Why the Hubble Space Telescope still matters

On April 24, 1990, humanity launched a scientific revolution.

I mean “launched” literally: on this date, the space shuttle Discovery roared into the sky with the Hubble Space Telescope nestled in its cargo hold. The telescope had a mission destined to forever change our view of the universe.

Hubble wasn’t the largest telescope ever designed (its 8-foot mirror is actually considered small these days), but its position above the atmosphere gave it superpowers. Our air bubbles and bubbles, blurring the view of the instruments on the floor. It also shines, faintly but enough to limit the low visibility of an object by astronomers. And third, our air absorbs most of the ultraviolet and infrared rays, which is where interesting things happen, from a cosmic perspective. Moving up, away from all that atmosphere, made Hubble one of the most important telescopes ever built.

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And it revolutionized astronomy. Hubble saw fainter objects than ever before. The telescope has studied the rate at which the universe is expanding, observed weather changes on the outer planets, and proven that every major galaxy has a supermassive black hole at its heart, to name just three incredible feats that come to mind. The major advances and discoveries that have resulted from this magnificent machine are so numerous, in fact, that even listing them here would be excessive (and also a bit tedious, if incredible astronomical exploration could ever be tedious).

And yet, despite these successes, I see a lot of discussion online (and even in the media) cavalierly dismissing Hubble, claiming that NASA’s James Webb Space Telescope (JWST) is Hubble’s “replacement.” This is not only unfair; It is fake.

JWST was never intended to supplant Hubble, and in fact can’t, given that it was designed for very different observations.

Hubble is optimized to observe the universe in visible light, the type of light we see with our eyes. It can also detect certain wavelengths in the ultraviolet and infrared, but Hubble cannot see most of these parts of the spectrum. JWST detects infrared light at much longer wavelengths, where different astrophysical processes dominate.

JWST is a much larger telescope, it’s true. It has a 6.5 meter wide mirror, allowing it to collect about seven times more light than Hubble. In general, a larger mirror also means higher resolution, a better ability to see the finer details of an observation. But it also depends on the observed wavelength, and in fact, at their respective best, Hubble beats JWST by a tiny bit! But that’s not really the point; both are exceptional telescopes that are at the forefront of the type of observations they can each perform.

Understanding Hubble’s power in visible light helps highlight a key area where JWST’s infrared vision surpasses it: glimpses of the universe’s first galaxies.

Hubble’s most extensive observations have shown that there is an unexpected wealth of galaxies in the distant universe, but the telescope has a limit. The farther away a galaxy is, the more its light redshifts as cosmic expansion pushes the galaxy further from us. At any given time, most of the galaxy’s light is emitted in the infrared, where Hubble can’t see it, but where JWST sees perfectly. That’s why the new observatory has been so prolific in breaking distance records and giving us unprecedented views of the early universe.

There is an irony here. The idea of ​​a space telescope was first proposed by astronomer Lyman Spitzer in 1946, and in the 1960s, astronomer Nancy Grace Roman began advocating for NASA to build one — she later became known as the “mother of Hubble,” and a space telescope scheduled to launch this year is named after her. However, delays and budget overruns plagued the Hubble project, which ultimately cost more than $10 billion and was launched much later than initially planned. The same thing happened with JWST; initially proposed to cost less than $1 billion and launch by 2004, its final cost was also around $10 billion, and it only increased in 2021. In this way, the two telescopes have a similar history.

But from another point of view, their story is extremely different. Hubble launched with a faulty mirror, a micron or two too flat at the edges – far less than the thickness of a human hair but more than enough to ruinously blur the telescope’s vision. I remember those blurry years well: during my Ph.D. In my research, I spent quite a bit of time working with software that mathematically corrected some of the blurry Hubble images. Fortunately, this problem was circumvented with the launch of corrective optics in 1993, and subsequent instruments incorporated corrections to ensure observations were focused.

Today, few people seem to know about these difficult times (there were congressional hearings on NASA’s mistake!), and many are now focused solely on Hubble’s success. And that’s fine, I suppose, as long as the lessons learned avoid similar mistakes for later space telescopes.

In the case of JWST, this is usually the case. The $10 billion figure I stated above is only half accurate; When the costs of this telescope and Hubble are compared in inflation-adjusted dollars (especially if you factor in the costs of Hubble’s shuttle servicing missions, which you should), the much larger JWST is actually cheaper despite its delays and technical problems. And of course, all that money bought a telescope that worked almost perfectly from the start, even after a series of seemingly impossible Rube Goldberg-style steps to make it operational in space.

The expected duration of the JWST’s primary mission is more than five years, which it will reach in 2027, but its expected lifespan is at least 20 years, thanks to careful management of its onboard fuel supply. Note that Hubble’s primary mission only lasted about fifteen years and is in its 35th year in space. It has also made more than 1.7 million observations since its launch.

Hubble is therefore hardly obsolete. In terms of cameras, instruments and even solar panels, it’s much better now than at launch! To be sure, its aging gyroscopes, needed to keep the observatory pointed precisely, have experienced numerous mission failures. But even then, engineers on the ground found ways to squeeze every last drop of efficiency out of Hubble’s only operational gyroscope.

NASA has a habit of making its missions last much longer than their nominal lifespan. The Chandra X-ray Observatory is in the 26th year of its five-year mission, the Spitzer Space Telescope has lasted 11 years past its expiration date, and the Fermi Gamma-ray Space Telescope is still operational after twice the duration of its original mission.

If JWST lasts as long as Hubble, I’ll be happy to see it still scanning the infrared sky in 2057. Hubble may be long gone by then, but I hope we’ll have other large observatories in space by then, not so much to replace it as to continue its legacy.