Webb Space Telescope Begins Multi-Instrument Alignment

NASA’s Webb Space Telescope

NASA’s James Webb Space Telescope. Credit: NASA Goddard Space Flight Center and Northrup Grumman

After meeting the major milestone of aligning the telescope to NIRCam, the Webb team is starting to extend the telescope alignment to the guider (the Fine Guidance Sensor, or FGS) and the other three science instruments. This six-week-long process is called multi-instrument multi-field (MIMF) alignment.

When a ground-based telescope switches between cameras, sometimes the instrument is physically taken off the telescope, and a new one is installed during the daytime when the telescope is not in use. If the other instrument is already on the telescope, mechanisms are in place to move part of the telescope’s optics (known as a pick-off mirror) into the field of view.

On space telescopes like Webb, all the cameras see the sky at the same time; to switch a target from one camera to another, we repoint the telescope to put the target into the field of view of the other instrument.

After MIMF, Webb’s telescope will provide a good focus and sharp images in all the instruments. In addition, we need to precisely know the relative positions of all the fields of view. 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 use to point the telescope. In another instrument milestone, FGS recently achieved “fine guide” mode for the first time, locking onto a guide star using its highest precision level. We have also been taking “dark” images, to measure the baseline detector response when no light reaches them – an important part of the instrument calibration.

Webb FGS Instruments

Webb’s guider (FGS) and four science instruments (NIRCam, NIRSpec, NIRISS, and MIRI) share the field of view of the Webb telescope optics, but they actually see different parts of the sky at any given observation. Credit: NASA

Webb’s mid-infrared instrument, MIRI, will be the last instrument that is aligned, as it is still waiting for the cryogenic cooler to chill it to its final operating temperature, just under 7 degrees above absolute zero. Interspersed within the initial MIMF observations, the two stages of the cooler will be turned on to bring MIRI to its operating temperature. The final stages of MIMF will align the telescope for MIRI.

You might be wondering: If all of the instruments can see the sky at the same time, can we use them simultaneously? The answer is yes! With parallel science exposures, when we point one instrument at a target, we can read out another instrument at the same time. The parallel observations don’t see the same point in the sky, so they provide what is essentially a random sample of the universe. With a lot of parallel data, scientists can determine the statistical properties of the galaxies that are detected. In addition, for programs that want to map a large area, much of the parallel images will overlap, increasing the efficiency of the valuable Webb dataset.

Written by:

  • Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
  • Stefanie Milam, Webb deputy project scientist for planetary science, NASA Goddard

4 Comments on "Webb Space Telescope Begins Multi-Instrument Alignment"

  1. Very Interesting. Some thoughts triggered. Sharing.

    1. Optician Diagnosis:
    a) Patient wants short-sight.
    b) Patient wants long-sight.
    c) Patient wants Normal clear 20/20 vision in visible spectrum.
    Patient is Telescope. WEBB.
    2. How to get the Patient (Telescope) to 20-20 vision for ALL-Spectrum of Light from Solar /
    Non-Solar (Light reflected from Other objects like moons, asteroids and other satteelites?)
    3. Answer: Both Hardware and Software involved. Both iportant for best view for future
    4. Objective is All Instrunent, All Spectrum , All View (360 Degree) Telescope ( Patient).
    5. Both highly integrated Hardware and Software Telescope like WEBB needs to be built in
    6. The technology from Space created the modern world on planet Earth. Now some of the technology from planet Earth, can be used in Space Missions and Building a better Telescope. How , you ask! Well look at the latest Apple I Phone with Integrated Hardware, low energy consumption, hifgly efficient product, ( as advertised) about to be released globally. Apply to Current Patient (Telescope).
    7. My preference is to make the future increasingly Software driven as far as possible, as it can be mnipulated and instructions sent to improve the focus of the Telescope much more easily , unless the observtory has robots whoch can be trained to integrate future hardware and new age chips.
    8. We need to move from Random samples of the Universe to a pulsating view of the Universe in all its glory.

    Views expressed are personal and not binding on nyone.

  2. Mike Westkamper | March 22, 2022 at 8:46 am | Reply

    A question; We have heat powered probes out in the nether lands, pioneer and voyager. While pioneer residual heat is really low, Voyagers are still producing 20 or so watts. Can WEBB spot them? We know where the Voyager’s are, and probably can make a good guess for Pioneer.

  3. Tiffany Morgan | March 23, 2022 at 9:10 pm | Reply

    This article got me wondering about the temperature in space. The temperature in space is just above absolute zero
    , 2.7 k or -455 f, why is necessary to cool the MIRI down to just under 7 degrees above absolute zero?

    • Temperature is a measurement of the kinetic energy of the molecules in the surroundings. In space, there are almost no molecules, that produce, very low kinetic energy to whatever thermometer there is and that means very low readings. But, heat energy can also travel as EM radiation, which means that the radiation from the sun can heat up the Telescope, thus it requiring cooling systems. It is the ozone layer of the earth that we don’t feel much heat as we would in space.

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