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Formation of Regular Satellites from Ancient Massive Rings in the Solar System
When a planetary tidal disk—like Saturn's rings—spreads beyond the Roche radius (inside which planetary tides prevent aggregation), satellites form and migrate away. Here, we show that most regular satellites in the solar system probably formed in this way. According to our analytical model, when the spreading is slow, a retinue of satellites appear with masses increasing with distance to the Roche radius, in excellent agreement with Saturn's, Uranus', and Neptune's satellite systems. This suggests that Uranus and Neptune used to have massive rings that disappeared to give birth to most of their regular satellites. When the spreading is fast, only one large satellite forms, as was the case for Pluto and Earth. This conceptually bridges the gap between terrestrial and giant planet systems.
Journal Article
Satellite : innovation in orbit
Right now, above our heads nearly imperceptible to us but hugely important to how we live are thousands of man-made objects that we have sent into space. Ubiquitous but mysterious, satellites are the technological infrastructure of our globally connected world, helping us do everything from orient ourselves on a map to watch our favorite television shows. Yet we rarely ever think about them. In this book, Doug Millard pays overdue tribute to the stoic existence of the satellite, tracing its simultaneous pathways through the cold silence of space and the noisy turbulence of the past century. How satellites ever came to be is, in itself, a remarkable story. Telling an astonishing history of engineering experimentation and ingenuity, Millard shows how the Cold War space race made the earliest satellites ones like Sputnik, Telstar, and Early Bird household names. He describes how they evolved into cultural signifiers that represented not only our scientific capabilities but our capacity for imagination, our ability to broaden the scope of our vision to the farthest reaches. From there he follows the proliferation of satellites in the second half of the twentieth century, examining their many different forms, how they evolved, all the things they do, what they have enabled, and how they have influenced our popular culture. Ultimately, Millard asks what we can still expect, what sort of space age the satellite has initiated that is yet to be fully realized. Published in association with the Science Museum, London, this beautifully illustrated book will appeal to any fan of space exploration and technology.
Book
An Integrity Monitoring Method for Navigation Satellites Based on Multi-Source Observation Links
The BeiDou-3 navigation satellite system (BDS-3) has officially provided positioning, navigation, and timing (PNT) services to global users since 31 July 2020. With the application of inter-satellite link technology, global integrity monitoring becomes possible. Nevertheless, the content of integrity monitoring is still limited by the communication capacity of inter-satellite links and the layout of ground monitoring stations. Low earth orbit (LEO) satellites have advantages in information-carrying rate and kinematic velocity and can be used as satellite-based monitoring stations for navigation satellites. Large numbers of LEO satellites can provide more monitoring data than ground monitoring stations and make it easier to obtain full-arc observation data. A new challenge of redundant data also arises. This study constructs multi-source observation links with satellite-to-ground, inter-satellite, and satellite-based observation data, proposes an integrity monitoring method with optimization of observation links, and verifies the performance of integrity monitoring with different observation links. The experimental results show four findings. (1) Based on the integrity status of BDS-3, the proposed system-level integrity mode can realize full-arc anomaly diagnosis in information and signals according to the observation conditions of the target satellite. Apart from basic navigation messages and satellite-based augmentation messages, autonomous messages and inter-satellite ranging data can be used to evaluate the state of the target satellite. (2) For a giant LEO constellation, only a small number of LEO satellites need to be selected to construct a minimum satellite-based observation unit that can realize multiple returns of navigation messages and reduce the redundancy of observation data. With the support of 12 and 30 LEO satellites, the minimum number of satellite-based observation links is 1 and 4, respectively, verifying that a small amount of LEO satellites could be used to construct a minimum satellite-based observation unit. (3) A small number of LEO satellites can effectively improve the observation geometry of the target satellite. An orbit determination observation unit, which consists of chosen satellite-to-ground and/or satellite-based observation links based on observation geometry, is proposed to carry out fast calculations of satellite orbit. If the orbit determination observation unit contains 6 satellite-to-ground monitoring links and 6/12/60 LEO satellites, the value of satellite position dilution of precision (SPDOP) is 38.37, 24.60, and 15.71, respectively, with a 92.95%, 95.49%, and 97.12% improvement than the results using 6 satellite-to-ground monitoring links only. (4) LEO satellites could not only expand the resolution of integrity parameters in real time but also augment the service accuracy of the navigation satellite system. As the number of LEO satellites increases, the area where UDRE parameters can be solved in real time is constantly expanding to a global area. The service accuracy is 0.93 m, 0.88 m, and 0.65 m, respectively, with augmentation of 6, 12, and 60 LEO satellites, which is an 8.9%, 13.7%, and 36.3% improvement compared with the results of regional service. LEO satellites have practical application values by improving the integrity monitoring of navigation satellites.
Journal Article
Moons of the solar system : from giant Ganymede to dainty Dactyl
This volume captures the complex world of planetary moons, which are more diverse than Earth's sole satellite might lead you to believe. New missions continue to find more of these planetary satellites, making an up-to-date guide more necessary than ever.
Book