James Webb Space Telescope:
Diving Deep into the Universe

By Leonard David
Senior Space Writer
posted: 07:00 am ET
08 January 2003

BOULDER, COLORADO -- Eye-catching is the watchword for the folks building the James Webb Space Telescope - a 21^st century high-tech space observatory that pledges to down shift the Hubble Space Telescope into humble mode.

This is NASA's promissory note to the future: The James Webb Space Telescope (JWST) will push the cosmological envelope, letting astronomers delve deeper and further back in time to better understand the origins of the Universe.

Work is underway at Northrop Grumman Space Technology, primary contractor for the JWST. This spaceborne wonder is slated to utilize a lightweight, light-gobbling mirror much larger in size contrasted to Hubble. Photons gathered by JWST will be fed to instruments that are exceptionally sensitive to infrared wavelengths.

Peering deeper into the Universe than Hubble, the increased light-collecting power of JWST should unveil an important but previously unobserved epoch of galaxy formation. It will stare through dust to witness the birth of stars and planetary systems similar to our own.

In putting JWST to work, scientists hope to shed light on such intriguing questions as dark matter - that mysterious, non-luminous matter, whose existence is suggested because of the effects of its gravity on the rotation rate of galaxies and the presence of clusters of galaxies.

To see into the depths of space, plans call for the JWST to carry a near-infrared camera, a multi-object spectrometer and a mid-infrared camera/spectrometer.

JWST is also outfitted with a huge shield that blocks the light from the Sun, Earth, and Moon. Rays of light streaming in from these objects would heat up the telescope and interfere with delicate observations. The shield cools the observatory to very low temperatures without the use of complex refrigeration equipment.

In addition, consider where JWST must be parked.

Unlike Hubble's close-in, Earth-orbiting address, JWST's working location is 940,000 miles (1.5 million kilometers) out in space - stationed at what's called the Lagrange Point 2, or L2 for short. It is in this locale where the spacecraft is fully deployed, fully ready for action, and balanced between the gravity of the Sun and the Earth. That balance of gravitational pull at the L2 point means that JWST will keep up with the Earth as it goes around the Sun.

At that distance -- again unlike Hubble -- astronauts couldn't service the telescope because it would be too far away from human or tele-robotic touch, according to present plans.

There is no doubt that the JWST is billed as one powerful astronomical tool. But given a now-projected liftoff of 2010 for the super-telescope, there's also much work to be done.

The Next Generation Space Telescope (NGST) will look back to an extremely important period
in the early history of the universe -- a time when the first stars and galaxies began to form --
and a point in cosmological history that could be called "the Dark Age".
Credit: NASA/Space Telescope Science Institute

Last September NASA awarded the key industry contract to construct what had been billed earlier as the Next Generation Space Telescope. Space agency chief, Sean O'Keefe, however, quickly gave the observatory an "all in the family" moniker - the James Webb Space Telescope.

O'Keefe selected NASA's second administrator as the telescope's guiding light namesake, bowing more to managerial panache of the past than to any astronomer's contribution, past or present.

Winning the project was TRW, Inc. -- recently acquired and now tagged Northrop Grumman Space Technology (NGST) in Redondo Beach, California -- with the firm teamed with Ball Aerospace here in Boulder. The contract to fabricate the new space telescope is valued at $824.8 million.

"In a sense, JWST is a breakthrough mission," said Greg Davidson, Director of Civil Space at NGST. "It's the first deployable optical system in space. Everything in the past has been constrained by the size of a launch vehicle. It’s sort of like bursting the girdle," he told SPACE.com.

Size does matter for two reasons, Davidson said, in terms of JWST's sensitivity and angular resolution.

"Basically, we want to see things far more distant and we want to see those things more clearly. That drives astronomers to need larger and larger systems. JWST is just the start of the rest of the future of astronomy," Davidson explained.

The James Webb Space Telescope by TRW/Ball Aerospace team.
Using technology similar to that of night vision goggles, this NGST will
study infrared emissions from the first objects created in the Universe.
Credit: TRW/Ball Aerospace

At the heart of the James Webb Space Telescope effort is use of advanced optical technology - particularly in the mastery of lightweight mirrors.

The diameter of JWST's primary mirror will measure some 21.3 feet (6.5 meters) and is comprised of 36 mirror segments, each roughly a 3.3 feet (1 meter) hexagon in size and shape. The reflective quality of the unfolded mirror segments will be computer-controlled via actuators that can adjust the shape of the mirror to give high quality, sharp images. These actuators must function at exceedingly cold temperatures.

Once those 36 mirror petals are phased in space, they are to form a nice and tight optical image, said Mark Bergeland, JWST Program Manager at Ball Aerospace. "It's a very robust design and we don't anticipate any problems on orbit," he added.

Bergeland told SPACE.com that a decision still forthcoming is use of either beryllium or glass for the primary mirror optics. "Both are contenders right now. It's a matter of which material is going to perform the best on orbit and which can be produced with the lowest amount of risk," he said.

To be sure, JWST program officials are mindful of the out-of-focus fiasco that initially plagued the Hubble Space Telescope's main mirror. "That's an area where we're paying special attention. We don't want another Hubble kind of incident to happen," Bergeland said. A member of the JWST team is Kodak of Rochester, New York who will have the responsibility for final telescope integration and end-to-end testing and verification before launch.

Teamwork between all the various JWST players is critical, said Davidson of Northrop Grumman. "Everyone has to get their goals in alignment to produce the best system they can within the budget," he said.

Davidson said the telescope project has very strong and robust performance margins. The next major milestone, he said, is a JWST mission confirmation review that's set for the March/April time frame.

The James Webb Space Telescope is a packaged deal. That is, once lobbed into space -- likely by Europe's Ariane 5 booster -- the observatory unfurls into a final configuration. At first glance, the number of critical high precision deployments necessary might make even the most seasoned space mechanical engineer raise a distress flag.

Not to worry, Davidson said, pointing to a company heritage of complicated deployments in such programs as NASA's Tracking Data Relay Satellite System. "That's at least as complex as our deployment schemes for JWST, if not more so," he said.

"It's a lot of tried and true mechanical elements that have been configured into a design that does the job," Davidson said.

Weighing in at 12,000 pounds (5,400 kilograms), the JWST is outfitted with a large sunshade. Like the telescope's unfolding main mirror segments, as well as the scope's secondary mirror, so too must the sunshield take shape in space. Once fully stretched out, the shield will measure in the range of 72 feet x 33 feet (22 meters x 10 meters) in size.

At the L2 orbit, the single-sided sunshield on only one side of the observatory can protect the JWST from the light and heat of both the Sun and Earth, thereby plunging it to very low temperatures. Those cold temperatures are required to prevent the telescope's own heat radiation from exceeding the brightness of

distant cool astronomical objects being targeted.

Once operational, JWST is expected to see objects 400 times fainter than the world's largest ground-based infrared telescopes or the current generation of space-based infrared telescopes.

After its boost into space, the JWST will take a three-month voyage to reach its L2 position.

First things first, however. That means getting the telescope's communication antenna and solar arrays deployed. "We need power and we need to be able to talk to the telescope. Those two are first," said Bergeland of Ball Aerospace.

No time will be wasted during the telescope's transit to L2. "Many of the deployment steps occur as it's heading out into orbit. Another thing the telescope will be doing en route is cooling down," Bergeland said.

From an engineering standpoint, JWST is a forerunner of things to come.

"Certainly, JWST will demonstrate the ability to deploy a large segmented telescope in orbit. That will be a first…and lead to follow-on programs like the Terrestrial Planet Finder, an even bigger telescope. The capability to deploy a large telescope on orbit is going to be a real milestone," Bergeland concluded.

A schematic overview of the TRW/Ball NGST concept.