KEYWORDS: James Webb Space Telescope, Observatories, Design, Systems modeling, Systems engineering, Online learning, Cryogenics, Equipment, Telescopes, Space operations
The James Webb Space Telescope is NASA’s flagship mission and successor to the highly successful Hubble Space Telescope. It is an infrared observatory featuring a cryogenic 6.6 m aperture, deployable optical telescope element with a payload of four science instruments assembled into an integrated science instrument module that provide imagery and spectroscopy in the near infrared band between 0.6 and 5 μm and in the mid-infrared band between 5 and 28 μm. JWST was successfully launched on December 25, 2021, aboard an Ariane 5 launch vehicle. All 50 major deployments were successfully completed by January 8, 2022. The observatory performed all mid-course correction maneuvers and achieved its operational mission orbit around the Sun-Earth second Lagrange Point. All commissioning and calibration activities have been completed and JWST has begun its science mission. Its present performance meets or out-performs all requirements. Launching over 20 years after its mission concept review, the JWST Observatory is a first and only of its kind of facility. This program faced many unique challenges that were not only technical in nature but also organizational and managerial. We describe the challenges faced by the JWST systems engineering team, the way the team addressed them, and make recommendations for focus areas of future flagship missions, which will likely face similar challenges. It will not explicitly address the cost challenges of the mission. We first describe the mission and its over-arching challenges. We then describe the tailoring of systems engineering processes and methods used to address these challenges and effectiveness. The events, tasks, issues, and their resolutions and the resulting specific lessons learned from the project are discussed with the over-arching recommendations for future flagship missions that derive from these lessons.
The long-awaited launch of the James Webb Space Telescope on December 25, 2021, initiated a complex commissioning campaign which successfully brought the observatory to readiness for carrying out its scientific observing program by early July, 2022. Commissioning began by bringing online the various spacecraft systems and executing a series of mission-critical deployments. The next few months involved a complex interplay of cooling toward the final cryogenic operating temperatures of the telescope and instruments, aligning the segmented, deployable telescope, bringing online Webb’s four scientific instruments (plus Fine Guidance Sensors), and beginning the process of preparing their many powerful observing modes for scientific use. We provide an overview of the process and timeline for executing the commissioning campaign and then focus on its final stages: for each instrument, acquiring the numerous pieces of performance data and carrying out the operational verifications that ultimately led to confirmation of each observing mode’s readiness for scientific operations.
KEYWORDS: James Webb Space Telescope, Observatories, Thermography, Telescopes, Control systems, Contamination control, Contamination, Wavefront sensors
The James Webb Space Telescope (JWST) is going through final integration and testing and is planned to launch in 2021. The last remaining optical challenge for JWST is to fully align the observatory in flight to meet the optical requirements but this effort involves many system considerations to do this safely and efficiently and the entire effort will take several months. This talk will cover what it takes to deploy and optically commission the telescope including the many interactions and constraints of deployment, thermal, optical, attitude control and contamination properties of the observatory. The talk will cover the final optical requirements that the telescope will need to meet and will provide the roadmap of timelines, cooldown profiles, Wavefront Sensing and Control steps, system constraint considerations, and implementation of lessons learned from the ground test campaign that will result in meeting those optical requirements.
Michael Menzel, Marie Bussman, Michael Davis, Gary Golnik, Sandra Irish, Jon Lawrence, Richard Lynch, Peiman Maghami, Landis Markley, Kimberly Mehalick, Gary Mosier, Danniella Muheim, Keith Parrish, Shaun Thomson, Paul Geithner, Joseph Pitman, James Wehner, Jonathan Arenberg, Brian Costanza, Satya Anandakrishnan, William Burt, Reem Hejal
KEYWORDS: Observatories, James Webb Space Telescope, Thermal modeling, Space telescopes, Cryogenics, Solid modeling, Systems engineering, Systems modeling, Integrated modeling, Space operations
The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2014.
System-level verification of critical performance requirements will rely on integrated observatory models that predict the
wavefront error accurately enough to verify that allocated top-level wavefront error of 150 nm root-mean-squared (rms)
through to the wave-front sensor focal plane is met. This paper describes the systems engineering approach used on the
JWST through the detailed design phase.
KEYWORDS: Systems modeling, James Webb Space Telescope, Observatories, Thermal modeling, Data modeling, Mathematical modeling, Solid modeling, Space telescopes, Performance modeling, Distortion
The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2014.
The imaging performance of the telescope will be diffraction limited at 2μm, defined as having a Strehl ratio >0.8.
System-level verification of critical performance requirements will rely on integrated observatory models that predict the
wavefront error accurately enough to verify that allocated top-level wavefront error of 150 nm root-mean-squared (rms)
through to the wave-front sensor focal plane is met. Furthermore, responses in several key disciplines are strongly crosscoupled.
The size of the lightweight observatory structure, coupled with the need to test at cryogenic temperatures,
effectively precludes validation of the models and verification of optical performance with a single test in 1-g. Rather, a
complex series of incremental tests and measurements are used to anchor components of the end-to-end models at
various levels of subassembly, with the ultimate verification of optical performance is by analysis using the assembled
models. The assembled models themselves are complex and require the insight of technical experts to assess their ability
to meet their objectives. This paper describes the modeling approach used on the JWST through the detailed design
phase.
KEYWORDS: James Webb Space Telescope, Space telescopes, Telescopes, Mirrors, Galactic astronomy, Observatories, Far infrared, Stars, Spectrometers, Cameras
We report on completion of the SAFIR Vision Mission study, as organized by the NASA Science Mission Directorate.
This study resulted in a focused baseline design for this large aperture space observatory that capitalizes on architectures
being actively developed for JWST and other missions. Special opportunities for achieving thermal performance of this
<10 K telescope are reviewed, as well as efforts to understand capabilities and needs for focal plane instrument and I and T
on this large (10 m-class) telescope.
The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2011. This is a continuation of a series of papers on modeling activities for JWST. The structural-thermal-optical, often referred to as "STOP", analysis process is used to predict the effect of thermal distortion on optical performance. The benchmark STOP analysis for JWST assesses the effect of an observatory slew on wavefront error. Temperatures predicted using geometric and thermal math models are mapped to a structural finite element model in order to predict thermally induced deformations. Motions and deformations at optical surfaces are then input to optical models, and optical performance is predicted using either an optical ray trace or a linear optical analysis tool. In addition to baseline performance predictions, a process for performing sensitivity studies to assess modeling uncertainties is described.
The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2011. System-level verification of critical optical performance requirements will rely on integrated modeling to a considerable degree. In turn, requirements for accuracy of the models are significant. The size of the lightweight observatory structure, coupled with the need to test at cryogenic temperatures, effectively precludes validation of the models and verification of optical performance with a single test in 1-g. Rather, a complex series of steps are planned by which the components of the end-to-end models are validated at various levels of subassembly, and the ultimate verification of optical performance is by analysis using the assembled models. This paper describes the critical optical performance requirements driving the integrated modeling activity, shows how the error budget is used to allocate and track contributions to total performance, and presents examples of integrated modeling methods and results that support the preliminary observatory design. Finally, the concepts for model validation and the role of integrated modeling in the ultimate verification of observatory are described.
Baseline configurations for NASA's Next Generation Space Telescope (NGST) include a multi-module science instrument package with near-infrared (near-IR) detectors passively cooled to below 30 K. This integrated science instrument model (ISIM) will also house mid-infrared (mid-IR) detectors that are cooled to 6-7 K with a mechanical cooler or stored cryogen. These complex cooling requirements, combined with the NGST concept of a large deployed aperture optical telescope passively cooled to below 40 K, makes NGST one of the most unique and thermally challenging missions flown to date. This paper describes the current status and baseline thermal/cryogenic systems design and analysis approach for the ISIM. The extreme thermal challenges facing the ISIM are presented along with supporting heat maps and analysis results.
Preliminary studies of passively cooling the NGST utilizing a lightweight deployable subshield are described. The NGST mission concept of a passively-cooled large-aperture optical telescope is unique from any other mission flown to date. We show that achieving operational temperatures of less than 50 K appears feasible by passive cooling alone through a combination of (i) operating the observatory far from the Earth so that the Sun becomes the only significant source of environmental heating, (ii) selecting an observatory configuration that isolates all significant heat dissipation from the cold telescope, and (iii) employing a high performance sunshield to attenuate the incident solar radiation. The observatory configuration consists of the sunshield with cold telescope and instrument elements on the anti-sun side, and warm spacecraft avionics and propulsion elements on the sun-side of the sunshield. A sunshield thermal configuration trade study, preliminary telescope thermal analyses, and a mechanical concept for a lightweight deployable sunshield are presented. Also discussed are the remaining issues to be addressed.
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