The James Webb Space Telescope (JWST) launched on December 25, 2021, and its optical performance in orbit has been even better than predicted pre-flight. The static wavefront error (WFE) is less than half the value specified for the requirement of having diffraction-limited image quality at 2 microns in the NIRCam shortwave channel, enabling the observatory to deliver both sharper images and higher sensitivity than anticipated. In addition to the excellent image quality, the optical stability has also exceeded expectations, both in terms of high-frequency dynamic contributions (which would be perceived as part of "static WFE") and in terms of drifts over minutes, hours, and days. Stability over long timescales is critical for several important science cases, including exoplanet transit spectroscopy and coronagraphy. JWST's stability success was achieved through detailed design and testing, with several important lessons learned for future observatories, especially the Habitable Worlds Observatory that is expected to need even higher levels of stability. We review the stability architecture, how it was technologically demonstrated, the ground test results and improvements, the on-orbit results, and the lessons learned.

Because of its size and complexity, the Observatory performance of the James Webb Space Telescope (JWST) in its operating condition was primarily verified by analysis prior to launch, breaking the standard NASA paradigm of test-as-you-fly. Most of the requisite analytical predictions were achieved through Integrated Modeling which combines models of the various physics and subsystem behaviors affecting system-level performance: thermal, jitter, structures thermal distortion, gravity release and alignments, optics, wavefront sensing and control, attitude control, straylight and launch loads analysis. We will briefly describe the process by which models were managed, constructed, verified, validated, and used to support the analyses. We will address how uncertainties were accounted for given the many unknowns of the nanometric performance of the first-of-its-kind large deployable cryogenic precision optics in space. Finally, we will compare the pre-flight predictions to actual performance on-orbit for several key analysis use cases and conclude with lessons learned for future missions. The term “jitter” is often synonymous with high-frequency, uncompensated contributions to line-of-sight (LOS) stability or image motion. For the James Webb Space Telescope (JWST) mission, this working definition was extended to include dynamic contributions to wavefront error (WFE). Pre-launch verification of on-orbit jitter performance was not possible via testing, therefore high-fidelity end-to-end modeling was needed for credible verification-by-analysis. The jitter analysis was a main thrust of the overall JWST Integrated Modeling effort and was supported by a robust model verification and validation activities. Following launch, during the latter stages of the 6-month commissioning phase, LOS measurements were obtained and compared to the pre-launch predictions, then to a set of revised predictions. Here we present the modeling methodology supporting the jitter analysis, the pre- and post-launch analysis results, the comparison with the flight data, and conclusions drawn from this comparison.

The James Webb Space Telescope (JWST) is a large, infrared space telescope that has recently started its science program which will enable breakthroughs in astrophysics and planetary science. Notably, JWST will provide the very first observations of the earliest luminous objects in the universe and start a new era of exoplanet atmospheric characterization. This transformative science is enabled by a 6.6 m telescope that is passively cooled with a 5 layer sunshield. The primary mirror is comprised of 18 controllable, low areal density hexagonal segments, that were aligned and phased relative to each other in orbit using innovative image-based wave front sensing and control algorithms. This revolutionary telescope took more than two decades to develop with a widely distributed team across engineering disciplines. We present an overview of the telescope requirements, architecture, development, superb on-orbit performance, and lessons learned. JWST successfully demonstrates a segmented aperture space telescope and establishes a path to building even larger space telescopes.

We present the key technologies and capabilities that will enable a future, large-aperture ultravioletopticalinfrared (UVOIR) space observatory. These include starlight suppression systems, vibration isolation and control systems, lightweight mirror segments, detector systems, and mirror coatings. These capabilities will provide major advances over current and near-future observatories for sensitivity, angular resolution, and starlight suppression. The goals adopted in our study for the starlight suppression system are 10-10 contrast with an inner working angle of 20 milliarcsec and broad bandpass. We estimate that a vibration and isolation control system that achieves a total system vibration isolation of 140 dB for a vibration-isolated mass of 5000 kg is required to achieve the high wavefront error stability needed for exoplanet coronagraphy. Technology challenges for lightweight mirror segments include diffraction-limited optical quality and high wavefront error stability as well as low cost, low mass, and rapid fabrication. Key challenges for the detector systems include visible-blind, high quantum efficiency UV arrays, photon counting visible and NIR arrays for coronagraphic spectroscopy and starlight wavefront sensing and control, and detectors with deep full wells with low persistence and radiation tolerance to enable transit imaging and spectroscopy at all wavelengths. Finally, mirror coatings with high reflectivity ( 90), high uniformity ( 1) and low polarization ( 1) that are scalable to large diameter mirror substrates will be essential for ensuring that both high throughput UV observations and high contrast observations can be performed by the same observatory.

The ATLAST 9.2m architecture has evolved to be more cost effective while also meeting a more thorough understanding of the driving science requirements. The new approach can fit in an existing Delta IV Heavy rocket and makes extensive use of heritage and selective use of technology in order to minimize development time and cost. We have performed a more thorough look at how to meet the stability requirements for both thermal and dynamics and have an approach consistent with an initial error budget. In addition, we have developed concepts to support robotic or human servicing in a cost effective manner through a modular approach that relies on simple, external access and metrology. These refinements to the architecture enable a cost-effective, long-lifecycle, and relatively low risk approach to development.

The Advance Mirror Technology Development (AMTD) project is in Phase 2 of a multiyear effort, initiated in FY12, to mature by at least a half TRL step six critical technologies required to enable 4 meter or larger UVOIR space telescope primary mirror assemblies for both general astrophysics and ultra-high contrast observations of exoplanets. AMTD continues to achieve all of its goals and accomplished all of its milestones to date. We have done this by assembling an outstanding team from academia, industry, and government with extensive expertise in astrophysics and exoplanet characterization, and in the design/manufacture of monolithic and segmented space telescopes; by deriving engineering specifications for advanced normal-incidence mirror systems needed to make the required science measurements; and by defining and prioritizing the most important technical problems to be solved.

The Advance Mirror Technology Development (AMTD) project is in Phase 2 of a multiyear effort, initiated in FY12, to mature by at least a half TRL step six critical technologies required to enable 4 meter or larger UVOIR space telescope primary mirror assemblies for both general astrophysics and ultra-high contrast observations of exoplanets. AMTD uses a science-driven systems engineering approach. We mature technologies required to enable the highest priority science AND provide a high-performance low-cost low-risk system. To give the science community options, we are pursuing multiple technology paths. A key task is deriving engineering specifications for advanced normal-incidence monolithic and segmented mirror systems needed to enable both general astrophysics and ultra-high contrast observations of exoplanets missions as a function of potential launch vehicles and their mass and volume constraints. A key finding of this effort is that the science requires an 8 meter or larger aperture telescope.

The Advanced Technology for Large Aperture Space Telescope (ATLAST) concept was assessed as one of the NASA Astrophysics Strategic Mission Concepts (ASMC) studies. Herein we discuss the 9.2-meter diameter segmented aperture version and its wavefront sensing and control (WFSC) with regards to coronagraphic detection and spectroscopic characterization of exoplanets. The WFSC would consist of at least two levels of sensing and control: (i) an outer coarser level of sensing and control to phase and control the segments and secondary mirror in a manner similar to the James Webb Space Telescope but operating at higher temporal bandwidth, and (ii) an inner, coronagraphic instrument based, fine level of sensing and control for both amplitude and wavefront errors operating at higher temporal bandwidths. The outer loop would control rigid-body actuators on the primary and secondary mirrors while the inner loop would control one or more segmented deformable mirror to suppress the starlight within the coronagraphic field-of-view. Herein we discuss the visible nulling coronagraph (VNC) and the requirements it levies on wavefront sensing and control and show the results of closed-loop simulations to assess performance and evaluate the trade space of system level stability versus control bandwidth.

The Advanced Concepts Office at Marshall Space Flight Center completed a brief spacecraft design study for the 8-meter monolithic Advanced Technology Large Aperture Space Telescope (ATLAST-8m). This spacecraft concept provides all power, communication, telemetry, avionics, guidance and control, and thermal control for the observatory, and inserts the observatory into a halo orbit about the second Sun-Earth Lagrange point. The multidisciplinary design team created a simple spacecraft design that enables component and science instrument servicing, employs articulating solar panels for help with momentum management, and provides precise pointing control while at the same time fast slewing for the observatory.

The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope. System-level verification of critical performance requirements will rely on integrated observatory models that predict optical response accurately enough to verify that the allocated top-level wavefront error of 150 nm root-mean-squared (rms) through to wavefront sensor focal plane is met. The assembled models themselves are complex and require the insight of technical experts working as a team across multiple disciplines and organizations. Furthermore, responses in several key disciplines are strongly cross-coupled. This paper describes the breadth of the systems engineering and modeling approach used on the JWST including technical performance metrics management. The scope of the systems-level modeling includes stowed dynamics, deployed dynamics, thermal, thermal distortion, straylight, optics and attitude control systems.

ATLAST-8m is an 8-meter monolithic UV/optical/NIR space observatory which could be placed in orbit at Sun-Earth L2 by a heavily lift launch vehicle. Two development study cycles have resulted in a detailed concept including a dual foci optical design; several primary mirror launch support and secondary mirror support structural designs; spacecraft propulsion, power and pointing control design; and thermal design. ATLAST-8m is designed to yield never before achieved performance to obtain fundamental astronomical breakthroughs.

The animation illustrates how the booms pivot and/or rotate during maneuvers to help maintain balance.

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.

iv provided a summary review of the development process of this standard up through the start of the review by the EMB. A thorough recount of the entire development process, major issues, key decisions, and all review processes are available in Ref. v. This is the second of a pair of papers providing a summary of the final version of the Standard. Its focus is the Credibility Assessment Scale, a key feature of the Standard, including an example of its application to a real-world M&S problem for the James Webb Space Telescope. The companion paper vi summarizes the overall philosophy of the Standard and an overview of the requirements. Verbatim quotes from the Standard are integrated into the text of this paper, and are indicated by quotation marks. II. Role of the Credibility Assessment Scale

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a set of mission concepts for the next generation of UVOIR space observatory with a primary aperture diameter in the 8-m to 16-m range that will allow us to perform some of the most challenging observations to answer some of our most compelling questions, including Is there life elsewhere in the Galaxy? We have identified two different telescope architectures, but with similar optical designs, that span the range in viable technologies. The architectures are a telescope with a monolithic primary mirror and two variations of a telescope with a large segmented primary mirror. This approach provides us with several pathways to realizing the mission, which will be narrowed to one as our technology development progresses. The concepts invoke heritage from HST and JWST design, but also take significant departures from these designs to minimize complexity, mass, or both. Our report provides details on the mission concepts, shows the extraordinary scientific progress they would enable, and describes the most important technology development items. These are the mirrors, the detectors, and the high-contrast imaging technologies, whether internal to the observatory, or using an external occulter. Experience with JWST has shown that determined competitors, motivated by the development contracts and flight opportunities of the new observatory, are capable of achieving huge advances in technical and operational performance while keeping construction costs on the same scale as prior great observatories.

This paper is part five of a series on the ongoing optical modeling activities for the James Webb Space Telescope (JWST). The first two papers discussed modeling JWST on-orbit performance using wavefront sensitivities to predict line of sight motion induced blur, and stability during thermal transients. The third paper investigates the aberrations resulting from alignment and figure compensation of the controllable degrees of freedom (primary and secondary mirrors), which may be encountered during ground alignment and on-orbit commissioning of the observatory, and the fourth introduced the software toolkits used to perform much of the optical analysis for JWST. The work here models observatory operations by simulating line-of-sight image motion and alignment drifts over a two-week period. Alignment updates are then simulated using wavefront sensing and control processes to calculate and perform the corrections. A single model environment in Matlab is used for evaluating the predicted performance of the observatory during these operations.

The James Webb Space Telescope (JWST) is a key component of NASA's Origins Program to understand the origins and future of the universe. JWST will be used to study the birth and formation of galaxies and planets. The mission requires a large (25m 2 aperture) but extremely stable (150 nm RMS wave front error) optical platform, where performance is a tightly coupled function of numerous physical processes. Distortion due to thermal loading is a significant error source. The process by which predicted heat loads are mapped to optical error is termed Structural-Thermal-Optical Performance (STOP) modeling. Thermal-optical performance is a function of heat loads, thermal properties (conductivities, radiative coupling coefficients), structural properties (moduli, geometry, thermal expansion coefficients, ply layup angles), and optical sensitivities. Sensitivities, the gradients of performance with respect to design parameters, give a direct way to identify the parameters that have the largest influence on performance. Additionally, gradients can identify the largest sources of uncertainty, and thus contribute to improving the robustness of the design, either via redesign or by placing requirements on parameter variability. The paper presents a general framework for developing the analytical sensitivities of the STOP prediction using the Chain Rule. The paper focuses on solving for the sensitivities of the steady-state, conduction-only, problem, using discipline modeling tools (thermal, structural, and optical) to compute the terms in the STOP gradients. The process is demonstrated on the SDR2 Rev. 1 cycle of the JWST modeling effort.