We present a method for extracting the zero-gravity surface figure of a mirror. If the structures and constraints of the mirror and its support mounts are invariable during measurement, we can use an algorithm to extract its zero-gravity surface figure by measured data obtained through three different orientations of the mirror. These orientations can be user-defined within the proposed rules, thereby reducing measuring constraints. The proposed algorithm is also available for the gravity-reversing method. To devise this algorithm, we propose and prove a nonlinear superposition property that the mirror system’s displacement of nodes at any gravity-included angle is equal to the sum of the projection of the displacement of nodes at θ  =  0 and θ  =  π  /  2. This method is verified through comparisons with a series of numerical stimulations.

Liquid crystal variable retarders (LCVRs) will be used in the polarization modulation packages (PMPs) of the instruments SO/PHI (Polarimetric and Helioseismic Imager) and METIS/COR (Multielement Telescope for Imaging and Spectroscopy, Coronagraph) of the Solar Orbiter Mission of the European Space Agency (ESA). Optical retarders are dependent on the angle of incidence (AOI). Since the optical retardances during the polarization modulations are optimized for a particular AOI, other angles increase the polarimetric measurement error. Coronagraphs, such as METIS, are characterized by having wide field-of-view (FoV), which involves large incidence angles through the entire instrument. METIS PMP will work with collimated beams and an AOI up to ±7.0  deg. For this reason, a double LCVR configuration with molecular tilts in opposite directions was selected for METIS PMP, which provides lower angular dependence. The polarimetric performance of the METIS PMP flight model was measured at different AOIs and compared to a single LCVR PMP. The results shown in this paper demonstrate that the functional concept used in METIS guarantees the polarimetric performances at the wide FoV expected in METIS coronagraph. Moreover, a detailed theoretical model is showed and compared to the experimental data, finding successful agreement, which can be very helpful for the design of instruments characterized by wide FoV.

One prototype carbon fiber-reinforced plastics (CFRP) panel for 5-m Dome A Terahertz Explorer antenna is replicated successfully in meeting the surface accuracy requirement of less than 10  μm rms by using resin-rich layer technology. By considering the unconventional thermal deformation behavior of a composite structure, a finite-element model (FEM) is produced to predict the thermal deformation behavior of the panel at low temperature. Effects of structural parameters on thermal deformation behavior of the panel are discussed and they are used in the design and in the structural optimization for minimizing surface thermal deformation error at low temperature. An experimental method based on high precision photogrammetry is used to measure the thermal deformation error of the prototype panel. The method has been used for updating the properties of the FEM so that the FEM becomes even more accurate. A prototype panel with high surface accuracy and high thermal stability has been manufactured recently based on the design parameters given by the updated FEM. Plans for improvements in structure design and molding process are also provided at the end of the paper.

Twinkle is an upcoming 0.45-m space-based telescope equipped with a visible and two near-infrared spectrometers covering the spectral range 0.4 to 4.5  μm with a resolving power R  ∼  250 (λ  <  2.42  μm) and R  ∼  60 (λ  >  2.42  μm). We explore Twinkle’s capabilities for small bodies science and find that, given Twinkle’s sensitivity, pointing stability, and spectral range, the mission can observe a large number of small bodies. The sensitivity of Twinkle is calculated and compared to the flux from an object of a given visible magnitude. The number, and brightness, of asteroids and comets that enter Twinkle’s field of regard is studied over three time periods of up to a decade. We find that, over a decade, several thousand asteroids enter Twinkle’s field of regard with a brightness and nonsidereal rate that will allow Twinkle to characterize them at the instrumentation’s native resolution with SNR  >  100. Hundreds of comets can also be observed. Therefore, Twinkle offers researchers the opportunity to contribute significantly to the field of Solar System small bodies research.

We investigate an image slicer module for an optical multiobject spectrograph, wide-field optical spectrograph (WFOS), which is one of the first-light instruments of the Thirty Meter Telescope (TMT). The image slicer divides the target image into three slices, thus providing a one-third narrower slit width. By positioning a suite of such modules at the telescope focal surface, multiobject spectroscopy with high spectral resolution can be achieved. Three optical designs are developed: a two-mirror design, a four-mirror design, and a flat-mirror design. Comparing them, the flat-mirror design is found to be the most preferable for WFOS. From a tolerance analysis, the tolerances of manufacturing and assembling appear challenging but not insurmountable. We describe how the steep field curvature of TMT requires at least nine module variants, tuned to reduce defocus in specific focal surface zones. Finally, we introduce a viable mechanical packaging concept.

X-ray polarimetry in astronomy has not been exploited well, despite its importance. The recent innovation of instruments is changing this situation. We focus on a complementary metal–oxide–semiconductor (CMOS) pixel detector with small pixel size and employ it as an x-ray photoelectron tracking polarimeter. The CMOS detector we employ is developed by GPixel Inc. and has a pixel size of 2.5  μm  ×  2.5  μm. Although it is designed for visible light, we succeed in detecting x-ray photons with an energy resolution of 176 eV (FWHM) at 5.9 keV at room temperature and the atmospheric condition. We measure the x-ray detection efficiency and polarimetry sensitivity by irradiating polarized monochromatic x-rays at BL20B2 in SPring-8, the synchrotron radiation facility in Japan. We obtain modulation factors of 7.63  %    ±  0.07  %   and 15.5  %    ±  0.4  %   at 12.4 and 24.8 keV, respectively. It demonstrates that this sensor can be used as an x-ray imaging spectrometer and polarimeter with the highest spatial resolution ever tested.

The Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) contains the only currently operating coronagraph in space that is not trained on the Sun. In an era of extreme-adaptive-optics-fed coronagraphs, and with the possibility of future space-based coronagraphs, we re-evaluate the contrast performance of the STIS CCD camera. The 50CORON aperture consists of a series of occulting wedges and bars, including the recently commissioned BAR5 occulter. We discuss the latest procedures in obtaining high-contrast imaging of circumstellar disks and faint point sources with STIS. For the first time, we develop a noise model for the coronagraph, including systematic noise due to speckles, which can be used to predict the performance of future coronagraphic observations. Further, we present results from a recent calibration program that demonstrates better than ^{10  −  6} point-source contrast at 0.6″, ranging to 3  ×  ^{10  −  5} point-source contrast at 0.25″. These results are obtained by a combination of subpixel grid dithers, multiple spacecraft orientations, and postprocessing techniques. Some of these same techniques will be employed by future space-based coronagraphic missions. We discuss the unique aspects of STIS coronagraphy relative to ground-based adaptive-optics-fed coronagraphs.

Terahertz spectrometers with a wide instantaneous frequency coverage for passive remote sensing are enormously attractive for many terahertz applications, such as astronomy, atmospheric science, and security. Here we demonstrate a wide-band terahertz spectrometer based on a single superconducting chip. The chip consists of an antenna coupled to a transmission line filterbank, with a microwave kinetic inductance detector behind each filter. Using frequency division multiplexing, all detectors are read-out simultaneously, creating a wide-band spectrometer with an instantaneous bandwidth of 45 GHz centered around 350 GHz. The spectrometer has a spectral resolution of F  /  ΔF  =  380 and reaches photon-noise limited sensitivity. We discuss the chip design and fabrication, as well as the system integration and testing. We confirm full system operation by the detection of an emission line spectrum of methanol gas. The proposed concept allows for spectroscopic radiation detection over large bandwidths and resolutions up to F  /  ΔF  ∼  1000, all using a chip area of a few cm². This will allow the construction of medium resolution imaging spectrometers with unprecedented speed and sensitivity.

A linear field of view (FOV) K-mirror system used for image derotation is presented as a case example for how to leverage freeform surfaces in dynamic optical configuration design. As the K-mirror rotates about the optical axis, points in the FOV sample the surface at distinct locations, allowing for highly local control of the system aberrations. This methodology is distinct from the typical benefits associated with freeform surfaces, and as such broadens the uses of freeform optics into the category of systems that exhibit changing optical configurations. We show that compared to an on-axis or off-axis conic design, the freeform surface has better distortion correction abilities. Furthermore, a real pupil is generated by the K-mirror system and analyzed for uniformity. The design ideas presented for the K-mirror are discussed in the context of astronomical applications, where systems may benefit from these techniques.

Near infrared camera spectrograph and polarimeter (NICSPol) is a near-infrared (NIR) imaging polarimeter developed for the Near-Infrared Camera and Spectrograph (NICS), one of the backend instruments of the 1.2-m Cassegrain telescope at the Mount Abu Infrared Observatory, India. The polarimeter consists of a rotating wire grid polarizer, which is mounted between the telescope optics and the NICS. The polarimetric observations are carried out by rotating the polarizer using a motorized mechanism to determine the Stokes parameters, which are then converted into the polarization fraction and polarization angle. We report the details of the instrument and the results of observations of infrared polarimetric standards. A set of polarized and unpolarized standards were observed using NICSPol over J, H, and Ks bands covering 0.8 to 2.5  μm. The observations of polarized standards using NICSPol show that NICSPol can constrain polarization within ∼1  %   for sources brighter than ∼16 magnitude in J, H, and Ks bands. NICSPol is a general purpose instrument that could be used to study variety of astrophysical sources such as AGNs, pulsars, XRBs, supernovae, and star-forming regions. With few NIR polarimeters available worldwide so far, NICSPol would be the first imaging NIR polarimeter in India.

This document describes the analysis, design, and prototype test results of the microwave section of a 10- to 19.5-GHz interferometer, aimed at obtaining polarization data of cosmic microwave background (CMB) radiation from the sky. First, receiver analysis is thoroughly assessed to study the contribution of each subsystem when obtaining the Stokes parameters of an input signal. Then, the receiver design is detailed starting from the front-end module, which works at cryogenic temperature, composed of a set of passive components: feedhorn, orthomode transducer, and polarizer, together with active components, such as very low-noise amplifiers. The back-end module (BEM) is directly connected, working at room temperature for further amplification, phase switching, and correlation of the signals. Moreover, the whole frequency band is split into two sub-bands (10 to 14 GHz and 16 to 20 GHz) using a high selective diplexer in the BEM in order to reject radiofrequency interferences. Phase switches allow phase difference steps of 5.625 deg, which modulate the correlated outputs to reduce systematic effects in the postdetection signal processing. Finally, measurements of all the subsystems comprising the microwave section of the receiver as well as the characterization of the complete microwave receiver are presented. The obtained results demonstrate successful performance of the microwave receiver that, together with an electro-optical correlator and a near-infrared camera, comprises the interferometer. Moreover, synthesized images corresponding to combinations of the Stokes parameters can be obtained with the whole system.

Indian Centre for Space Physics is engaged in studying terrestrial and extraterrestrial high-energy phenomena from meteorological balloon borne platforms. A complete payload system with such balloons is at the most about 5 kg of weight. One has to adopt innovative and optimal design for various components of the experiment, so that the data can be procured at decent heights of ∼35 to 42 km; at the same time, some scientific goals are achieved. We mainly describe the instruments in detail and present their test and calibration results. We discuss how we implemented and tested three major instruments, namely, a Geiger–Müller counter, a single-crystal scintillator detector, and a phoswich type scintillator detector for our missions. We also present some flight data of a few missions to demonstrate the capability of such experiments.

A 1  k  ×  1  k CCD camera is designed, implemented, and tested for the CSTAR2 telescope in Antarctica, including its mechanics, CCD controller, and low-noise power system. In the design of mechanics and electronics, low-temperature environment is taken into full consideration. The camera has demonstrated mechanical and electrical stability. The system readout noise is as low as 3.99  erms− when the CCD readout frequency is 100 kHz. Every part of the camera is fully tested in a cryogenic refrigerator (−86  °  C) and proved that the camera has the ability to work in Antarctica for a long term. Finally, the camera is installed on the CSTAR2 telescopes to take observations and the imaging function is well implemented.

Heliotropic orbits and frozen orbits possess unique advantages in Earth observation missions and communication service. However, few scholars have found an orbit that possesses heliotropic and frozen characteristics at the same time. Heliotropic frozen orbits are obtained through a proposed control strategy, which is accomplished by adjusting the area-to-mass ratio and the attitude angles. First, we construct the dynamical model of high area-to-mass ratio spacecraft under the effect of J₂ perturbation and solar radiation pressure. Then, nominal heliotropic frozen orbits are solved by assuming that the obliquity angle of the ecliptic with respect to the equator is zero. Finally, a control strategy is proposed to maintain heliotropic frozen orbits when the obliquity angle of the ecliptic with respect to the equator is considered. In addition, practical examples are provided to verify the heliotropic and frozen characteristics and the robustness of the controlled orbits. Orbit design for Earth observation and communication service is also studied.

Infrared hybridized detectors are widely used in astronomy, and their performance can be degraded by image persistence. This results in remnant images that can persist in the detector for many hours, contaminating any subsequent low-background observations. A different but related problem is reciprocity failure whereby the detector is less sensitive to low flux observations. It is demonstrated that both of these problems can be explained by trapping and detrapping currents that move charge back and forward across the depletion region boundary of the photodiodes within each pixel. These traps have been characterized in one 2.5-μm and two 5.3-μm cutoff wavelength Teledyne H2RG detectors. We have developed a behavior model of these traps using a five-pole infinite impulse response digital filter. This model allows the trapped charge in a detector to be constantly calculated for arbitrary exposure histories, providing a near-real-time correction for image persistence.

Building on the successful development of the 10-μm mercury cadmium telluride (HgCdTe) detector arrays for the proposed NEOCam mission, the University of Rochester Infrared Detector team and Teledyne Imaging Systems are working together to extend the cutoff wavelength of HgCdTe detector arrays initially to 13  μm, with the ultimate goal of developing 15-μm HgCdTe detector arrays for space and ground-based astronomy. The advantage of HgCdTe detector arrays is that they can operate at higher temperatures than the currently used arsenic doped silicon detector arrays at the longer wavelengths. Our infrared detector team at the University of Rochester has received and tested four 13-μm detector arrays from Teledyne Imaging Systems with three different pixel designs, two of which are meant to reduce quantum tunneling dark current. The pixel design of one of these arrays has mitigated the effects of quantum tunneling dark currents for which we have been able to achieve, at a temperature of 28 K and applied bias of 350 mV, a well depth of at least 75ke⁻ for 90% of the pixels with a median dark current of 1.8e⁻  /  s. These arrays have demonstrated encouraging results as we move forward to extending the cutoff wavelength to 15  μm.

Agile Earth observation satellites (AEOSs) possess high-attitude maneuverability and achieve better efficiency than traditional platforms in imaging missions. Onboard mission scheduling of agile satellites requires rapid and accurate prediction of imaging opportunities. This problem has not yet been fully investigated in the previous literature. Our study presents a precise analytical model for field-of-regard (FoR) representation of agile satellites and applies a self-adaptive Hermite interpolation technique for rapid determination of imaging opportunities. The FoR of an agile satellite is regarded as a large virtual field-of-view (FoV) synthesized from infinite instantaneous FoVs of onboard camera corresponding to all possible orientations of agile satellite within limits of maximum maneuverability. Analytical equations of the bounding envelope of the FoR are formulated through quadratic curve fitting. Visibility criteria of the analytical FoR model are derived and piecewise cubic polynomials featured with autonomous searching for interpolation points are used to approximate the visibility functions. Numerical simulations show that the analytical FoR model approximates the truth model with an accuracy of better than 99%. In addition, the self-adaptive algorithm significantly reduces the computational cost for imaging opportunity determination compared to traditional trajectory checking method.

The Daniel K. Inouye Solar Telescope (DKIST) is designed to deliver accurate spectropolarimetric calibrations across a wide wavelength range and large field of view for solar disk, limb, and coronal observations. DKIST instruments deliver spectral resolving powers of up to 300,000 in multiple cameras of multiple instruments sampling nanometer scale bandpasses. We require detailed knowledge of optical coatings on all optics to ensure that we can predict and calibrate the polarization behavior of the system. Optical coatings can be metals protected by many dielectric layers or several-micron-thick dichroics. Strong spectral gradients up to 60 deg retardance per nanometer wavelength and several percent diattenuation per nanometer wavelength are observed in such coatings. Often, optical coatings are not specified with spectral gradient targets for polarimetry in combination with both average- and spectral threshold-type specifications. DKIST has a suite of interchangeable dichroic beam splitters using up to 96 layers. We apply the Berreman formalism in open-source Python scripts to derive coating polarization behavior. We present high spectral resolution examples on dichroics where transmission can drop 10% with associated polarization changes over a 1-nm spectral bandpass in both mirrors and dichroics. We worked with a vendor to design dichroic coatings with relatively benign polarization properties that pass spectral gradient requirements and polarization requirements in addition to reflectivity. We now have the ability to fit multilayer coating designs which allow us to predict system-level polarization properties of mirrors, antireflection coatings, and dichroics at arbitrary incidence angles, high spectral resolving power, and on curved surfaces through optical modeling software packages. Performance predictions for polarization at large astronomical telescopes require significant metrology efforts on individual optical components combined with system-level modeling efforts. We show our custom-built laboratory spectropolarimeter and metrology efforts on protected metal mirrors, antireflection coatings, and dichroic mirror samples.

Recent instrumentation projects have allocated resources to develop codes for simulating astronomical images. Physics-based models are essential for understanding telescope, instrument, and environmental systematics in observations. A deep understanding of these systematics is especially important in the context of weak gravitational lensing, galaxy morphology, and other sensitive measurements. We present an adaptation of a physics-based ab initio image simulator: the photon simulator (PhoSim). We modify PhoSim for use with the near-infrared camera (NIRCam)—the primary imaging instrument aboard the James Webb Space Telescope. This photon Monte Carlo code replicates the observational catalog, telescope and camera optics, detector physics, and readout modes/electronics. Importantly, PhoSim-NIRCam simulates both geometric aberration and diffraction across the field of view. Full field- and wavelength-dependent point spread functions are presented. Simulated images of an extragalactic field are presented. Extensive validation is planned during in-orbit commissioning.

The Echelle spectrograph operating at Vainu Bappu Telescope, India, is a general purpose instrument used for many high-resolution spectroscopic observations. A concerted effort is being made to expand the scientific capability of the instrument in emerging areas of observational astronomy. We aim at evaluating the feasibility of the spectrograph to carry out precision radial velocity (RV) measurements. In the current design, major factors limiting the RV precision of the spectrograph arise from the movable grating and slit, optical aberrations, positional uncertainty associated with optomechanical mounts, and environmental and thermal instabilities in the spectrograph room. RV instabilities due to temperature and pressure variations in the environment are estimated to vary between 120 and 400  ms^−  1, respectively. The positional uncertainty of the grating in the spectrograph could induce a spectral shift of ∼1.4  km s^−  1 across the Echelle orders. A Zemax model is used to overcome the uncertainty in the zero-positioning and lack of repeatability of the moving components. We propose to obtain the Th-Ar lamp observations and using the Zemax model as the reference, predict the drifts in the positions of the optical components. The perturbations of the optical components from the nominal position are corrected at the beginning of the observational run. After a good match is obtained between the model and the observations, we propose to use a Zemax model to improve the wavelength calibration solution. We could match the observations and model within ±1  pixels accuracy after the model parameters are perturbed in a real-time setup of the spectrograph. We present the estimation of the perturbations of optical components and the effect on the RV obtained.

At wavelengths longwards of the sensitivity of silicon, hybrid structured mercury–cadmium–telluride (HgCdTe) detectors show promise to enable extremely precise radial velocity (RV) measurements of late-type stars. The most advanced near-infrared (NIR) detector commercially available is the HAWAII series (HxRG) of NIR detectors. While the quantum efficiency of such devices has been shown to be ≈90  %  , the noise characteristics of these devices, and how they relate to RV measurements, have yet to be quantified. We characterize the various noise sources generated by H4RG arrays using numerical simulations. We present recent results using our end-to-end spectrograph simulator in combination with the HxRG Noise Generator, which emulates the effects of read noise, parameterized by white noise, correlated and uncorrelated pink (1  /  f) noise, alternating column noise, and picture frame noise. The effects of nonlinear pixel response, dark current, persistence, and interpixel capacitance on RV precision are also considered. Our results have implications for RV error budgets and instrument noise floors that can be achieved with NIR Doppler spectrographs that utilize this kind of detector.

Wavefront sensors (WFSs) encode phase information of an incoming wavefront into an intensity pattern that can be measured on a camera. Several kinds of WFSs are used in astronomical adaptive optics. Among them, Fourier-based WFSs perform a filtering operation on the wavefront in the focal plane. The most well-known example of a WFS of this kind is the Zernike WFS. The pyramid WFS also belongs to this class. Based on this same principle, WFSs can be proposed, such as the n-faced pyramid (which ultimately becomes an axicon) or the flattened pyramid, depending on whether the image formation is incoherent or coherent. To test such concepts, the LAM/ONERA on-sky pyramid sensor (LOOPS) adaptive optics testbed hosted at the Laboratoire d’Astrophysique de Marseille has been upgraded by adding a spatial light modulator (SLM). This device, placed in a focal plane produces high-definition phase masks that mimic otherwise bulk optic devices. We first present the optical design and upgrades made to the experimental setup of the LOOPS bench. Then, we focus on the generation of the phase masks with the SLM and the implications of having such a device in a focal plane. Finally, we present the first closed-loop results in either static or dynamic mode with different WFS applied on the SLM.

Robo-AO is the first robotic autonomous laser-guided adaptive optics (AO) system operating in the sky. It is a very economical AO system especially suitable for observations with 1- to 3-m class telescopes. A second Robo-AO system, which works both in the visible and near-infrared wavelengths, has been developed to improve the image quality of the 2-m diameter telescope at Inter-university Centre for Astronomy and Astrophysics Girawali Observatory in India. We present the optomechanical design and development of the Laser Guide Star Facility (LGSF) and the Cassegrain AO facility with various test results. Effects of different projection geometries of the LGSF have been discussed with modeling results. Comprehensive study of an atmospheric dispersion corrector with dispersion model and development of a generic software are elaborated with experimental results. Toward the end, AO loop test results in the presence of artificial turbulence generated in the laboratory are presented.

The polarimetric and helioseismic imager instrument for the Solar Orbiter mission from the European Space Agency requires a high stability while capturing images, specially for the polarimetric ones. For this reason, an image stabilization system has been included in the instrument. It uses global motion estimation techniques to estimate the jitter in real time with subpixel resolution. Due to instrument requirements, the algorithm has to be implemented in a Xilinx Virtex-4QV field programmable gate array. The algorithm includes a 2-D paraboloid interpolation algorithm based on 2-D bisection. We describe the algorithm implementation and the tests that have been made to verify its performance. The jitter estimation has a mean error of 125  pixel of the correlation tracking camera. The paraboloid interpolation algorithm provides also better results in terms of resources and time required for the calculation (at least a 20% improvement in both cases) than those based on direct calculation.

In recent years, phase retrieval methods recovering the phase of an object from coded diffraction patterns have gained popularity. A numerical phase retrieval method called PhaseLift that recovers the phase of an object from a very limited number of coded diffraction patterns was recently proposed. Performance of PhaseLift has been analyzed for different types and the number of masks modulating an object. We present a unique application of PhaseLift that uses four rotations of a single mask, modulating only the amplitude of an object. In simulations, a phase screen with the root-mean-square (RMS) value 0.294  μm was used as the test object. The RMS value of the retrieved phase screen after smoothing was 0.257  μm. In experiments, the RMS value of a wavefront measured with a Shack–Hartmann wavefront sensor was 0.094 while that of the retrieved wavefront after smoothing was 0.054  μm. While PhaseLift is able to recover a wavefront using this kind of modulation, a serious limitation to applicability of this method is its high computational cost and time.

Adaptive optics (AO) systems deliver high-resolution images that may be ideal for precisely measuring positions of stars (i.e., astrometry) if the system has stable and well-calibrated geometric optical distortions. A calibration unit equipped with a back-illuminated pinhole mask can be utilized to measure instrumental optical distortions. AO systems on the largest ground-based telescopes, such as the W. M. Keck Observatory and the Thirty Meter Telescope (TMT), require pinhole positions known to be ∼20  nm to achieve an astrometric precision of 0.001 of a resolution element. In pursuit of that goal, we characterize a photolithographic pinhole mask and explore the systematic errors that result from different experimental setups. We characterized the nonlinear geometric distortion of a simple imaging system using the mask, and we measured 857-nm root mean square of optical distortion with a final residual of 39 nm (equivalent to 20  μ for TMT). We use a sixth-order bivariate Legendre polynomial to model the optical distortion and allow the reference positions of the individual pinholes to vary. The nonlinear deviations in the pinhole pattern with respect to the manufacturing design of a square pattern are 47.2 nm ± 4.5 nm (random) ± 10.8 nm (systematic) over an area of 1788  mm². These deviations reflect the additional error induced when assuming that the pinhole mask is manufactured perfectly square. We also find that ordered mask distortions are significantly more difficult to characterize than random mask distortions as the ordered distortions can alias into optical camera distortion. Future design simulations for astrometric calibration units should include ordered mask distortions. We conclude that photolithographic pinhole masks are >10 times better than the pinhole masks deployed in first-generation AO systems and are sufficient to meet the distortion calibration requirements for the upcoming 30-m-class telescopes.