Large space telescope considered successor to Hubble assembled
By Shruti Iyer
Oct. 25, 2019 1:52 a.m.
The assembly of the largest space telescope to date was completed early October.
The James Webb Space Telescope, a NASA-led international collaborative project, recently finished its assembly process, taking a step towards its planned launch date in March 2021. With a 6.5-meter diameter mirror, the JWST is the largest space telescope ever made.
Tommaso Treu, a UCLA physics and astronomy professor and a member of the JWST Users Committee, said the telescope is extremely complicated to build because of its size and needs to be able to operate in extremely cold temperatures of around 30 Kelvin. The project was originally intended to be completed in 2010, but faced frequent delays.
“It’s been more than 20 years from conception to get to this point,” Treu said.
Treu added that these temperatures are much closer to absolute zero than the temperatures the Hubble Space Telescope operates at. The JWST is considered to be the successor to Hubble, which is currently the largest telescope in space, Treu said.
There are three parts to the JWST: the sun shield, the telescope itself and a package of several attached instruments, Treu said.
The sun shield, designed to block out light from the sun, is about the size of a tennis court and is made from a material called Kapton, said Massimo Stiavelli, head of the JWST Mission Office at the Space Telescope Science Institute in Baltimore, Maryland.
Kapton is a polyimide film that makes up all five layers of the sun shield; each layer is coated with either silicone or aluminum, said Jonathan Arenberg, who was the chief engineer on the JWST at Northrop Grumman Aerospace Systems.
“The sun shield is like a high-performance parasol,” Arenberg said.
Instead of having the JWST orbit the Earth, the telescope will orbit the Earth-Sun system at a point 1.5 million million kilometers away from the Earth. It will operate for about 10 years, Treu added.
Treu said that the most important property of a telescope is the diameter of the primary mirror, which determines how faint and detailed the telescope can see.
“(The JWST) can see infrared light that Hubble cannot see.” Treu added.
The primary mirror is made out of beryllium, an element that allows scientists to control the expansion and contraction of the mirror. This mirror is coated with a thin layer of gold to enhance its infrared reflectivity.
The diameter of the mirror was bigger than the largest rocket NASA has available, so the mirror had to be designed to be foldable and later deployable.
“The diameter of the telescope is almost three times as big as Hubble.” Treu said
The instrument package consists of four devices, which were put together at the NASA Goddard Space Flight Center, Arenberg said.
The first instrument is a near-infrared camera, called NIRCam. The second is the Near-InfraRed Spectrograph, which detects the chemical composition of galactic objects, Arenberg said.
The Mid-Infrared Instrument will take images in the mid-infrared range, while the Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph helps position the JWST at a point in space.
“The (FGS/NIRISS) has exquisite precision, that if you were to stand on Royce Hall and Lady Liberty were to be holding a typical piece of paper, 8 inches by 11 inches, folded in half, and if you had a laser pointer, you’d be able to point to the paper.” Arenberg said. “Obviously this is impossible because the Earth is curved, but these are the kind of numbers we’re talking about.”
Alice Shapley, the current vice chair of astronomy and astrophysics at UCLA, said that she is a potential user of the JWST and plans to use the telescope for her research.
Arenberg, a three-time UCLA alum, said he is proud to have a chance to contribute to this scientific endeavor.
“Every time humanity has pointed a telescope at the sky, where we’ve never made observations before, going all the way back to Galileo, changes the way we view the universe.” Arenberg said. “We have an opportunity to see these very first stars and galaxies for the first time. It’s essentially the last great unexplored chapter of cosmic history.”
