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NASA NTRS2019

The Large UV/Optical/Infrared Surveyor Decadal Mission Concept Thermal System Architecture

The Large Ultraviolet/Optical/Infrared (LUVOIR) Surveyor is one of four large strategic mission concept studies commissioned by NASA for the 2020 Decadal Survey in Astronomy and Astrophysics. Slated for launch to the second Lagrange point (L2) in the mid-to-late 2030s, LUVOIR seeks to directly image habitable exoplanets around sun-like stars, characterize their atmospheric and surface composition, and search for biosignatures, as well as study a large array of astrophysics goals including galaxy formation and evolution. Two observatory architectures are currently being considered which bound the trade-off between cost, risk, and scientific return: a 15-meter diameter segmented aperture primary mirror in a three-mirror anastigmat configuration, and an 8-meter diameter unobscured segmented aperture design. To achieve its science objectives, both architectures require milli-Kelvin level thermal stability over the optics, structural components, and interfaces to attain picometer wavefront RMS stability. A 270 Kelvin operational temperature was chosen to balance the ability to perform science in the near-infrared band and the desire to maintain the structure at a temperature with favorable material properties and lower contamination accumulation. This paper will focus on the system-level thermal designs of both LUVOIR observatory architectures. It will detail the various thermal control methods used in each of the major components - the optical telescope assembly, the spacecraft bus, the sunshade, and the suite of accompanying instruments - as well as provide a comprehensive overview of the analysis and justification for each design decision. It will additionally discuss any critical thermal challenges faced by the engineering team should either architecture be prioritized by the Astro2020 Decadal Survey process to proceed as the next large strategic mission for development.

Yang, Kan↗

NASA NTRS2019

The Large UV/Optical/Infrared Surveyor Decadal Mission Concept Thermal System Architecture

Yang, Kan↗

NASA NTRS2017

Sensitivity of WFIRST Coronagraph Broadband Contrast Performance to DM Actuator Errors

The WFIRST/AFTA 2.4 m space telescope currently under study includes a stellar coronagraph for the imaging and the spectral characterization of extrasolar planets. The coronagraph employs sequential deformable mirrors to compensate for phase and amplitude errors. Using the optical model of an Occulting Mask Coronagraph (OMC) testbed at the Jet Propulsion Laboratory (JPL), we have investigated the sensitivity of a Hybrid Lyot Coronagraph (HLC) broadband contrast performance to DM actuator errors and actuator limits. Considered case include drifts in actuator gains or actuator response curves, paired actuators, as well as the limits imposed by a neighboring-actuator rule. Actual data about the actuator drifts and the knowledge about the paired-actuators obtained in several DM characterization experiments conducted at JPL, as well as the neighboring-actuator rule implemented on the OMC testbed were used in simulations. We obtained good agreement between the model prediction and the testbed measurement in terms of static HLC contrast floor and contrast chromaticity.

Sidick, Erkin↗

NASA NTRS2017

Optimizing the Regularization in Broadband Wavefront Control Algorithm for WFIRST Coronagraph

The WFIRST/AFTA 2.4 m space telescope currently under study includes a stellar coronagraph for the imaging and the spectral characterization of extrasolar planets. The coronagraph employs sequential deformable mirrors to compensate for phase and amplitude errors. Using the optical model of an Occulting Mask Coronagraph (OMC) testbed at the Jet Propulsion Laboratory (JPL), we have investigated and compared through modeling and simulations the performance of several actuator regularization-schemes in broadband wavefront control algorithm used to generate dark holes in an OMC, such as a Hybrid Lyot Coronagraph (HLC). Using the concept of a Tikhonov filter constituting the G-matrix, we have explained what the different regularization schemes do to singular-modes during a wavefront control process called Electric Field Conjugation (EFC). In some cases we confirmed the numerical predictions with the testbed measured results. We present our findings in this paper.

Sidick, Erkin↗

NASA NTRS2016

WFIRST/AFTA coronograph contrast performance sensitivity studies: simulation versus experiment

The WFIRST/AFTA 2.4 m space telescope currently under study includes a stellar coronagraph for the imaging and the spectral characterization of extrasolar planets. The coronagraph employs sequential deformable mirrors to compensate for phase and amplitude errors. Using the optical model of an Occulting Mask Coronagraph (OMC) testbed at the Jet Propulsion Laboratory, we have investigated through modeling and simulations the sensitivity of dark hole contrast in a Hybrid Lyot Coronagraph (HLC) for several error cases, including lateral and longitudinal translation errors of two deformable mirrors, DM1 and DM2, lateral and/or longitudinal translation errors of an occulting mask and a Lyot-Stop, clocking errors of DM1 and DM2, and the mismatch errors between the testbed and the model sensitivity matrices. We also investigated the effects of a control parameter, namely the actuator regularization factor, on the control efficiency and on the final contrast floor. We found several error cases which yield contrast results comparable to that observed on the HLC testbed. We present our findings in this paper.

Nemati, Bijan↗

DOE OSTI2025

Electromagnetic Analysis of ITER Electron Cyclotron Emission Components and Support Structures for the Preliminary Design Review

The ITER electron cyclotron emission (ECE) diagnostic system is located at Design Shield Module (DSM) 2, Equatorial Port (EP) 9 to measure electron temperature profile and electron temperature fluctuations and also to assess nonthermal electron distributions via the oblique view. Therefore, ECE has both radial and oblique views with two couples of mirrors for two different optical views. This ECE diagnostic system shall be exposed to significant power due to unabsorbed electron cyclotron heating power in the plasma. It shall also receive large electromagnetic (EM) loads up to 100 MN/m 3 force density due to the eddy currents generated by the short 16-ms transient plasma disruption. The global EM models of EP12 and EP11 with the worst case of plasma disruption Major Disruption Downward Exponential 16 ms Category III (MD_DW_EXP16MS_CATIII) have been provided by ITER. However, the support structure for these critical components, including four mirrors, is still under the design and development phase, especially during the period of preliminary design reviews (PDRs). For those small in-vessel components that are not modeled explicitly for the PDRs, we can extract the magnetic field (B) data and flux variations (dB/dt) at those locations from the global model and then use the B and dB/dt method to calculate the eddy currents, EM forces, and torques on those components in the local submodels. In conclusion, this paper will present the detailed PDR EM analysis results of the ECE components and support structures.

Electromagnetic↗

DOE OSTI2025

Unconventional Spintronics from Chiral Perovskites

Spintronic devices typically employ heterostructures with ferromagnets which break time-reversal symmetry and have non-vanishing magnetization. With the growing class of materials that support spin-polarized carriers, current, and excitations, it is possible to envision emerging spintronic applications that are not limited to magnetoresistance. Here, chiral perovskites with no net magnetization are considered, where the space-inversion and mirror symmetries are broken to induce chiral structure. The known importance of these perovskites is further expanded by the demonstration of the chiral-induced spin selectivity (CISS). However, the generation of the spin-polarized carriers across the interface with these chiral perovskites remains to be fully understood. These first-principles studies for 2D PbBr4-based chiral perovskites provide their electronic structure and an orbital-based symmetry analysis, which allows to establish an effective Hamiltonian to elucidate the underlying origin of their chirality. The same analysis is used for the Edelstein effect, responsible for electrical generation of the nonequilibrium spin polarization in many materials, which in chiral perovskites can be a mechanism contributing to CISS. Furthermore, by examining optical properties of chiral perovskites and the opportunity to use them to realize tunable altermagnets, another class of zero-magnetization spintronic materials, a versatile materials platform is put forth for unconventional spintronics.

14 SOLAR ENERGY↗

NASA NTRS1989

Pulsed, high-current, in-line reversal electron attachment detector

A new, pulsed, high-current, in-line reversal electron attachment ionizer/detector is described. The ionizer is capable of delivering a beam of electrons into an electrostatic mirror field to form a planar wall of electrons having zero kinetic energy. Electron attachment to a molecular target at the reversal point produces either parent or fragment negative ions through a zero-energy (s-wave) state. The atomic or molecular ion is pulsed out of the attachment region approximately 2 microsec after the electrons are pulsed off, and focused onto the entrance plane of a quadrupole mass analyzer. The sensitivity of the apparatus is preliminarily assessed, and its higher-energy behavior with regard to molecular attachment and ionization is described.

Bernius, Mark T.↗

NASA NTRS1991

Pseudomorphic In(y)Ga(1-y)As/GaAs/Al(x)Ga(1-x)As single quantum well surface-emitting lasers with integrated 45 deg beam deflectors

The paper reports on the first demonstration of pseudomorphic InGaAs single quantum well surface-emitting lasers (SELs), with etched vertical mirrors and integrated 45-deg beam deflectors fabricated by ion beam etching. 100-micron-wide broad-area SELs exhibited a threshold current of 320 mA, a total power of 126 mW, and a total external differential quantum efficiency of 0.09 W/A for a 500-micron-long cavity. The perpendicular far-field pattern of broad-area SELs showed a full width at half maximum of about 20 deg. Lasers with various types of cavities fabricated from the same wafer were compared. Broad-area edge-emitting lasers had a threshold current of 200 mA, a total power of 700 mW, and a total external differential quantum efficiency of 0.52 W/A.

Kim, Jae-Hoon↗

NASA NTRS1992

Ozone Measurements with the US EPA UV-DIAL: Preliminary Results

A compact airborne down-looking lidar system was developed at the Environmental Protection Agency in Las Vegas. This differential absorption lidar (DIAL) was designed to simultaneously measure range-resolved concentrations of ozone (O3) and sulfur dioxide (SO2) in the lower troposphere, together with an indication of the aerosol distribution. The five laser wavelengths (i.e., lambda(sub 1) = 277 nm, lambda(sub 2) = 292 nm, lambda(sub 3) = 313 nm, lambda(sub4) = 319 nm, lambda(sub 5) = 369 nm) were generated via Raman conversion of a focused KrF excimer laser. The system is currently installed in a truck-based mobile laboratory. For the ground testing, an opening in the truck floor together with a folding mirror under the truck makes a horizontal, or upwardly inclined direction of measurement possible. Initial ground testing has been performed in the vicinity of a Desert Research Institute (DRI) ambient air monitoring site, located at Cottonwood Cove approximately 85 km south east of Las Vegas, Nevada. At this site O3 and SO2 concentrations are continuously monitored with an average accuracy better than +/- 10 percent. A temporary ozone measurement station with identical accuracy was set up at a distance to get a second point of comparison for the range-resolved DIAL measurements.

Moosmueller, H.↗

NASA NTRS1991

The use of activity-based cost estimation as a management tool for cultural change

It will be shown that the greatest barrier to American exploration of the planet Mars is not the development of the technology needed to deliver humans and return them safely to earth. Neither is it the cost of such an undertaking, as has been previously suggested, although certainly, such a venture may not be inexpensive by some measures. The predicted costs of exploration have discouraged serious political dialog on the subject. And, in fact, even optimistic projections of the NASA budget do not contain the resources required, under the existing development and management paradigm, for human space exploration programs. It will be demonstrated that the perception of the costs of such a venture, and the cultural responses to the perceptions are factors inhibiting American exploration of the moon and the planet Mars. Cost models employed in the aerospace industry today correctly mirror the history of past space programs, and as such, are representative of the existing management and development paradigms. However, if, under this current paradigm no major exploration programs are feasible, then cost analysis methods based in the past may not have great utility in exploring the needed cultural changes. This paper explores the use of a new type of model, the activity based cost model, which will treat management style as an input variable, in a sense providing a tool whereby a complete, affordable program might be designed, including both the technological and management aspects.

Mandell, Humboldt↗

NASA NTRS2001

XRCF Testing Capabilities

The Space Optics Manufacturing Technology Center's X-ray Calibration Facility has been recently modified to test Next Generation Space Telescope (NGST) developmental mirrors at cryogenic temperatures (35 degrees Kelvin) while maintaining capability for performance testing of x-ray optics and detectors. The facility's current cryo-optical testing capability and potential modifications for future support of NGST will be presented.

Reily, Cary↗

NASA NTRS2002

The X-ray Mirrors for the Astro-E2 Mission

The X-Ray telescopes (XRT) for the US/Japan collaborative mission Astro-E2 will be of the same basic design as those built for the original Astro-E mission which failed to reach orbit in Feb. 2000. The NASA/GSFC X-ray Astrophysics Branch will again provide the five lightweight, broad-band mirrors for the mission. X-ray calibrations of the mirrors delivered for the original Astro-E instrument showed spatial resolutions characterized by Half-Power Diameters (HPD) in the range of 1.8 - 2.2 minutes of arc, essentially independent of photon energy in the soft X-ray band. For the mission Astro-E2, both funding constraints and management decisions drastically limit any design modifications, so reflector fabrication and assembly procedures have remained largely unchanged. Nevertheless, in view of the importance in scientific return of attaining even a modest improvement in the spatial resolution of these mirrors, we have carefully considered the various sources of spatial error and, whenever possible, incorporated promising modifications. In this paper, we discuss our current understanding of the various error components as well as the small changes we have been able to implement.

Chan, Kai-Wing↗

NASA NTRS2002

Test and Analysis Capabilities of the Space Environment Effects Team at Marshall Space Flight Center

Marshall Space Flight Center has developed world-class space environmental effects testing facilities to simulate the space environment. The combined environmental effects test system exposes temperature-controlled samples to simultaneous protons, high- and low-energy electrons, vacuum ultraviolet (VUV) radiation, and near-ultraviolet (NUV) radiation. Separate chambers for studying the effects of NUV and VUV at elevated temperatures are also available. The Atomic Oxygen Beam Facility exposes samples to atomic oxygen of 5 eV energy to simulate low-Earth orbit (LEO). The LEO space plasma simulators are used to study current collection to biased spacecraft surfaces, arcing from insulators and electrical conductivity of materials. Plasma propulsion techniques are analyzed using the Marshall magnetic mirror system. The micro light gas gun simulates micrometeoroid and space debris impacts. Candidate materials and hardware for spacecraft can be evaluated for durability in the space environment with a variety of analytical techniques. Mass, solar absorptance, infrared emittance, transmission, reflectance, bidirectional reflectance distribution function, and surface morphology characterization can be performed. The data from the space environmental effects testing facilities, combined with analytical results from flight experiments, enable the Environmental Effects Group to determine optimum materials for use on spacecraft.

Finckenor, M. M.↗

NASA NTRS2015

Effect of DM Actuator Errors on the WFIRST/AFTA Coronagraph Contrast Performance

The WFIRST/AFTA 2.4 m space telescope currently under study includes a stellar coronagraph for the imaging and the spectral characterization of extrasolar planets. The coronagraph employs two sequential deformable mirrors (DMs) to compensate for phase and amplitude errors in creating dark holes. DMs are critical elements in high contrast coronagraphs, requiring precision and stability measured in picometers to enable detection of Earth-like exoplanets. Working with a low-order wavefront-sensor the DM that is conjugate to a pupil can also be used to correct low-order wavefront drift during a scientific observation. However, not all actuators in a DM have the same gain. When using such a DM in low-order wavefront sensing and control subsystem, the actuator gain errors introduce high-spatial frequency errors to the DM surface and thus worsen the contrast performance of the coronagraph. We have investigated the effects of actuator gain errors and the actuator command digitization errors on the contrast performance of the coronagraph through modeling and simulations, and will present our results in this paper.

adaptive optics↗

NASA NTRS2002

Study of Lightweight Ni-Co Alloy Mirrors Obtained by Electroforming Techniques

One contribution in reducing the costs of optics in space can be provided by production of ultralight mirrors. The decrease in the weight of the primary mirror of a telescope is anticipated to lead to the possibility of increasing the size of the telescopes, therefore increasing the amount and distance from which information is received. An electroplating process of ultralight replica mirrors from nickel sulfamate solution will be described. Based on an experimental setup with cylindrical symmetry, flat mirrors with a diameter of 7 inches and thickness of 1.5 mm are made from a Ni-Co alloy. The composition of the resulting deposit is analyzed using Rutherford Backscattering Spectrometry (RBS) and Proton Induced X-ray Emission (PIXE). In order to resolve Ni and Co, 10 MeV nitrogen ions are used as projectiles in the RBS measurements. Solution parameters monitored during the deposition process using optical absorption and polarography will be correlated with the final concentration of Ni and Co in the deposit. Bath parameters like temperature, current density, agitation level and acidity are chosen at certain values and maintained constant from one sample to another throughout the deposition process. The purpose of the experiment is to obtain mirrors with near zero stress, and predetermined composition and hardness. This study is an intermediate step in obtaining through the same process, but with a larger scale setup, ultralight large aperture replica mirrors.

Jones, Ruth↗

NASA NTRS2012

Mars Sample Return Using Solar Sail Propulsion

Many Mars Sample Return (MSR) architecture studies have been conducted over the years. A key element of them is the Earth Return Stage (ERS) whose objective is to obtain the sample from the Mars Ascent Vehicle (MAV) and return it safely to the surface of the Earth. ERS designs predominantly use chemical propulsion [1], incurring a significant launch mass penalty due to the low specific impulse of such systems coupled with the launch mass sensitivity to returned mass. It is proposed to use solar sail propulsion for the ERS, providing a high (effective) specific impulse propulsion system in the final stage of the multi-stage system. By doing so to the launch mass of the orbiter mission can be significantly reduced and hence potentially decreasing mission cost. Further, solar sailing offers a unique set of non-Keplerian low thrust trajectories that may enable modifications to the current approach to designing the Earth Entry Vehicle by potentially reducing the Earth arrival velocity. This modification will further decrease the mass of the orbiter system. Solar sail propulsion uses sunlight to propel vehicles through space by reflecting solar photons from a large, mirror-like surface made of a lightweight, reflective material. The continuous photonic pressure provides propellantless thrust to conduct orbital maneuvering and plane changes more efficiently than conventional chemical propulsion. Because the Sun supplies the necessary propulsive energy, solar sails require no onboard propellant, thus reducing system mass. This technology is currently at TRL 7/8 as demonstrated by the 2010 flight of the Japanese Aerospace Exploration Agency, JAXA, IKAROS mission. [2]

Johnson, Les↗

NASA NTRS1992

Radio emission from chemically peculiar stars

In five VLA observing runs the initial survey of radio emission from magnetic Bp-Ap stars by Drake et al. is extended to include a total of 16 sources detected at 6 cm out of 61 observed, giving a detection rate of 26 percent. Of these stars, three are also detected at 2 cm, four at 3.6 cm, and five at 20 cm. The 11 new stars detected as radio sources have spectral types B5-A0 and are He-weak and Si-strong. No classical (SrCrEu-type) Ap stars have yet been detected. The 16 detected sources show a wide range of radio luminosities with the early-B He-S stars on average 20 times more radio luminous than the late-B He-W stars and 1000 times more luminous than Theta Aurigae. Multifrequency observations indicate flat spectra in all cases. Four stars have a detectable degree of circular polarization at one or more frequencies. It is argued that the radio-emitting CP (chemically peculiar) stars form a distinct class of radio stars that differs from both the hot star wind sources and the active late-type stars. The observed properties of radio emission from these stars may be understood in terms of optically thick gyrosynchrotron emission from a nonthermal distribution of electrons produced in a current sheet far from the star. In this model the electrons travel along magnetic fields to smaller radii and higher magnetic latitudes where they mirror and radiate microwave radiation.

Linsky, Jeffrey L.↗