be the lack of transportation options for large space station equipment.

Astronaut Charlie Hobaugh (left), STS-129 commander; along with astronauts Robert Satcher (center) and Randy Bresnik, both mission specialists, attired in training versions of their shuttle launch and entry suits, await the start of a Full Fuselage Trainer (FFT) mock-up training session in the Space Vehicle Mock-up Facility at NASA's Johnson Space Center. Image credit: NASA

In addition to all the modules and truss segments that the shuttle has been hauling into space for the past 10 years, there have been occasional ORUs – or orbital replacement units, a fancy word for spare parts – many of which were big. Too big, in fact, to be brought up on any other vehicle that visits the space station or any that’s being planned.

“What you’ve done,” Kirk Shireman, International Space Station program deputy manager, said, “is take away the 18-wheeler and replace it with a bunch of small pickup trucks.”

For STS-129, the 18-wheeler’s cargo hold will be full of spares to keep the station going after the big wheels have stopped rolling. There will be a spare control moment gyroscope, a spare nitrogen tank assembly and a spare ammonia tank assembly. A spare latching end effector for the station’s robotic arm, and a spare trailing umbilical system for the rail car that the arm travels on. A spare antenna and a spare high pressure gas tank.

There will be plenty more spares to come before the last shuttle flight, but STS-129 is definitely a start.

“This should last us for some time,” Shireman said.

5: STS-130—A Room with a View

STS-130 will represent a major milestone mission, as it will be bringing up the last major United States addition to the space station. And as usual, last doesn’t equal least.

Not only will space shuttle Endeavour be bringing up the final node – this one named Tranquility – and giving the expanded crew plenty of space to spread out in, but as this node will come attached to the six-windowed cupola, it’s likely to become everyone’s favorite room on the station.

“This flight will, I think, grab the public’s attention,” Shireman said. “It’s just going to be a really, really neat module for those on board. The dream of being able to go out and just have an unencumbered view of space – we’ll have it. You can open up all the windows and look around and really feel like you’re out there.”

The windows aren’t just for fun, however – they’ll be working windows. As more cargo vehicles begin frequenting the space station, the station’s robotic arm is going to be called into action to capture some of them as they approach and guide them into their docking port. A good view of that operation will be a welcomed help to those at the controls of the arm.

4: STS-131 — Experiment Experience

Astronauts Alan Poindexter (left), STS-131 commander; and James P. Dutton Jr., pilot, occupy their stations on the flight deck during a Full Fuselage Trainer (FFT) mock-up training session in the Space Vehicle Mock-up Facility at NASA's Johnson Space Center. Image credit: NASA

Much of the science done on the International Space Station involves difficult-to-understand concepts with long, hard-to-pronounce names. But the STS-131 mission will prove that’s not always the case. The experiment racks space shuttle Atlantis will deliver to the space station inside its multi-purpose logistics module focus on things regular people here on Earth do every day: exercise and look out the window.

The experiment racks that STS-131 will deliver to the station – the window observational research facility and the muscle atrophy research and exercise system rack – are pretty much exactly what they sound like. The window observational research facility is designed to beef up the work that astronauts are able to do looking out the window of the Destiny laboratory by adding cameras, multispectral and hyperspectral scanners, camcorders and sensors. With those instruments, the crew will be able to study global climates, land and sea formations and crop weather damage like never before.

Meanwhile, the muscle atrophy research and exercise system rack – or MARES – will give the crew members a way to assess the strength of their muscles while in space. The deterioration of muscles not used while astronauts are floating in microgravity has long been a concern for space programs. This rack will mean that the crew members don’t have to wait until they’re back on solid ground to find out how their time in space affected their health. Instead, the MARES will help them exercise seven different human joints, gauge the strength of the muscles around those joints and decide how the countermeasures designed to prevent muscle atrophy are working.

3: STS-132—Finishing Touches

The last International Space Station modules to be delivered by a space shuttle will come up on the STS-132 mission.

The last space station module to be delivered by a shuttle also happens to be the first Russian module delivered to the ISS by a shuttle. It will be filled, for the launch, with pressurized U.S. cargo, installed by a Canadian robotic arm and include a European robotic arm – all of which underscores once more the very international nature of the International Space Station.

2: STS-133—Spares in Space

STS-133 was originally scheduled to be the final shuttle flight of the fleet, and as such, it was packed to the brim with one last load of spares.

There are debris shields for the Zvezda service module, and antennas for the S-Band communication system. There’s a spare ammonia tank assembly, a spare flex hose rotary coupler, several remote power control modules and even a spare arm for the Special Purpose Dexterous Manipulator.

“It isn’t glamorous, but it’s really important for the space station to execute its mission,” Shireman said.

Besides, even though none of the equipment will actually be installed, it will still take at least three spacewalks to get it all in position to be ready when needed. And this flight (along with the next) will also be used to try out a new relative navigation sensor that could be used on Orion, the next U.S. vehicle that will take astronauts to the International Space Station. So there should still be excitement to spare, as well as equipment.

“There are no boring shuttle flights,” John Shannon, Space Shuttle program manager, said.

1: STS-134—Shuttle Says Goodbye

It’s appropriate that the last flight of the Space Shuttle Program is scheduled to bring up the Alpha Magnetic Spectrometer. Designed to detect cosmic rays, it should continue the tradition of discovery that the space shuttles have fueled for almost three decades. Even so, it’s unlikely that will make it any easier to say goodbye. Shannon said it’s hard to imagine the end of the program at this point, but he expects it to be bittersweet.

“I’m sure it will be emotional,” he said. “But I suspect that it will not be sadness over the passing of that era, but happiness that we were a part of it. The assembly of the space station could not have been done without the space shuttle, and the assembly of the space station is one of the great engineering achievements of mankind.

“So the space shuttle will have done a good job.”