Free Astronomy Magazine March-April 2022

MARCH-APRIL 2022 N ASA’s James Webb Space Telescope separates from its Ariane 5 rocket with the bright blue Earth in the background in this view captured after its launch on Dec. 25, 2021. [NASA TV] ! components might begin radiating infrared energy and corrupting the observations. This approach of engi- neering a reflective cooling system into the design is in stark contrast to the approach taken with Spitzer, where liquid helium cooling was employed to keep the detectors cold – a method that certainly kept the telescope cold enough for IR obser- vations, but which also then greatly reduced the usability of the scope to the time it took to deplete the he- lium. The one onboard cryocooler on Webb, a necessary addition for the Mid-InfraRed Instrument (MIRI) to achieve ultra-cold conditions (7 K) at its detectors, employs a pulse- tube cooling approach that has no moving parts and requires no chem- ical refrigerant, meaning no un- wanted vibrations through the telescope and a cryocooler lifetime that is expected to well-exceed the operational lifetime of the tele- scope itself. A final word on finality. Much has been mentioned about JWST and how “it has to work.” Unlike Hubble, which benefited greatly from two service missions and actual astro- nauts to perform the procedures, JWST is nowhere near what anyone would describe as a repair-accessible location. Hubble remains about 540 km (335 mi) away from us at any given time, a distance one could cover on a highway in a long after- noon on a single charge for some electric cars now on the market. From Thomas Zurbuchen (NASA Sci- ence Mission Directorate) on down, no one has offered the proposal (se- rious or otherwise) that an issue with Webb could be resolved with a mis- sion, crewed or otherwise. The only clear sign of optimism for any type of visitation to JWST before the end of its operational lifetime is a re- ported refueling port. Interestingly, a web search for this port will take you to many space news websites discussing the manners of approach and dangers to the sunshields of re- fueling through robotic missions, but none of these sites end in nasa.gov. Concerns about a failure in such a complicated undertaking as an un- folding telescope in space ignores, of course, the fact that NASA excels at one-way missions. In most re- spects, almost every mission beyond the Earth-Moon system is one-way and, by nature, “has to work.” While the JWST is a modern (albeit expensive) and complicated engi- neering feat, no one can deny the great successes of the Voyagers, Cassini, various Mars missions, New Horizons, and the many other probes either retired or still actively doing great science. This is all to say that the “flawless” and “perfect” descriptors of the launch and un- folding of JWST are welcome from NASA, but not a surprise. With its deployment complete and no expec- tation of technical issues from here on out, the JWST is nearly ready to begin what could be two decades of groundbreaking observations. The great expectations cover nearly the entirety of the history of the uni- verse itself, from the earliest stars to the possible detections of life-com- patible conditions in our own celes- tial neighborhood.