Space Telescope Reader Response (Draft 3)

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 eight diffraction spikes (Lawrence, 2022), and can be easily seen on brighter stars. 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, using an operating wavelength of 5 to 28 microns (Cooper, 2021), MIRI will be able to deliver wide-angle images of the cosmos. 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.

For starters, there are various spectrographs, each with a slightly different function available on the JWST. 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.

Next, are 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, 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. 

Additionally, 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.

Although the JWST has improved our observation capabilities, its operating lifespan is limited by the amount of fuel on board. Owing to a seamless launch, Szondy (2021) estimates that the JWST is expected to have enough propellant to operate for more than a decade, provided other systems do not break down. Manned maintenance and refueling efforts will be almost impossible, due to the remote location of JWST. However, NASA is exploring unmanned missions to refuel and conduct maintenance in the near future.

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:

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

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

Lawrence, P. (2022, September 13). Why do all the stars have 8 points in the James Webb images? An astronomer explains. BBC Science Focus Magazine. https://www.sciencefocus.com/space/diffraction-spikes-jwst/

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

Szondy, D. (2021, December 29). Extra fuel may keep James Webb Space Telescope going for over a decade. New Atlas. https://newatlas.com/space/extra-fuel-james-webb-space-telescope-extend-science-mission/