Strapped to the back of a modified Boeing (News - Alert) 747 carrier jet, NASA’s space shuttle Discovery headed to the Smithsonian’s Air and Space Museum Annex in Virginia. And with that, the space shuttle program truly passes into history.

“It’s sad to see this happening,” said NASA astronaut Nicole Stott, a member of Discovery’s final crew. “But you look at it and you just can’t help but be impressed by it. That’s my hope now, that every time someone looks at that vehicle they are impressed, that they feel that this is what we can do when we challenge ourselves.”

NASA’s next challenge is building ships that can carry human passengers beyond the 240-mile-high orbit of the International Space Station. To carry out this feat, NASA plans to work with commercial cargo carriers and to eventually work with commercial carriers who can launch human and robotic crews into orbit.

“We’re excited about what President Obama is allowing us to do, working hard with the commercial entities,” said Charles Bolden, Jr., NASA’s administrator, in a CBS interview last year. “We hope to fly our first commercial cargo missions early next year.”

The Space Exploration Technologies Corporation, or SpaceX (News - Alert), plans to launch a test version of their Dragon Capsule to take cargo to the International Space Station. The launch was originally scheduled for February 7, but the launch date has been pushed back to allow for additional testing.

“They will be American-made rockets flying cargo to the International Space Station, and we’re already starting to work with commercial entities,” said Bolden. “We hope to release a request for proposal on commercial contracts to take crews to orbit; maybe three years after we let the contract, we’ll have a capability.”

Discovery was scheduled to make a loop around Washington, D.C., before landing at Dulles International Airport. From there, it will be transferred to the Smithsonian’s Steven F. Udvar-Hazy Center in Chantilly, Virginia.

Discovery’s fellow shuttle, Endeavor, will head to the California Science Center in Los Angeles later this year. The third remaining shuttle, Atlantis, will be displayed at the Kennedy Space Center Visitor Complex in Florida.

“It’s a very emotional, poignant, bittersweet moment,” said former astronaut Mike Mullane, a veteran of three space shuttle missions. “When it’s all happening you think, ‘This will never end,’ but we all move on.”