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Hubble versus James Webb: How the 2 powerful telescopes compare

While the Hubble Space Telescope ages, the James Webb Telescope prepares to launch.

James Webb Telescope

As anyone who has had an older computer that increasingly requires rebooting knows, it’s a sign that something is about to give way. It might take months, it might be tomorrow, but you’d better back up your data and make plans.

Unfortunately, NASA’s Hubble Space Telescope is showing those signs.

The aging science instrument, which first entered Earth orbit in 1990, switched into “safe mode” on Monday, and remains offline while NASA investigates a technical issue. It’s the second safe mode incident for the Hubble this year following an issue in June that left the Hubble in safe mode for about a month.

NASA hopes to get the Hubble humming and producing stunning images again, potentially for years to come, but the space agency knows it can’t live forever.

Thankfully, the Hubble’s immediate successor, the long-delayed James Webb Space Telescope, is finally nearing its launch in December. Once operational, the Webb will ideally provide new and exciting images and data for scientists in addition to those coming from the venerable Hubble — but it will also be ready to accept the passing of the torch when the time comes.

Here’s how NASA’s two flagship space telescopes stack up with each other.

How will the James Webb Telescope be different from Hubble?

At their cores, the Hubble and Webb telescopes are very similar. They share a mission to look into the deep recesses of space and time and bring back images and data of faint and distant objects inaccessible to other instruments.

Conceptually, they are even the same type of telescope: A Cassegrain reflector, which uses a primary mirror to collect and focus light on a smaller secondary mirror, which in turn focuses an image on sensor instruments.

An illustration of the light-path in the Hubble Space telescope.


But the way the Webb telescope goes about this is physically and technologically very different from the Hubble and will operate under very different conditions.

Looking a bit like a silvery, segmented coffee can, the 43-foot-long cylindrical Hubble exterior houses a glass primary mirror just more than seven feet across, and scientific instruments capable of interpreting light focused by that mirror in the near-infrared, visible and ultraviolet bands of the electromagnetic spectrum. It was deployed in low Earth orbit by the Space Shuttle, which could fit the entire Hubble observatory in its cargo bay.

The Webb, by contrast, is currently folded up like a flower bud in preparation for launch aboard an Ariane 5 rocket from French Guiana on December 18, 2021.

Once unfolded in space, it will look more like a large radio antenna than a cylindrical telescope housing, with its 21-foot-diameter primary mirror — composed of 18 hexagonal beryllium segments coated in gold — exposed to space.

An illustration of the to-be deployed James Webb Space Telescope.

QAI Publishing/Universal Images Group/Getty Images

The Webb will use mylar-like sun shades the size of a tennis court to block light and heat from our star. This is an important part of its mission given the Webb is designed to look further into the infrared spectrum than the Hubble, a key ability for seeing more distant objects than Hubble.

It will only view the redder end of the visible spectrum and will not image the ultraviolet at all.

Who are the Hubble and James Webb Telescopes named after?

The Hubble telescope is named after the late American astronomer Edwin Hubble. In the 1920s Hubble proved the existence of galaxies beyond the Milky Way by measuring the degree to which light from distant galaxies shifted toward the red and infrared of the spectrum. This helped establish the fact that the universe is itself is expanding.

A 2002 photograph of the Hubble telescope floating over Earth.


Originally known as the Next Generation Space Telescope, the Webb telescope is named after the late NASA Administrator James Webb, the second leader of the space agency who is credited with guiding NASA during the Apollo moon program.

The choice of Webb as the namesake for the Next Generation Space Telescope has come under recent criticism by some space scientists. Why?

  • Webb was not an astronomer or scientist, unlike the figures honored in the names of the Hubble, Chandra, or Spitzer space telescopes.
  • For another, new evidence has surfaced of Webb’s involvement in purges of gay and lesbian people from the government during the “Lavender Scare” of the 1950s.

Following a petition signed by members of the space community, NASA’s investigated Webb the administrator but announced the agency found no reason to change the name of Webb the Telescope.

Cost of Hubble versus cost of James Webb Telescope

The Hubble telescope cost $4.7 billion, in 2010 dollars, at the time it was launched. If you factor in the 1993 mission that repaired Hubble's flawed optics, that figure rises to $5.8 billion.

The Webb telescope, by contrast, will cost an estimated $9.7 billion by the time it launches in December. Assuming it does launch in December — the May 2021 Government Accountability Office report that made that cost estimate also notes the seven years of delays have added to the cost.

How far will the James Webb telescope see?

While seeing further than Hubble is not the only metric for success for the Webb telescope, it was a core element of the new space telescope’s design — its larger primary mirror and sensitivity to the infrared are ideal for capturing objects too faint to be seen by existing telescopes like the Hubble.

To understand just how far the Webb telescope will see, it’s better to think in terms of time than space. The most distant galaxies are so far away, it takes billions of years for their light to reach Earth. Imaging them is akin to taking a snapshot of the early universe.

The Hubble telescope can take snapshots of galaxies several billion light-years away or just 480 million years after the Big Bang 13.8 billion years ago. NASA describes these as “toddler” galaxies, not the first to form in the universe, but close.

The Hubble Deep Field image revealed never-before-seen distant galaxies.


The Webb telescope, it’s believed, will be capable of seeing “baby” galaxies, the very first to form in the universe less than 200 million years after the Big Bang.

Where is Hubble located?

The Hubble telescope flies in a low Earth orbit around 340 miles above the Earth.

It’s an orbit that was easily accessible by the Space Shuttle, which last served the Hubble in 2009, but with the retirement of the shuttle fleet, NASA has no means for effecting repairs on the Hubble should any hardware fail permanently.

Every 95 minutes, Hubble makes one orbit around Earth.


The vehicles in NASA’s Commercial Crew program, the SpaceX Dragon capsule and still in development Boeing Starliner, are designed to ferry crew and cargo to the International Space Station — not to service aging space telescopes.

Where will the James Webb telescope be located?

Even with its sun shades, Webb’s instruments would be blinded by the heat from Earth if they were deployed in an orbit like the Hubble.

Instead, Webb will take weeks to navigate to Lagrangian point two (L2) — a spot around 745,000 miles behind the Earth as seen from the Sun where the Earth and Sun’s gravity cancel out.

That distance also means the Webb is not designed to be serviced or upgraded.

Will the James Webb Telescope replace Hubble?

NASA doesn’t call the Webb a replacement for Hubble, preferring instead to call it Hubble's “successor.”

The space agency hopes to continue operating both space telescopes as long as the Hubble will allow. Webb’s capabilities overlap but do not fully duplicate those of the Hubble.

But when the day comes to finally put the Hubble to sleep for good, Webb will be the only space telescope of similar capability in service — at least until the Nancy Grace Roman Space Telescope is launched in 2027.

Is the James Webb Telescope better than Hubble?

Better is a relative term. Hubble, while not a spring chicken, can still conduct ultraviolet astronomy studies that the Webb, with all its cutting edge technology, simply cannot.

But the Webb will be better than the Hubble at certain things, especially viewing the distant reaches of space and deep eras of time. And as a newer piece of technology, it will hopefully continue operating for decades to come.

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