The James Webb Space Telescope, launched in 2021, is an infrared observatory of novel design: deployable, with active optics, fully open to space for radiative cooling and orbiting the Lagrange point no. 2. This article explains the rationale leading to this specific design and describes the various other architectures that were considered along the way: from a monolithic 10-meter telescope in geosynchronous orbit to a 6-meter one in High Earth Orbit, then a 16-meter observatory on the Moon, a 4- or 6-meter one in an elliptical heliocentric orbit, and a segmented 8-meter one passively cooled to 50 K at L2, which was finally descoped to 6.6 meters. It also addresses the optimization for scientific performance, the challenge of dealing with such an ultra-low operating temperature, cost issues, supporting technology, modifications made during final design and, finally, how the architecture performs on orbit.

The special section of JATIS was originally intended to collect lessons learned over a wide variety of large astronomical projects, ground, space, studies and flight programs.While that was the intention, it was not the result.All the submissions for this section come from experience on a single program, NASA's James Webb Space Telescope.The most important lesson that we can learn from and about the Webb telescope is that it is functioning as intended.Heading into its third year of science operations, it is functioning at or beyond required levels.In this section, Feinberg et al. indicate that the wavefront is twice as good as specification, allowing for significantly more science.The clear lesson is that with good, careful engineering even the seemingly impossible is, in fact, possible.Webb's achievements have been recognized with numerous awards, including the highest award in U.

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 mu m and in the mid-infrared band between 5 and 28 mu m. 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. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Reuse of a proven design can save a mission significant time, money and risk. At least two of the decadal missions, HabEx and Origins Space Telescope, are considering the reuse of some or most of the James Webb Space Telescope flight hardware design for one of their studied architectures. Another, LUVOIR, will benefit highly from learning the necessary lessons on I&T and architecture reuse. This paper compares the performance of the Webb Telescope against the requirements for the HabEx and OST missions to identify the subsystem designs that can be reused without revisions. We will also highlight the areas where new work must be accomplished. We conclude with a net assessment that that shows Webb reuse is a viable program option and a good deal for science.

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.

The various kinematic mounts for the Integrated Science Instrument Module (ISIM) for the James Webb Space Telescope are shown. Included are views of a monopod Strut and a Bipod Strut.

The James Webb Space Telescope (JWST) is a 6.5 meter cryogenic observatory planned to launch in 2013. The observatory includes a three mirror anastigmat telescope with a deployed 18 segment primary mirror. Unlike the Hubble Space Telescope (HST), JWST will be difficult to service and therefore the development team needs to be highly confident the telescope will work after launch. Consequently, it is imperative that the team building JWST apply the lessons learned from the HST program so as to avoid repeating mistakes that led to a major optical error in HST. The purpose of this paper is to summarize what the JWST program is doing to apply the lessons learned from HST. It includes a summary of how the HST optical error was made, the lessons learned there from, and how the JWST program is applying these lessons to avoid the mistakes of the past and ensure correct JWST optical performance.

Cryogenic optical testing and verification the James Webb Space Telescope is one of the biggest challenges in the I&T program. JWST has constructed an incremental verification program for the optical telescope and the integrated science instrument module to ensure compliance and to mitigate the severity of problems on flight hardware.

In February, NASA is scheduled to launch the second servicing mission for the Hubble Space Telescope: The authors describe the new equipment Hubble will receive and updates to equipment already in place.

The Calibrated Infrared Source (CIRCE) is a radiometrically calibrated, highly uniform, infrared source for the calibration of the Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument. The CIRCE output encompasses the entire NICMOS spectral range, from 0.8 to 2.5 micrometers . CIRCE is designed to operate in vacuum, thus allowing calibration of NICMOS under flight- like conditions. CIRCE is the calibration standard for several tests, including: throughput measurement, flat fields, sensitivity, polarizer characterization, and Red Leak Test.