The light is then reflected and divided and directed to the science instruments by pick-off mirrors. JWST is a three-mirror anastigmat telescope.
While telescope alignment continues, Webbs Mid-Infrared Instrument (MIRI) is still in cooldown mode. MIRI, which will be the coldest of Webbs 4 instruments, is the only instrument that will be actively cooled by a cryogenic refrigerator, or cryocooler. This cryocooler utilizes helium gas to bring heat from MIRIs optics and detectors out to the warm side of the sunshield. To manage the cooldown process, MIRI likewise has heaters onboard, to secure its delicate parts from the threat of ice forming. The Webb team has started gradually changing both the cryocooler and these heaters, to guarantee a slow, controlled, stable cooldown for the instrument. Soon, the group will shut off MIRIs heating units totally, to bring the instrument to its operating temperature of less than 7 kelvins (-447 degrees Fahrenheit, or -266 degrees Celsius).
In the meantime, after achieving alignment with the Near-Infrared Camera (NIRCam), Webb engineers have begun lining up the telescope to the remaining near-infrared instruments. For more about this six-week process, we hear today from Michael McElwain and Charles Bowers, members of the Webb team at NASAs Goddard Space Flight:.
” Webbs positioning at the NIRCam field showed some incredible diffraction-limited images, producing an alluring look of the capabilities this observatory will carry for its science program. Due to the fact that it required nearly all of the observatory systems to be operating as designed, this was a major milestone. It all worked along with we dared to hope, and it was certainly a minute to commemorate.
” The next step is to ensure the telescope is well-aligned to the instruments besides NIRCam, including the guider (the Fine Guidance Sensor, or FGS) and the other 3 science instruments: the Near-Infrared Slitless Spectrograph (NIRISS), Near-Infrared Spectrometer (NIRSpec), and MIRI. All the near-infrared instruments have actually currently been passively cooled, are approaching their functional temperature levels, and are taking part in this next alignment stage. MIRI requires active cooling by a cryocooler, which is now underway, and it will be ready for positioning in a few weeks.
” This is the sixth stage of our telescope alignment strategy, the Telescope Alignment Over Instrument Fields of View. Each of the instruments occupies a part of the telescope focal plane, simply slightly balanced out with regard to each other. Little misalignments of this type will be evident in images in instruments farther from the center of the telescope field of view.
” The initial step was to simply look at star fields as seen by NIRCam, NIRISS, FGS, and NIRSpec to see whether they were in focus. The stars looked nearly in-focus, which was a sign that the main to secondary mirror alignment was already excellent. A more precise optical mistake measurement has been carried out at five to 10 field positions within each operational science instrument, utilizing data taken with the secondary mirror positioned out of focus. This dataset provided a definitive decision of the telescope alignment state.
” The Webb optics group analyzed the multi-instrument dataset and identified that only minor focus changes are needed on the secondary mirror and science instruments. Considering that the telescope is still cooling together with the MIRI instrument, we will not apply the corrections at this time and will defer them up until the next round.
” When MIRI is available, an extra round of measurements will be conducted by each science instrument to determine the final state of the telescope alignment. We will repeat this procedure as required to guarantee the telescope efficiency is optimized for all of the instruments. After the telescope positioning to all instruments is total, we will transition to the final 2 months of commissioning, where we will perform optical stability tests and measure the science instrument efficiency prior to starting the Cycle 1 science program.”.
Composed by:.
While telescope alignment continues, Webbs Mid-Infrared Instrument (MIRI) is still in cooldown mode. MIRI, which will be the coldest of Webbs four instruments, is the only instrument that will be actively cooled by a cryogenic refrigerator, or cryocooler.” The next step is to ensure the telescope is well-aligned to the instruments other than NIRCam, consisting of the guider (the Fine Guidance Sensor, or FGS) and the other 3 science instruments: the Near-Infrared Slitless Spectrograph (NIRISS), Near-Infrared Spectrometer (NIRSpec), and MIRI.” This is the sixth phase of our telescope alignment strategy, the Telescope Alignment Over Instrument Fields of View. After the telescope alignment to all instruments is complete, we will shift to the last two months of commissioning, where we will carry out optical stability tests and determine the science instrument efficiency prior to embarking on the Cycle 1 science program.”.
Michael McElwain, Webb observatory project researcher, NASA Goddard.
Charles Bowers, Webb deputy observatory project scientist, NASA Goddard.
