GREENBELT, Md. – The Hubble Space Telescope turns 25 on Friday, but no one should call it old. It’s mature. It’s the great silverback of astronomy, grizzled from wear and tear and yet still powerful and utterly dominant in its field.

The Hubble changed our understanding of the age of the universe, the evolution of galaxies and the expansion of space itself. Along the way it has had the equivalent of knee and hip replacement surgery: Five times, astronauts on the space shuttle paid a visit to swap out old batteries and install new instruments, including, in 2009, the best camera the telescope has ever had.

How deep into the cosmos can the Hubble see? Deeper than you, punk.

“It’s fantastic. It’s better than ever. That’s not just hype, it’s the truth,” said Jennifer Wiseman, the senior project scientist for the Hubble at NASA’s Goddard Space Flight Center.

“This is 1970s technology, and it is still, after 25 years, the most powerful scientific instrument in the world,” said astrophysicist Patrick McCarthy of the Giant Magellan Telescope under construction in Chile.

Hubble’s fate, however, is cloudy. The great telescope is essentially stranded in space.

The Hubble was designed to be serviced by the space shuttle. But the space shuttle fleet was retired in 2011, and the Hubble hasn’t had a repair job since that 2009 mission. At some point, under the laws of entropy that dominate the cosmos, the Hubble will begin to deteriorate – for example, losing its navigational ability as its gyroscopic sensors fail one by one.

“It’s kind of like predicting when’s the next time your car’s going to break down,” said Jim Jeletic, deputy project manager for the Hubble at NASA Goddard, who on a recent morning led a reporter and photographer on a tour of the telescope’s operations center.

Electronics eventually go haywire in a space environment that is flush with radiation. As it orbits the Earth 15 times a day, the 44-foot-tall Hubble goes in and out of sunlight, expanding and contracting, and that puts stress on various systems. Micrometeorites ding the exterior. A Hubble antenna has a hole in it that looks as if someone hit it with a squirrel gun.

The Hubble was conceived in the 1940s, designed in the 1970s and 1980s and still has vintage hardware on board, including a 1980s-era computer that freezes up occasionally and has to be rebooted remotely.

And then there’s gravity. The Hubble is orbiting the Earth about 340 miles above the surface, significantly higher than the International Space Station. There’s just a trace of atmosphere that high, but it’s enough to drag the Hubble a tiny bit and cause it to descend a little over a mile per year.

NASA said this week that, based on current orbital projections, the Hubble is expected to re-enter the atmosphere “around 2037.” The telescope has no means of propulsion.

One option would be to send a robotic craft to dock with the Hubble and guide it to a fiery, but controlled, re-entry into the Pacific Ocean. The charred remnants of the great telescope would sink to the bottom of the sea. Another option would be to boost the telescope to a higher, “parking” orbit where it would stay for centuries as a piece of space junk.

“When the time comes, NASA will make a decision on the disposal plan. Until then, NASA will continue operating Hubble as long as the hardware lasts, enabling it to be remain scientifically productive,” NASA spokesman Dwayne Brown said.

As Jeletic gave his tour at Goddard, the Hubble was pointed at a quasar – an extremely bright source of light at the core of a distant galaxy with a black hole at the center.

That’s just one of Hubble’s many projects. Built with the assistance of the European Space Agency, the Hubble is a global resource. NASA gets more than 1,000 proposals a year from scientists around the world hoping to take advantage of the telescope’s unique capabilities. Jeletic describes the resolution of the Hubble as equivalent to shining a laser on a dime 200 miles away.

That wasn’t the case at first: The Hubble has a 2.4-meter diameter mirror with a notorious “spherical aberration” that blurred the telescope’s initial images. Astronomers could do plenty of science, but they couldn’t get the gorgeous pictures because the stars weren’t points of light but rather looked like squashed spiders.

Three years later, in 1993, astronauts fixed the problem. They installed a series of coin-sized mirrors that corrected the light as it bounced through the telescope, plus a new camera with the optical corrections already built in.

That inaugurated the new era in which Hubble dazzled the world with one spectacular image after another. The telescope became something of a celebrity. When lawmakers threatened to cancel a repair mission, school kids turned over their lunch money to help pay for it.

“Hubble gave us beauty in a way that no other telescope had ever done,” said John Mather, the Nobel Prize-winning astrophysicist at NASA Goddard who is the senior scientist for the James Webb Space Telescope, scheduled to be launched in late 2018.

The Hubble also helped nail down the age of the universe. Before the Hubble, astronomers said the universe was 10 billion to 20 billion years old. Now they say it’s 13.8 billion years old.

The Hubble played a key role in the stunning discovery, announced in 1998, that the expansion of the universe is accelerating. Astronomers detected this acceleration, which they attribute to a mysterious force they call “dark energy,” in part by using the Hubble to study supernovas in extremely distant galaxies.

The deep gaze of the Hubble offers a view into the remote past; all telescopes are time machines of sorts, gathering light emitted long ago. The Hubble, thanks to new instruments, can see deeper into space than anyone had anticipated when the telescope was first designed, said astronomer John Grunsfeld, NASA’s top official for science, who as an astronaut visited and repaired the Hubble three times.

“Before Hubble, we didn’t know how many galaxies there are in the universe,” Grunsfeld said.

The orthodoxy was that there were tens of billions of galaxies. Now, thanks to the Hubble, scientists can say there are roughly 200 billion.

That estimate stems from Hubble’s “deep field” images, obtained by training the Hubble on a single point of seemingly empty, dark space and holding it there for a couple of weeks, collecting the thin stream of photons (particles of light) coming from the farthest regions of the universe. The Hubble might get just one photon per minute from the faintest objects.

Some astronomers assumed that, looking far back in time, they wouldn’t see much.

“When the Hubble Deep Field pictures were taken, people didn’t expect to see anything. It had thousands and thousands of galaxies in it. We were so far off it was incredible,” said Goddard’s Mather.

“That’s one of the pleasures of astronomy,” Mather said. “It’s an observational science, and it’s a surprise science.”

Wiseman points out that those early galaxies looked different than the ones we see today. They were small, fragmentary, and made of hydrogen and not much else. Closer to us in space and time we see larger galaxies, including the majestic spiral galaxies akin to our own Milky Way galaxy, which have heavier elements that include carbon and oxygen – the stuff of life as we know it.

This cosmic narrative is written in ancient light, and it is ready to be decoded and appreciated by any species that can figure out how to build the right instruments.

Jeletic thinks that the Hubble can keep doing good science at least until 2020. That might mean the Hubble would overlap for a couple of years with the operations of the Webb telescope.

Five of Hubble’s six gyros, the navigation sensors, still work. The sixth failed last year, but the Hubble can navigate with only three gyros, Jeletic said. In fact, he said, NASA engineers think they might be able to find scientific uses for the Hubble even with only one gyro or no gyros.

It might not be able to point accurately anymore, but there’s something interesting anywhere you look.