Looking in on the Next-Generation Space Telescope

A closer look at the James Webb Space Telescope

James Webb Space Telescope

It's one of the truisms of space exploration that there's always a need for the most powerful equipment, whether it's a telescope or a spaceship. That's certainly true in orbital astronomy, which has been dominated by amazing observatories such as the Hubble Space Telescope (HST), the Kepler Space Telescope (KST) , the infrared-enabled Spitzer Space Telescope (which is still functioning, although in a reduced way) and many others that have opened up windows on the universe. In all cases, these orbital instruments have enabled powerful science that couldn't easily be done from the ground.

The latest entry in the ranks of orbiting observatory facilities is the James Webb Space Telescope (JWST) an infrared-sensitive telescope that will be launched into a distant orbit around the Sun perhaps as early as October, 2018. It's named in honor of James Webb, a former NASA administrator. 

Replacing Hubble

The big question facing astronomers these days is, "How long will Hubble Space Telescope last?" This grande dame of space observatories has been on orbit since April 1990. Sadly, parts of HST will eventually wear out, and it will come to the end of its useful lifetime. HST has given us amazing views of the cosmos in visible, ultraviolet, and infrared light. But, the James Webb Space Telescope will fill the infrared gap left when HST dies. It's specially designed to be the formal successor to HST, particularly delivering infrared astronomy data, and there's a lot riding on its wings.

JWST Science

So, what kinds of objects will JWST study in the infrared? The infrared (IR) regime includes a great many dim, distant objects that aren't always visible in other wavelengths of light. That includes older stars and galaxies, which give off a great deal more infrared. Also, it will be able to spot very distant objects whose light has been stretched by the expansion of the universe to infrared wavelengths. Among other things, JWST will be able to peer directly into the hearts of star-forming regions, where star birth warms up the birth clouds surrounding hot, young stellar objects. In short, JWST's infrared-sensitive eye will be able to see things cooler than stars. That includes planets and other objects in the solar system, too.

JWST will spend its time on four major goals: to search for light from the earliest stars and galaxies (some 13.5 billion years ago), to trace the formation and evolution of galaxies, to give scientists new insight into how stars form, and to look for other planets and possible origins of life on those worlds.

Building JWST

Infrared-sensitive telescopes need to orbit far away from the heat that Earth gives off. For that reason, JWST is going to do its work from a special point in Earth's orbit around the Sun. It also needs a sunshield to protect it from sunlight (which would swamp the dim infrared signals it will be searching out). To do its best work, JWST needs to be kept very cold, under 50 K (-370° F, -220° C), which requires the sunshield and special orbit.

JWST and the Giant Mirror

The James Webb Space Telescope's primary eye on the sky is a 6.5-meter (21.3 feet) wide beryllium-coated mirror. It's actually a foldable mirror, divided into 18 hexagonal segments that will unfold like a flower once the telescope arrives at its final orbit.

Of course, the mirror isn't the only thing onboard the spacecraft's "bus" (the framework). It will also carry a near-infrared camera for imaging, a spectrograph that will dissect infrared wavelengths of light for further study, a mid-infrared instrument for wavelengths between 5 and 27 micrometers, and a suite of fine guidance sensors and spectrographs for navigation and fine-detail studies of the light from distant objects.

The JWST Timeline

This giant space telescope (measuring some 66.6 by 46.5 feet) will head off to its mission atop an Ariane 5 ECA rocket. Once it leaves Earth, the telescope will head to what's called the second LaGrange point, which should take about two weeks for the trip. It will orbit opposite Earth and will take about a half an Earth year to make one trip around the Sun.

The projected mission length is 5 years, and the main science work will start after a six-month commissioning phase to test and calibrate all the instruments onboard. It's highly likely the main mission will last up to ten years, and planners are sending along enough propellant to help the telescope maintain its orbit around the Sun for that long.

The mission of the James Webb Space Telescope, like most missions to explore the stars and galaxies, is sure to reveal some amazing objects and facts about the universe. With this infrared eye on the cosmos, astronomers will be filling in more details in the story of our ever-changing and fascinating universe.