Coronographic missions require ultra-stable mirror systems to achieve 10 E-10 contrast. The LUVOIR ULTRA study is assessing technological capabilities for a 15-meter telescope requiring sub nanometer optical stability. For ULTRA individual mirror stabilities at the picometer level are required. Thermal sensitivities for a proposed mirror design have been incorporated into a stability budget that indicates the level of stability required is attainable. Key factors to meeting stability allocations are an athermal design, acceptable mirror CTE homogeneity and mirror mount pad design. This paper will present the sensitivities and error budget used to predict the on-orbit mirror stability.
The author requests that a paper given by Matt East from Harris come before this presentation if both are presented.
Direct imaging of exoearths with high-contrast internal coronagraphs depends on ultra-stable opto-mechanical systems. Ultra-stable mirror assemblies enable decadal survey missions like LUVOIR and HabEx. To precisely define the necessary level of stability, the essential first step is to budget the maximum allowable disturbances for each optic in the system. Ideally, allocations are budgeted with respect to spatial- and time-domain frequencies. If allocations do not span these domains, the optic assembly designer cannot take advantage of frequency bands where requirements are looser because of assumptions about telescope control systems and internal coronagraph filtering. This paper explores how mirror assembly technologies and designs are predicted to impact stability, especially within the frequency bands that drive coronagraph contrast performance.
The Origins Space Telescope will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did galaxies evolve from the earliest galactic systems to those found in the universe today? How do habitable planets form? How common are life-bearing worlds? To answer these alluring questions, Origins will operate at mid- and far-infrared wavelengths and offer powerful spectroscopic instruments and sensitivity three orders of magnitude better than that of Herschel, the largest telescope flown in space to date. After a 3 ½ year study, the Origins Science and Technology Definition Team will recommend to the Decadal Survey a concept for Origins with a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. A mid-infrared instrument (MISC-T) will measure the spectra of transiting exoplanets in the 2.8 – 20 μm wavelength range and offer unprecedented sensitivity, enabling definitive biosignature detections. The Far-IR Imager Polarimeter (FIP) will be able to survey thousands of square degrees with broadband imaging at 50 and 250 μm. The Origins Survey Spectrometer (OSS) will cover wavelengths from 25 – 588 μm, make wide-area and deep spectroscopic surveys with spectral resolving power R ~ 300, and pointed observations at R ~ 40,000 and 300,000 with selectable instrument modes. Origins was designed to minimize complexity. The telescope has a Spitzer-like architecture and requires very few deployments after launch. The cryo-thermal system design leverages JWST technology and experience. A combination of current-state-of-the-art cryocoolers and next-generation detector technology will enable Origins’ natural backgroundlimited sensitivity.
To meet the ambitious science goal of characterizing exo-Earths via direct imaging and spectroscopy, future space-based astronomical telescopes will have requirements for optical stability at least several orders of magnitude beyond the current state of the art. Mission concepts requiring stability on the order of picometers include the Large UV/Optical/Infrared (LUVOIR) Surveyor and the Habitable Exoplanet (HabEx) Observatory, which use large primary mirrors and internal coronagraphs to perform high contrast imaging. The Ultra-stable Large Telescope Research and Analysis (ULTRA) Program is a system study performed by an industry consortium led by Ball Aerospace to evaluate potential architectures, perform trade studies, and identify technology gaps that must be addressed to enable picometerlevel optical stability in space. This paper will describe the results of the study, including identification and prioritization of technology gaps and a development roadmap to raise the technology readiness level (TRL) of key enhancing/enabling technologies.
The HabEx mission concept is intended to directly image planetary systems around nearby stars, and to perform a wide range of general astrophysics and solar system observations. The baseline HabEx design would use both a coronagraph and a starshade for exoplanet discovery and characterization. We describe a lower-cost alternative HabEx mission design, which would only use a starshade for exoplanet science. The starshade would provide excellent exoplanet science performance, but for a smaller number of detected exoplanets of all types, including exoEarth candidates, and a smaller fraction of exoplanets with measured orbits. The full suite of HabEx general astrophysics and solar-system science would be supported.
A novel seldom used, thermal analysis approach for system-level thermal design is developed that leverages frequencybased techniques and metrics common in structural dynamics modeling. The ULTRA study, which is assessing technological capabilities for a 15-meter telescope requiring sub nanometer optical stability was the foundation for the initial thermal math model and requirements design space discussed in this paper. For such a large, space-based system under tight tolerances, a typical thermal analysis approach will not generate a meaningful understanding of which effects drive the thermal management design. To address this issue, a perturbance-based thermal modeling approach, which is more suited to generating an understanding of the bulk system-level sensitivities, was used instead. The model developed begins by running discrete sensitivities over a range of input perturbance frequencies. The output quantifies the system response to the various sources of thermal energy input. Results are gathered and combined to from Bode plots to quantify the effect of the system perturbances. These plots can quickly characterize the impact of certain thermal designs in relation to a frequency-based wave front error budget. Resulting sensitivities at the system / sub-system scale and the process for producing such results for the LUVOIR thermal math model utilized in the Ultra study are presented. Thermal stability is key to achieving coronographic missions with 10 E-10 contrast.
The Origins Space Telescope (OST) will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did the universe evolve in response to its changing ingredients? How common are life-bearing planets? To accomplish its scientific objectives, OST will operate at mid- and far-infrared wavelengths and offer superlative sensitivity and new spectroscopic capabilities. The OST study team will present a scientifically compelling, executable mission concept to the 2020 Decadal Survey in Astrophysics. To understand the concept solution space, our team studied two alternative mission concepts. We report on the study approach and describe both of these concepts, give the rationale for major design decisions, and briefly describe the mission-enabling technology.
NASA is exploring telescope and mirror technology options to meet the demanding science goals of the proposed HabEx space telescope. A key priority for the HabEx mission concept would be to leverage affordable telescope solutions that can meet challenging telescope performance requirements with a demanding program timeline. The baseline approach for HabEx is to use an unobscured, monolithic primary mirror with a coronagraph to optimize system performance. NASA is performing an initial study to investigate the feasibility of a HabEx Lite concept which would not leverage a coronagraph and would therefore, have lower exoEarth yield as a consequence, but could provide system mass, cost, and schedule advantages. The HabEx Lite concept leverages replicated, ULE® mirror segments to provide an attractive, alternative telescope architecture to meet the HabEx threshold mission needs. We present the initial mirror design and performance assessment for the HabEx Lite concept.
The HabEx mission concept is intended to directly image planetary systems around nearby stars, and to perform a wide range of general astrophysics and solar system observations. Its main goal is the discovery and characterization of Earthlike exoplanets through high-contrast imaging and spectroscopy. The baseline HabEx concept would use both a coronagraph and a starshade for exoplanet science. We describe an alternative, “HabEx Lite” concept, which would use a starshade (only) for exoplanet science. The benefit is lower cost: by deleting the complex coronagraph instrument; by lowering observatory mass; by relaxing tolerances and stability requirements; by permitting use of a compact on-axis telescope design; by use of a smaller launch vehicle. The scientific penalty of this lower cost option is a smaller number of detected exoplanets of all types, including exoEarth candidates, and a smaller fraction of exoplanets with measured orbits. Our approach uses a non-deployed segmented primary mirror, whose manufacture is within current capabilities.
For internal coronagraph options on the LUVOIR or HabEx mission concepts, the stated challenge of 10 picometers RMS wavefront stability over 10 minutes will govern the performance of every structure that connects the focal plane assembly to each optical surface. This paper interrogates wavefront stability of a mounted mirror assembly for a primary mirror segment assembly, and stability of the optical surface. Analysis describes stability of each element in a primary mirror segment assembly (PMSA) to understand the impact of each component of the PMSA on surface figure error (SFE) over short time periods.
Large visible telescopes present challenging requirements for manufactured surface figure and stability. By comparison, far infrared (IR) telescopes relax many of these requirements by ~100x. These relaxed requirements may translate into reduced cost, schedule, mass, and system complexity. This paper explores how different mirror substrate materials might take advantage of these requirements while operating in a cryogenic environment. Primary mirror materials are evaluated for an Origins Space Telescope (OST) concept, using a 9.1 m segmented aperture in a 30 μm diffraction limited system.