Space Telescope Summary Reader Response (Draft 1)

The article "Why stars look spiky in images from the James Webb Space Telescope" (Griggs, 2022) explains why there exists a spiky feature when stars are pictured by the James Webb Space Telescope (JWST). It is a National Aeronautics and Space Administration (NASA) telescope currently in L2 orbit (1.5 million kilometers) around Earth. The telescope produces images with six diffraction spikes, unlike Hubble's four. (Griggs, 2022). Onboard the JWST are three instruments: Near Infrared Camera (NIRCam), Near InfraRed Spectrograph (NIRSpec), and Mid-Infrared Instrument (MIRI). As mentioned on NASA's website, NIRCam is outfitted with a coronagraph and will be the primary imager for the universe's faintest and most distant objects. NIRSpec uses the light collected by NIRCam to perform up to 100 simultaneous observations. The data collected is then further analyzed using spectrometry. In addition, MIRI will deliver wide-angle images of the cosmos using an operating wavelength of 5 to 28 microns. A critical component of the JWST is its sun shield, insulating its sensors to achieve an optimal operating temperature of 39K (-234 C). The JWST space telescope's imaging accuracy is significantly better owing to several improved features and innovations, enabling astronomers to continue deep space exploration into the next decade.

Various spectrographs, each with a slightly different function, are available in JWST. For starters, the scientific cameras and sensors onboard are more sensitive and have a higher resolution than the Hubble Space Telescope (HST). Regions of space are depicted in two dimensions by cameras operating in the visible light spectrum. In contrast, MIRI records mid-infrared images, and NIRCam records near-infrared images, which cannot be seen with the naked eye. The only tool without a camera is NIRSpec, which consists only of spectrographs. These sensors disperse light into a spectrum, measuring the brightness of each wavelength, and can identify specific elements and molecules.

Moreover, all instruments onboard are equipped with spectrographs operating at different wavelengths. Another function is the coronagraphs, which are opaque disks that block stars' bright light so that planets and debris disks orbiting the star can be detected. NIRCam and MIRI are both equipped with coronagraphs.

Next comes the tennis court-sized sun shields, which shield the telescope from the Sun's thermal heat. The construction of each layer comes from a unique composite material called Kapton, which has high thermal stability. The sunshade receives about 200 kW of energy on the side facing the Sun, while only 23 mW (Maloney, 2022) can get through to the cold side. This form of passive cooling maintains the instruments at a subzero 40 K temperature, which is adequate for the three near-IR instruments. The cooler it gets, the more accurate the sensors get. Fundamentally, space telescopes conduct observations in the infrared spectrum, which is essentially thermal heat. The interferences caused by the JWST's thermal emission can be mitigated by getting the instruments as cool as possible. Each insulation layer has a specific thickness and size; they all need to be precisely spaced apart for optimal heat dissipation. There are unique ripstop seams and reinforcements to address potential damage from micrometeorites. 

JWST boasts a state-of-the-art cooling system to maintain the operating temperature of 7 Kelvin required for MIRI. The Cryocooler Compressor Assembly (CCA) is the primary component of the cryocooler (Cooper, 2021), housed in the spacecraft bus located on the telescope's warm side. It is linked to MIRI and uses helium as a refrigerant. Helium is pumped through these tubes to MIRI via the Cryocooler ColdHead Assembly (CHA) after being pre-cooled inside the CCA. This process decreases the temperature to -266 degrees Celcius, enabling MIRI to operate at utmost accuracy.

Still, although there has been some limitation to Hubble, the telescope has provided astronomers with valuable data and is a testament to its success over its long years of operation. However, it is not the end for Hubble. Another reason Webb is not a replacement for Hubble is that its capabilities are not identical. Hubble studies the universe primarily at optical and ultraviolet wavelengths, while Webb observes it in the infrared. 

In conclusion, the enhanced capabilities brought forth by JWST will enable astronomers to continue deep space exploration where Hubble could not see in the infrared spectrum. It will also explore and discover exoplanets in our neighboring galaxies and search for conditions that may sustain life. 

References:

Griggs, M. B. (2022, July 15). Why stars look spiky in images from the James Webb Space Telescope. The Verge. Retrieved September 26, 2022, from https://www.theverge.com/23220109/james-webb-space-telescope-stars-diffraction-spike

Maloney, D. (2022, May 5). About As Cold As It Gets: The Webb Telescope's Cryocooler. Hackaday. Retrieved September 30, 2022, from https://hackaday.com/2022/05/05/about-as-cold-as-it-gets-the-webb-telescopes-cryocooler/

Cooper, K. (2021, December 20). The ten-billion-dollar gamble: Keeping the JWST cool – Physics World. Physics World. Retrieved September 30, 2022, from https://physicsworld.com/a/the-ten-billion-dollar-gamble-keeping-the-jwst-cool/