For the past 400 years, astronomers have sought to observe and interpret the Universe by building more powerful telescopes. These incredible instruments extend the capabilities of one of our most i...

Scientific discovery with the James Webb Space Telescope

The Habitable Exoplanet Observatory, or HabEx, has been designed to be the Great Observatory of the 2030s. For the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing Earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. Such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. HabEx is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (UV) to near-IR. These capabilities allow for a broad suite of compelling science that cuts across the entire NASA astrophysics portfolio. HabEx has three primary science goals: (1) Seek out nearby worlds and explore their habitability; (2) Map out nearby planetary systems and understand the diversity of the worlds they contain; (3) Enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the UV through near-IR. This Great Observatory science will be selected through a competed GO program, and will account for about 50% of the HabEx primary mission. The preferred HabEx architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an L2 orbit. HabEx employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument.

The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Interim Report

The 2-dimensional Power Spectral Density (PSD) can be used to characterize the mid- and the high-spatial frequency components of the surface height errors of an optical surface. We found it necessary to have a complete, easy-to-use approach for specifying and evaluating the PSD characteristics of large optical surfaces, an approach that allows one to specify the surface quality of a large optical surface based on simulated results using a PSD function and to evaluate the measured surface profile data of the same optic in comparison with those predicted by the simulations during the specification-derivation process. This paper provides a complete mathematical description of PSD error, and proposes a new approach in which a 2-dimentional (2D) PSD is converted into a 1-dimentional (1D) one by azimuthally averaging the 2D-PSD. The 1D-PSD calculated this way has the same unit and the same profile as the original PSD function, thus allows one to compare the two with each other directly.

/pdf/power-spectral-density-specification-and-analysis-of-large-3o18mmugyx.pdf

Power Spectral Density Specification and Analysis of Large Optical Surfaces

This paper is an introduction to the specification and tolerancing of Mid-spatial frequency (MSF) ripple or waviness. We begin with an introduction to the definition of ripple, spatial frequencies, and MSF ripple as a class of surface error (as opposed to figure or form, roughness, and surface imperfections or defects.) We then cover the derivation of spatial frequency bands of interest, specifications methods and notations, and relative amplitudes for typical manufacturing processes.

/pdf/specification-and-control-of-mid-spatial-frequency-wavefront-3peqndpm7n.pdf

Specification and Control of Mid-Spatial Frequency Wavefront Errors in Optical Systems

The Origins Space Telescope (Origins) traces our cosmic history, from the formation of the first galaxies and the rise of metals to the development of habitable worlds and present-day life. Origins does this through exquisite sensitivity to infrared radiation from ions, atoms, molecules, dust, water vapor and ice, and observations of extra-solar planetary atmospheres, protoplanetary disks, and large-area extragalactic fields. Origins operates in the wavelength range 2.8 to 588 microns and is 1000 times more sensitive than its predecessors due to its large, cold (4.5 K) telescope and advanced instruments. 
Origins was one of four large missions studied by the community with support from NASA and industry in preparation for the 2020 Decadal Survey in Astrophysics. This is the final study report.

Origins Space Telescope Mission Concept Study Report

Specifications for optical surfaces have traditionally been given in terms of low frequency and high frequency components, often with a separate classification for surface slope. Low spatial frequency components are commonly referred to as figure errors and can be described by the standard 37-term Zernike polynomial set. High spatial frequency errors are commonly referred to as finish and are quantified using rms roughness. Specification with the qualitative scratch and dig classification is done usually for cosmetic or aesthetic purposes. Mid-spatial frequency errors such as waviness, ripple, and quilting can be important and are not explicitly covered by such traditional figure and finish specifications. In order to bridge the gap to cover mid-spatial frequencies, in terms of quantifying surface characteristics, Power Spectral Density (PSD) can be utilized. For such usage, it is important for the greater optics community to understand the metric, how to calculate it, and how to use it. The purpose of this paper is to provide an overview of PSD, its application in optics, and an outline of calculations needed to effectively apply it to specify optical surfaces.

An overview of power spectral density (PSD) calculations

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 or the key tests that were performed and the results of these tests.

/pdf/james-webb-space-telescope-optical-telescope-element-mirror-2p9txm32rd.pdf

James Webb Space Telescope Optical Telescope Element Mirror Development History and Results

James Webb Space Telescope (JWST) Optical Telescope Element (OTE) mirror coating program has been completed. The science goals of the JWST mission require a uniform, low stress, durable optical coating with high reflectivity over the JWST spectral region. The coating has to be environmentally stable, radiation resistant and compatible with the cryogenic operating environment. The large size, 1.52 m point to point, light weight, beryllium primary mirror (PM) segments and flawless coating process during the flight mirror coating program that consisted coating of 21 flight mirrors were among many technical challenges. This paper provides an overview of the JWST telescope mirror coating program. The paper summarizes the coating development program and performance of the flight mirrors.

https://ntrs.nasa.gov/api/citations/20120013496/downloads/20120013496.pdf

James Webb Space Telescope Optical Telescope Element Mirror Coatings

The James Webb Space Telescope (JWST) is an on axis three mirror anastigmat telescope with a primary mirror, a
secondary mirror, and a tertiary mirror. The JWST mirrors are constructed from lightweight beryllium substrates and the
primary mirror consists of 18 hexagonal mirror segments each approximately 1.5 meters point to point. Ball Aerospace
and Technologies Corporation leads the mirror manufacturing team and the team utilizes facilities at six locations across
the United States. The fabrication process for each individual mirror assembly takes approximately six years due to
limitations dealing with the number of segments and manufacturing & test facilities. The primary mirror Engineering
Development Unit (EDU) recently completed the manufacturing process with the final cryogenic performance test of the
mirror segment assembly. The 18 flight primary mirrors segments, the secondary mirror, and the tertiary mirror are all
advanced in the mirror production process with many segments through the final polishing process, coating process, final
assembly, vibration testing, and final acceptance testing. Presented here is a status of the progress through the
manufacturing process for all of the flight mirrors.

JWST mirror production status

The fabrication and coating of the mirrors for the James Webb Space Telescope has been completed. The
spectral reflectivity of the protected gold coated beryllium mirrors has been measured. The predicted
end-of-life transmission through the telescope builds from these values. The additional phenomena that
have been analyzed are contamination effects and effects of the environment for the JWST operation
about the Earth-Sun L2 Lagrange libration point. The L2 environment analysis has been based on
radiation testing of mirror samples and hypervelocity testing to assess the micrometeoroid impact effects.
The mirror showed no change in reflectance over the VIS-SWIR wavelengths after exposure to 6-9 Grad
(Si) that simulated 6 years orbiting the L2 Lagrange point. The effects of hypervelocity particle impacts
on the mirrors from test data has been extrapolated to the to the anticipated flux characteristics for
micrometeoroids at the L2 environment. The results show that the micrometeoroid effects are orders of
magnitude below the particulate contamination effects. The final end-of-life transmission for the mirrors
including all of these phenomena will meet the performance requirements for JWST.

Benjamin B. Gallagher

Papers

An overview of power spectral density (PSD) calculations

James Webb Space Telescope Optical Telescope Element Mirror Development History and Results

James Webb Space Telescope Optical Telescope Element Mirror Coatings

JWST mirror production status

Optical transmission for the James Webb Space Telescope