NASAs James Webb Space Telescope. Credit: NASA Goddard Space Flight Center and Northrup Grumman
After fulfilling the major milestone of lining up the telescope to NIRCam, the Webb team is beginning to extend the telescope alignment to the guider (the Fine Guidance Sensor, or FGS) and the other 3 science instruments. This six-week-long process is called multi-instrument multi-field (MIMF) positioning.
When a ground-based telescope changes in between cameras, in some cases the instrument is physically taken off the telescope, and a brand-new one is set up throughout the daytime when the telescope is not in usage. If the other instrument is currently on the telescope, systems remain in location to move part of the telescopes optics (called a pick-off mirror) into the field of vision.
On area telescopes like Webb, all the cams see the sky at the very same time; to change a target from one electronic camera to another, we repoint the telescope to put the target into the field of view of the other instrument.
After MIMF, Webbs telescope will offer a good focus and sharp images in all the instruments. In addition, we need to specifically understand the relative positions of all the field of visions. Over last weekend, we mapped the positions of the three near-infrared instruments relative to the guider and updated their positions in the software that we utilize to point the telescope. In another instrument turning point, FGS just recently accomplished “great guide” mode for the very first time, locking onto a guide star utilizing its highest accuracy level. We have actually likewise been taking “dark” images, to determine the standard detector response when no light reaches them– a vital part of the instrument calibration.
Webbs guider (FGS) and 4 science instruments (NIRCam, NIRSpec, NIRISS, and MIRI) share the field of vision of the Webb telescope optics, however they in fact see various parts of the sky at any offered observation. Credit: NASA
Webbs mid-infrared instrument, MIRI, will be the last instrument that is aligned, as it is still waiting on the cryogenic cooler to chill it to its final operating temperature, simply under 7 degrees above absolute zero. Sprinkled within the initial MIMF observations, the two stages of the cooler will be turned on to bring MIRI to its operating temperature level. The final phases of MIMF will line up the telescope for MIRI.
You might be questioning: If all of the instruments can see the sky at the same time, can we use them concurrently? The response is yes! With parallel science exposures, when we point one instrument at a target, we can read out another instrument at the very same time. The parallel observations do not see the very same point in the sky, so they supply what is basically a random sample of deep space. With a lot of parallel data, scientists can determine the statistical homes of the galaxies that are discovered. In addition, for programs that wish to map a large area, much of the parallel images will overlap, increasing the effectiveness of the valuable Webb dataset.
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After MIMF, Webbs telescope will supply an excellent focus and sharp images in all the instruments. Over last weekend, we mapped the positions of the 3 near-infrared instruments relative to the guider and updated their positions in the software application that we utilize to point the telescope. Webbs mid-infrared instrument, MIRI, will be the last instrument that is lined up, as it is still waiting for the cryogenic cooler to chill it to its last operating temperature level, just under 7 degrees above absolute no. The final stages of MIMF will align the telescope for MIRI.
Jonathan Gardner, Webb deputy senior task scientist, NASAs Goddard Space Flight Center
Stefanie Milam, Webb deputy job researcher for planetary science, NASA Goddard