This paper describes the development of a new system from the vantage point of our previous experience on Chandra and James Webb. We introduce and define what we call the problem of newness, namely system development with an incomplete understanding of the system performance. We will discuss programmatic and technical approaches to maximize engineering productivity in the development of a new complex system like NASA’s Habitable Worlds Observer or other future flagship missions.
Modeling played a vital role on the James Webb Space Telescope (JWST) program. From early modeling to aid in requirements development to final verification and on-orbit performance determination, modeling evolved and grew as the program progressed. With the heavy reliance on modeling that large, complex missions like JWST has had and Habitable Worlds Observatory (HWO) will have, enabling accurate and timely modeling results as the design matures is extremely important. This paper will discuss the types of modeling necessary and the lessons learned during the development of JWST that are applicable to HWO.
The Habitable Worlds Observatory (HWO) will need unprecedented stability in order to achieve the desired science performance. Achieving this stability will push the state of the art in structural damping, environmental shielding, thermal sensing and heater control, control architecture, etc. and will even involve consideration of effects that were previously negligible such as low-energy micrometeorites and bulk charging of mirrors. In this paper, we explore the interactions between basic architectural trades and the ability of the observatory to meet the stability requirements. As an example, we discuss how the need for an ultra-stable structure translates to requirements on an environmental shield. We then look at options for the architecture of such a shield and interactions between these possible shield configurations and other design considerations such as verifiability, manufacturability, mass, risk, serviceability, and lifetime.
KEYWORDS: Design, Observatories, Telescopes, James Webb Space Telescope, Systems modeling, Space operations, Performance modeling, Online learning, Stray light, Mirrors
We formulate the lessons Northrop Grumman personnel have learned from their work on development of the James Webb Space Telescope. These lessons are strategic in nature and bear on the common behavior during development of all large complex systems, such as astrophysics missions, also known colloquially as Flagships. To justify the expense, a Flagship must be a large leap in scientific capability, demanding new architectures and technologies coupled with an intolerance to risk. We define “The Problem of Newness” based on our experience and data from Webb’s development. This unseen hand was present during Webb, and it is only in retrospect that we have been able to define it and present it as a lesson for the future. Future missions, Flagships in particular, should recognize the challenge of newness as a natural consequence of development and take steps to minimize its impact.
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.
KEYWORDS: Telescopes, James Webb Space Telescope, Image segmentation, Observatories, Mirrors, Space operations, Space telescopes, Galactic astronomy, Wavefronts, Stars
The James Webb Space Telescope (Webb) is a large, infrared space telescope that recently completed its on-orbit commissioning activities and has now embarked on its first year of approved science. Its architecture includes many first-of-its kind innovations for space, including a segmented primary mirror that is 6.6 m in diameter and a 5-layer sunshield used to passively cool the telescope and its four science instruments. Although Webb had an extensive test program, the system-level performance often relied on predictions based on integrated modeling, using conservative factors for the model uncertainties and primarily focusing on evaluating the performance at the end of life. A set of commissioning activities were designed for a system-level characterization of the performance. This proceeding will provide the status of the mission, including a discussion of the major events, on-orbit system performance, and early science highlights.
Pursuing ground breaking science in a cost and funding constrained environment presents new challenges to the development of future space astrophysics missions. Within the conventional cost models for large observatories, executing a flagship “mission after next” appears to be unstainable. To achieve our nation’s space astrophysics ambitions requires new paradigms in program design, system design, development and manufacture. Implementation of this new paradigm requires that the space astrophysics community adopt new answers to a new set of questions. This paper continues our discussion the origins of these new questions and the steps to their answers.
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.
Pursuing ground breaking science in a highly cost and funding constrained environment presents new challenges to the development of future large space astrophysics missions. Within the conventional cost models for large observatories, executing a flagship “mission after next” appears to be unstainable. To achieve our nation’s space astrophysics ambitions requires new paradigms in system design, development and manufacture. Implementation of this new paradigm requires that the space astrophysics community adopt new answers to a new set of questions. This paper will discuss the origins of these new questions and the steps to their answers.
KEYWORDS: Adaptive optics, Mirrors, James Webb Space Telescope, Cryogenics, Telescopes, Optical alignment, Space telescopes, Photogrammetry, Monte Carlo methods, Actuators
The James Webb Space Telescope is a large space-based astronomical telescope that will operate at cryogenic temperatures. Because of its size, the telescope must be stowed in an inoperable configuration for launch and remotely reconfigured in space to meet the operational requirements using active Wave Front Sensing and Control (WFSC). Predicting optical performance for the flight system relies on a sequence of incremental tests and analyses that has culminated with the cryogenic vacuum test of the integrated Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM) referred to as OTIS. The interplay between the optical budgeting process, test verification results at incrementally increasing levels of integration, use of test validated models, and the WFSC process to produce the final optical performance predictions for final verification by analysis will be presented.
KEYWORDS: Space telescopes, Telescopes, James Webb Space Telescope, Astrophysics, Manufacturing, Systems modeling, Mirrors, Observatories, Optical instrument design, Diffraction
Pursuing ground breaking science in a highly cost-constrained environment presents new challenges to
the development of future space astrophysics missions. Within the conventional cost models for large
observatories, executing a flagship “mission after next” appears to be unsustainable. To achieve our
nation’s science ambitions requires not a paradigm shift but a completely new paradigm of system
design, development and manufacture. This paper explores the nature of the current paradigm and
proposes a series of steps to guide the entire community to a sustainable future.
Significant progress has been made in the development of the Optical Telescope Element (OTE) for the James Webb
Space Telescope (JWST) Observatory. At the time of the conference, the OTE will have been completely
assembled, including deployment testing and optics alignment and installation. This paper will discuss those
accomplishments.
The James Webb Space Telescope (JWST) is a 6.5m, segmented, IR telescope that will explore the first light of the universe after the big bang. In 2014, a major risk reduction effort related to the Alignment, Integration, and Test (AI and T) of the segmented telescope was completed. The Pathfinder telescope includes two Primary Mirror Segment Assemblies (PMSA’s) and the Secondary Mirror Assembly (SMA) onto a flight-like composite telescope backplane. This pathfinder allowed the JWST team to assess the alignment process and to better understand the various error sources that need to be accommodated in the flight build. The successful completion of the Pathfinder Telescope provides a final integration roadmap for the flight operations that will start in August 2015.
A JWST OTE Pathfinder telescope that includes two spare primary mirror segments, a spare secondary mirror, and a large composite structure with a deployed secondary support structure is in the assembly stage and will be fully completed this year. This Pathfinder will check out key steps in the ambient mirror integration process and also be used at the Johnson Space Center (JSC) to check out the optical Ground Support Equipment (GSE) and associated procedures that will be used to test the full JWST telescope and instruments at JSC. This paper will summarize the Pathfinder integration and testing flow, the critical Ground Support Equipment it will test and the key tests planned with the Pathfinder.
KEYWORDS: Astrophysics, Space telescopes, James Webb Space Telescope, Manufacturing, Telescopes, Standards development, Mirrors, Optical instrument design, Observatories, Design for manufacturability
Pursuing ground breaking science in a highly cost-constrained environment presents new challenges to the development of future space astrophysics missions. Within the conventional cost models for large observatories, executing a flagship “mission after next” appears to be unstainable. To achieve our nation’s science ambitions requires a new paradigm of system design, development and manufacture. This paper explores the nature of the current paradigm and proposes a series of steps to guide the entire community to a sustainable future.
Significant progress has been made in the development of the Optical Telescope Element (OTE) for the James Webb Space Telescope (JWST) Observatory. All of the mirror assemblies are complete and delivered. The composite Primary Mirror Backplane Support Structure (PMBSS) has completed assembly and in Static Load testing. All the deployment mechanisms have completed their qualification programs. This paper will discuss the current status of all the OTE components and the plan forward to completion.
The James Webb Space Telescope (JWST) is a 6.5m, segmented, IR telescope that will explore the first light of the universe after the big bang. 2014 is an incredible year for the Telescope Alignment, Integration, and Test portion of the program. Long awaited and planned, the two segment Pathfinder telescope will be built and the Optical Ground Support Equipment (OGSE) will be integrated into the large cryo-vacuum chamber at the Johnson Spaceflight Center. The current status of the integration equipment and the demonstrations leading up to the flight-like Pathfinder telescope will be provided as the first step to the final verification of the complex cryo test equipment. The plans and status of bringing the OGSE on-line and ready for a series of risk reduction cryo tests starting in 2015 on the Pathfinder Telescope will also be presented.
2014 marks the crystal (15th) anniversary of the launch of the Chandra X-ray Observatory, which began its existence as the Advanced X-ray Astrophysics Facility (AXAF). This paper offers some of the major lessons learned by some of the key members of the Chandra Telescope team. We offer some of the lessons gleaned from our experiences developing, designing, building and testing the telescope and its subsystems, with 15 years of hindsight. Among the topics to be discussed are the early developmental tests, known as VETA-I and VETA-II, requirements derivation, the impact of late requirements and reflection on the conservatism in the design process.
KEYWORDS: Mirrors, James Webb Space Telescope, Beryllium, Cryogenics, Optical telescopes, Optical components, Aerospace engineering, Space telescopes, Polishing, Off axis mirrors
In a little under a decade, the James Webb Space Telescope (JWST) program has designed, manufactured,
assembled and tested 21 flight beryllium mirrors for the James Webb Space Telescope Optical Telescope
Element. This paper will summarize the mirror development history starting with the selection of
beryllium as the mirror material and ending with the final test results. It will provide an overview of the
technological roadmap and schedules and the key challenges that were overcome. It will also provide a
summary of the key tests that were performed and the results of these tests.
Significant progress has been made in the development of the Optical Telescope Element (OTE) for the James Webb
Space Telescope (JWST) Observatory. All of the mirror assemblies are complete and through final testing. The
composite Pathfinder Primary Mirror Backplane Support Structure (PMBSS) has been completed and the flight
structure is making significant progress. This paper will discuss the current status of all the OTE components and
the plan forward to completion.
The James Webb Space Telescope (JWST) is an infrared space telescope designed to explore four major science themes: first light and reionization, the assembly of galaxies, the birth of stars and protoplanetary systems, and planetary systems and origins of life. JWST is a segmented architecture telescope with an aperture of 6.6 m. It will operate at cryogenic temperature (40 K), achieved via passive cooling, in an orbit about the Earth-Sun second Lagrange point (L2). Passive cooling is facilitated by means of a large sunshield that provides thermal isolation and protection from direct illumination from the Sun. The large size of the telescope and spacecraft systems require that they are stowed for launch in a configuration that fits the Ariane 5 fairing, and then deployed after launch. Routine wavefront sensing and control measurements are used to achieve phasing of the segmented primary mirror and initial alignment of the telescope. A suite of instruments will provide the capability to observe over a spectral range from 0.6- to 27-μm wavelengths with imaging and spectroscopic configurations. An overview is presented of the architecture and selected optical design features of JWST are described.
A Pathfinder of the James Webb Space Telescope (JWST) Optical Telescope Element is being developed to check out
critical ground support equipment and to rehearse integration and testing procedures. This paper provides a summary of
the baseline Pathfinder configuration and architecture, objectives of this effort, limitations of Pathfinder, status of its
development, and future plans. Special attention is paid to risks that will be mitigated by Pathfinder.
The James Webb Space Telescope (JWST) Optical Telescope Element has completed its Critical Design Review and is
well into fabrication. This paper will summarize efforts to date in the design, manufacturing and planning for integration
and testing. This will include a top level summary of mirror performance to date, hardware results, and planning status
for the integration and testing program. The future plans for manufacturing, assembly, alignment and testing will also be
summarized at a top level.
It is imperative that we have high confidence that the optical performance capability of JWST is well-understood
before launch. With the telescope operating at cryogenic temperatures and sporting a 6.6 meter primary mirror
diameter, the optical metrology equipment required to measure the optical performance can be quite complex. The
JWST Test team undertook an effort to greatly simplify the optical metrology approach, while retaining the key
measurements and verification methodology. The result is a cryogenic optical test configuration and
implementation using Chamber A at NASA's Johnson Space Center that uses the science instruments to help
understand JWST's optical performance.
The James Webb Space Telescope (JWST) is a large aperture (6.6 m primary mirror) cryogenic telescope with active
control of the segmented primary and secondary mirror optical elements. The architecture of the telescope makes full
end-to-end testing on the ground prohibitive due to both cost and technical considerations. Additionally, because the
telescope will be launched in a folded configuration to fit in the Ariane V launch fairing and aligned during flight using
image-based Wavefront Sensing and Control (WFS&C), the telescope cannot be tested in the classical "test-as-you-fly"
architecture. Due to these considerations, the primary optical performance requirements will be verified through analysis.
In order to have high confidence in this approach, a robust analysis validation program has been developed based on
testing from the component level through the integrated telescope level. This verification approach focuses on ground
testing at the telescope level to ensure there will be adequate range in the adjustable optics for alignment on orbit. In
addition to the incremental test program planned for optical verification, a double-pass sampled aperture test of the integrated
telescope and instruments is planned at flight-like temperatures as a crosscheck to the analytic verification for
flight. Error budgets have been developed to understand the uncertainty propagation through the test and analysis program.
KEYWORDS: Curium, James Webb Space Telescope, Cryogenics, Composites, Temperature metrology, Space telescopes, Mirrors, Manufacturing, Metrology, Analytical research
The need for JWST's metering structure to be stable over time while at cryogenic temperatures is derived from its
scientific objectives. The operational scenario planned for JWST provides for the optical system to be adjusted on
regular intervals based upon image quality measurements. There can only be a limited amount of optical
degradation between the optical system adjustments in order to meet the scientific objectives. As the JWST primary
mirror is segmented, the structure supporting the mirror segments must be very stable to preclude degradation of the
optical quality. The design, development and, ultimately, the verification of that supporting structure's stability rely
on the availability of analysis tools that are credibly capable of accurately estimating the response of a large
structure in cryogenic environments to the nanometer level. Validating the accuracy of the analysis tools was a
significant technology demonstration accomplishment. As the culmination of a series of development efforts, a
thermal stability test was performed on the Backplane Stability Test Article (BSTA), demonstrating TRL-6 status
for the design, analysis, and testing of Large Precision Cryogenic Structures. This paper describes the incremental
development efforts and the test results that were generated as part of the BSTA testing and the associated TRL-6
demonstration.
Significant progress has been made in the development of the Optical Telescope Element (OTE), one of three elements of the James Webb Space Telescope (JWST) Observatory. To achieve the 25 square meters of collecting area, JWST will employ the first segmented, deployed optical telescope, requiring a wavefront sensing and control (WFS&C) system to align and phase the telescope's optics, while operating at cryogenic temperatures. The OTE is comprised of the optical components of the three mirror anastigmat and a steering mirror, the structure to deploy and support the optics, the WFS&C system to determine the adjustments necessary to align them, the electronics to control them, and the thermal components to manage the OTE temperatures. Technology development and risk reduction hardware are being produced to address critical technical areas. Subsystem development has progressed with the successful completion of several key design reviews and significant progress on the production of the flight Primary Mirror Segment Assemblies.
KEYWORDS: Distortion, James Webb Space Telescope, Manufacturing, Magnetism, Temperature metrology, Composites, 3D modeling, Aluminum, Space telescopes, Metrology
The unprecedented stability requirements of JWST structures can only be conclusively
verified by a combination of analysis and ground test. Given the order of magnitude of the
expected motions of the backplane due to thermal distortion and the high level of confidence
required on such a large and important project, the demonstration of the ability to verify the
thermal distortion analysis to the levels required is a critical need for the program. The
demonstration of these analysis tools, in process metrology and manufacturing processes
increases the technology readiness level of the backplane to required levels. To develop this
critical technology, the Backplane Stability Test Article (BSTA) was added to the JWST
program. The BSTA is a representative substructure for the full flight backplane, manufactured
using the same resources, materials and processes. The BSTA will be subject to environmental
testing and its deformation and damping properties measured. The thermally induced
deformation will be compared with predicted deformations to demonstrate the ability to predict
thermal deformation to the levels required. This paper will review the key features and
requirements of the BSTA and its analysis, the test, measurement and data collection plans.
KEYWORDS: Mirrors, Observatories, James Webb Space Telescope, Space telescopes, Telescopes, Image segmentation, Actuators, Space operations, Wavefronts, Stars
JWST will be used to help understand the shape and chemical composition of the universe, and the evolution of galaxies, stars and planets. With a 6.5 meter primary mirror, the Observatory will observe red shifted light from the early history of the universe, and will see objects 400 times fainter than those seen from large ground-based telescopes or the current generation of space-based infrared telescopes. NASA Goddard Space Flight Center (GSFC) manages JWST with contributions from a number of academic, government, and industrial partners. The contract to build the space-based Observatory for JWST was awarded to the Northrop Grumman Space Technology (NGST)/Ball/Kodak/ATK team.
KEYWORDS: Telescopes, James Webb Space Telescope, Space telescopes, Phase modulation, Cryogenics, Mirrors, Optical testing, Space operations, Point spread functions, Observatories
JWST will have 5 to 10 times the collecting area of the Hubble Space Telescope, making it the largest optical system put into space by a large margin. Moreover, to keep the self-emission of the optics and detectors below the background, JWST will operate at cryogenic temperatures. In addition, JWST will operate at L2, where servicing is not a viable option; therefore, we must know that the JWST performs the way we expect it to before it launches. This requires establishing a high-confidence integration and verification process for a very large, cryogenic system while remaining affordable. This paper describes the verification process planned for JWST and the trades that led to this plan. The verification considers the all-important optical performance of the telescope itself, as well as the sunshield, the wavefront sensing and control system, the vibration isolation system, the spacecraft, and the end-to-end (photons in to data storage on the ground) performance verification. We discuss testing configurations, metrology methods, facilities, and the role of analytical modeling and testing at various stages of integration to ensure the performance is understood.
KEYWORDS: James Webb Space Telescope, Cryogenics, Interferometers, Metrology, Temperature metrology, Helium, Space telescopes, Distortion, Telescopes, Mirrors
At 6-7 meters in diameter, the James Webb Space Telescope (JWST) will require structures that remain stable to levels that are on the order of 10 nanometers under dynamic and thermal loading while operating at cryogenic temperatures. Moreover, the JWST will be the first telescope in space that is deployed, resulting in an aperture that is not only segmented, but has hinge-lines and the associated joining systems or latches in it. In order to understand the behavior and reduce the risk associated with very large, deployed structures and the stability of the associated structure and latches, we developed and tested the largest cryogenic structure ever built and then characterized its stability. This paper presents a description of the design of the Development Optical Telescope Assembly (DOTA), the testing performed, and the results of the testing performed on it. We discuss the material selection and characterization processes, give a description of the test configurations, describe the metrology equipment and the validation process for it, provide the test results, and summarize the conclusions drawn from the results. The testing and associated results include characterization of the thermal stability of the large-scale structure, characterization of the micro-dynamic stability of the latching system, and measurements of the deployment capability of the mechanisms. We also describe how the DOTA design relates to the JWST design and how the test results relate to the JWST requirements.
NASA wants to launch a Terrestrial Planet Finder (TPF) mission in 2014 to detect and characterize Earth-like planets around nearby stars, perform comparative planetology studies, and obtain general astrophysics observations. The detection of a 30th magnitude planet located within 80 milli-arcseconds of a 5th (Visual) magnitude star is an exceptionally challenging objective. Observations in the thermal infrared (7-17 mm) are somewhat easier since the planet is 'only' 15m fainter than the star at these wavelengths, but many severe challenges must still be overcome, including: Designing a spacecraft, a telescope and an IR coronagraph for star-planet separations equal to λ/D;(i) Providing a stable (~30K) thermal environment for the optics and isolating them from vibration sources; (ii)Developing a deployment scheme for a 28-m space telescope that can fit in an existing launch vehicle; (iii) Minimizing telescope mass to enable launch to L2 or a driftway orbit with a single launch vehicle; (iv) Generating a manufacturing plan that will permit TPF to be developed at a reasonable cost and schedule; (v) Identifying the key enabling technologies for TPF. This paper describes the IR Coronagraph we designed during our recent TPF Mission Architecture study in an effort to meet these challenges.
NASA plans to launch a Terrestrial Planet Finder (TPF) mission in 2014 to detect and characterize Earth-like planets around nearby stars, to perform comparative planetology studies, and to obtain general astrophysics observations. As part of our recently completed TPF Mission Architecture study for NASA/JPL we developed the conceptual design for a Large Aperture IR Coronagraph that meets these mission objectives. This paper describes the optical design of the telescope and the coronagraph to detect and characterize exo-solar planets. The telescope design was optimized to provide a well-corrected image plane that is large enough to feed several instruments and control scattered light while accommodating packaging for launch and manufacturing limitations. The coronagraph was designed to provide a well corrected field of view with a radius > 5 arcsec around the star it occults in the 7-17 microns wavelength region. A design for this instrument as well as results of a system simulation model are presented. The methodology for wavefront error correction and control of scattered and diffracted light are discussed in some detail as they are critical parameters to enable detecting planets at separations of down to ~λ/D.
The Next Generation Space Telescope will be the premier instrument for astrophysical research a decade from now. This paper describes the reference concept for the observatory being studied by a prime contractor team led by TRW and Ball Aerospace. We give an overview of the space segment of the mission, and the rationale for its heliocentric orbit at the Sun-Earth L2 Lagrangian point. At the time of this meeting many details of the engineering design are still open for trade studies. We highlight a few whose resolution will have implications for the scientific performance of the observatory, and for which preferences and recommendations from the scientific community are welcomed.
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