James Webb Telescope Versus Hubble Space Telescope

The Hubble Telescope has been around for ages. It was launched in orbit in 1990, and since then made history more than once. Its images served as much to research as they did to inspire people and make them pursue astronomy. It gave us views of the farthest places seen in the Universe. We even saw the places where stars like our Sun are being born. Who doesn’t know of the “Pillars of Creation”? But this monumental engineering piece is on its final road. We now have something even better. The James Webb Telescope, whose launch is a very awaited event, is now fully assembled. But how is this telescope different to Hubble?

"The Pillars of Creation" (Image Credits: NASA)

The Story and Purpose of Hubble 

The Hubble Telescope has a very long story. It all began back in 1946, when the brilliant astronomer Lyman Spitzer discussed in his paper, “Astronomical advantages of an extraterrestrial observatory”, the benefits of a space telescope. He found two main advantages over ground-based telescopes. The first regards angular resolution: in space, it would be limited only by diffraction. On Earth, the atmosphere is a big impediment to observation. Second, a space telescope can observe in UV and infrared light. So we can give credit to Lyman Spitzer for the efforts he made, even after publishing his paper, to making a space telescope. 

After long disputes over funding, the work for the Hubble Telescope began in 1978, with Congress approved funding of $36 million. The Marshall Space Center was handling the design, development and construction, and the Goddard Space Flight Center had been given the responsibility of controlling the scientific instruments and handling the ground control. 

Optically, the Hubble Telescope is designed as a Cassegrain reflector. That is a combination of a primary concave mirror, and a secondary convex mirror.

Also Read: An introduction to the basic concept of telescopes.

The Optics of Hubble

Finally, the telescope was launched in 1990, on April 24. Still, after a few weeks, a blurry picture sent by Hubble gave headaches to the people of NASA. After years of working on the telescope and after launching it into space, the telescope was far from flawless. Actually, it was unusable. So because of a mirror wrong assembled by Perkin-Elmer, the company responsible for the mirrors, a team of astronauts was sent in 1993 to add another piece of mirrors, with exactly the same error, but with opposite sense, to cancel the error of the mirror. A total of 5 servicing missions were sent to Hubble since 1993 to 2009. 

The Hubble Telescope had a lot of scientific purposes, and all of them meant tackling some of the toughest questions in astrophysics and cosmology. Overall, Hubble’s job was to study the interstellar field, which it did extremely well, giving information about some of the farthest corners of the Universe. Also, it was going to be used in determining the exact value of the Hubble constant. But Hubble did more than that. Among its achievements is the confirmation of the existence of black holes, for example. 

Pushing Limits - The James Webb Space Telescope 

The idea of a successor to the Hubble Telescope has been around for many years now. And that is exactly what the James Webb Space Telescope is. 

Year 1997 was the first official year of the JWST. That was the year the project got first funded. Half a million dollars were put in the telescope in the first year, with an expected launch in 2007. By 2006, the launch was scheduled to 2014. Slowly, year by year, it came to be expected to launch in 2021. Today, the telescope is fully assembled. 

How is JWST different to Hubble? Well, in popular terms, it can be said that it is 100 times better than Hubble. Technically, it is more complicated than that. 

Infrared telescopes need to be constantly cooled. That is because the telescope itself has a certain temperature which interferes with the measurements. So instrument cooling has been a problem with most of the space telescopes, problem which has been solved in different ways. First, the telescopes were cooled with liquid helium. The Hubble telescope has used cryo-coolers, or thermo-electrical cooling. James Webb is particularly effective because of its cooling system. The telescope uses a combination of Sun shading and cryo-cooling.

James Webb Telescope
JWST's Mirror (Image Credits: NASA)

Also, James Webb’s primary mirror is much larger than Hubble’s. It is more than 2 times larger in diameter, and around 6 times larger in area. Larger mirror means more space to collect light, which means more information to us. 

Another interesting feature of the James Webb Space Telescope is its location in space. In order to obtain those Sun shades I told you about, and to use the least fuel for corrections, the telescope will be placed in the fixed point L2. Or the second Lagrange point. That means it will be 930,000 miles away from Earth. 

James Webb Telescope
The Lagrange Points

Waiting for 2021

Overall, the James Webb Space Telescope is a major achievement in science and engineering. It will give us insight into some of the deepest secrets of the Universe. Will we ever know the Universe? Maybe not. But with every new day, we go further in our adventure. We create more, we imagine more, and we build more. The telescope’s performance will be the product of decades of thinking and dreaming.

That doesn’t mean Hubble’s achievements are less amazing. Actually, James Webb would have never existed without Hubble. The 60s dream of having a telescope had been achieved. Hubble is part of our story.

Also Read: Buying your first telescope - a short guide

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