The Hubble Space Telescope is 35 years old!
For those who need a reminder, Hubble is a large space-based observatory, and it was launched by NASA in 1990. It orbits the Earth and captures high-resolution images and data in ultraviolet, visible, near-infrared light. Red and violet bookend the visible light spectrum i.e. the colours we can see. Ultraviolet is simply shades of violet beyond what we can see and the same applies to Infrared light. Hubble uses this range of light to bring out extra detail in the objects it's observing.
Because Hubble is orbiting above the atmosphere, it avoids the distortion from the air and weather that affects ground-based telescopes. And this is what enables the ground-breaking discoveries it's made about galaxies, stars and planets - and even about the age of our universe.
Hubble had a troubled start. After it was launched, it quickly became apparent that something was seriously wrong as its images were blurry and out of focus. The issue was traced back to a flawed primary mirror.
As to what went wrong, there was a defect in its optics - and it didn't take a big one to cause a huge problem. Hubble's primary mirror is 2.4 meters in diameter, and the defect was that it was slightly too flat to an extent of 2.2 microns. How big is 2.2 microns? Well, it's about 1 50th the thickness of a human hair!
The contractor responsible, Perkin-Elmer, used a faulty testing device during the manufacturing process. Their test equipment, called a Null Corrector, had been incorrectly assembled, and this led to the wrong shape being deemed correct.
What was a pity was that they used other tests to double-check the shape of the mirror. A second corrector, built by Kodak, indicated a problem, but they chose to ignore these findings and went with their primary test results instead.
So Hubble was launched, but didn't work, a huge embarrassment for NASA. A solution had to be found, and found it was. In 1993, some three years after Hubble was launched, NASA launched the STS-61 servicing mission. Astronauts flew aboard the space shuttle Endeavour up to the Hubble telescope to fix it. The astronauts installed a corrective optics system called COSTAR (which, if you're interested, stands for Corrective Optics Space Telescope Axial Replacement). Essentially, COSTAR acted like glasses for Hubble and fixed its vision. And, while they were at it, the astronauts took the opportunity to upgrade some of Hubble's instruments, improving the telescope further.
After the fix, Hubble began delivering the stunning images that we've become so used to, and the great news is that it's still doing it. I've got one of them as the image for my blog. You can look these up online e.g. https://nypost.com/2025/04/23/science/nasa-releases-new-photos-of-faraway-galaxies-to-celebrate-35th-anniversary-of-hubble-telescope.
There's a beautiful image of Mars in ultraviolet, revealing things like the blue hues from water ice clouds above Mars itself (yes, Mars does have clouds, they're just very tenuous). Then there are wonderful pictures of nebulae, for example NGC 2899, which is a colourful moth-shaped nebula, and the Rosetta Nebula, showing dark clouds of hydrogen spewing away as a result of the explosion of the star that formed it. And finally, there's a picture of a spiral galaxy, which is kind of similar to our own, except this one is described a flocculent, which means that it has flaky spiral arms that are breaking up.
And Hubble is still doing useful scientific work. Just recently, it's been involved in mapping Andromeda's dwarf galaxies. The Andromeda galaxy is the closest major galaxy to our own (it's actually visible with the naked eye). And Hubble has been building a precise 3D map of the dwarf galaxies that orbit around Andromeda. It's also been looking at the rotational period of Uranus and, after 10 years of observations, it's calculated that Uranus's day lasts 17 hours, 14 minutes and 52 seconds. Then there's the observations it's made of the small Magellanic cloud - this is a dwarf galaxy that orbits our own Milky Way. And Hubble has revealed about 2,500 infant stars that are forming within it.
The big question now is how long will Hubble keep going for? Well, it's already massively exceeded its design lifespan of 15 years. But it is showing its age.
One of the challenges is that there are no more servicing missions scheduled. This might change, but at the moment nothing is planned, largely because the space shuttle program ended in 2011 and that was the best vehicle for the job. There's really no way to get up to Hubble with the amount of kit you'd need to do a proper servicing mission with the spacecraft we have available now.
Possibly the key issue that Hubble is suffering from relates to its gyroscopes. Hubble needs gyroscopes to point itself in the right direction. It started with six, and now it's down to one fully operational gyroscope, which limits its performance and manoeuvrability. And of course, its other components are also aging. Batteries, thermal blankets, electronics, they're all decades old and working on borrowed time.
NASA is doing clever things with software to keep Hubble going, and they think it could last until the early 2030s, maybe longer, if nothing major fails. But it is just one critical issue away from stopping completely.
On the bright side, while nothing's planned, there is talk of a possible mission to re-boost the telescope to a higher orbit. Hubble's orbit is slowly decaying over time, and if nothing is done it will eventually break up in the atmosphere. While the telescope is being boosted, it's possible that other things could also be done to extend its life, but nothing's confirmed.
Hubble's successor is the James Webb Space Telescope, which is a next generation telescope producing next level images. At the moment, Hubble and JWST work well as cosmic tag team partners. But eventually, the James Webb Telescope will have to carry on alone.
So, for now, let's raise a glass to Hubble - while it's still around.