We assess how propulsion and operational constraints affect exo-Earth characterization with a starshade rendezvous mission for a Habitable Worlds Observatory (HWO)-like telescope at Sun-Earth L2. Using end-to-end Monte Carlo simulations with EXOSIMS, we model a 60 m starshade for visible-band spectroscopy (500-1000 nm) and a 35 m starshade for near-ultraviolet characterization (250-550 nm). For the 60 m design, we compare AEPS Hall, NEXT ion, and Starlink-class Hall thrusters and examine sensitivity to propellant capacity, the fraction of each retargeting slew spent accelerating and decelerating, and on-orbit refueling. With 1000-3000 kg of initial propellant and no refueling, NEXT provides the highest characterization yield: 9-13
High-precision optical telescopes used for astronomical observation and low-Earth-orbit (LEO) object tracking require control systems capable of achieving accurate tracking, rapid disturbance rejection, and robust performance under complex conditions. To address these challenges, this paper presents an observer-based robust preview control scheme for a discrete-time uncertain linear parameter-varying (LPV) system subjected to disturbance and noise. The method integrates a robust state and disturbance observer with an H∞-optimized robust preview controller, achieving disturbance-rejection performance and enhancing tracking accuracy while maintaining robust stability. The simulation experiment, conducted using the system parameters and characteristics of a 2 m-class optical telescope, compares the proposed method with PID, active disturbance rejection control (ADRC), and a modified dynamic output feedback control. The results demonstrate that the proposed method achieves better tracking performance and robustness under complex conditions.
This paper presents a detailed study of the fundamental noise properties of silicon-based charge-coupled devices (CCDs). The focus of this work is on understanding the dependence of dark current on detector temperature, substrate voltage, and ambient environment temperature in which the detector is operated. We utilize a previously reported electron-multiplying CCD (EMCCD) detector test setup, designed to control detector temperature in a light-tight environment precisely. The setup can simulate different ambient temperatures with a temperature-controlled shroud. Using this highly automated setup, we have collected dark images in photon counting mode for a range of detector temperatures (163 to 183 K) and ambient temperatures (230, 273, and 298 K) at different substrate voltages (0 to 4 V). For each combination of test parameters, we have accumulated dark and bias images with progressively increasing exposure time. This dataset is reduced using a new EMCCD data reduction pipeline designed to remove cosmic rays and cosmic ray tails—charge spilled to trailing pixels, apply thresholding for photon counting, and estimate dark rate and clock-induced charge. The pipeline is designed to reduce large datasets by scaling seamlessly from a single machine to multiple nodes on a high performance computer. An interactive browser tool is used for initial optimization with a selection of images. We found that the measured dark rate decreases with ambient temperature. The dark rate is highest when the detector is operated without a shroud, with the ambient temperature of the vacuum enclosure walls, at ∼298 K. In this configuration, the dark rate drops to a plateau for detector temperatures below 173 K. The dark rate drops when the shroud is installed and is cooled passively by radiative coupling with the detector cooling chain. Cooling the shroud actively to 230 K reduces the dark rate slightly. Based on the simulation and measured results, we found that at low detector temperature, the thermal emission from the shroud dominates over the intrinsic dark rate of the detector. This is in agreement with the inverted-mode surface dark current model for this detector; however, the dark rate still plateaus around 170 K, although at a lower level, indicating a non-thermal limit that needs further investigation.
In 2018, China proposed the Multiple spacecraft Exoplanet Aperture sYnthetic INterferometer (MEAYIN) project to explore habitable planets near other solar systems. We have established a Dual-mode Variable-array Imaging Interferometer Testbed (DVIIT) in the laboratory to develop some key technologies for the MEAYIN. The precise measurement method of the entrance pupil baselines for each sub-aperture is one of the key technologies to be developed. A measurement method of entrance pupil baselines based on dual-comb femtosecond laser absolute ranging technology has been proposed. It uses independently developed ranging optical ruler and a reference aperture to measure the distance from the system optical axis of the DVIIT to each sub-aperture. Measure the motion errors of each sub-aperture and then correct the distance based on the measurement results to obtain more accurate entrance pupil baselines. Theoretical analysis and test result indicated that the method can achieve micrometer level measurement accuracy for the entrance pupil baselines of the DVIIT. In addition, the method has the feasibility of being extended to the MEAYIN project with longer baselines.
We present the design, implementation, and initial performance of the ultraviolet-visible (UV-VIS) arm of the Son Of X-Shooter (SOXS) spectrograph, developed for medium-resolution time-domain spectroscopy on the ESO 3.6 m New Technology Telescope. SOXS is a dual-arm spectrograph optimized for rapid spectroscopic follow-up of faint and evolving transient sources. The UV-VIS arm covers the wavelength range 350 to 850 nm at a resolving power of R∼4500 for a 1-arcsec slit. It employs a multi-band first-order dispersion concept in which the optical bandpass is divided into four spectral intervals and dispersed by dedicated high-efficiency gratings, with all spectra recorded simultaneously on a single charge-coupled device (CCD) detector. This architecture enables broad wavelength coverage with high throughput and operational simplicity. We describe the optical and mechanical design of the UV-VIS spectrograph; summarize the assembly, integration, and testing campaign carried out across multiple sites; and present initial laboratory and on-sky performance, including image quality, resolving power, throughput, and flexure characterization. We also discuss practical lessons learned during integration, particularly alignment strategies and distributed collaboration. The experience gained during the development and commissioning of SOXS provides guidance for future medium-resolution spectrograph projects designed, among others, for time-domain astronomy.
