Focal plane wavefront sensing is an appealing technique to cophase multiple aperture telescopes. Phase diversity (PD), operable with any aperture configuration or source extension, generally suffers from high computing load. We introduce, characterize, and experimentally validate the linearized analytical phase diversity (LAPD) algorithm, based on a fast linearized PD algorithm with a capture range comparable to classic PD. We demonstrate that a typical performance of λ  /  75  RMS wavefront error can be reached.

I describe the plans, flows, key facilities, test beds, pathfinders, simulators, and ground support equipment that could be used to fully integrate, functionally test, and qualify the Origins Space Telescope (Origins). The Origins observatory consists of the spacecraft bus module and the cryogenic payload module, which comprises the telescope and three science instruments. The telescope is a three-mirror anastigmat and is composed of four mirrors: three with optical power (the elliptical primary, hyperbolic secondary, and elliptical tertiary mirrors) and a flat field-steering mirror. The three science instruments spanning the wavelength range 2.8 to 588  μm provide the powerful new spectroscopic and imaging capabilities required to achieve the scientific objectives. The Origins Survey Spectrometer uses six gratings in parallel to take multibeam spectra simultaneously across the 25- to 588-μm window through long slits enabling deep three-dimensional extragalactic surveys. The far-IR imager/polarimeter provides imaging and polarimetric measurement capabilities at 50 and 250  μm. Its fast mapping enables rapid follow-up of transient or variable sources and efficient monitoring campaigns. The mid-infrared spectrometer simultaneously provides spectroscopy over 2.8 to 20  μm with exquisite stability and precision (<5  ppm between 2.8 and 10  μm, <20  ppm between 11 to 20  μm). All the instruments are delivered for integration and test fully qualified and calibrated. The integration and test program implemented at each level of assembly is discussed as well as the separation of thermal vacuum testing between the hot and cold zones of the observatory.

Mid-infrared detector arrays operating from 2.8 to 20  μm are baselined in the design of the Origins Space Telescope Mid-Infrared Spectrometer Instrument. This instrument is designed to detect and measure the spectral signatures of gases of biogenic origin in the atmospheres of exoplanets as they transit their host stars. In order to make these detections, the detector array’s pixels need to have high-signal stability when exposed to a constant flux in multiple time-series integration over a typical transit time of a few hours. With the use of a densified pupil spectrometer design, pointing effects can be mitigated because pointing variations do not displace spectra on the detector and each wavelength of light is averaged over a large number of pixels, giving good spectrophotometric stabilities. The current state-of-the-art detector arrays do not achieve these stabilities, although with a feasible development program this level of performance should be achievable. Three detector technologies are under consideration for this development, HgCdTe arrays, Si:As impurity band conduction arrays, and transition edge superconductor bolometer arrays. We primarily treat the HgCdTe technology development, but also introduce the paths forward for the other two technologies. After a few years-long investigative programs, a down-select will be undertaken to select the flight technology.

Effective area is one of the most important parameters of x-ray telescopes. It can be increased by enlarging the entrance aperture or maximizing the reflectivity through the proper designing and optimization of the reflecting coating. A method to increase the reflectivity of grazing incidence x-ray mirrors in the 0.5- to 8-keV energy region is analyzed. The idea consists in the use of a trilayer reflecting coating instead of single-layer one (e.g., C/Ni/Pt mirror instead of Pt one). Deposition of low-absorbing medium-Z and low-Z layers onto the top of strongly absorbing high-Z material results in essential increase in the reflectivity while keeping the same width of the reflectivity plateau. In particular, C/Ni/Pt trilayer mirror demonstrates enhancement of the double reflection coefficient by a factor achieving 1.5 to 3.5 compared to that of Pt-coated mirror. The effective area of a telescope is also considerably increased. The experimental results are in a very good agreement with the theoretical predictions. In addition, the C/Ni/Pt trilayer mirror exhibits a reasonable thermal stability and a relatively low compressive stress of about −550  MPa.

Next-generation radio telescopes, such as the Square Kilometre Array (SKA) and Next Generation Very Large Array (ngVLA), require precise microwave frequency reference signals to be transmitted over fiber links to each dish to coherently sample astronomical signals. Such telescopes employ phase stabilization systems to suppress the phase noise imparted on the reference signals by environmental perturbations on the links; however, the stabilization systems are bandwidth limited by the round-trip time of light traveling on the fiber links. A phase-locked receiver module (RM) is employed on each dish to suppress residual phase noise outside the round-trip bandwidth. The SKA RM must deliver a 3.96-GHz output signal with 4 MHz of tuning range and <100  fs of timing jitter. We present an RM architecture to meet both requirements. Analytical modeling of the RM predicts 30 fs of output jitter when the reference signal is integrated between 1 Hz and 2.8 GHz. The proposed RM was conceived with best practice electromagnetic compatibility in mind and to meet size, weight, and power requirements for the SKA dish indexer. As the ngVLA reference design also incorporates a round-trip phase stabilization system, this RM may be applicable to future ngVLA design.

The Kepler mission was a National Aeronautics and Space Agency (NASA) Discovery-class mission designed to continuously monitor the brightness of at least 100,000 stars to determine the frequency of Earth-size and larger planets orbiting other stars. Once the Kepler proposal was chosen for a flight opportunity, it was necessary to optimize the design to accomplish the ambitious goals specified in the proposal and still stay within the available resources. To maximize the science return from the mission, a merit function (MF) was constructed that relates the science value (as determined by the PI and the Science Team) to the chosen mission characteristics and to models of the planetary and stellar systems. This MF served several purposes; predicting possible science results of the proposed mission, evaluating the effects of varying the values of the mission parameters to increase the science return or to reduce the mission costs, and supporting quantitative risk assessments. The MF was also valuable for the purposes of advocating the mission by illustrating its expected capability. During later stages of implementation, it was used to keep management informed of the changing mission capability and support rapid design tradeoffs when mission down-sizing was necessary. The MF consisted of models of the stellar environment, assumed exoplanet characteristics and distributions, detection sensitivity to key design parameters, and equations that related the science value to the predicted number and distributions of detected exoplanet. A description of the MF model and representative results are presented. Examples of sensitivity analyses that supported design decisions and risk assessments are provided to illustrate the potential broader utility of this approach to other complex science-driven space missions.

The payload of the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2), the second generation of the FIREBall instrument (PI: C. Martin, Caltech), has been calibrated and launched from the NASA Columbia Scientific Balloon Facility in Fort Sumner, New Mexico. FIREBall-2 was launched for the first time on the September 22, 2018, and the payload performed the very first multi-object acquisition from space using a multi-object spectrograph. Our performance-oriented paper presents the calibration and last ground adjustments of FIREBall-2, the in-flight performance assessed based on the flight data, and the predicted instrument’s ultimate sensitivity. This analysis predicts that future flights of FIREBall-2 should be able to detect the HI Lyα resonance line in galaxies at z  ∼  0.67, but will find it challenging to spatially resolve the circumgalactic medium.

HaloSat is a CubeSat-class microsatellite sensitive in the 0.4 to 7.0 keV energy band and designed to survey the entire sky in search of soft x-ray emissions from highly ionized oxygen residing in the halo of the Milky Way galaxy. Those observations will help constrain the mass and spatial distribution of the Milky Way halo and help us understand if hot galactic halos constitute a significant contribution to the overall cosmological baryon budget. We describe the science instrument calibration products, including channel-to-energy transformation, instrument energy resolution and instrument response, and the on-ground efforts that led to their creation. We also describe the alignment process used to obtain the field of view information for the HaloSat science instrument.

In interstellar travel, parallax and stellar aberration have a non-negligible influence on the star identification of star sensors. Through the analysis of the working principle of star sensors, only the guide star catalog generation can solve this problem. The influence mechanism of parallax and stellar aberration is synthetically analyzed by four-dimensional time-space diagrams, and a generation algorithm of the guide star catalog for the interstellar star identification is presented. The update cycle of the catalog is studied, and a block update method based on the distance distribution is given. The Hipparcos catalog is adopted as the fundamental catalog. On the premise of meeting the accuracy requirement of star identification, the maximum travel distance supported by the catalog is about 0.3 light-years. In order to balance the star identification and the influence of parallax, eliminating 30% to 40% of the nearby guide stars is an optimal criterion for the guide star selection. The analysis of the catalog distribution shows that the parallax and the stellar aberration have opposite effects on the distribution of guide stars. The methods and conclusions provide a theoretical basis for interstellar celestial navigation.

We present an analytical design method for the three-mirror anastigmatic (TMA) telescope with mirror spacings as the free design parameter. After the optical designer determines, the system focal length and the mirror spacings according to the design requirements, the design solutions of all TMA telescopes that meet the conditions can be obtained directly according to the formulas for the mirror radius and conic constants derived. The method here can predetermine the mirror position and system envelope size before design, and can quickly give all design solutions. We give a design example using the method and compare and discuss all design solutions of TMA.

Deformable mirrors (DMs) are a critical technology to enable coronagraphic direct imaging of exoplanets with current and planned ground- and space-based telescopes as well as future mission concepts, such as the Habitable Exoplanet Observatory and the Large UV/Optical/IR Surveyor. The latter concepts aim to image exoplanet types ranging from gas giants to Earth analogs. This places several requirements on the DMs such as requires a large actuator count (≳3000), fine surface height resolution (≲10  pm), and radiation hardened driving electronics with low mass and volume. We present the design and testing of a flight-capable, miniaturized DM controller. Having achieved contrasts on the order of 5  ×  ^{10  −  9} on a coronagraph testbed in vacuum in the high contrast imaging testbed facility at NASA’s Jet Propulsion Laboratory (JPL), we demonstrate that the electronics are capable of meeting the requirements of future coronagraph-equipped space telescopes. We also report on functionality testing on-board the high-altitude balloon experiment “Planetary Imaging Concept Testbed Using a Recoverable Experiment – Coronagraph,” which aims to directly image debris disks and exozodiacal dust around nearby stars. The controller is designed for the Boston Micromachines Corporation Kilo-DM and is readily scalable to larger DM formats. The three main components of the system (the DM, driving electronics, and mechanical and heat management) are designed to be compact and have low-power consumption to enable its use not only on exoplanet missions, but also in a wide-range of applications that require precision optical systems, such as direct line-of-sight laser communications. The controller is capable of handling 1024 actuators with 220 V maximum dynamic range, 16-bit resolution, 14-bit accuracy, and 1 kHz operating frequency. The system fits in a 10  ×  10  ×  5  cm³ volume, weighs <0.5  kg, and consumes <8  W. We have developed a turnkey solution reducing the risk for future missions, lowering their cost by significantly reducing volume, weight, and power consumption of the wavefront control hardware.

Stellar coronagraphs rely on deformable mirrors (DMs) to correct wavefront errors and create high-contrast images. Imperfect control of the DM limits the achievable contrast, and therefore, the DM control electronics must provide fine surface height resolution and low noise. We study the impact of quantization errors due to the DM electronics on the image contrast using experimental data from the High Contrast Imaging Testbed facility at NASA’s Jet Propulsion Laboratory. We find that the simplest analytical model gives optimistic predictions compared to real cases, with contrast up to 3 times better, which leads to DM surface height resolution requirements that are incorrectly relaxed by 70%. We show that taking into account the DM actuator shape, or influence function, improves the analytical predictions. However, we also find that end-to-end numerical simulations of the wavefront sensing and control process provide the most accurate predictions and recommend such an approach for setting robust requirements on the DM control electronics. From our experimental and numerical results, we conclude that a surface height resolution of ∼6  pm is required for imaging temperate terrestrial exoplanets around solar-type stars at wavelengths as small as 450 nm with coronagraph instruments on future space telescopes. Finally, we list the recognizable characteristics of quantization errors that may help determine if they are a limiting factor.

We have fabricated a blazed x-ray reflection grating with a period of 160 nm using thermally activated selective topography equilibration (TASTE) and electron-beam (ebeam) physical vapor evaporation. TASTE makes use of grayscale ebeam lithography to create three-dimensional (3-D) structures in resist, which can then be thermally reflown into a desired profile. A blazed grating profile can be fabricated by selectively reflowing a periodic staircase structure into a wedge. This was done for the first time at a grating period of 160 nm, 2.5 times smaller than previous x-ray gratings fabricated using TASTE. The grating was patterned over a 10 mm by 60 mm area in a 147-nm-thick layer of poly(methyl methacrylate) resist and coated with 5 nm of chromium and 15 nm of gold using ebeam evaporation. The diffraction efficiency of the grating was measured using beamline 6.3.2 at Lawrence Berkeley National Laboratory’s Advanced Light Source. The results show a total absolute diffraction efficiency ≳40  %   at lower energies, with maximum single-order diffraction efficiency ranging from 20% to 40%. The total diffraction efficiency was ≳30  %   across the measured bandpass of 180 to 1300 eV.

We present the current status of Hα high-contrast imaging observations with Subaru/Subaru Coronagraphic Extreme Adaptive Optics + VAMPIRES. Our adaptive optics correction at optical wavelengths in combination with (double) spectral differential imaging (SDI) and angular differential imaging (ADI) was capable of resolving a ring feature around omi Cet and detect the Hα counterpart of jet around RY Tau. We tested the post-processing by changing the order of ADI and SDI and both of the contrast limits achieved ∼10^−  3 to 5  ×  10^−  4 at 0.3″, which is comparable to other Hα high-contrast imaging instruments in the Southern Hemisphere such as very large telescope (VLT)/spectro-polarimetric high-contrast exoplanet research, VLT/MUSE, and Magellan AO. Current wavefront sensing and adaptive optics correction at optical wavelengths empirically depend on airmass, and Subaru/VAMPIRES provide great opportunities for Hα high-contrast imaging for Northern Hemisphere targets.

Future space telescopes with coronagraph instruments will use a wavefront sensor (WFS) to measure and correct for phase errors and stabilize the stellar intensity in high-contrast images. The HabEx and LUVOIR mission concepts baseline a Zernike wavefront sensor (ZWFS), which uses Zernike’s phase contrast method to convert phase in the pupil into intensity at the WFS detector. In preparation for these potential future missions, we experimentally demonstrate a ZWFS in a coronagraph instrument on the Decadal Survey Testbed in the High Contrast Imaging Testbed facility at NASA’s Jet Propulsion Laboratory. We validate that the ZWFS can measure low- and mid-spatial frequency aberrations up to the control limit of the deformable mirror (DM), with surface height sensitivity as small as 1 pm, using a configuration similar to the HabEx and LUVOIR concepts. Furthermore, we demonstrate closed-loop control, resolving an individual DM actuator, with residuals consistent with theoretical models. In addition, we predict the expected performance of a ZWFS on future space telescopes using natural starlight from a variety of spectral types. The most challenging scenarios require ∼1 h of integration time to achieve picometer sensitivity. This timescale may be drastically reduced by using internal or external laser sources for sensing purposes. The experimental results and theoretical predictions presented here advance the WFS technology in the context of the next generation of space telescopes with coronagraph instruments.

There is interest in deploying digital micromirror devices (DMDs) in space for use in multi-object spectrometers, but the devices must first be qualified for space deployment. An environmental test campaign has been carried out on eXtended Graphics Array (XGA) DMDs to qualify the devices for space deployment. The campaign has included mechanical shock and vibration, low temperature, proton radiation, and heavy ion radiation testing. XGA DMDs have passed each test at a level suitable for space deployment. Our paper reports on gamma radiation testing of XGA DMDs, the final portion of the environmental test campaign. Gamma radiation causes total ionizing dose (TID). A total of 19 DMDs were irradiated to TIDs between 16 and 45 krad(Si) while biased and 24 and 76 krad(Si) while unbiased. The effects of TID on DMDs are similar to other electrostatically operated micro-electrical mechanical systems, and all irradiated DMDs were fully recovered by annealing. In addition to testing, radiation modeling of the space environment was performed to determine the expected TID for various space mission scenarios. DMDs have minimal susceptibility to TID effects, and the effects do not significantly compromise the use of the devices for space missions in orbit at L2 or low Earth orbit.

Direct imaging instruments have the spatial resolution to resolve exoplanets from their host star. This enables direct characterization of the exoplanets atmosphere, but most direct imaging instruments do not have spectrographs with high enough resolving power for detailed atmospheric characterization. We investigate the use of a single-mode diffraction-limited integral-field unit that is compact and easy to integrate into current and future direct imaging instruments for exoplanet characterization. This achieved by making use of recent progress in photonic manufacturing to create a single-mode fiber-fed image reformatter. The fiber link is created with three-dimensional printed lenses on top of a single-mode multicore fiber that feeds an ultrafast laser inscribed photonic chip that reformats the fiber into a pseudoslit. We then couple it to a first-order spectrograph with a triple stacked volume phase holographic grating for a high efficiency over a large bandwidth. The prototype system has had a successful first-light observing run at the 4.2-m William Herschel Telescope. The measured on-sky resolving power is between 2500 and 3000, depending on the wavelength. With our observations, we show that single-mode integral-field spectroscopy is a viable option for current and future exoplanet imaging instruments.

We have published the optical design and early test results of the Roman Space Telescope grism spectrometer in previous SPIE proceedings. We report the follow-on activity of the spectral and radiometric calibrations, including the calibration methods, experiment designs, and test equipment calibration, such as the light source and detectors used in the test. The grism calibration includes the throughput versus wavelength, which is largely determined by the diffraction efficiency of the two diffractive surfaces. It also includes spectral resolution, point spread function, and relative radiometric measurements. The measured results are presented. The comparisons between the test data and the theoretical simulations are also presented. The tests and results presented are from the engineering test unit in ambient room temperature environment. The thermal/vacuum tests are planned to verify the results when the flight unit is ready.

The Nancy Grace Roman Space Telescope (Roman) formerly known as the Wide-Field Infrared Survey Telescope will answer fundamental questions about the evolution of dark energy over time and expand the catalog of known exoplanets into new regions of parameter space. Using a Hubble-sized mirror and 18 newly developed HgCdTe 4K  ×  4K photodiode arrays (H4RG-10), the Roman Space Telescope will measure the positions and shapes of hundreds of millions of galaxies, the light curves of thousands of supernovae, and the microlensing signals of over a thousand exoplanets toward the bulge of the Galaxy. These measurements require unprecedented sensitivity and characterization of the Wide Field Instrument, particularly its detectors. The Roman project undertook an extensive detector development program to create focal plane arrays that meet these science requirements. These prototype detectors have been characterized and their performance demonstrated in a relevant space-like environment (thermal vacuum, vibration, acoustic, and radiation testing), advancing the H4RG-10’s technology readiness level (TRL) to TRL-6. We present the performance characteristics of these TRL-6 demonstration devices.

In our Ultra-Fast Astronomy (UFA) program, we aim to improve measurements of variability of astronomical targets on millisecond and shorter time scales. In this work, we present initial on-sky measurements of the performance of silicon photomultiplier detectors (SiPMs) for UFA. We mounted two different SiPMs at the focal plane of the 0.7-m aperture Nazarbayev University Transient Telescope at the Assy-Turgen Astrophysical Observatory, with no filter in front of the detector. The 3  mm  ×  3  mm SiPM single-channel detectors have a field of view of 2.2716^′  ×  2.2716^′. During the nights of October 28–29, 2019, we measured sky background, bright stars, and an artificial source with a 100-Hz flashing frequency. We compared detected SiPM counts with Gaia satellite G-band flux values to show that our SiPMs have a linear response. With our two SiPMs (models S14520-3050VS and S14160-3050HS), we measured a dark current of ∼130 and ∼85 kilo counts per second (kcps), and a sky background of ∼201 and ∼203  kcps, respectively. We measured an intrinsic crosstalk of 10.34% and 10.52% and derived a 5σ sensitivity of 13.9 and 14 Gaia G-band magnitude for 200-ms exposures, for the two detectors, respectively. For a 10-μs window, and allowing a false alarm rate of once per 100 nights, we derived a sensitivity of 22 detected photons, or six Gaia G-band magnitudes. For nanosecond timescales, our detection is limited by crosstalk to 12 detected photons, which corresponds to a fluence of ∼155 photons per square meter.

Understanding and reducing in-orbit instrumental backgrounds are essential to achieving high sensitivity in hard x-ray astronomical observations. The observational data of the Hard X-ray Imager (HXI) onboard the Hitomi satellite provide useful information on the background components due to its multilayer configuration with different atomic numbers: the HXI consists of a stack of four layers of Si (Z  =  14) detectors and one layer of cadmium telluride (CdTe) (Z  =  48, 52) detector surrounded by well-type Bi₄Ge₃O₁₂ active shields. Based on the observational data, the backgrounds of the top Si layer, the three underlying Si layers, and the CdTe layer are inferred to be dominated by different components, namely, low-energy electrons, albedo neutrons, and proton-induced radioactivation, respectively. Monte Carlo simulations of the in-orbit background of the HXI reproduce the observed background spectrum of each layer well, thereby quantitatively verifying the above hypothesis. In addition, we suggest the inclusion of an electron shield to reduce the background.

Recently, complementary metal–oxide–semiconductor (CMOS) sensors have progressed to a point where they may offer improved performance in imaging x-ray detection compared to the charge-coupled devices often used in x-ray satellites. We demonstrate x-ray detection in the soft x-ray band (250 to 1700 eV) by a commercially available back-illuminated Sony IMX290LLR CMOS sensor using the Advanced Photon Source at Argonne National Laboratory. While operating the device at room temperature, we measure energy resolutions (full width at half maximum) of 48 eV at 250 eV and of 83 eV at 1700 eV, which are comparable to the performance of the “Chandra” ACIS and the “Suzaku” XIS. Furthermore, we demonstrate that the IMX290LLR can withstand radiation up to 17.1 krad, making it suitable for use on spacecraft in low Earth orbit.

Multiobject spectroscopy is applied in numerous modern astronomical facilities conducting observations of a large number of targets per pointing. Assigning the maximum number of targets to these instruments requires efficient algorithms. We present a simple and effective algorithm, the averaging (Aver) algorithm, to maximize the number of assigned targets for the first few visits of a given field. In comparison to the draining (Dra) algorithm, our algorithm increases the target completeness by 1% to 2% by employing Poisson distributed and real catalogs from the Large Sky Area Multiobject Fiber Spectroscopic Telescope survey. Moreover, our algorithm performs ∼375 times faster than the conventionally applied simulated annealing algorithm and yields a slightly higher completeness. We further optimize the Aver and Dra algorithms by combining the genetic algorithm (GA) and the differential evolution method. The Aver is slightly optimized by this method, whereas the Dra algorithm is improved by 0.9% to 1.6%, suggesting that our proposed Aver algorithm approaches maximum completeness. Furthermore, we find that the GA can optimize the rotation angle with a specially designed fitness function in the case of focal-plane rotation that is expected to be realized in the future, achieving a 1.8% increase in the number of the targets observed. In particular, our Aver algorithm assigns the maximum number of targets within the first few visits.

HERMES is a scientific mission composed of 3U nanosatellites dedicated to the detection and localization of high-energy astrophysical transients, with a distributed space architecture to form a constellation in Earth orbits. The space segment hosts novel miniaturized detectors to probe the x-ray temporal emission of bright events, such as gamma-ray bursts, and the electromagnetic counterparts of gravitational wave events, playing a crucial role in future multimessenger astrophysics. During operations, at least three instruments separated by a minimum distance shall observe a common area of the sky to perform a triangulation of the observed event. An effective detection by the nanosatellite payload is achieved by guaranteeing a beneficial orbital and pointing configuration of the constellation. The design has to cope with the limitations imposed by small space systems, such as the lack of on-board propulsion and the reduced systems budgets. We describe the methodologies and the proposed strategies to overcome the mission limitations, while achieving a satisfactory constellation visibility of the sky throughout the mission duration. The mission design makes use of a high-fidelity orbit propagator, combined with an innovative mission analysis tool that estimates the scientific performances of the constellation. The influence of the natural relative motion, which is crucial to achieve an effective constellation configuration without on-board orbit control, is assessed. The presented methodology can be easily extended to any kind of distributed scientific space applications, as well as to constellations dedicated to Earth and planetary observation. In addition, the visibility tool is applicable in the context of the constellation flight dynamics operations, yielding optimized results and pointing plans based on actual satellite orbital positions.

The NASA/ASI imaging x-ray polarimetry explorer, which will be launched in 2021, will be the first instrument to perform spatially resolved x-ray polarimetry on several astronomical sources in the 2- to 8-keV energy band. These measurements are made possible owing to the use of a gas pixel detector (GPD) at the focus of three x-ray telescopes. The GPD allows simultaneous measurements of the interaction point, energy, arrival time, and polarization angle of detected x-ray photons. The increase in sensitivity, achieved 40 years ago, for imaging and spectroscopy with the Einstein satellite will thus be extended to x-ray polarimetry for the first time. The characteristics of gas multiplication detectors are subject to changes over time. Because the GPD is a novel instrument, it is particularly important to verify its performance and stability during its mission lifetime. For this purpose, the spacecraft hosts a filter and calibration set (FCS), which includes both polarized and unpolarized calibration sources for performing in-flight calibration of the instruments. We present the design of the flight models of the FCS and the first measurements obtained using silicon drift detectors and charge-coupled device cameras, as well as those obtained in thermal vacuum with the flight units of the GPD. We show that the calibration sources successfully assess and verify the functionality of the GPD and validate its scientific results in orbit; this improves our knowledge of the behavior of these detectors in x-ray polarimetry.

A bi-axial centralized butterfly flexure hinge for a fast steering mirror (FSM) was presented to adapt highly stabile accuracy of beam-pointing control performance in space laser communication. According to the requirements of two-dimensional reciprocating movements and high bandwidth provided for the FSM, the solid model of the bi-axial centralized butterfly flexure hinge was designed. By applying Castigliano’s displacement theorem, the numerical model was simplified and deduced. Furthermore, to quantify the numerical model, natural frequencies of the finite-element analysis (FEA) and experiments were carried out the results of which were compared with the analytic solutions. The experimental results show that the in-plane natural frequencies are 66.37 and 112.2 Hz, respectively. The comparison shows that the errors between numerical analytic and experimentation are 3.0% and 1.4%, respectively, and errors between FEA and experimentation are 1.7% and 2.4%, respectively. It is proven that the bi-axial centralized butterfly flexure hinge we built is an appropriate structure as a two-axis guide mechanism in two-dimensions for an FSM system with a large bandwidth of 225 Hz.

A frequent problem arising for deep space missions is the discrepancy between the amount of data desired to be transmitted to the ground and the available telemetry bandwidth. A part of these data consists of scientific observations, being complemented by calibration data to help remove instrumental effects. We present our solution for this discrepancy, implemented for the Polarimetric and Helioseismic Imager on-board the Solar Orbiter mission, the first solar spectropolarimeter in deep space. We implemented an on-board data reduction system that processes calibration data, applies them to the raw science observables, and derives science-ready physical parameters. This process reduces the raw data for a single measurement from 24 images to five, thus reducing the amount of downlinked data, and in addition, renders the transmission of the calibration data unnecessary. Both these on-board actions are completed autonomously.

The impact on an optical surface by a micrometeoroid gives rise to a specific type of stray light inherent only in the space optical instruments. This causes a double source of light scattering: the impact crater and the ejected contamination. We propose a method of stray light estimation and apply it to the case of the Laser Interferometer Space Antenna telescope. We estimate the backscattering fraction for nominal (4 years) and extended (10 years) mission durations.

Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) is the latest instrument installed at the European Southern Observatory (ESO)-Very Large Telescope (VLT) site in Chile. To fulfill its scientific requirements, ESPRESSO can operate both in 1-UT mode (using any of the four VLT unit telescopes) and in 4-UT mode. In 4-UT mode, the light of the four 8-m telescopes is combined in an incoherent focus to form a 16-m equivalent telescope, thus providing the largest collecting area ever at optical-NIR wavelengths. In ESPRESSO, dedicated front end units (FEUs) allow collection of the light coming from the telescope tunnels conveying it through fibers to the spectrograph. All the functionalities of the FEUs are managed by the instrument control electronics (ICE) and software. We aim to provide the detailed description of the realization of this ICE, based on Beckhoff programmable logic controllers. In particular, we show ESPRESSO ICE functions distribution, the motion control characteristics, and the main validation tests performed during the European and Chilean integration phase, which led to technical acceptance of ESPRESSO by ESO before its first light achieved at the end of 2017.

We investigate the design of an active support system for the thin primary mirror of a mid-sized telescope system used for optical satellite communication and space debris observation. To handle the complexity of this task, a general design methodology is proposed. The design for the axial and lateral support is separated into several subtasks to reduce the number of design variables in every design step. Due to the independence of mirror geometry and material, this methodology is also applicable to larger mirrors. Utilizing the proposed procedure, an active support for a 1-m meniscus mirror with 25 mm thickness and the requirement to achieve diffraction-limited optical performance is developed. The final system consists of 32 axial and 8 lateral actuators supporting the mirror with a maximal simulated RMS error of 8.8 nm and PV error of 48.0 nm when pointing to zenith. Simulations show that the obtained design ensures the required performance even under commonly occurring mirror deformations.

This erratum corrects the omission of authors and references from the paper as it was originally published.