Very Large Space Optics for an Investigation of the Extreme Universe
This viewgraph presentation describes the utilization of very large space optics to test the extreme universe.
Adams, James H.↗
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Formation metrology and control for large separated optics space telescopes
In this paper we present formation flying performance analysis initial results for a representative large space telescope composed of separated optical elements [Mett 02]. A virtual-structure construct (an equivalent rigid body) is created by unique metrology and control that combines both centralized and decentralized methods. The formation may be in orbit at GEO for super-resolution Earth observation, as in the case of Figure 1, or it may be in an Earth-trailing orbit for astrophysics, Figure 2. Extended applications are envisioned for exo-solar planet interferometric imaging by a formation of very large separated optics telescopes, Figure 3. Space telescopes, with such large apertures and f/10 to f/100 optics, are not feasible if connected by massive metering structures. Instead, the new virtual-structure paradigm of information and control connectivity between the formation elements provides the necessary spatial rigidity and alignment precision for the telescope.
formation flying virtual-structure telescopes↗
White-Light Phase-Conjugate Mirrors as Distortion Correctors
White-light phase-conjugate mirrors would be incorporated into some optical systems, according to a proposal, as means of correcting for wavefront distortions caused by imperfections in large optical components. The proposal was given impetus by a recent demonstration that white, incoherent light can be made to undergo phase conjugation, whereas previously, only coherent light was known to undergo phase conjugation. This proposal, which is potentially applicable to almost any optical system, was motivated by a need to correct optical aberrations of the primary mirror of the Hubble Space telescope. It is difficult to fabricate large optical components like the Hubble primary mirror and to ensure the high precision typically required of such components. In most cases, despite best efforts, the components as fabricated have small imperfections that introduce optical aberrations that adversely affect imaging quality. Correcting for such aberrations is difficult and costly. The proposed use of white-light phase conjugate mirrors offers a relatively simple and inexpensive solution of the aberration-correction problem. Indeed, it should be possible to simplify the entire approach to making large optical components because there would be no need to fabricate those components with extremely high precision in the first place: A white-light phase-conjugate mirror could correct for all the distortions and aberrations in an optical system. The use of white-light phase-conjugate mirrors would be essential for ensuring high performance in optical systems containing lightweight membrane mirrors, which are highly deformable. As used here, "phase-conjugate mirror" signifies, more specifically, an optical component in which incident light undergoes time-reversal phase conjugation. In practice, a phase-conjugate mirror would typically be implemented by use of a suitably positioned and oriented photorefractive crystal. In the case of a telescope comprising a primary and secondary mirror (see figure) white light from a distant source would not be brought to initial focus on one or more imaging scientific instrument(s) as in customary practice. Instead, the light would be brought to initial focus on a phase-conjugate mirror. The phase-conjugate mirror would send a phase-conjugate image back, along the path of the incoming light, to the primary mirror. A transparent, highly efficient diffractive thin film deposited on the primary mirror would direct the phase-conjugate image to the imaging instrument(s).
Frazier, Donald↗
Aberrations for Grazing Incidence Optics
Large number of grazing incidence telescope configurations have been designed and studied. Wolte1 telescopes are commonly used in astronomical applications. Wolter telescopes consist of a paraboloidal primary mirror and a hyperboloidal or an ellipsoidal secondary mirror. There are 8 possible combinations of Wolter telescopes. Out of these possible designs only type 1 and type 2 telescopes are widely used. Type 1 telescope is typically used for x-ray applications and type 2 telescopes are used for EUV applications. Wolter-Schwarzshild (WS) telescopes offer improved image quality over a small field of view. The WS designs are stigmatic and free of third order coma and, therefore, the PSF is significantly better over a small field of view. Typically the image is more symmetric about its centroid. As for the Wolter telescopes there are 8 possible combinations of WS telescopes. These designs have not been widely used because the surface equations are complex parametric equations complicating the analysis and typically the resolution requirements are too low to take full advantage of the WS designs. There are several other design options. Most notable are wide field x-ray telescope designs. Polynomial designs were originally suggested by Burrows4 and hyperboloid-hyperboloid designs for solar physics applications were designed by Harvey5. No general aberration theory exists for grazing incidence telescopes that would cover all the design options. Several authors have studied the aberrations of grazing incidence telescopes. A comprehensive theory of Wolter type 1 and 2 telescopes has been developed. Later this theory was expanded to include all possible combinations of grazing incidence and also normal incidence paraboloid-hyperboloid and paraboloid-ellipsoid telescopes. In this article the aberration theory of Wolter type telescopes is briefly reviewed.
Saha, Timo T.↗
Larger, Lighter Space Telescopes by Implementing In-Space Manufacturing Concepts
There is a continuous demand for larger, lighter, and higher quality telescopes from both the astronomical and global surveillance communities one looking up and the other down. Enabling technologies must be developed and implemented that will allow this goal to be financially and technically feasible. The optical systems needed far high spatial resolution surveillance and astronomical applications require large optical, apertures with mention of future systems up to 150 meter in diameter. With traditional optical manufacturing technologies, large optical aperture means high mass and long fabrication lead times with associated high costs. Completely new approaches to optical fabrication must be developed to enable the fabrication of such optical systems. The cost and lead time associated with the fabrication of lightweight, high quality optical systems limits the feasible size of the optics. A primary factor in the launch cost of space optical systems is volume and mass. To minimize the mass of the high quality optics, optical fabricators implement materials with high specific stiffness and use honeycomb, or other structural minimization patterns, to support the optical surface; however, the structure must still be designed to survive launch loads. This sigmficantly adds to the fabrication difficulty and dramatically increases launch costs. One approach to minimizing launch volume and negating the need for the design to survive launch loads is to send the manufacturing facility and raw materials into space and perform the fabrication in-situ. We, are currently performing feasibility studies of initial concepts for inspace manufacturing of optical systems. By utilizing the micro-gravity and vacuum environment of space while eliminating the constraints defined by high launch forces and limited volume of the launch vehicle, the development of large, high quality glass membrane mirrors may be feasible. Several concepts were investigated to address the manufacturing of both optical surfaces and telescope structure. We will describe one of the primary approaches to utilize the space environment for optical manufacturing and describe initial results.
Mooney, James t.↗
Status and Path Forward for the Large Ultraviolet Optical Infrared Surveyor (LUVOIR) Mission Concept Study
In preparation of the 2020 Astrophysics Decadal Survey, National Aeronautics and Space Administration (NASA) has commenced a process for the astronomical community to study several large mission concepts leveraging the lessons learned from past Decadal Surveys. This will enable the Decadal Survey committee to make more informed recommendations to NASA on its astrophysics science and mission priorities with respect to cost and risk. Four astrophysics large mission concepts were identified. Each of them had a Science and Technology Definition Teem(STDT) chartered to produce scientifically compelling, feasible, and executable design reference mission (DRM)concepts to present to the 2020 Decadal Survey. In addition, The Aerospace Corporation will perform an independent cost and technical evaluation (CATE) of each of these mission concept studies in advance of the 2020 Decadal Survey by interacting with the STDTs to provide detailed technical details on certain areas for which deep dives are appropriate. This paper presents the status and path forward for one of the four large mission concepts, namely, the Large UltraViolet, Optical, InfraRed surveyor (LUVOIR).
Study Office: science analyses↗
Pixelized Device Control Actuators for Large Adaptive Optics
A fully integrated, compact, adaptive space optic mirror assembly has been developed, incorporating new advances in ultralight, high-performance composite mirrors. The composite mirrors use Q-switch matrix architecture-based pixelized control (PMN-PT) actuators, which achieve high-performance, large adaptive optic capability, while reducing the weight of present adaptive optic systems. The self-contained, fully assembled, 11x11x4-in. (approx.= 28x28x10-cm) unit integrates a very-high-performance 8-in. (approx.=20-cm) optic, and has 8-kHz true bandwidth. The assembled unit weighs less than 15 pounds (=6.8 kg), including all mechanical assemblies, power electronics, control electronics, drive electronics, face sheet, wiring, and cabling. It requires just three wires to be attached (power, ground, and signal) for full-function systems integration, and uses a steel-frame and epoxied electronics. The three main innovations are: 1. Ultralightweight composite optics: A new replication method for fabrication of very thin composite 20-cm-diameter laminate face sheets with good as-fabricated optical figure was developed. The approach is a new mandrel resin surface deposition onto previously fabricated thin composite laminates. 2. Matrix (regenerative) power topology: Waveform correction can be achieved across an entire face sheet at 6 kHz, even for large actuator counts. In practice, it was found to be better to develop a quadrant drive, that is, four quadrants of 169 actuators behind the face sheet. Each quadrant has a single, small, regenerative power supply driving all 169 actuators at 8 kHz in effective parallel. 3. Q-switch drive architecture: The Q-switch innovation is at the heart of the matrix architecture, and allows for a very fast current draw into a desired actuator element in 120 counts of a MHz clock without any actuator coupling.
Knowles, Gareth J.↗
Toward a NASA Deep Space Optical Communications System
As discussed at SpaceOps in 2016, we expect the data rates from deep space missions to increase approximately one order of magnitude per decade for the next 50 years. The first order of magnitude improvement will come from existing plans for radio frequency (RF) communications including enhancements to both spacecraft and Deep Space Network (DSN) facilities. The next two orders of magnitude are predicted to come from the introduction of deep space optical communications. Studies indicate that optical receive apertures of between 8m12m are desired. The large cost of dedicated receive telescopes makes this method unrealistic – at least in the near-term. The cost of large optical ground terminals is driven primarily by the cost of the optics and by the cost of a stable structure for the telescope. We propose a novel hybrid design in which existing DSN 34m beam waveguide (BWG) radio antennas can be modified to include an 8m equivalent optical primary. By utilizing a low-cost segmented spherical mirror optical design, pioneered by the optical astronomical community, and by exploiting the already existing extremely stable large radio aperture structures in the DSN, we can minimize both of these cost drivers for implementing large optical communications ground terminals. Two collocated hybrid RF/optical antennas could be arrayed to synthesize the performance of an 11.3m receive aperture to support more capable or more distant space missions or used separately to communicate with two optical spacecraft simultaneously. NASA is in the midst of building six new 34m BWG antennas in the DSN. The final two are planned to be built at the DSN Goldstone, California and Canberra complexes. We are now investigating building these last two antennas as RF/optical hybrids. By delaying their operational dates by two years, we would be able to add the 8m optical receive capability for these two antennas while fitting within existing budgetary constraints. This paper describes the hybrid antenna design, the technical challenges being addressed, and plan for using this concept, together with ongoing work on optical flight terminals, to infuse operation optical communications into deep space missions.
Cornwell, Donald M.↗
Large Volume, Optical and Opto-Mechanical Metrology Techniques for ISIM on JWST
The final, flight build of the Integrated Science Instrument Module (ISIM) element of the James Webb Space Telescope is the culmination of years of work across many disciplines and partners. This paper covers the large volume, ambient, optical and opto-mechanical metrology techniques used to verify the mechanical integration of the flight instruments in ISIM, including optical pupil alignment. We present an overview of ISIM's integration and test program, which is in progress, with an emphasis on alignment and optical performance verification. This work is performed at NASA Goddard Space Flight Center, in close collaboration with the European Space Agency, the Canadian Space Agency, and the Mid-Infrared Instrument European Consortium.
ISIM↗
Geometry dependence of optical pulse broadening in multiple scattering media
A Monte Carlo simulation method has been used to evaluate the temporal response at a variety of receivers to an instantaneous laser pulse input to a turbid medium. The results are compared to the description of the ensemble of all transmitted photons for which a diffusion theory was developed. It was shown that the arrival times for all photons transmitted through the cloud are exponentially distributed with a mean time that varies as the product of the cloud thickness and the momentum transfer optical depth. For large optical depths the mean time delay associated with all reflected photons was found to depend only on the cloud thickness. The impulse response function for receivers on the beam axis varied with field of view and for small fields of view it was dominated by single scattering even for optically thick clouds. In these cases, the mean time delay could be up to 10 to the 6th times shorter than that associated with all transmitted photons with a related increase in the maximum modulation frequency.
Thomas, R. W. L.↗
Ocean observations with EOS/MODIS: Algorithm development and post launch studies
An investigation of the influence of stratospheric aerosol on the performance of the atmospheric correction algorithm was carried out. The results indicate how the performance of the algorithm is degraded if the stratospheric aerosol is ignored. Use of the MODIS 1380 nm band to effect a correction for stratospheric aerosols was also studied. The development of a multi-layer Monte Carlo radiative transfer code that includes polarization by molecular and aerosol scattering and wind-induced sea surface roughness has been completed. Comparison tests with an existing two-layer successive order of scattering code suggests that both codes are capable of producing top-of-atmosphere radiances with errors usually less than 0.1 percent. An initial set of simulations to study the effects of ignoring the polarization of the the ocean-atmosphere light field, in both the development of the atmospheric correction algorithm and the generation of the lookup tables used for operation of the algorithm, have been completed. An algorithm was developed that can be used to invert the radiance exiting the top and bottom of the atmosphere to yield the columnar optical properties of the atmospheric aerosol under clear sky conditions over the ocean, for aerosol optical thicknesses as large as 2. The algorithm is capable of retrievals with such large optical thicknesses because all significant orders of multiple scattering are included.
Gordon, Howard R.↗
Beyond Solar-B: MTRAP, the Magnetic Transition Region Probe
The next generation of solar missions will reveal and measure fine-scale solar magnetic fields and their effects in the solar atmosphere at heights, small scales, sensitivities, and fields of view well beyond the reach of Solar-B. The necessity for, and potential of, such observations for understanding solar magnetic fields, their generation in and below the photosphere, and their control of the solar atmosphere and heliosphere, were the focus of a science definition workshop, 'High-Resolution Solar Magnetography from Space: Beyond Solar-B,' held in Huntsville Alabama in April 2001. Forty internationally prominent scientists active in solar research involving fine-scale solar magnetism participated in this Workshop and reached consensus that the key science objective to be pursued beyond Solar-B is a physical understanding of the fine-scale magnetic structure and activity in the magnetic transition region, defined as the region between the photosphere and corona where neither the plasma nor the magnetic field strongly dominates the other. The observational objective requires high cadence (less than 10s) vector magnetic field maps, and spatially resolved spectra from the IR, visible, vacuum UV, to the EUV at high resolution (less than 50km) over a large FOV (approximately 140,000 km). A polarimetric resolution of one part in ten thousand is required to measure transverse magnetic fields of less than 30G. The latest SEC Roadmap includes a mission identified as MTRAP to meet these requirements. Enabling technology development requirements include large, lightweight, reflecting optics, large format sensors (16K x 16K pixels) with high QE at 150 nm, and extendable spacecraft structures. The Science Organizing Committee of the Beyond Solar-B Workshop recommends that: (1) Science and Technology Definition Teams should be established in FY04 to finalize the science requirements and to define technology development efforts needed to ensure the practicality of MTRAP's observational goals; (2) The necessary technology development funding should be included in Code S budgets for FY06 and beyond to prepare MTRAP for a new start no later than the nominal end of the Solar-B mission, around 2010.
Davis, John M.↗
Doppler Lidar for Wind Measurements on Venus
NASA Langley Research Center has a long history of developing 2-micron laser transmitter for wind sensing. With support from NASA Laser Risk Reduction Program (LRRP) and Instrument Incubator Program (IIP), NASA Langley Research Center has developed a state-of-the-art compact lidar transceiver for a pulsed coherent Doppler lidar system for wind measurement. The transmitter portion of the transceiver employs the high-pulse-energy, Ho:Tm:LuLiF, partially conductively cooled laser technology developed at NASA Langley. The transceiver is capable of 250 mJ pulses at 10 Hz. It is very similar to the technology envisioned for coherent Doppler lidar wind measurements from Earth and Mars orbit. The transceiver is coupled to the large optics and data acquisition system in the NASA Langley VALIDAR mobile trailer. The large optics consists of a 15-cm off-axis beam expanding telescope, and a full-hemispheric scanner. Vertical and horizontal vector winds are measured, as well as relative backscatter. The data acquisition system employs frequency domain velocity estimation and pulse accumulation. It permits real-time display of the processed winds and archival of all data. This lidar system was recently deployed at Howard University facility in Beltsville, Mary-land, along with other wind lidar systems. Coherent Doppler wind lidar ground-based wind measurements and comparisons with other sensors will be presented. A simulation and data product for wind measurement at Venus will be presented.
Singh, Upendra N.↗
Design of a support and foundation for a large lunar optical telescope
Design analysis and considerations are presented for the support structure and the foundation of the 16-m large lunar telescope (LTT). The proposed graphite/magnesium composite hexapod structure will support the 16-m mirror through a gimbal and trunnion assembly, with each hexapod leg consisting of seven 51-mm diameter 2-mm thick tubes bundled together. The foundation consists of three 152-cm diameter spud-can type footings. Results of the finite element analysis of the load-displacement characteristics of the support structure and the foundation are reported.
Chua, Koon M.↗
11 Foot Unitary Plan Tunnel Facility Optical Improvement Large Window Analysis
The test section of the 11 by 11-foot Unitary Plan Transonic Wind Tunnel (11-foot UPWT) may receive an upgrade of larger optical windows on both the North and South sides. These new larger windows will provide better access for optical imaging of test article flow phenomena including surface and off body flow characteristics. The installation of these new larger windows will likely produce a change to the aerodynamic characteristics of the flow in the Test Section. In an effort understand the effect of this change, a computational model was employed to predict the flows through the slotted walls, in the test section and around the model before and after the tunnel modification. This report documents the solid CAD model that was created and the inviscid computational analysis that was completed as a preliminary estimate of the effect of the changes.
computer aided design↗
OCCAMS: Optically Controlled and Corrected Active Meta-Material Space Structures
Telescopes require sub-wavelength figure (shape) error in order to achieve acceptable Strehl ratios. Traditional methods of achieving this require rigid and therefore heavy mirrors and reaction structures as well as proportionally heavy and expensive spacecraft busses and launch vehicles. This effectively limits the diameter and therefore resolution and collecting area of space optics. Large diameter telescopes must either be heavy or actively controlled. Space telescopes of the size proposed for missions such as TPF (Terrestrial Planet Finder), TPI (Terrestrial Planet Imager), etc. will likely require large active primaries and structures and corrective optics to implement downstream wavefront control. We propose a novel viable enabling technology. High resolution space imaging requires the production of lightweight large aperture optics subject to design tradespace constraints based on nanometer physical tolerances, low system aerial density, high control authority, suitable thermal and mechanical properties, deployment capability, launch vehicle volume constraints, as well as production cost and schedule risk mitigation. Segmented systems impose additional requirements on segment alignment, wavefront phasing, and telescope mass with increased edge diffraction. Photons weigh nothing. Why must even small space telescopes "weigh" tons? Our team is working to demonstrate that they do not, by leveraging 15 years of effort and a novel advanced concept.The ultimate research goal is to refine technology to produce a mission capable ultra-lightweight membrane optic whose shape can be remotely controlled using a laser beam. Using our novel optically-controlled molecular actuators allows substitution of optically-induced control for rigidity and mirror mass. In analogy with noise-canceling headphones, this technique also potentially provides a way to excite vibratory modes to couple with and damp out normal modes of oscillation induced by slewing, other motion and thermal changes, thus allowing a robust response to repointing of a large aperture.
Astronomy↗
Making Optical Correctors by Diamond Turning
Large Optics Diamond Turning Machine (LODTM) at Lawrence Livermore National Laboratory used to make highly amorphic reflecting wavefront-corrector plates with rms difference between desired and measured reflector surfaces of only 0.075 wave. Measured errors correspond to one standard deviation of uncertainties in digitization and reduction of interferograms of surface. Appears accuracy of LODTM-generated surface exceeds current ability to measure it. Work demonstrates feasibility of single-point diamond turning for manufacture of generalized wavefront-control surfaces or other unusual surfaces desired by optical designers.
Meinel, Aden B.↗
ASCIE: An integrated experiment to study CSI in large segmented optical systems
A description of the advanced structures/control integrated experiment (ASCIE) experimental setup, a generic test bed for several essential technologies was presented. In particular its multi-input, multi-output, non-collocated control system and its complex structural dynamics, characteristic of large segmented systems make it an ideal test bed for Control-Structure Interaction (CSI) experiments. The high accuracy of its measurement system will make it possible to investigate the dynamics of microvibrations and its implication for the CSI phenomenon.
Aubrun, Jean-Noel↗