How Fast Is James Webb Traveling and Where Is NASA's Space Telescope Going?

The James Webb Space Telescope (JWST) is currently traveling through space heading towards its destination, after launching from Europe's Spaceport in the South American territory of French Guiana on December 24, 2021.

A joint collaboration between NASA, the European Space Agency, and the Canadian Space Agency, Webb is the largest and most powerful space observatory ever built, promising to revolutionize our understanding of the universe.

But where is the telescope currently traveling to, and how fast is it moving?

Webb's final destination is a special point in space known as the second Lagrange point, or L2, which is located approximately 930,000 miles away from the Earth in the exact opposite direction from the sun.

Unlike the pioneering Hubble Space Telescope, which orbits our planet, JWST will technically be in orbit around the sun.

The second Lagrange point is special because it enables the telescope to stay in line with the Earth as it moves around the sun. This allows JWST's large sunshield to protect the telescope from the light and heat of the sun, Earth and the moon.

The Importance of Shields and Infrared

This is important because Webb's telescope primarily observes the universe in infrared light and thus needs to be shielded from any bright, hot sources, that could interfere with observations. For JWST's sunshield to be effective at this job, the observatory needs to be in an orbit where the sun and Earth are in about the same direction, which is what L2 offers.

"A huge advantage of deep space (like L2) when compared to Earth orbit is that we can radiate the heat away," Jonathan Gardner, deputy senior project scientist on the Webb Telescope mission, and chief of the Observational Cosmology Laboratory at NASA's Goddard Space Flight Center, said in a statement.

"Webb works in the infrared, which is heat radiation. To see the infrared light from distant stars and galaxies, the telescope has to be cold. Webb's large sunshield will protect it from both sunlight and earthlight, allowing it to cool to 225 degrees below zero Celsius (-370 Fahrenheit)."

Eric Smith, Webb program scientist at NASA headquarters in Washington, D.C., told Newsweek that L2 was chosen because it's roughly million-mile distance from the Earth decreases the amount of infrared radiation the observatory received from our planet by a factor or approximately 10 million, when compared with low-Earth orbit.

"This decrease in the infrared background signal is critical to Webb's success," Smith said.

L2 is also the "perfect place to park" the observatory due to the fact that the point is a "wonderful accident of gravity," according to NASA.

There are five Lagrange points—areas where gravity from the sun and Earth balance the orbital motion of a satellite. Placing a spacecraft in any one of these points enables it to stay in a fixed position relative to the Earth and sun while using a minimal amount of energy—in the form of rocket thrusts—to help it stay in place.

Essentially, Webb will be locked in perfect unison with the Earth's yearly orbit around the sun.

Even though JWST will be further out than the Earth, the combined gravitational pull of the sun and our planet will mean that the telescope will be able to keep up with the Earth throughout the year.

The other benefit of L2 is that Webb can be in constant communication with the Earth as the observatory will always be at the same location relative to our planet.

The Journey Nears Its End

Webb is currently 18 days into a 29-day journey to L2, although it has already completed around 82 percent of the distance, according to NASA's tracker.

The observatory was traveling at much higher speeds earlier in its trip, when it covered most of the distance. After separating from its launch vehicle, JWST began to slow rapidly and it is now traveling at a cruising speed of around 0.2 miles per second towards L2, or roughly 720 miles per hour.

This is because the gravity of the Earth and sun slow the observatory down as it moves away from our planet. Since the rocket that propelled Webb into space used up its fuel, the spacecraft has been coasting. You can think of its journey toward L2 like someone on a bike going uphill while no longer pedaling.

"Getting Webb to its orbit around L2 is like reaching the top of a hill by pedaling a bicycle vigorously only at the very beginning of the climb, generating enough energy and speed to spend most of the way coasting up the hill so as to slow to a stop and barely arrive at the top," NASA said in a factsheet.

The telescope has already fully deployed its 21-foot, gold-coated primary mirror—completing its final major deployment. Over the next five months, the telescope will be fine-tuned and calibrated before it begins science operations.

Update 01/21/22, 12:02 a.m. ET: This article was updated to include comments from Eric Smith.