GWEN IFILL: Now to a sight that captivated people in and around the nation's capital this morning: the space shuttle flying through normally closed federal airspace en route to its last mission.
Cameras and crowds greeted Discovery as it soared over Washington this morning, flying piggy-back style atop a Boeing 747.
MAN: Just could not believe I was seeing what I was seeing.
MAN: Kind of a once-in-a-lifetime opportunity to see a space shuttle coming in.
BOY: It was so loud that my ears kept making that noise over and over and over and over again.
GWEN IFILL: It was the final flight and the last hurrah for the 100-ton spacecraft, landing at Dulles International Airport and bound for retirement and permanent display.
Discovery completed its active service career in March 2011, after 39 missions and multiple milestones. It carried the Hubble space telescope in 1990 and later ferried John Glenn, the first American to orbit the Earth, back into space at the age of 77.
And after the Challenger and Columbia disasters, it was Discovery that revived the program for NASA.
NewsHour science correspondent Miles O'Brien spent the day at Kennedy Space Center in Florida, which he said has been hit hard by the shuttle's end.
MILES O'BRIEN, science correspondent: The goal from the outset for the shuttle program was to provide cheap, reliable access to space. And it did neither. It's a complex craft, an expensive craft. And ultimately we lost two crews, 14 men and women who we lost along the way, proving itself to be not a very safe way to get to space either.
So, on a lot of fronts, the shuttle fell short. Having said that, the main reason you have a space shuttle is to build an International Space Station. And there is an International Space Station orbiting our planet now thanks in large part to the space shuttle.
GWEN IFILL: Discovery is now headed for the Smithsonian Institution's National Air and Space Museum annex just outside Washington in Chantilly, Va.
It replaces the prototype orbiter Enterprise bound for New York City's Intrepid Sea, Air and Space Museum at the end of the month. A second shuttle, the Endeavour, will eventually make its home at the California Science Center in Los Angeles. And a third, Atlantis, will be displayed in the location where it all began, at the Kennedy Space Center.
But with the shuttles grounded for good, the future of U.S. space travel, whether private or public, remains uncertain.
MILES O'BRIEN: NASA pushed very hard under the Obama administration to focus on giving low-Earth orbit over to small startup entities, like SpaceX run by the PayPal billionaire Elon Musk, to try to make a business of it.
NASA is currently involved in a project to build a -- what they call a heavy-lift rocket, which could take the space agency someday to an asteroid or perhaps even on to Mars.
But a lot of people would look at the money spent on the commercial side and the money spent on this big, heavy-lift rocket and say that there's not enough budget for either program.
GWEN IFILL: In the meantime, the first SpaceX flight to the space station on a cargo run is slated for April 30.
And for more on all this, we're joined by Valerie Neal, a curator at the Smithsonian's National Air and Space Museum.
So how has the shuttle program, after all these years, all this time, a collective 12 spent space, up and down, up and down, how has it transformed our notion of space exploration?
VALERIE NEAL, Smithsonian National Air and Space Museum: I think the space shuttles served three real purposes for us.
One was, it was a very ambitious attempt to establish routine space flights, create the sense that people could go into space, live and work, do useful things there. But the flip side of that coin was that the two tragedies reminded us that the spaceflight may never be routine due to the inherent risks.
GWEN IFILL: So this idea we had that we would go back and forth, it would be almost like commuting to go back and forth in space, that, we had to let go of.
VALERIE NEAL: Well, not really, because we continued to do it after both of the tragedies. And 135 missions in 30 years is a pretty good commuting record. But I think we can no longer take for granted that it's perfectly safe.
And I think the engineers and managers knew that all along, but the public was lured into the idea that this was going to be so easy, that all the rest of us might have a chance to go into space too. And that isn't going to happen for a while.
GWEN IFILL: Not for a while.
Miles was just mentioning the space station and how the fact that it is up there orbiting the Earth proves that something was achieved, that something major was achieved. What happens to the space station now without the shuttle fleet to service it?
VALERIE NEAL: Well, it will continue in operation, but it will be serviced by much smaller vehicles, the Russian Soyuz and then some small automated supply craft. It will not be able to receive major components anymore, because there's no big space truck anymore.
GWEN IFILL: Yes.
How was it decided where these retired vehicles, spacecraft would go?
VALERIE NEAL: Well, NASA basically solicited applications from interested museums and had everyone fill out their proposal, their application.
GWEN IFILL: Did they get a lot?
VALERIE NEAL: I don't know. I wasn't on the inside of that.
I only know what I heard in the media. But, evidently, they evaluated those and decided on suitable sites. And they seemed to have had a preference for major population centers with high tourism rates.
GWEN IFILL: Museums that already were existing and already were drawing people.
VALERIE NEAL: Right, and in locations that would draw a maximum number of visitors.
GWEN IFILL: So if I am taking the kids to go see the space shuttle or the adults to go see the space shuttle, what do they see?
VALERIE NEAL: Well, they will see at our facility the space shuttle in parked or landed configuration. The payload bay doors will be closed. And it will look as if it's just returned from a mission. But the big difference between Discovery and Enterprise is that Enterprise looks pristine and Discovery looked well-used.
GWEN IFILL: Enterprise is the orbiter that's there now.
VALERIE NEAL: That's correct. It was the prototype, as you said.
It never flew in space. It only flew in the atmosphere. But Discovery has been to space and back 39 times. And it looks like it. It's more beige than white and it's more charcoal gray than black.
GWEN IFILL: Do you get to go inside if you go to visit it?
VALERIE NEAL: No, not directly, but indirectly. Through a virtual reality experience, you'll be able to go inside and command it.
GWEN IFILL: Now, today, when this was flying around Washington, I know we got very excited here. We looked out the window and saw it going by.
Did you notice this reaction and think to yourself, gee, the idea, the romance of spaceflight is still alive in the public mind?
VALERIE NEAL: I think so.
I think it's probably a surprise to everyone how the public turned out today with such enthusiasm. And it's quite clear that Americans are still very much interested in human spaceflight and very proud of their space shuttle.
GWEN IFILL: Enough to imagine this ever returning to service or something like it returning to service?
VALERIE NEAL: It appears that for the near future, something smaller will go into service.
I think it's likely to be a very long time before we see a big winged craft, a space plane. But what goes around comes around. And the space plane concept was popular in the 1950s, but we went into space in capsules. And now we're going back to space in capsules, but maybe some day there will be a jet that will go into space, a Buck Rogers jet.
GWEN IFILL: A Buck Rogers jet, boy, that takes me back.
Valerie Neal of the Smithsonian, thank you very much.
VALERIE NEAL: It's a pleasure to be here. Thank you.