The world is still reeling from the release of the first images from the james wbb telescope. The kind of science operations that will be conducted over the next 20 years were provided in these. The most sensitive and detailed look at some of the most famous astronomy objects, as well as a deep field view of some of the most distant galaxies in the Universe, were included. We have been treated to a glimpse of objects in the Solar System since they were released.
The full report titled " Characterization of JWST science performance from commission" was released by the collaboration. The paper covers everything from the telescope's navigation to the performance of its instruments. One of the micrometeoroid impacts caused "uncorrectable change" in one mirror segment.
Researchers from NASA, the European Space Agency, and the Canadian Space Agency were involved in the study. The National Research Council Canada, the Max-Planck-Institut fr Astronomie, and the UK Astronomy Technology Centre are included.
The paper they compiled looks at the performance during the six-month period before it entered service. The observatory's on-orbit performance, the design and architecture, and the pre-launch predicted performance were all part of this. They were compared to the performance of the ground system. The section on optical performance addresses how the various instruments worked during the commission period.
There are eighteen hexagonal segments in the primary mirror. All segments are aligned to ensure the best resolution and sensitivity possible. Wavefront Error is a measure of how light collected by the telescope's mirrors deviates from the expected wavelength of light. The spherical average of the entire wavefront is used to calculate the extent.
The units of the particular wavelength are used to express this in a mathematical way. The section addresses the impact of micrometeoroids on the optical performance. The assessment starts by reminding readers that any spacecraft will inevitably encounter micrometeoroids, and then lists how many impacts were expected during the commission period.
“During commissioning, wavefront sensing recorded six localized surface deformations on the primary mirror that are attributed to impact by micrometeoroids. These occurred at a rate (roughly one per month) consistent with pre-launch expectations. Each micrometeoroid caused degradation in the wavefront of the impacted mirror segment, as measured during regular wavefront sensing. Some of the resulting wavefront degradation is correctable through regular wavefront control; some of it comprises high spatial frequency terms that cannot be corrected.”
They show that these impacts were detected far in the future. A combined total of less than 1 nanometer was contributed to the wavefront error by five of the six detected impacts. Between May 22nd and May 24th there was a significant uncorrectable change in the overall figure of segment C3. The lower right side of the mirror is where this segment is located, and the effect is shown in the Report.
The effect was small since only a small part of the telescope area was affected. The telescope alignment was brought to a minimum of 59 nautical miles per second, which is 5 to 10 nautical miles above the previous best wavefront errorRMS values. At which point, wavefront control is typically performed, the authors of the Report note thatdrifts and stability levels in the telescope typically result in a "telescope contribution" of between 60 and 80 NM.
It is not known at this time if the May 2022, impact to segment C3 was rare or if it is something that can happen frequently throughout the mission. The mission teams hope to determine if the telescope will be more vulnerable to damage by micrometeoroids than pre-launch modeling predicted.
“The project team is conducting additional investigations into the micrometeoroid population, how impacts affect beryllium mirrors, and the efficacy and efficiency tradeoffs of potential mitigations such as pointing restrictions that would minimize time spent looking in the direction of orbital motion, which statistically has higher micrometeoroid rates and energies.”
Concerns were raised about the impact on the C3 segment. The upside is that they were able to address it and it won't affect the long-term science operations. The report summarizes.
“The key outcome of six months of commissioning is this: JWST is fully capable of achieving the discoveries for which it was built. JWST was envisioned ‘to enable fundamental breakthroughs in our understanding of the formation and evolution of galaxies, stars, and planetary systems’… we now know with certainty that it will. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.”
The report concludes that the performance of the JWST has been better than expected. The fine guidance system that points the observatory and the optical alignment of its mirrors have exceeded expectations. The mirrors are cleaner and the science instruments give higher total system throughput than expected. It adds up to some positive appraisals.
“Collectively, these factors translate into substantially better sensitivity for most instrument modes than was assumed in the exposure time calculator for Cycle 1 observation planning, in many cases by tens of percent. In most cases, JWST will go deeper faster than expected. In addition, JWST has enough propellant on board to last at least 20 years.”
Further information will be presented in a series of papers. These will be included in a special issue of the Publications of the Asian Society of the Pacific.
ArXiv is further reading.
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