In an effort to manufacture high-angular-resolution, grazing-incidence, x-ray optics, Marshall Space Flight Center (MSFC) is taking measures to improve its electroformed replicated optics. A key development is the use of computer-numerical control (CNC) polishing to deterministically improve the surface of electroless nickel mandrels used to replicate grazing-incidence optics. Metrology, control software and polishing parameters must function together seamlessly to reach the specifications required to replicate sub-arcsecond optics. Each change in polishing parameters effects the wear pattern of the polishing head. Using Richardson-Lucy deconvolution, the controller software fits the wear pattern to metrology data to calculate the changing feedrates across the mandrel. Here we present an overview of our process, and early results showing the effectiveness of deterministic polishing for replicated optics.
Recently NASA Marshall Space Flight Center has made good progress in employing computer numerical control (CNC) polishing techniques on electroless nickel mandrels, as part of our replicated grazing incidence optics program. CNC polishing has afforded the ability to deterministically refine mandrel figure, therefore improving mirror performance. The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a MSFC-led sounding rocket instrument that comprises some of the first mirrors produced at MSFC using this polishing technique. Here we present the predicted mirror performance obtained from metrology, after completion of CNC polishing, as well as the results of X-ray tests performed on the MaGIXS telescope mirror before, and after mounting.
The Habitable Exoplanet Observatory Mission (HabEx) is one of four missions under study for the 2020 Astrophysics Decadal Survey. Its goal is to directly image and spectroscopically characterize planetary systems in the habitable zone around nearby sun-like stars. Additionally, HabEx will perform a broad range of general astrophysics science enabled by 100 to 2500 nm spectral range and 3 × 3 arc-minute FOV. Critical to achieving its the HabEx science goals is a large, ultrastable UV/Optical/Near-IR (UVOIR) telescope. The baseline HabEx telescope is a 4-meter off-axis unobscured threemirror- anastigmatic, diffraction limited at 400 nm with wavefront stability on the order of a few 10s of picometers. This paper summarizes the opto-mechanical design of the HabEx baseline optical telescope assembly, including a discussion of how science requirements drive the telescope’s specifications, and presents analysis that the baseline telescope structure meets its specified tolerances.
Lynx is the future x-ray observatory with superb imaging capabilities (<1 arc sec half-energy width) and large throughput (2 m2 effective area @ 1 keV), which is being considered in the U.S. to take over Chandra. The implementation of the x-ray mirror module represents a very challenging aspect, and different approaches are being considered. Thin and low-weight substrates, working in grazing incidence configuration, are necessary to meet the severe mass constraints, but they have to also preserve the requirement of an excellent angular resolution. The use of monolithic glass (fused silica) shells is an attractive solution, provided that their thickness is kept very small [<4 mm for mirror shells up of 3-m diameter]. We present the optomechanical design of the Lynx mirror assembly based on this approach, together with the ongoing technological development process. In particular, we discuss the figuring process, which is based on direct polishing followed by an ion-beam figuring correction. A temporary structure is specifically devoted to support the shell during the figuring and polishing operations and to manage the handling of the shell through all phases up to integration into the final telescope supporting spoke wheel. The results achieved so far on a prototype shell will be discussed.
NASA’s Marshall Space Flight Center (MSFC) maintains an active research program toward the development of high-resolution, lightweight, grazing-incidence x-ray optics to serve the needs of future x-ray astronomy missions such as Lynx. MSFC development efforts include both direct fabrication (diamond turning and deterministic computer-controlled polishing) of mirror shells and replication of mirror shells (from figured, polished mandrels). Both techniques produce full-circumference monolithic (primary + secondary) shells that share the advantages of inherent stability, ease of assembly, and low production cost. However, to achieve high-angular resolution, MSFC is exploring significant technology advances needed to control sources of figure error including fabrication- and coating-induced stresses and mounting-induced distortions.
Lynx is an X-ray mission concept with superb imaging capabilities (< 1arcsec Half Energy Width, HEW) and large throughput (2 m<sup>2</sup> effective area @1keV). Several approaches are being considered to meet the challenging technological task of the mirror fabrication. Thin and light substrates are necessary to meet mass constraints. Monolithic fused silica shells are a possible solution if their thickness can be maintained to below 4 mm for mirror shells up to 3 m diameter. In this paper we present the opto-mechanical design of the mirror assembly, the technological processes, and the results achieved so far on a prototypal shells under development. In particular, emphasis is placed on the figuring process that is based on direct polishing and on ion beam figuring and on a temporary stiffening structure designed to support the shell during the figuring and polishing operations and to manage the handling of the shell through all phases up to integration into the telescope supporting structure.
Lynx is a concept under study for prioritization in the 2020 Astrophysics Decadal Survey. Providing orders of magnitude increase in sensitivity over Chandra, Lynx will examine the first black holes and their galaxies, map the large-scale structure and galactic halos, and shed new light on the environments of young stars and their planetary systems. In order to meet the Lynx science goals, the telescope consists of a high-angular resolution optical assembly complemented by an instrument suite that may include a High Definition X-ray Imager, X-ray Microcalorimeter and an X-ray Grating Spectrometer. The telescope is integrated onto the spacecraft to form a comprehensive observatory concept. Progress on the formulation of the Lynx telescope and observatory configuration is reported in this paper.
The Habitable Exoplanet Imaging Mission (HabEx) is a NASA flagship mission to be considered for the 2020 Decadal Survey in Astronomy and Astrophysics. The concept is to develop an imaging system to detail the characteristics of planetary systems surrounding solar-type stars. The system must provide high contrast imaging and spectroscopy with a high signal-to-noise ratio and high stability. In this paper, we will present a point design for a 4 meter, off-axis, monolithic primary mirror to be used in the HabEx imaging system. An initial optimization of design parameters was performed to minimize distortions due to vibration while also maintaining a low areal density. Finite Element Models (FEM) of mirrors were created with varying mounting configurations, materials, depths, rib thicknesses, cell sizes, facesheet thicknesses, and depths. A harmonic analysis was performed on each model, and the corresponding displacements were output from the optical surface. The data from each model was imported into MATLAB and the distortion on the optical surface of each model was analyzed. Thus, the optimal design parameters were chosen based on the vibration performance of each design. The analysis and the chosen point design will be discussed further throughout the paper.
MSFC has a long history of developing full-shell grazing-incidence x-ray optics for both narrow (pointed) and wide
field (surveying) applications. The concept presented in this paper shows the potential to use active optics to switch
between narrow and wide-field geometries, while maintaining large effective area and high angular resolution. In
addition, active optics has the potential to reduce errors due to mounting and manufacturing lightweight optics. The
design presented corrects low spatial frequency error and has significantly fewer actuators than other concepts
presented thus far in the field of active x-ray optics. Using a finite element model, influence functions are calculated
using active components on a full-shell grazing-incidence optic. Next, the ability of the active optic to effect a
change of optical prescription and to correct for errors due to manufacturing and mounting is modeled.
In order to advance significantly scientific objectives, future x-ray astronomy missions will likely call for x-ray telescopes
with large aperture areas (≈ 3 m<sup>2</sup>) and fine angular resolution (≈ 1<sup>2</sup>). Achieving such performance is programmatically
and technologically challenging due to the mass and envelope constraints of space-borne telescopes and to the need for
densely nested grazing-incidence optics. Such an x-ray telescope will require precision fabrication, alignment, mounting,
and assembly of large areas (≈ 600 m2) of lightweight (≈ 2 kg/m<sup>2</sup> areal density) high-quality mirrors, at an acceptable cost
(≈ 1 M$/m<sup>2</sup> of mirror surface area). This paper reviews relevant programmatic and technological issues, as well as possible
approaches for addressing these issues-including direct fabrication of monocrystalline silicon mirrors, active (in-space
adjustable) figure correction of replicated mirrors, static post-fabrication correction using ion implantation, differential
erosion or deposition, and coating-stress manipulation of thin substrates.
Future astrophysical missions will require fabrication technology capable of producing high angular resolution x-ray optics. A full-shell direct fabrication approach using modern robotic polishing machines has the potential for producing high resolution, light-weight and affordable x-ray mirrors that can be nested to produce large collecting area. This approach to mirror fabrication, based on the use of the metal substrates coated with nickel phosphorous alloy, is being pursued at MSFC. A model of the wear pattern as a function of numerous physical parameters is developed and verified using a mandrel sample. The results of the polishing experiments are presented.
The next generation of astrophysical missions will require fabrication technology capable of producing high angular resolution x-ray mirrors. A full-shell direct fabrication approach using modern robotic polishing machines has the potential for producing stiff and light-weight shells that can be heavily nested, to produce large collecting areas, and are easier to mount, align and assemble, giving improved angular resolution. This approach to mirror fabrication, is being pursued at MSFC. The current status of this direct fabrication technology is presented.
NASA's Marshall Space Flight Center (MSFC) engages in research, development, design, fabrication, coating, assembly, and testing of grazing-incidence optics (primarily) for x-ray telescope systems. Over the past two decades, MSFC has refined processes for electroformed-nickel replication of grazing-incidence optics, in order to produce highstrength, thin-walled, full-cylinder x-ray mirrors. In recent years, MSFC has used this technology to fabricate numerous x-ray mirror assemblies for several flight (balloon, rocket, and satellite) programs. Additionally, MSFC has demonstrated the suitability of this technology for ground-based laboratory applications—namely, x-ray microscopes and cold-neutron microscopes and concentrators. This mature technology enables the production, at moderately low cost, of reasonably lightweight x-ray telescopes with good (15–30 arcsecond) angular resolution. However, achieving arcsecond imaging for a lightweight x-ray telescope likely requires development of other technologies. Accordingly, MSFC is conducting a multi-faceted research program toward enabling cost-effective production of lightweight high-resolution x-ray mirror assemblies. Relevant research topics currently under investigation include differential deposition for post-fabrication figure correction, in-situ monitoring and control of coating stress, and direct fabrication of thin-walled full-cylinder grazing-incidence mirrors.
As part of ongoing development efforts at MSFC, we have begun to investigate mounting strategies for highly nested xray
optics in both full-shell and segmented configurations. The analytical infrastructure for this effort also lends itself to
investigation of active strategies. We expect that a consequence of active figure control on relatively thin substrates is
that errors are propagated to the edges, where they might affect the effective precision of the mounting points. Based
upon modeling, we describe parametrically, the conditions under which active mounts are preferred over fixed ones, and
the effect of active figure corrections on the required number, locations, and kinematic characteristics of mounting
The future of x-ray astronomy depends upon development of x-ray telescopes with larger aperture areas (≈ 3 m<sup>2</sup>) and
fine angular resolution (≈ 1″). Combined with the special requirements of nested grazing-incidence optics, the mass and
envelope constraints of space-borne telescopes render such advances technologically and programmatically challenging.
Achieving this goal will require precision fabrication, alignment, mounting, and assembly of large areas (≈ 600 m<sup>2</sup>) of
lightweight (≈ 1 kg/m<sup>2 </sup>areal density) high-quality mirrors at an acceptable cost (≈ 1 M$/m<sup>2 </sup>of mirror surface area). This
paper reviews relevant technological and programmatic issues, as well as possible approaches for addressing these
issues—including active (in-space adjustable) alignment and figure correction.
Future x-ray telescopes will likely require lightweight mirrors to attain the large collecting areas needed to accomplish the science objectives. Understanding and demonstrating processes now is critical to achieving sub-arcsecond performance in the future. Consequently, designs not only of the mirrors but of fixtures for supporting them during fabrication, metrology, handling, assembly, and testing must be adequately modeled and verified. To this end, MSFC is using finite-element modeling to study the effects of mounting on thin, full-shell grazing-incidence mirrors, during all processes leading to flight mirror assemblies. Here we report initial results of this study.
New technology in grazing-incidence mirror fabrication and assembly is necessary to achieve subarcsecond optics for large-area x-ray telescopes. In order to define specifications, an understanding of performance sensitivity to design parameters is crucial. MSFC is undertaking a systematic study to specify a mounting approach, mirror substrate, and testing method. Lightweight mirrors are typically flimsy and are, therefore, susceptible to significant distortion due to mounting and gravitational forces. Material properties of the mirror substrate along with its dimensions significantly affect the distortions caused by mounting and gravity. A parametric study of these properties and their relationship to mounting and testing schemes will indicate specifications for the design of the next generation of lightweight grazing-incidence mirrors. Here we report initial results of this study.
Quantifying the results for a multi-conjugate adaptive optics (MCAO) system is more complex than a
traditional adaptive optics (AO) system. The complexity of analyzing a MCAO system stems from using
multiple deformable mirrors (DMs) and quantifying the influence functions at the wavefront sensor (WFS).
In this paper, analysis tools are developed to quantify MCAO performance. Influence functions from two
deformable mirrors are propagated to a WFS using CODEV to simulate an MCAO design comparable to
the Dunn Solar Telescope (DST). Using MATLAB, the propagated influence functions are mapped to the
appropriate field positions, and reconstructor matrices are built using the mapped influence functions. Next,
a correctability analysis was performed using theoretical random phase screens. The developed tools are
versatile and useful as a system design tool and in a laboratory setting.
We have implemented a MCAO experiment at the Dunn Solar Telescope. The MCAO system uses 2 deformable mirrors, one conjugated to the telescope entrance pupil and other one conjugated to a layer in the upper atmosphere. For our initial experiments we have used a staged approach in which the 97 actuator, 76 subaperture correlating Shack-Hartmann solar adaptive optics system normally operated at the DST is followed by the second DM and the tomographic wavefront sensor, which used three "solar guide stars". We have successfully and stably locked the MCAO system on solar structure. We varied the height of the upper conjugate between 3km and 9 km. A large number of images were recorded in order to evaluate the performance of the system. The data analysis is still ongoing. We present preliminary results and discuss future plans.
An important part of a large solar telescope is the ability to correct, in real time, optical alignment errors caused by gravitational bending of the telescope structure and wavefront errors caused by atmospheric seeing. The National Solar Observatory is currently designing the 4 meter Advanced Technology Solar Telescope (ATST). The ATST wavefront correction system, described in this paper, will incorporate a number of interacting wavefront control systems to provide diffraction limited imaging performance. We will describe these systems and summarize the interaction between the various sub-systems and present results of performance modeling.
We describe the design and operation of a high-speed adaptive optics system using a robust H controller. The system is also general purpose—it can be used in almost any application with minimal modifications and can be set up and operated by a minimally trained operator. The demonstrated system uses a wavefront sensor camera operating at 955 frames/s, a Xinetics 37-channel deformable mirror, and a dual processor computer to perform computations. The system exhibits control of up to 5 waves of focus, a closed-loop bandwidth of ~50 Hz, with a residual error of /75 rms.