TY - JOUR A1 - Roelofs, Freek A1 - Blackburn, Lindy A1 - Lindahl, Greg A1 - Doeleman, Sheperd S. A1 - Johnson, Michael D. A1 - Arras, Philipp A1 - Chatterjee, Koushik A1 - Emami, Razieh A1 - Fromm, Christian A1 - Fuentes, Antonio A1 - Knollmüller, Jakob A1 - Kosogorov, Nikita A1 - Müller, Hendrik A1 - Patel, Nimesh A1 - Raymond, Alexander A1 - Tiede, Paul A1 - Traianou, Efthalia A1 - Vega, Justin T1 - The ngEHT analysis challenges JF - Galaxies N2 - The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the Event Horizon Telescope (EHT) array, with ∼10 new antennas and instrumental upgrades of existing antennas. The increased uv-coverage, sensitivity, and frequency coverage allow a wide range of new science opportunities to be explored. The ngEHT Analysis Challenges have been launched to inform the development of the ngEHT array design, science objectives, and analysis pathways. For each challenge, synthetic EHT and ngEHT datasets are generated from theoretical source models and released to the challenge participants, who analyze the datasets using image reconstruction and other methods. The submitted analysis results are evaluated with quantitative metrics. In this work, we report on the first two ngEHT Analysis Challenges. These have focused on static and dynamical models of M87* and Sgr A* and shown that high-quality movies of the extended jet structure of M87* and near-horizon hourly timescale variability of Sgr A* can be reconstructed by the reference ngEHT array in realistic observing conditions using current analysis algorithms. We identify areas where there is still room for improvement of these algorithms and analysis strategies. Other science cases and arrays will be explored in future challenges. KW - very long baseline interferometry KW - black holes KW - active galactic nuclei KW - radio astronomy KW - imaging KW - instrument design KW - telescopes KW - algorithms KW - data analysis Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-304976 SN - 2075-4434 VL - 11 IS - 1 ER - TY - JOUR A1 - Wang, Xiaoliang A1 - Liu, Xuan A1 - Xiao, Yun A1 - Mao, Yue A1 - Wang, Nan A1 - Wang, Wei A1 - Wu, Shufan A1 - Song, Xiaoyong A1 - Wang, Dengfeng A1 - Zhong, Xingwang A1 - Zhu, Zhu A1 - Schilling, Klaus A1 - Damaren, Christopher T1 - On-orbit verification of RL-based APC calibrations for micrometre level microwave ranging system JF - Mathematics N2 - Micrometre level ranging accuracy between satellites on-orbit relies on the high-precision calibration of the antenna phase center (APC), which is accomplished through properly designed calibration maneuvers batch estimation algorithms currently. However, the unmodeled perturbations of the space dynamic and sensor-induced uncertainty complicated the situation in reality; ranging accuracy especially deteriorated outside the antenna main-lobe when maneuvers performed. This paper proposes an on-orbit APC calibration method that uses a reinforcement learning (RL) process, aiming to provide the high accuracy ranging datum for onboard instruments with micrometre level. The RL process used here is an improved Temporal Difference advantage actor critic algorithm (TDAAC), which mainly focuses on two neural networks (NN) for critic and actor function. The output of the TDAAC algorithm will autonomously balance the APC calibration maneuvers amplitude and APC-observed sensitivity with an object of maximal APC estimation accuracy. The RL-based APC calibration method proposed here is fully tested in software and on-ground experiments, with an APC calibration accuracy of less than 2 mrad, and the on-orbit maneuver data from 11–12 April 2022, which achieved 1–1.5 mrad calibration accuracy after RL training. The proposed RL-based APC algorithm may extend to prove mass calibration scenes with actions feedback to attitude determination and control system (ADCS), showing flexibility of spacecraft payload applications in the future. KW - reinforcement learning KW - antenna phase center calibration KW - K band ranging (KBR) KW - micrometre level microwave ranging KW - MSC: 49M37 KW - MSC: 65K05 KW - MSC: 90C30 KW - MSC: 90C40 Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-303970 SN - 2227-7390 VL - 11 IS - 4 ER - TY - JOUR A1 - Renaut, Léo A1 - Frei, Heike A1 - Nüchter, Andreas T1 - Lidar pose tracking of a tumbling spacecraft using the smoothed normal distribution transform JF - Remote Sensing N2 - Lidar sensors enable precise pose estimation of an uncooperative spacecraft in close range. In this context, the iterative closest point (ICP) is usually employed as a tracking method. However, when the size of the point clouds increases, the required computation time of the ICP can become a limiting factor. The normal distribution transform (NDT) is an alternative algorithm which can be more efficient than the ICP, but suffers from robustness issues. In addition, lidar sensors are also subject to motion blur effects when tracking a spacecraft tumbling with a high angular velocity, leading to a loss of precision in the relative pose estimation. This work introduces a smoothed formulation of the NDT to improve the algorithm’s robustness while maintaining its efficiency. Additionally, two strategies are investigated to mitigate the effects of motion blur. The first consists in un-distorting the point cloud, while the second is a continuous-time formulation of the NDT. Hardware-in-the-loop tests at the European Proximity Operations Simulator demonstrate the capability of the proposed methods to precisely track an uncooperative spacecraft under realistic conditions within tens of milliseconds, even when the spacecraft tumbles with a significant angular rate. KW - pose tracking KW - uncooperative space rendezvous KW - lidar KW - normal distribution transform Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-313738 SN - 2072-4292 VL - 15 IS - 9 ER - TY - JOUR A1 - Johnson, Michael D. A1 - Akiyama, Kazunori A1 - Blackburn, Lindy A1 - Bouman, Katherine L. A1 - Broderick, Avery E. A1 - Cardoso, Vitor A1 - Fender, Rob P. A1 - Fromm, Christian M. A1 - Galison, Peter A1 - Gómez, José L. A1 - Haggard, Daryl A1 - Lister, Matthew L. A1 - Lobanov, Andrei P. A1 - Markoff, Sera A1 - Narayan, Ramesh A1 - Natarajan, Priyamvada A1 - Nichols, Tiffany A1 - Pesce, Dominic W. A1 - Younsi, Ziri A1 - Chael, Andrew A1 - Chatterjee, Koushik A1 - Chaves, Ryan A1 - Doboszewski, Juliusz A1 - Dodson, Richard A1 - Doeleman, Sheperd S. A1 - Elder, Jamee A1 - Fitzpatrick, Garret A1 - Haworth, Kari A1 - Houston, Janice A1 - Issaoun, Sara A1 - Kovalev, Yuri Y. A1 - Levis, Aviad A1 - Lico, Rocco A1 - Marcoci, Alexandru A1 - Martens, Niels C. M. A1 - Nagar, Neil M. A1 - Oppenheimer, Aaron A1 - Palumbo, Daniel C. M. A1 - Ricarte, Angelo A1 - Rioja, María  J. A1 - Roelofs, Freek A1 - Thresher, Ann C. A1 - Tiede, Paul A1 - Weintroub, Jonathan A1 - Wielgus, Maciek T1 - Key science goals for the next-generation Event Horizon Telescope JF - Galaxies N2 - The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide. KW - black holes KW - general relativity KW - interferometry KW - accretion KW - relativistic jets KW - very-long-baseline interferometry KW - EHT KW - ngEHT Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-313525 SN - 2075-4434 VL - 11 IS - 3 ER - TY - JOUR A1 - Chatterjee, Koushik A1 - Chael, Andrew A1 - Tiede, Paul A1 - Mizuno, Yosuke A1 - Emami, Razieh A1 - Fromm, Christian A1 - Ricarte, Angelo A1 - Blackburn, Lindy A1 - Roelofs, Freek A1 - Johnson, Michael D. A1 - Doeleman, Sheperd S. A1 - Arras, Philipp A1 - Fuentes, Antonio A1 - Knollmüller, Jakob A1 - Kosogorov, Nikita A1 - Lindahl, Greg A1 - Müller, Hendrik A1 - Patel, Nimesh A1 - Raymond, Alexander A1 - Traianou, Efthalia A1 - Vega, Justin T1 - Accretion flow morphology in numerical simulations of black holes from the ngEHT model library: the impact of radiation physics JF - Galaxies N2 - In the past few years, the Event Horizon Telescope (EHT) has provided the first-ever event horizon-scale images of the supermassive black holes (BHs) M87* and Sagittarius A* (Sgr A*). The next-generation EHT project is an extension of the EHT array that promises larger angular resolution and higher sensitivity to the dim, extended flux around the central ring-like structure, possibly connecting the accretion flow and the jet. The ngEHT Analysis Challenges aim to understand the science extractability from synthetic images and movies to inform the ngEHT array design and analysis algorithm development. In this work, we compare the accretion flow structure and dynamics in numerical fluid simulations that specifically target M87* and Sgr A*, and were used to construct the source models in the challenge set. We consider (1) a steady-state axisymmetric radiatively inefficient accretion flow model with a time-dependent shearing hotspot, (2) two time-dependent single fluid general relativistic magnetohydrodynamic (GRMHD) simulations from the H-AMR code, (3) a two-temperature GRMHD simulation from the BHAC code, and (4) a two-temperature radiative GRMHD simulation from the KORAL code. We find that the different models exhibit remarkably similar temporal and spatial properties, except for the electron temperature, since radiative losses substantially cool down electrons near the BH and the jet sheath, signaling the importance of radiative cooling even for slowly accreting BHs such as M87*. We restrict ourselves to standard torus accretion flows, and leave larger explorations of alternate accretion models to future work. KW - black holes KW - general relativity KW - accretion KW - relativistic jets KW - very-long-baseline interferometry Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-304084 SN - 2075-4434 VL - 11 IS - 2 ER -