How the James Webb Space Telescope exceeded all expectations

On December 25, 2021, the James Webb Space Telescope blasted off into space.

On December 25, 2021, the James Webb Space Telescope successfully launched into orbit from an Ariane 5 rocket. The rocket was the only way to successfully propel a spacecraft substantial distances through space.

(Credit: ESA-CNES-ArianeSpace/CSG Video Optics/NASA TV)

The plan called for six months of deployment, cooling, and calibration.

The secondary mirror deployment sequence is shown in this time-lapse image. It must be located precisely a little less than 24 feet, or a little more than 7 meters, from the main mirror. This was one of several hundred steps that needed to go as planned, without fail, to get a fully functional JWST online.

(Credit: NASA/James Webb Space Telescope Team)

Then science operations would begin, giving an expected lifespan of 5–10 years.

James Webb Space Telescope

When all optics are properly deployed and the telescope is fully calibrated, James Webb should be able to see any object beyond Earth’s orbit in the cosmos with unprecedented accuracy, with its primary and secondary mirrors focusing light on instruments, where data can be taken, reduced and sent back to Earth.

(Credit: NASA/James Webb Space Telescope Team)

Yet by April 28, 2022, the alignment of each instrument was complete, with an expected lifespan of around 20 years.

This image shows the 18 individual segments that make up James Webb’s main mirror, and the three sets of independent mirrors, labeled with the letters A, B, and C and numbers 1 through 6, which correspond to each mirror’s installed position on the deployed telescope.

(Credit: NASA/James Webb Space Telescope Team)

The telescope and the team performed dazzlingly, exceeding expectations overall.

This multi-panel image shows the detail returned by each of the JWST’s instruments in the same pointing/field of view. For the first time, all full field of view instruments are properly and fully calibrated, bringing JWST one step closer to being ready to begin science operations.

(Credit: NASA/STScI)

First: the fuel preserved from the virgin launch on the course intended for course correction.

As the solar array unfolded 29 minutes after launch and about 4 minutes ahead of schedule, it became clear that NASA’s James Webb Space Telescope was operational and receiving power, and was in good health. way to its final destination. The launch was an unprecedented success.

(Credit: NASA TV/YouTube)

JWST reached its destination, the Lagrange point L2, earlier than expected.

Each planet orbiting a star has five locations around it, Lagrange points, which co-orbit. An object located precisely at L1, L2, L3, L4 or L5 will continue to orbit the Sun with exactly the same period as the Earth, which means that the Earth-spacecraft distance will be constant. L1, L2, and L3 are unstable equilibrium points, requiring periodic course corrections to maintain a spacecraft’s position there, while L4 and L5 are stable. Webb has successfully inserted into orbit around L2 and must always face the Sun for cooling purposes.

(Credit: NASA)

Every component deployed correctly and cooled as expected.

The current status of the JWST shows the progress of each of its deployment stages, including the calibration of various components and the temperature of each instrument. Science operations are almost ready to begin.

(Credit: NASA/JWST Team/STScI)

In early February, the 7-step alignment/commissioning process began.

james webb hubble

A portion of the Hubble eXtreme Deep Field that was imaged for a total of 23 days, unlike the simulated view expected by JWST in infrared. By choosing its targets wisely, the James Webb Space Telescope should be able to reveal extraordinary details about the most distant objects in the Universe that no other observatory could hope to reveal. Once the calibration is complete, this type of scientific work can begin.

(Credit: NASA/ESA and Hubble/HUDF team; JADES collaboration for the NIRCam simulation)

First, the images produced by each mirror segment were identified.

james webb spikes

This image mosaic was created by pointing the telescope at a bright, isolated star in the constellation Ursa Major known as HD 84406. This star was chosen specifically because it is easily identifiable and not cluttered by other stars of similar brightness, which helps reduce confusing background noise. Each point in the mosaic is labeled by the corresponding primary mirror segment that captured it. These first results correspond well to expectations and simulations.

(Credit: NASA)

Second, the images were aligned, then third, they were stacked.

This three-panel animation shows the difference between 18 individual unaligned images, those same images after each segment has been better configured, and then the final image where the individual images from all 18 mirrors have been stacked and co-added together. The pattern created by this star, known as the “nightmare snowflake”, can be improved with better calibration.

(Credits: NASA/STScI, compiled by E. Siegel)

Fourth, the coarse phasing synthesized 18 small telescopes into one big one.

After image stacking, where all the light is placed in one place on the detector, the segments still need to be aligned with each other to an accuracy of less than the wavelength of the light. Coarse phasing measures and corrects for vertical displacement (i.e. piston difference) of mirror segments. Smaller piston errors create fewer “barber pole” bands in this NASA simulation.

(Credit: NASA)

Fifth, NIRCam fine phasing occurred, creating the first fully focused image.

james webb spikes

The very first finely phased image ever released by NASA’s James Webb Space Telescope shows a single image of a star, with six prominent (and two less prominent) diffraction spikes, with background stars and galaxies revealed behind it . As remarkable as this image is, it’s probably the worst James Webb Space Telescope image you’ll ever see as of now.

(Credit: NASA/STScI)

JWST’s unique set of tips stems from the optical design of the telescope.

The point spread function for the James Webb Space Telescope, as predicted in a 2007 paper. The four factors of a hexagonal (non-circular) primary mirror, consisting of a set of 18 tiled hexagons, each with spaces of about 4mm between them, and with three support spacers to hold the secondary mirror in place, all work to create the inevitable series of spikes that appear around bright point sources imaged with JWST.

(Credit: RB Makidon, S. Casertano, C. Cox & R. van der Marel, STScI/NASA/AURA)

Sixth, alignment coverage has expanded to JWST’s instrument suite and full field of view.

After fine phasing, the telescope is only properly aligned at one point in NIRCam’s field of view. By making measurements at several field points on each of the instruments, the variations in intensity can be reduced until they are optimal, thus obtaining a telescope well aligned with all the scientific instruments.

(Credit: NASA)

Seventh, final iterative fixes completed the alignment.

Engineered images of perfectly focused stars in each instrument’s field of view demonstrate that the telescope is fully aligned and in focus. For this test, Webb pointed to a portion of the Large Magellanic Cloud, a small satellite galaxy to the Milky Way, providing a dense field of hundreds of thousands of stars through all of the observatory’s sensors.

(Credit: NASA/STScI)

Now NIR Cam,

Originally, when the first images of JWST’s spectacular bright ‘8-pointed’ star were produced, it indicated that the spacecraft’s onboard working camera, NIRCam, had been calibrated at some point. Now this calibration applies to the entire JWST field of view, the entire NIRCam field as well as the fields of all other instruments.

(Credit: NASA/STScI)

fine guide sensor,

The fine guidance sensor on board the JWST will track guide stars to point the observatory with precision and accuracy, and will take calibration images rather than images used to extract scientific data.

(Credit: NASA/STScI)


The near-infrared imager and slitless spectrograph, which are part of the same instrument as the fine guidance sensor, are designed to excel in the detection, characterization and transit spectroscopy of exoplanets. If there are biological clues around the exoplanets, the NIRISS instrument should find them.

(Credit: NASA/STScI)


NIRSpec is a spectrograph rather than an imager, but can take images, such as the 1.1 micron image shown here, for calibrations and target acquisition. The dark regions visible in parts of the NIRSpec data are due to the structures of its micro-shutter array, which has several hundred thousand controllable shutters that can be opened or closed to select the light sent into the spectrograph.

(Credit: NASA/STScI)

and the MIRI instruments are all lined up.

Although the MIRI (Mid-InfraRed Instrument) of the James Webb Space Telescope achieves the lowest resolution due to the long wavelengths it is sensitive to, it is also the most powerful instrument in many respects, capable to reveal the most distant features of the universe of all. .

(Credit: NASA/STScI)

All that remains is the commissioning of the instrument and the final calibrations.

This is a simulated JWST/NIRCam mosaic that was generated using JAGUAR and the NIRCam Guitarra image simulator, at the expected depth of the JADES Deep program. It is highly likely that in his first year of science operations, James Webb will break many records set by Hubble over his 32 years (and counting), including records for the most distant galaxy and the farthest star.

(Credit: C. Williams et al., ApJ, 2018)

With fuel savings and quick alignment, about 20+ years of science operations will soon begin.

Mostly Mute Monday tells an astronomical story in pictures, visuals and no more than 200 words. Talk less; smile more.

Leave a Reply