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Advanced Optical Systems and Fabrication/Testing/Control Technologies for Extended-Ultraviolet/Optical to Mid/Far-Infrared Telescopes

Description:

Scope Title:

Materials, Substrates, Structures, and Mechanisms for Advanced Optical Systems

Scope Description:

This scope solicits mirror system technology solutions that enable or enhance telescopes for missions of any size (from balloon or CubeSat to Probe or Flagship) operating at any wavelength from UV/optical to mid/far-infrared. A mirror system is defined as the substrate (material and core structure), supporting structure, with associated mechanisms and active wavefront or thermal sense and control systems. After mission-specific performance specifications, the most important metrics are affordability or areal cost (cost per square meter of collecting aperture) and mass. Also important is the ability to predict ‘in-use’ performance via validated integrated structural thermal optomechanical performance (STOP) modeling.

 

Potential balloon science missions are either in the extreme UV (EUV), UV/optical (UVO), or in the infrared/far-infrared (IR/FIR): EUV missions require optical components with surface slopes of <0.1 µrad; UVO science missions require 1-m-class telescopes diffraction limited at 500 nm; and Mid-IR missions require 2-m-class telescopes diffraction limited at 5 µm. In all cases, telescopes must be able to maintain diffraction-limited performance for elevation angles ranging from 10° to 65° over a temperature range of 220 to 280 K. Also, the telescopes need to have a total mass of less than 300 kg and be able to survive a 10g shock (on landing) without damage. For packaging reasons, the primary mirror assembly should have a radius of curvature 3 m (nominal) and a mass <150 kg.

 

Potential FIR space missions require telescopes with apertures up to 6 m monolithic or 16 m segmented with diffraction-limited performance as good as 5 µm (400 nm rms transmitted wavefront), operating at lower than 10 K (survival temperature from 4 to 315 K). Mirror substrate thermal conductivity at 4 K must be greater than 2 W/m·K. Ideally, the mirror should have less than 100 nm rms surface figure change from 300 to 10 K.  Mirror areal density goal is 25 kg/m2 for the primary mirror substrate and 50 kg/m2 for the primary mirror assembly (including structure). Areal cost goal is total cost of the primary mirror at or below $100K/m2. Potential solutions include, but are not limited to, materials with a low coefficient of thermal expansion (CTE), homogenous CTE, and high thermal conductivity; metal alloys, nanoparticle composites, carbon fiber, graphite composites, ceramic, or SiC materials; and additive manufacture or direct precision machining.

 

Potential ultraviolet/optical (UVO) space missions require telescopes with apertures up to 6-m monolithic or 16-m segmented with better than 500 nm diffraction-limited performance (40 nm rms transmitted wavefront) achieved either passively or via active control operating at 250 to 270 K (nominal). Optical components need to have <5 nm rms surface figures. Additionally, a potential exoplanet mission, using an internal coronagraph, requires total telescope wavefront stability of less than 3 pm rms. This stability specification places severe constraints on the dynamic mechanical and thermal performance. Potential enabling technologies include: ultrastable mirror substrate and support structures (60 to 500 Hz first mode), athermal telescope structures, athermal mirror struts, ultrastable joints with low CTE, vibration compensation or isolation of  >140 dB, and active thermal control of <1 mK.

 

Mirror areal density depends upon available launch vehicle capacities to Sun-Earth L2 (i.e., 15 kg/m2 for a 5-m-fairing Evolved Expendable Launch Vehicle (EELV) versus 150 kg/m2 for a new heavy lift vehicle. Regarding areal cost, a good goal is to keep the total cost of the primary mirror at or below $100M. Thus, a 6-m-class mirror (with ~30 m2 of collecting area) should have an areal cost of less than $3.5M/m2. Also, a 16-m-class mirror (with 200 m2 of collecting area) should have an areal cost of less than $0.5M/m2.

 

CubeSAT missions need low-cost, compact, scalable, diffraction-limited, and athermalized off-axis reflective and on-axis telescopes. One potential mission is for near-infrared/short-wave-infrared- (NIR/SWIR-) band optical communication. A NIR/SWIR optical-communication system needs to have an integrated approach that includes fiber optics, fast-steering mirrors, and applicable detectors.

Expected TRL or TRL Range at completion of the Project: 3 to 5

Primary Technology Taxonomy:

  • Level 1 08 Sensors and Instruments
  • Level 2 08.2 Observatories

Desired Deliverables of Phase I and Phase II:

  • Analysis
  • Prototype
  • Hardware
  • Research

Desired Deliverables Description:

An ideal Phase I deliverable would be an optical component or telescope system of at least 0.25 m or a relevant subcomponent of a system leading to a successful Phase II delivery and a preliminary design and manufacturing plan that demonstrates feasibility. While detailed analysis will be conducted in Phase II, the preliminary design should address how optical, mechanical (static and dynamic), and thermal designs and performance analyses will be done to show compliance with all requirements. Past experience or technology demonstrations that support the design and manufacturing plans will be given appropriate weight in the evaluation.

An ideal Phase II project further advances the technology to produce a flight-qualifiable and scalable optical system, subsystem or relevant components (with TRL in the 4 to 5 range) with the required performance. Deliverables would be accompanied by all necessary documentation, including the optical performance assessment and all data on processing and properties of its substrate materials. A successful mission-oriented Phase II would have a credible plan to deliver for the allocated budget a fully assembled and tested telescope assembly that can be integrated into the potential mission as well as demonstrate an understanding of how the engineering specifications of their system meets the performance requirements and operational constraints of the mission (including mechanical and thermal stability analyses).

State of the Art and Critical Gaps:

Current SOA (state-of-the-art) normal-incidence space mirrors cost $4 million to $6 million per square meter of optical surface area. This research effort seeks to improve the performance of advanced precision optical components while reducing their cost by 5× to 50×, to between $100K/m2 and $1M/m2

 

Current SOA balloon mission mirrors require lightweighting to meet balloon mass limitations and have difficulty meeting optical to mid-IR diffraction-limited performance over the wide temperature range because of the CTE limitations and gravity sag change as a function of elevation angle.

 

Currently, SOA optical communications on-axis or axisymmetric designs are problematic because of the central obscuration. Off-axis designs provide superior optical performance because of the clear aperture; however, they are more complex to design, manufacture, and test.

Relevance / Science Traceability:

This subtopic scope primarily matures technologies for potential Astrophysics Division missions ranging from advanced mirror/structure materials to innovative fabrication and test processes/tools that address technology gaps identified by the 2022 Astrophysics Biennial Technology Report (https://apd440.gsfc.nasa.gov/technology.html) and the 2022 Exoplanet Exploration Program Technology Gap List (https://exoplanets.nasa.gov/internal_resources/2269/). Specific examples include large-aperture ultra-stable telescopes and large-aperture cryogenic telescopes.

Additionally, it matures technologies for potential balloon missions flying higher than 45,000 ft to perform UV and mid/far-IR science at wavelengths inaccessible from the ground.

Optical communications enable high-data-rate downlink of science data. The initial motivation for this scalable off-axis optical design approach is for bringing high-performance reflective optics within reach of laser communication projects with limited resources. 
 

References:

NASA: "2022 Astrophysics Biennial Technology Report," https://apd440.gsfc.nasa.gov/technology.html

NASA: "2022 Exoplanet Exploration Program Technology Gap List," https://exoplanets.nasa.gov/internal_resources/2269/

Dankanich et. al.: “Planetary Balloon-Based Science Platform Evaluation and Program Implementation - Final Report,” available from https://ntrs.nasa.gov/ (search for "NASA/TM-2016-218870").

For additional information about scientific balloons: https://www.csbf.nasa.gov/docs.html

An example of an on-axis design has been utilized in the Lunar Laser Communications Demonstration (LLCD): https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10563/105630X/NASAs-current-activities-in-free-space-optical-communications/10.1117/12.2304175.full?SSO=1

An example of an off-axis design is being developed by the Jet Propulsion Laboratory (JPL) for Deep Space Optical Communications (DSOC): https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10096/100960V/Discovery-deep-space-optical-communications-DSOC-transceiver/10.1117/12.2256001.full

Scope Title:

Fabrication, Test, and Control of Optical Components and Telescopes

Scope Description:

The ability to fabricate, test, and control optical surfaces is enabling for future missions of all spectral bands (ultraviolet (UV), optical, infrared (IR), and far-IR). This scope solicits technology advances that enable the manufacture of optical components (of all diffraction limits, sizes, and operating temperatures) for a lower cost. Achieving this goal requires technologies that enable/enhance the deterministic manufacture of optical components to their desired optical prescription, control of the shape of optical components "in flight," and fully characterize surface errors.

Given that deterministic optical fabrication is relatively mature, technology advances are solicited that primarily reduces cost—particularly for large mirrors. Technology that increases remove rate (to reduce processing time) while producing smoother surfaces (less mid- and high-spatial frequency error) are potentially enhancing. Potential technologies for improvement include (but are not limited to): computer controlled grinding/polishing; electrolytic in-process dressing (ELID) processes; electrochemical processes; on-machine in-process metrology feedback; roller embossing at optical tolerances; and slumping, or replication, technologies. 

To achieve high-contrast imaging for exoplanet science using a coronagraph instrument, systems must maintain wavefront stability to <3 pm rms during critical observations. This requires new technologies and techniques for wavefront sensing, metrology, and verification and validation of optical system wavefront stability. Current methods of wavefront sensing include image-based techniques such as phase retrieval, focal-plane contrast techniques such as electric field conjugation and speckle nulling, and low-order and out-of-band wavefront sensing that uses nonscience light rejected by the coronagraph to estimate drifts in the system wavefront during observations. These techniques are limited by the low stellar photon rates of the dim objects being observed (~5 to 11 Vmag), leading to tens of minutes between wavefront control updates. New methods may include: techniques of using out-of-band light to improve sensing speed and spatial frequency content, new control laws incorporating feedback and feedforward for more optimal control, new algorithms for estimating absolute and relative wavefront changes, and the use of artificial guide stars for improved sensing signal-to-noise ratio and speed. Current methods of metrology include edge sensors (capacitive, inductive, or optical) for maintaining segment cophasing and laser distance interferometers for absolute measurement of system rigid-body alignment. Development of these techniques to improve sensitivity, speed, and component reliability is desired. Low-power, high-reliability electronics are also needed. Metrology techniques for system verification and validation at the picometer level during integration and test (I&T) are also needed. High-speed spatial and speckle interferometers are currently capable of measuring single-digit picometer displacements and deformations on small components in controlled environments. Extension of these techniques to large-scale optics and structures in typical I&T environments is needed.

Finally, mirror segment actuators are needed to align and co-phase segmented aperture mirrors to diffraction-limited tolerances. Depending upon the mission, these mechanisms may need precisions of <1 nm rms and the ability to operate at temperatures as low as 10 K. Potential technologies include superconducting mechanisms.

 

Expected TRL or TRL Range at completion of the Project: 3 to 5

Primary Technology Taxonomy:

  • Level 1 08 Sensors and Instruments
  • Level 2 08.2 Observatories

Desired Deliverables of Phase I and Phase II:

  • Research
  • Analysis
  • Hardware
  • Software
  • Prototype

Desired Deliverables Description:

An ideal Phase I deliverable would be a prototype demonstration of a fabrication, test, or control technology leading to a successful Phase II delivery. Past experience or technology demonstrations that support the design and manufacturing plans will be given appropriate weight in the evaluation.

An ideal Phase II project would further advance the technology to demonstrate the manufacturing process, metrology instrument, or sense and control system on a flight-traceable optical component. Phase II deliverables would be accompanied by all necessary documentation, including the optical performance assessment and all data on processing properties. A successful mission-oriented Phase II would have a credible plan for how to integrate the technology into a potential mission as well as demonstrate an understanding of how the engineering specifications of their system meets the performance requirements and operational constraints of the mission (including mechanical and thermal stability analyses). 

State of the Art and Critical Gaps:

Deterministic optical fabrication is relatively mature. There are multiple small and large companies offering commercial products and services. The Webb and Roman telescopes were/are being fabricated by deterministic processes. However, these processes are expensive. Technology advances are required to enhance these processes and reduce their cost—particularly for large mirrors.

Wavefront sensing using star images, including dispersed-fringe and phase-retrieval methods, is at TRL 6, qualified for space by Webb. WF sensing and control for coronagraphs, including electric field conjugation and low-order wavefront sensing (LOWFS), is at TRL4 and is being developed and demonstrated by the Wide Field Infrared Survey Telescope Coronagraph Instrument (WFIRST/CGI). But none of these technologies have the precision and frequency bandwidth to enable <3 pm rms stability needed for exo-Earth coronagraphy.

Laser-distance interferometers for point-to-point measurements with accuracies from nanometers to picometers have been demonstrated on the ground by the Space Interferometry Mission and other projects and in orbit by the LISA Pathfinder and Grace Follow-On missions. Application to telescope alignment metrology has been demonstrated on testbeds to TRL 4 for nanometer accuracy. Picometer accuracy for telescopes awaits demonstration.

Edge sensors are in use on segmented ground telescopes but are not yet on space telescopes. New designs are needed to provide picometer sensitivity and millimeter range in a space-qualified package.

Higher order wavefront sensing for coronagraphs using out-of-band light is beginning development, with data limited to computer simulations.

Mechanism SOA is defined by the JWST actuators. They provide ample range for far-IR applications, but are more precision than necessary and are expensive. Furthermore, they are not adequate for UVO applications.

Potential solutions for achieving <3 pm wavefront stability include, but are not limited to: metrology, passive control, and active control for optical alignment and mirror phasing; active vibration isolation; metrology; and passive and active thermal control.

Relevance / Science Traceability:

This subtopic scope primarily matures fabrication/test and wavefront control technologies for potential Astrophysics Division missions that address technology gaps identified by the 2022 Astrophysics Biennial Technology Report (https://apd440.gsfc.nasa.gov/technology.html) and the 2022 Exoplanet Exploration Program Technology Gap List (https://exoplanets.nasa.gov/internal_resources/2269/https://exoplanets.nasa.gov/internal_resources/2269/). Specific examples include large-aperture ultra-stable telescopes and large-aperture cryogenic telescopes.

Fabrication and testing technologies for deterministic optical manufacturing are enabling/enhancing for large monolithic and segmented aperture telescopes for missions ranging from UV to optical to far-IR. Control technologies are enabling for coronagraph-equipped space telescopes and segmented space telescopes. 

References:

NASA: "2022 Astrophysics Biennial Technology Report," https://apd440.gsfc.nasa.gov/technology.html
NASA: "2022 Exoplanet Exploration Program Technology Gap List," https://exoplanets.nasa.gov/internal_resources/2269/

Scope Title:

Special Topics:Near Angle Scatter and Ultra-Stiff Biologically InspiredMirror Substrates

Scope Description:

Topic #1: Near Angle Scatter

Near angle scatter from surface microroughness, optical coating columnar structure, surface defects, contamination, radiation exposure, and micrometeoroid impacts can limit the ability to detect and characterize Earth-like planets in the habitable zones of Sun-like stars. Models, validated by experiment, that predict scattered light amplitude at angular separation from the host star from 40 to 500 milliarcseconds as a function of these sources are needed to help define component specifications for a potential 6-m mission to perform exo-Earth science.

Topic #2: Ultra-Stiff Biologically Inspired Mirror Substrates

This special topic solicits companies that can manufacture exotic mirror substrate structures, either of their own design or of NASA’s design. Telescope stability is enabling for missions at all wavelengths (ultraviolet (UV), optical, infrared (IR), and far-IR). It is particularly enabling for coronagraph and interferometric instruments. The stiffer an optical component and structure is, the more stable the resulting telescope will be. Stiffness is also important for balloon missions which need to minimize change in gravity sag of its primary mirror as a function of elevation angle. Historically, high-stiffness low-mass mirrors and structures have been achieved using low-density materials (such as beryllium or SiC) or extreme lightweighting of glass mirrors. Currently, this subtopic is investing in additively manufactured mirrors. In all previous cases, however, the fabricated mirrors used "classical" geometric architectural forms. Biologically inspired architectures might yield mirrors and telescope structures with lower mass and higher stiffness. Biologically inspired architectures might enable the design of structures that more efficiently distribute load and control modal responses. 

Expected TRL or TRL Range at completion of the Project: 2 to 3

Primary Technology Taxonomy:

  • Level 1 08 Sensors and Instruments
  • Level 2 08.2 Observatories

Desired Deliverables of Phase I and Phase II:

  • Research
  • Analysis
  • Prototype
  • Hardware
  • Software

Desired Deliverables Description:

For Topic #1: Near Angle Scatter

  • Phase I detailed theoretical analysis of how to predict near angle scatter in the 40 to 500 milliarcseconds region and an implementable test plan to validate the model.
  • Phase II data that validates with greater than 99% confidence a model for predicting near-angle scatter in the 40 to 500 milliarcseconds region.

For Topic #2: Ultra-Stiff Biologically Inspired Mirror Substrates

  • An ideal Phase I deliverable would be a precision optical system of at least 0.15 m or a relevant subcomponent of a system whose stiffness or modal properties can be modeled and verified by test. 
  • An ideal Phase II project would further advance the technology by producing a flight-qualifiable optical system greater than 0.5 m or a relevant subcomponent (with a TRL in the 4 to 5 range).
  • Phase I and Phase II system or component deliverables would be accompanied by all necessary documentation, including the optical performance assessment and all data on processing and properties of its substrate materials. 

State of the Art and Critical Gaps:

For Topic #1: Near Angle Scatter

Rayleigh-Rice surface scatter theory is widely accepted for smooth surfaces, but is physically unrealistic for describing near angle scatter in 40 to 500 milliarcseconds regime. Harvey-Shack scatter theory is widely accepted for rough surfaces and includes the effects of mid-spatial errors. But, it has a lower limit and may or may not be valid below 500 milliarcseconds.  

For Topic #2:  Ultra-Stiff Biologically Inspired Mirror Substrates

High-stiffness low-mass mirrors and structures have been achieved using low-density materials such as beryllium or extreme lightweighting of glass mirrors. Previously, this subtopic has invested in alternative materials such as SiC and graphite fiber composites. Currently, this subtopic is investing in additive manufacturing technologies. In all previous cases, however, the fabricated mirrors used "classical" geometric architectural forms.

Relevance / Science Traceability:

Mirror technology is enabling for all potential Science Mission Directorate (SMD) science. Special Topic #1 is directly traceable to the Decadal recommended exo-planet mission.  Special Topic #2 has applicability to any mission requiring a large-aperture low-mass stiff telescope.

References:

NASA: "X-ray and Cryogenic Facility," https://optics.msfc.nasa.gov/tech-2/

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