CNSA WatcherCNSAWatcherRenderings of the Xuntian Telescope.
QuoteCNSA WatcherCNSAWatcherRenderings of the Xuntian Telescope. Source: https://m.weibo.cn/status/Q80zqkgbahttps://x.com/CNSAWatcher/status/1975477142948655562
Quote from: catdlr on 10/07/2025 10:02 amQuoteCNSA WatcherCNSAWatcherRenderings of the Xuntian Telescope. Source: https://m.weibo.cn/status/Q80zqkgbahttps://x.com/CNSAWatcher/status/1975477142948655562
Rapidly growing satellite constellations have raised strong concerns among the scientific community. Reflections from satellites can be visible to the unaided eye and extremely bright for professional telescopes. These trails already affect astronomical images across the complete electromagnetic spectrum, with a noticeable cost for operations and mitigation efforts. Contrary to popular perception, satellite trails affect not only ground-based observatories but also space observatories such as the Hubble Space Telescope5. However, the current number of satellites is only a fraction (less than 3%) of those to be launched in the next decade. Here we show a forecast of the satellite trail contamination levels for a series of international low-Earth-orbit telescopes on the basis of the proposed telecommunication industry constellations. Our results show that if these constellations are completed, one-third of the images of the Hubble Space Telescope will be contaminated, while the SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer), ARRAKIHS (Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys) and Xuntian space telescopes will have more than 96% of their exposures affected, with 5.6+/-0.3, 69+21-22 and 92+11-10 trails per exposure, respectively, with an average surface brightness of μ = 19 ± 2 mag arcsec−2. Our results demonstrate that light contamination is a growing threat for space telescope operations. We propose a series of actions to minimize the impact of satellite constellations, allowing researchers to predict, model and correct unwanted satellite light pollution from science observations
Xuntian has docking and maneuvering capabilties, and CASC has advanced OTV/Space tug capabiltiies as proven by Shijian 21/25, if it gets too critical for observations it should be possible to launch a space tug that will boost Xuntian to a slightly higher orbit (even 600 vs 400km makes a big difference according to this article) and only bring it back for the occasional Tiangong inspections/maintenance.Of course the budget for such an OTV must exist first.
Latest Progress of China's Space Telescope (CSST)A few days ago, the Chinese Academy of Sciences (CAS) released a report on the CSST main survey [http://t.cn/AXyYR8gF]. This 2.6-gigapixel "cosmic camera" has broken space astronomy records in terms of focal size. The presenter was our familiar researcher, Zhan Hu. Although the CSST's long-term "slow and steady progress" has been somewhat tiresome, this report still had some highlights. The first half of the report devoted a large portion to introducing the scientific objectives, but since I am not very familiar with them, and other popular science articles have already covered them in considerable detail, I will skip that part. Here, I will only briefly summarize the content regarding the development history and the latest engineering progress that everyone is most concerned about, including the specific details of some key components.Most of the information-rich PPT slides in the report are shown in screenshots (Figures 1 to 12). Some screenshots with the speaker's name are because the original video did not include a pure PPT slide. Also, due to the 18-image limit on Weibo, I have combined some related PPT slides.First, the key points: The main survey uses a mix of imported and domestically produced CCDs. The qualification certificate was delivered in November 2024. From February to May 2025, joint testing and commissioning with the optical system were completed at the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP). Extensive vacuum testing has been completed, and prototype development is currently underway.The following is a complete summary: The survey project began its feasibility study in 2010, leveraging the momentum of second-generation surveys driven by the international dark energy hotspot. Considering the limited aperture of the primary mirror and the lack of advantages in precision measurement, the focus was on surveying the sky, maximizing the field of view, making it the space survey project with the largest field of view.The survey camera is the most important scientific payload of CSST, utilizing 70% of the telescope's on-orbit time. The survey camera's feasibility study began in 2010, and in 2015, a joint team led by the National Astronomical Observatories (NAOC) and the Institute of Optics and Electronics (IOE), with participation from the Shanghai Institute of Technical Physics, Xi'an Institute of Optics and Precision Mechanics, and Nanjing Institute of Astronomical Optics and Physics, was selected to be responsible for its development.The most crucial component is the primary focal plane for the sky survey, boasting a scale of 2.6 billion pixels, making it the largest focal plane in space astronomy projects. Key challenges include achieving high sensitivity and low noise performance under stringent constraints related to weight, size, power consumption, and heat dissipation. To reduce dark current noise, it needs to operate at -85°C, and the required high cooling power presents a significant challenge to platform development. In terms of lifespan, it needs to operate for seven years within a ten-year platform design life, requiring 700,000 shutter openings and closings.Such high-performance devices already have mature products internationally, but none have been developed domestically. Considering the difficulties and risks of importing such devices, domestic technological breakthroughs were initiated. After seven years of research, the ultraviolet CCD sensor (9200*9200 pixels, 10-micron pixel size) developed by the 44th Research Institute of China Electronics Technology Group Corporation (CETC) meets the technical specifications and even surpasses imported products in several aspects (Figure 4 lists other advantageous indicators; the imported product is likely Teledyne e2V 290-99). For example, in terms of image uniformity, it lacks the interference stripes left by the back-illumination process found in imported products. In actual measurements using the 80cm telescope at the Xinglong Station of the National Astronomical Observatories, it also demonstrated performance comparable to imported products. Ultimately, CSST adopted a hybrid approach using both imported and domestically produced CCDs. Furthermore, Changguang Chenxin also successfully developed an ultraviolet CMOS sensor (9000*9200 pixels, 10 micrometers per pixel), which will be applied in several subsequent projects.The CSST team's main role in sensor development was establishing a detailed indicator system covering space astronomical observations and providing testing standards and feedback.To conduct various experiments, including vacuum, thermal, and mechanical tests, a qualification module needed to be produced first. The stitched focal plane qualification module consists of 30+1 CCD sensors, with a main imaging area size of 500mm*600mm and a flatness better than ±30 micrometers at operating temperature. Different sensor colors are optimized for different wavelengths, and it also includes a mechanical component without electrical properties (Figure 6, likely only for experimental purposes), scheduled for delivery in November 2024.To conduct low-temperature vacuum testing, the team independently developed cooling equipment and a low-temperature surface shape measurement instrument, verifying the flatness at operating temperature within a vacuum chamber. Many other examples of self-developed instruments were also developed during the development process.Currently, the focal plane, filters, and gratings have been assembled and integrated with the electrical box and other structures onto the camera body at the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP). Overall thermal balance, thermal vacuum, and thermal optical tests have been completed. Prior to testing, an abnormal increase in background noise (4.5 electrons → 6.3 electrons) was observed after integration. After three weeks of investigation, the cause of the radiated interference was identified as the antenna effect of the heating element behind the focal plane.In the thermal vacuum chamber, the prototype obtained its first dark-field image of the entire system—an image obtained through sensor integration in a completely dark environment—verifying that readout noise and dark current fully meet requirements. The image also shows analog signals from the mechanical elements and amplifier signals from the electrical elements, sensors not involved in the testing.From February to May of this year, the sky survey camera prototype completed joint debugging and testing with the optical system at the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) and has now entered the prototype development stage.Beyond the survey module, the CSST's precision measurement module includes four observation instruments: a terahertz instrument (for molecular spectral line surveying, Purple Mountain Observatory), a coronagraph (for direct imaging of exoplanets, Nanjing Institute of Astronomical Optics and Fine Mechanics), a dual-channel imager, and an integrating field-of-view spectrometer (for both three-color and spectroscopic observations, jointly developed by the Shanghai Institute of Technical Physics and the Shanghai Astronomical Observatory). The entire telescope system also includes a survey optics facility (Changchun Institute of Optics, Fine Mechanics and Physics), a precision image stabilization system (Shanghai Institute of Technical Physics), a ground application system (Space Application Center), a scientific data processing system (National Astronomical Observatories and Shanghai Astronomical Observatory), and a flight platform (China Academy of Space Technology).The optical system employs a unique off-axis three-mirror design. Through the degrees of freedom of the three mirrors, aberrations can be calibrated to a very high level, ensuring high image quality. Furthermore, the off-axis design avoids interference from the mirror support structure on imaging, eliminates starbursts caused by diffraction, and yields very circular image spots, which is highly advantageous for measuring galaxy shapes.The CSST is expected to launch within the next few years, becoming the only large-aperture space telescope in the world covering the ultraviolet to visible light band within the next decade. It will possess both survey and precision measurement capabilities, with a particularly strong ultraviolet band offering advantages in both field of view and depth, giving it significant scientific competitiveness.The following are some random thoughts, which may contain some controversial statements.Remember during the peak of the space station construction, discussions about the launch time of the survey telescope were frequent? Over the past few years, it seems everyone has become accustomed to the wait. But in reality, the sheer technological leap of the CSST fully justifies the wait. Before this, my country had virtually no presence in the field of large-aperture space optical telescopes. Extending this to ground-based telescopes, my country currently only has a few 2-meter diameter mirrors and its only truly competitive telescope internationally—LAMOST. Despite these fundamental limitations, CSST directly aims for world-class standards, joining the ranks of the three most advanced space survey telescopes of our time, alongside ESA's Euclid and NASA's Roman Nancy, shouldering the responsibility for space optical surveys around the 2030s. The three telescopes are both complementary and competitive. CSST emphasizes self-consistency, possessing the richest collection of scientific instruments and the widest coverage of wavelengths, the largest field of view and planned survey area, unique advantages in multicolor and spectral capabilities, and has already established preliminary collaborative teams with other companies. However, such a significant leap comes at a price. First, it has the longest delay among the three telescopes—although the initially announced launch date was unrealistic from the start. Second, there's the issue of mass; CSST's launch mass is eight times that of Euclid and twice that of Roman Nancy. The first step is always the hardest.This report also reveals some interesting changes, such as the rise of CMOS. CMOS has long since completely replaced CCD in the civilian sector, but in the field of high-end scientific sensors, it has always been the last bastion of CCD. In many key metrics, current CMOS still lags behind CCD. However, CMOS, with its rapid development and greater potential, has already begun to see applications in the scientific field, and its growth is still in its early stages, such as in time-domain astronomy. Even more encouraging is that the gap between my country and the world's most advanced CMOS technology is narrowing. In the development of the CSST, the 44th Research Institute of China Electronics Technology Group Corporation (CETC) spent seven years only catching up with the initial internationally available, mature off-the-shelf products; the gap in the infrared band is even more striking. While Chinese manufacturers are making significant strides in the civilian market, in the scientific field, companies like Changguang Chenxin have also secured a place, comparable to several established giants.Looking back, we now see another new problem with CSST: interference from low-Earth orbit constellations. When CSST was separated from the space station in 2014, and a plan to co-orbit with the space station was finalized for maintenance reasons, probably no one could have predicted that just over a decade later, the number of satellites in low Earth orbit would surge to such an extent. Starlink has already had a considerable impact on ground-based astronomical observations. And in the future, not only will Starlink's growth continue, but my country's StarNet and Qianfan constellations will also enter a period of intensive construction. To make matters worse, the CSST's orbital altitude is lower than the planned altitude of most low-Earth orbit constellations, making it one of the most severely affected by interference among key space optics projects worldwide. According to a simulation paper (Alejandro S. Borlaff et al., Satellite Megaconstellations Will Threaten Space-based Astronomy), with the current constellation of nearly 10,000 low-Earth orbit satellites, CSST is expected to have around 70% of its images contaminated, averaging two star orbits per image, affecting 0.04% of the field of view. If several more constellations are completed in the future, reaching 100,000 satellites, these figures will increase to over 90%, averaging nearly 20 star orbits per image, affecting more than 0.4% of the field of view. (Figure 13 shows the orbital altitude and density of several space telescopes and low-Earth orbit constellations; Figure 14 shows simulated interference imaging; Figure 15 shows the degree of interference as a function of the number of constellations.) Fortunately, we noticed this problem early on, and relevant units have conducted research and studies, using algorithms to minimize the impact. Another potentially feasible method is to share an orbital plane with the space station but increase the altitude; even reaching an altitude of 600km would significantly improve the situation, but this would place higher demands on the entire mission planning.Euclide has been operational for over two years now, and CSST and Roman Nancy are expected to launch in 2027, beginning their respective sky survey missions and further advancing our understanding of the universe. Beyond sky surveys, projects under the Space Science Pioneer Program Phase II and the Tianwen-1 project are increasingly targeting cutting-edge international fields, forging paths uncharted by predecessors. Looking back to Earth, a series of ground-based telescope projects, including the Lenghu project, have entered intensive construction or preparation phases.In a sense, these "spectacles," which do not directly serve social production, also embody the principle of "alignment of rights and responsibilities" at the national level. Just like the 18-piece gold-plated beryllium primary mirror on the James Webb Telescope, which hovers alone at the Sun-Earth L2 point, shining with the last rays of the Western "beacon of humanity." In the future, as the global balance of power shifts, my country will see an increasing number of such projects, and CSST will become the starting point of that glorious era.
