Space Station 98% Complete with 4 Shuttle Flights Remaining

With the successful landing of the space shuttle Endeavour Sunday night, the International Space Station is on the verge of completion after $100 billion and 11 years of construction. NASA plans just four more missions to wrap up its few remaining station deliveries.

For Endeavour, in particular, Sunday's shuttle landing marked the beginning of the end. The spacecraft is the youngest of NASA's three aging space shuttles and engineers quickly began working to prepare it to launch one final spaceflight in July.

"We'll go into that with our heads held high," shuttle launch director Mike Leinbach said after the landing. "It's a little bit [of a] sad note, but a great ending to a great mission and we're looking forward to the next one."

Endeavour's 14-day mission delivered a seven-window observation deck and a new room to the International Space Station.

With the new additions — NASA's final major pieces for the space station — the orbiting laboratory is 98 percent complete.

NASA plans to retire its three space shuttles ? Discovery, Atlantis and Endeavour ? by the end of September. After that, American astronauts will have to hitch rides to the space station on Russian Soyuz spacecraft.

Earlier this month, President Barack Obama canceled NASA's Constellation program responsible for building new spaceships and rockets to replace the shuttle fleet.

Instead of building its own spaceships, NASA is banking on the rise of commercial spacecraft capable of ferrying astronauts to orbit so it can focus on loftier goals such as the moon, asteroids or Mars. The space agency already has contracts in place with companies to provide unmanned launches to deliver cargo to the space station.

Leinbach said there's a "whole series of lasts" coming, and he feels for the engineers responsible for priming each of those final steps.

Endeavour's STS-130 mission was NASA's 130th shuttle mission since the fleet began flying in 1981, and the 24th flight for Endeavour.

Fully formed space station

When the first station crew of three astronauts took up residence in November 2000, the outpost was made up of just three modules. Now, its external truss segments span the length of a football field and the station can easily be seen from Earth by the unaided eye.

The station can now support permanent crews of six astronauts. It has three airlocks and 12 rooms, counting the new bay window compartment delivered by Endeavour. It has enough living space to rival the cabin of a Boeing 747 jumbo jet.

The dome-shaped observation deck gives astronauts stunning panoramic views of the Earth from space. It also doubles as a lookout during robotic arm operations. The new room, called Tranquility, will serve as a hub for life support systems and exercise equipment.

Both compartments were built for NASA by the European Space Agency. Together, they cost nearly $409 million and boosted the space station's mass to nearly 800,000 pounds (362,873 kg).

The next four shuttle missions include several spare parts delivery flights, as well as the installation of a small Russian module and a $1 billion experiment called the Alpha Magnetic Spectrometer.

Next up on the launch pad will be the space shuttle Discovery, the oldest one after the Columbia and Challenger orbiters, both of which were lost in shuttle tragedies.

Discovery is due to launch on April 5 to deliver new science experiment gear and spare parts to the space station.

Shuttle era closing

Mike Moses, NASA's shuttle integration manager, said Endeavour's successful mission is a great start to the space shuttle era's final year. The shuttle launched one day late due to cloudy weather.

"We're off to a great running start with the year here," Moses said.

Cold weather in Florida has delayed Discovery's flight from its original March 18 launch target to April. But barring an unexpected setback or major payload delivery delay, NASA should be able fly all four remaining missions by the end of September as planned, Moses said.

But there is still a sense of loss for the space shuttle fleet. By the end of 2010, the world's only reusable space plane currently capable of reaching space will be grounded for good.

"The people fall in love with the machines, and it's going to be hard to let them go," Leinbach said. "We're professional about it, so we're going to prepare and process that last mission, and we'll move on."

That love was evident among Endeavour's crew after the shuttle landed late Sunday night. Shuttle commander George Zamka beamed with pride for his spaceship.

"Endeavour, my goodness, what a machine," he said from the runway. "She was perfect throughout the flight and we brought her back safe and sound thanks to Mission Control."

Mission specialist Kathryn "Kay" Hire, who started out at NASA as a shuttle engineer before joining the astronaut ranks, said she and her crewmates tried to be gentle with the spacecraft.

"I hope we didn't beat it up too much, because we know that you're going to be turning it around one more time to fly it again," she said.

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