HOUSTON - The oldest surviving artificial Earth satellite, Vanguard 1, turned 50 years old on Monday — and continued to turn in its orbit, just as it has done since its launch at the dawn of the Space Age. The craft is in a high orbit that promises to be stable for centuries. Circling there, it has outlived almost all of the human beings who created it.

The satellite already has completed more than 197,000 Earth orbits, racking up more than 6 billion miles (10 billion kilometers) of travel. Only the Pioneer and Voyager probes, currently speeding away on the edge of the solar system, have gone farther.

Vanguard 1's current orbit ranges from 400 to 2,400 miles (653 to 3,839 kilometers) in altitude, and the high point has dropped only about 60 miles (100 kilometers) in the past half-century. It reliably records one additional orbit every 133 minutes. But the craft's orbital stability is guaranteed only as long as there’s no outside interference. And now there's a chance that America's longest-lived spacefarer could have another round of "space pioneering" ahead of it.

Vanguard 1 was the first artificial earth satellite powered by solar cells, and its small suite of instruments provided unprecedented information on Earth's size and shape, air density and temperature ranges, and the micrometeorite density in space. Tracking its orbit helped geophysicists realize that Earth is not round but slightly pear-shaped, with a slight, symmetric equatorial bulge. It’s not just squashed, it’s lumpy.

The 3.25-pound (1.5-kilogram), 6.4-inch-wide (16.3-centimeter-wide) sphere was so small in comparison with Sputnik and Sputnik 2 that Soviet Premier Nikita Khrushchev scoffed at what he derided as a "grapefruit satellite." The jibe rebounded, Moscow jokesters reported, when most Russians responded to the putdown by asking what a "grapefruit" was.

The project was named Vanguard in 1955 when scientists hoped it would be the very first element, or "vanguard." of human expansion into space. History upset those semantic intentions when the Soviet Union's Sputnik and America's Explorer went into orbit first. Vanguard 1 was actually the fourth satellite to reach orbit. Two larger and more heavily instrumented successors were to follow.

Vanguard 2 was launched on Feb. 17, 1959, into a very similar orbit — where it continues to circle Earth and will do so for centuries, if left alone. Vanguard 3, launched Sept. 18, 1959, is on a similar space track. All three satellites were accompanied by castoff third-stage rocket casings that are in similar orbits.

The launches also left behind smaller orbital debris items such as metal straps, which have decayed more quickly because of their higher drag and lower mass. And according to satellite catalog scholar Jonathan McDowell of the Harvard-Smithsonian Astrophysical Observatory, one small piece from Vanguard 2, which was detected 15 years after launch, re-entered the atmosphere and burned up last October.

Bringing it home?

Vanguard 1's experiments and transmitter fell silent in 1964, and the satellite has been out of contact with Earth since then. But now fate is offering Vanguard yet another chance to live up to its pioneering name. Well before it is threatened with atmospheric immolation, Vanguard 1 could become the first satellite brought home, for museum display, by a new generation of robotic space vehicles.

Space entrepreneur Dennis Wingo, who has specialized in spaceflight applications of robotics and teleoperations, is the author of "Moonrush: Improving Life on Earth with the Moon's Resources." He told msnbc.com that bringing Vanguard 1 back to Earth could yield at least two important benefits.

"This could be a demonstration of a robust on-orbit servicing capability for industry," he said in an e-mail. Wingo added that studying the recovered Vanguard craft "could give scientists insights not possible otherwise regarding the long-term environmental effects of space and space debris on a spacecraft" orbiting much higher than the international space station and other vehicles accessible to astronauts.

Slideshow: Space Shots In 1984, the space shuttle Discovery brought home two errant communications satellites that it had chased down and picked up. Both were later launched again, one of them on a Chinese booster. Shuttles have visited other satellites to repair them, and have brought back replaced hardware from them. Shuttles have also deployed and then retrieved science probes on the same mission. But Vanguard 1 would be an entirely new kind of quarry, using entirely new kinds of tools.

The operation could mark a historical milestone, said Robert Pearlman, editor of the CollectSpace Web site, which focuses on space history and memorabilia.

"Most of mankind's pioneering spacecraft, the early unmanned satellites, were lost when they re-entered the Earth's atmosphere," Pearlman said in an e-mail. "Saving Vanguard as a representative of that early era of the Space Age would serve as an important touchstone for future generations who look back and wonder how it all started. Vanguard's primary mission in space may be long over, but its mission back on Earth holds the potential to last far longer."

Looking beyond the emotional appeal, private companies might find it worth their while to offer a prize for the safe retrieval of the Vanguard 1. The operation would demonstrate technologies to scour the spacelanes for dangerous "space derelicts," removing them before they are reduced to dangerous clouds of debris by some random space-to-space collision.

"The recovery of a space artifact of the historical importance of Vanguard would be an incredibly difficult, yet rewarding adventure," Wingo said. "However, a prize, and a prize large enough to cover most if not all of the costs, would be required, as it is unlikely that shareholders would be entirely happy with only a scientific and publicity-related return on investment."

Who owns Vanguard?

Legally, Vanguard 1 isn’t "space junk." It remains the property of the U.S. government, and quite probably the property of NASA. That agency didn't even exist when Vanguard 1 was launched, but it took over the project (and the satellite’s operations) later in 1958. Through analogy with maritime law, government property is not subject to automatic salvage rights when abandoned, as private property (at sea, and presumably in space) is.

Still, if some private company wanted to retrieve the satellite as a demonstration of its space-repair capabilities, some arrangement could be worked out.

One proposal calls for a low-thrust ion-engined robot to hitchhike into orbit as the ballast section of a communications satellite launch — then take a year or two to match orbits with Vanguard, grab it, and wrap it in an inflatable hollow shell that would increase its air drag a thousand times, bringing it down in a few years. With enough power, the robot itself could lower Vanguard’s orbit even sooner.

Just before the final descent, another small robot could chase the Vanguard package down and install an inflatable thermal shield and a recovery beacon. Then the robot would nudge it strongly enough to hit a target continent such as Australia — or push it close enough to the international space station for pickup by a visiting spacecraft (by then, no longer a space shuttle).

It might just work. The only remaining controversy would be figuring out which museum gets to keep the far-ranging probe.

In 1999, the Kansas Cosmosphere and Space Center and the Discovery Channel mounted an operation to recover the Mercury space program's Liberty Bell 7 capsule, which sank to the bottom of the Atlantic at the end of astronaut Gus Grissom's flight in 1961. The recovered capsule was seen by millions during a national tour, and is now is on permanent display in Kansas.

If Vanguard 1 were somehow recovered, it's more likely to go to the Smithsonian Institution's National Air and Space Museum — which Pearlman pointed out already has custody of the Freedom 7 space capsule and the Apollo 11 spacecraft, among other riches of space history.

"Vanguard 1 deserves its place of honor among the United States' first manned orbital capsule and the spacecraft that carried three men on the first lunar landing mission," Pearlman said.

NBC News space analyst James Oberg spent 22 years at NASA's Johnson Space Center as a Mission Control operator and an orbital designer. A shorter version of this article appeared in March's issue of Astronomy magazine.