JWST set to explore uncharted territory


By Tom Burns - Stargazing



Here’s the first line of a column I started more than 10 years ago.

The James Webb Space Telescope (JWST) is on its way!

Over a quarter century in the making, JWST will eventually park in orbit around the sun that parallels Earth’s orbit.

The telescope’s beryllium mirror is a marvel of human ingenuity. Its 18 hexagonal segments combine to form a light-gathering surface 21 feet in diameter. The mirror is coated with a microscopically thin layer of gold, a quantity of the metal amounting to only .12 ounces.

On Christmas day, JWST launched from the European Space Agency’s Guiana Space Centre in French Guiana aboard an Ariane 5 rocket. When it finally reaches orbit around the sun and is fully deployed in six months, JWST will provide us with spectacular views of and groundbreaking data about our universe.

JWST’s mission is not primarily in the visual portion of the spectrum. Instead, it will explore the universe by collecting infrared light, invisible to human eyes.

In that way, it can see beyond the thin veil of dust that hides our view of galactic formation just one billion years after the Big Bang.

It will discover new planets orbiting distant stars. It will observe the atmospheres of already-discovered planets and evaluate their atmospheric temperatures and compositions.

The project has undergone numerous delays. NASA initially conceived the telescope in 1996 with a projected launch date of 2007.

The undertaking is also way over budget. Its projected cost of $500 million has ballooned to $10 billion.

As taxpayers, you deserve an explanation. Here’s the short answer.

The telescope will work from a position in space that makes repair and resupply nearly impossible. It is among the most mechanically complicated telescopes ever built. Six months will pass before the telescope is fully deployed and ready to observe the universe.

Any failure of the over 300 deployment elements will mean the end of its scientific mission. Every mechanical element had to be tested and retested.

NASA scientists will have to get that deployment just right the first and only time they do it.

Here’s the long answer.

The telescope is far too bulky to launch fully deployed. Instead, NASA technicians must meticulously unfold and align the mirror’s hexagonal segments.

Solar panels provide energy to the telescope’s scientific instruments. And — guess what — the panels must be systematically unfolded.

NASA technicians must maintain the telescope’s temperature at an unvarying -350 degrees Fahrenheit. Consequently, it must be shielded from the sun’s heat. Its tennis-court-sized sun shield must unfurl flawlessly.

The telescope will not orbit Earth. Instead, it will orbit the sun at Earth’s L2 Lagrangian point to prevent interference from Earthly sources.

Earth’s Lagrangian points are places near Earth’s orbit where the gravitational effects of the sun and Earth are perfectly balanced. A spacecraft sent to one of them tends to stay put.

The L2 point is about one million miles farther from the sun than Earth is. The JWST will thus orbit the sun in sync with Earth’s orbit.

The L2 is a prime location for an orbiting telescope. The telescope is close enough to Earth for effective communication. With the sun at its back, it can orient its solar panels to provide energy to its instruments. In front, where its light-gathering mirror sits, it can face away from the sun to see better into the dark depths of space.

Unfortunately, JWST’s L2 location makes the telescope extremely difficult to resupply and repair. A service mission with humans on board would be far too dangerous. Besides, we don’t have a human-piloted spacecraft capable of reaching L2.

And we haven’t developed the robotic technology to perform such a non-human mission. Thus, JWST has a limited lifespan — at least five years, which might stretch to 10.

After that, the spacecraft will run out of two key elements. It requires fuel to reorient the telescope to observe its many astronomical targets and make critical orbital corrections.

Also, JWST uses liquid helium to maintain its frigid operating temperature. Any leaks in the helium system will significantly shorten the telescope’s lifespan.

Still, hope springs eternal. The spacecraft is equipped with ports to refuel its aiming system and replenish its liquid helium if the requisite technology develops in the next 10 years.

The long journey toward a large, space-based infrared telescope began more than two centuries ago.

In 1800, William Herschel used a prism to spread out the light from the sun into the rainbow band called the spectrum.

Using a simple hand thermometer, he measured the temperature of the red light at the low-frequency end of the spectrum. Then, he measured the temperature of a spot next to the red light where no light seemed to be shining.

The temperature of the supposedly blank area beside the red was one degree warmer than the red area.

Herschel concluded that the spectrum of light is not limited to the colors we see in the visible spectrum. He had discovered infrared energy, the invisible light below the spectrum’s red light.

In a sense, Herschel hadn’t discovered anything new. Although humans can’t see infrared light, we detect it as heat. Every time you feel the heat of the sun on your skin, you are detecting infrared radiation.

After Herschel’s discovery, infrared astronomy languished until the 1960s. As it turns out, infrared radiation from deep space is exceedingly difficult to detect from Earth’s surface.

Our atmosphere absorbs most of the infrared radiation it receives from the universe. In addition, the atmosphere generates infrared radiation of its own. The tiny amount of infrared we get from the cosmos is overwhelmed by local conditions on Earth.

As a result, astronomers must locate Earth-based telescopes at very high altitudes. For example, the infrared telescope perched on Hawaii’s Mona Kea sits 13,796 feet above sea level.

The ultimate solution is to send telescopes into space, but that way out creates new problems, not the least of which are significant resupply issues.

Nasa’s IRAS telescope went into orbit in 1983. It ran out of liquid-helium coolant just ten months later. The Spitzer Space Telescope worked for six years before its helium was exhausted, and most of its instruments were rendered useless.

In JWST’s case, it’s worth the trouble. JWST’s size and location make the telescope sensitive enough to detect light from distant galaxies just a short time after the Big Bang.

However, astronomers cannot effectively examine distant galaxies in visible light because of their Doppler shifts.

Astronomers have known for some time that the spectrum of a moving star or galaxy is different from one at rest. If the object is moving away from us, all the color bands shift toward the red (i.e., low-frequency) end of the spectrum. If it is moving closer, they move toward the blue (high frequency) side.

You can experience the effect from sound, which exhibits similar characteristics. In 1842, Christian Doppler noticed that if, for example, you are standing by a railroad track and you hear the whistle of an approaching train, the pitch rises (gets shriller) as it comes toward you. It decreases (gets deeper) as it moves away.

The same Doppler shift happens with light. As a galaxy speeds away, its “pitch” decreases toward the red.

The faster the object is moving away, the more significant the shift. And those distant galaxies are moving at nearly the speed of light. Their visible light has shifted mostly into the infrared.

Thus, if astronomers want to see ancient galaxies coming into being, they have little choice. They must send an infrared telescope to a remote and otherwise unreachable location far from the influence of Earth and its atmosphere.

To launch such a large telescope, they have to fold it up. But unfolding creates thousands of points of failure that they can’t do anything about, given the telescope’s remote and otherwise inaccessible location.

So they test and test again. They design and redesign if they have to, and they often have to.

The decades pass. The cost increases twentyfold. But they keep their faith and ask you to open up your pocketbooks again and again. They want to understand the universe’s dim beginnings because, in a sense, they are our own dim beginnings.

That’s why they were willing to wait 26 years and spend $10 billion on a telescope that will last, they hope, a whole decade.

As I write these lines, JWST has successfully deployed its solar panels. Its sun-shield deployment is well underway. Thanks to a perfect launch and a couple of fuel-efficient mid-course corrections, the telescope may continue its astronomical mission for “significantly more than a 10-year science lifetime,” according to NASA.

So far, so good.

Accordingly, on behalf of all the astronerds of the world, I say to the James Webb Space Telescope, Godspeed. Our hopes and dreams travel with you as you embark on your lonely journey into the dark depths of space.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.