Webb telescope launch opens new era in deep space astronomy

The National Aeronautics and Space Administration's 14,300-pound James Webb Space Telescope, launched into space Dec. 25, 2021, aboard a French Ariane 5 rocket from the European Spaceport at Kourou in French Guiana. This heralds a new chapter in deep space astronomy. 

The new telescope, which NASA views as the successor to the Hubble Space Telescope that was launched in 1990, will see wavelengths from 0.6 to 28 microns. This is the range from the visible yellow-orange colors to the longer near-infrared radiation associated with heat that is invisible to the human eye. 

The near-infrared band includes wavelengths of light that we receive from the far outskirts of the universe 13.5 billion light years away, as well as light coming from star- and planet-forming regions of our own galaxy where dust clouds normally obscure the light emitted at visible wavelengths. 

The collecting area of the Webb’s mirror array is 4.5 square meters, more than six times greater than the Hubble and 15 times the area of Hubble’s specialized near-infrared camera (NICMOS), allowing far greater observational capabilities. Webb will also see with greater resolution than the significantly smaller Spitzer Space Telescope, which was specialized for infrared viewing and retired a year ago. 

Webb is known technically as a three-mirror anastigmat telescope. In this configuration the primary mirror is concave and the secondary mirror convex, like many amateur telescopes, but it works slightly off-axis. The tertiary mirror removes the resulting astigmatism (blurriness) and also flattens the focal plane. This also allows for a wider field of view.

Mission to the L2 point

The major advantage of space telescopes is that they orbit well above the Earth’s atmosphere, avoiding all the obscuring effects of atmosphere, wind and heat. 

Hubble is in an orbit around the Earth and about 570 kilometers (353 miles) away, the Webb is being sent to a point in space known as the second Lagrange point, or L2, about 1.5 million kilometers (930,000 miles) from Earth.

L2 is one of the five stable points near Earth’s orbit about the sun, first calculated by the 18th Century Italian-French astronomer Joseph-Louis Lagrange. 

L2 is on a direct line connecting the Earth to the sun but 1.5 million miles farther away from the sun. At the L2 point, the gravitational pull of the Earth and the sun are nearly equal, so the telescope will keep up with the Earth as it orbits, requiring only very minor rocket thrusts to keep it in position. 

The L2 positioning will allow the space telescope to shield itself from the sun’s rays and those reflected by the Earth and moon, by deploying a sunshield about the size of a tennis court. Otherwise, the solar radiation would greatly disturb reception of the infrared radiation from deep space. 

Protected by the sunscreen, the telescope mirrors and science instruments will operate at a temperature of –388º Fahrenheit (–233º C). The hot side of the array facing the sun, including the solar panel, communications antenna, and steering equipment, will be at 185º Fahrenheit (85º C). 

The L2 position also facilitates communication to Earth. As the Webb will always be at the same position in the midnight sky, continuous communications will be maintained as the Earth rotates by making use of the by the Deep Space Network which utilizes three large antennas located on the ground in Australia, Spain, and California.

Mirror unfolded

It will take 30 days for the Webb to get to its final destination and 6 months before full operations can begin. But before that, even as it glides toward L2, some things can be accomplished. Deployment of the huge sunshield began in the first week after launch. 

A milestone was reached Jan. 8, two weeks into flight, when unfolding of the huge primary mirror array was completed. 

The 21-foot-4-inch-diameter mirror consists of 18 hexagonal sections weighing 46 pounds each. The sections are made of beryllium, a strong, lightweight metal often used in supersonic aircraft construction. They are covered with a microscopically thin layer of gold, which optimizes them for reflecting infrared light. 

To fit into the space craft, two “wings,” consisting of three hexagonal sections each, had to be folded back. After raising the secondary mirror tower, the successful unfolding and positioning of the primary mirror sections was viewed as a key step.

Webb won't be ready for work until around July according to NASA, and that's only if all 300 '‘points of failure'’ don't fail. 

However, as Mark McCaughrean, a senior adviser to the European Space Agency and member of the Webb’s Science Working Group put it in a Tweet Jan. 8, “To quote Mr. [Winston] Churchill, now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning. Five months of cooling, aligning, and commissioning remain, hard work for the teams involved, before science begins. But today is a big step. Huge congrats to all the teams involved.”

The telescope is named after Webb, NASA administrator from 1961 to 1968, during the heyday of the “space race” during the presidencies of John F. Kennedy and Lyndon Johnson.

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Sources:

NASA website, Webb vs. Hubble Telescope.

NASA website, Webb Orbit.

NASA website, Webb’s Mirrors.