Results of comparing astronomical-geodetic and navigational-geodetic methods of determining the components of the deflection of vertical

The authors present the results of comparing the components of deflection of vertical obtained through astronomical-geodetic and navigational-geodetic methods. The first one is based on comparing astronomical and geodetic coordinates of a location. This method has recently been widely implemented in a digital zenith camera systems using a small-sized digital telescope with an astronomical camera based on CCD or CMOS technologies, a high-precision inclinometer and satellite navigation system receiver. In this case, the combination of a telescope, an astronomical camera and an inclinometer enables determining the local direction of the plumb line, expressed by astronomical coordinates, from observations of stars at the zenith and using high-precision star catalogs. The navigational-geodetic method is based on comparing the results of the normal heights’ increments, defined through geometric leveling, and geodetic heights, computed with the relative method of satellite coordinate determinations. For each method, random and systematic components of the error and its confidence bounds were calculated; the absolute values of the deflection of vertical components at two geographically separated points were compared.

Design and Experimental Research of a New Type of Asteroid Anchoring System

Asteroid detection is of great significance to the study of the formation of the solar system and the origin of life. However, there are many types of asteroids, and they are far away from the earth, and the understanding of their various characteristics is not clear, which brings huge technical challenges to the landing and attachment of star catalogs. At present, the world is mainly based on surround, overflight, and short-term contact detection, and long-term attachment detection has not yet been realized. In order to solve the long-term attachment detection requirements of asteroids, focusing on the geological characteristics of various types of stars, this paper proposes a new type of asteroid attachment mechanism based on the beetle bionic theory, which can realize intelligent and flexible attachment and has strong adaptability. Around this design, this paper analyzes the mechanism of adhesion and realizes the adaptive matching of unascertained terrain landing point adhesion. On this basis, a prototype of the asteroid landing attachment mechanism was developed and verified by experiments. The experiment proved that the mechanism has strong multiterrain matching ability and can obtain an adhesion force of not less than 36 N on ordinary concrete ground.

The mystery of Copernicus’ star catalogue (Part III)

The author of “The Catalog of Zodiac signs and stars” published in De Revolutionibus, was Ptolemy. Copernicus used this catalog and all available observations of the Sun, Moon and planets, for improvement of the theory and tables of their motions. E. P. Fedorov wants to support with the authoritative opinion of Copernicus the idea of replacing the main optic reference frame to radio system JCRF. Having mastered the experience of previous generations Copernicus knew that the principles of establishing coordinate systems do not change along with opinions on the structure of the universe. Had the places of stars in catalogs not been dependent on the location of the Sun, Copernicus would have had no opportunity to prepare the time and coordinate systems required for solution of his problem. In his manuscript he preserved the idea the principles of compiling star catalogs, which were not included in the published edition along with excerpts from the originally conceived chapters. The words irrefutably prove that the idea of establishing the main reference system from VLBJ observations without the place of vernal equinox could not be supported by reference to Copernicus`s opinion.

New precise positions in 2013–2019 and a catalog of ground-based astrometric observations of 11 Neptunian satellites (1847–2019) based on Gaia-DR2

Context. Developing high-precision ephemerides for Neptunian satellites requires not only the continuation of observing campaigns but also the collection and improvement of existing observations. So far, no complete catalogs of observations of Neptunian satellites are available. Aims. We aim to provide new, precise positions, and to compile a catalog including all available ground-based astrometric observations of Neptunian satellites. The observations are tabulated in a single and consistent format and given in the same timescale, the Terrestrial Time (TT), and reference system, the International Celestial Reference System (ICRS), including necessary changes and corrections. Methods. New CCD observations of Triton and Nereid were made at Lijiang 2.4-m and Yaoan 0.8-m telescopes in 2013–2019, and then reduced based on Gaia-DR2. Furthermore, a catalog called OCNS2019 (Observational Catalog of Neptunian Satellites (2019 version)) was compiled, after recognizing and correcting errors and omissions. Furthermore, in addition to what was considered for the COSS08 catalog for eight main Saturnian satellites, all observed absolute and relative coordinates were converted to the ICRS with corrections for star catalog biases with respect to Gaia-DR2. New debiasing tables for both the modern and old star catalogs, which were previously not provided based on Gaia-DR2, are developed and applied. Treatment of missing positions of comparison bodies in conversions of observed relative coordinates are proposed. Results. OCNS2019 and the new debiasing tables are publicly available online. OCNS2019 includes 24996 observed coordinates of 11 Neptunian satellites obtained over 3741 nights from 1847 to 2019. All observations are given in TT and ICRS. The star catalog biases are removed, which are significant for Nereid and outer satellites. We obtained 880 (5% of total now available) new coordinates for Triton over 41 nights (1% of total observation nights so far), and 790 (14%) for Nereid over 47 nights (10%). The dispersions of these new positions are about 0.″03 for Triton and 0.″06 for Nereid. Conclusions. OCNS2019 should be useful in improving ephemerides for the above-mentioned objects.

Guide Star Selection for the Three-FOV Daytime Star Sensor

To realize the application of the star sensor in the all-day carrier platform, a three-field-of-view (three-FOV) star sensor in short-wave infrared (SWIR) band is considered. This new prototype employs new techniques that can improve the detection capability of the star sensor, when the huge size of star identification feature database becomes a big obstacle. Hence, a way to thin the guide star catalog for three-FOV daytime star sensor is studied. Firstly, an introduction of three-FOV star sensor and an example of three-FOV daytime star sensor with narrow FOV are presented. According to this model and the requirement of triangular star identification method, two constraints based on the number and the brightness of the stars in FOV are put forward for guide star selection. Then on the basis of these constraints, the improved spherical spiral method (ISSM) is proposed and the optimal number of reference points of ISSM is discussed. Finally, to demonstrate the performance of the ISSM, guide star catalogs are generated by ISSM, magnitude filter method (MFM), 1st order self-organizing guide star selection method (1st-SOPM) and the spherical spiral method (SSM), respectively. The results show that the guide star catalog generated by ISSM has the smallest size and the number and brightness characteristics of its guide stars are better than the other methods. ISSM is effective for the guide star selection in the three-FOV daytime star sensor.

Design Improvement and Structural Analysis of a Carbon Fiber Reinforced Polymer Star Sensor "Baffle".

For any space mission to be successful it is necessary to guide the satellite to revolve in the right orbit and gather all the required data without any flaws. Among the many spacecraft subsystems contributing in this regard, Star sensors are the attitude estimation sensors installed in the satellites in order to determine the exact location of the satellite. It helps to bring back the satellite to the required position if there is any deviation from its path. Star sensor captures the image of any of the predetermined reference star. This image is compared with that of the image of the same star captured from the Earth. By this comparison and with the help of star catalogs, digitizers and microprocessors, the attitude and inclination of the satellite is determined.

Mathematical Problems in Creating Large Astronomical Catalogs

The next stage after performing observations and their primary reduction is to transform the set of observations into a catalog. To this end, objects that are irrelevant to the catalog should be excluded from observations and gross errors should be discarded. To transform such a prepared data set into a high-precision catalog, we need to identify and correct systematic errors. Therefore, each object of the survey should be observed several, preferably many, times. The problem formally reduces to solving an overdetermined set of equations. However, in the case of catalogs this system of equations has a very specific form: it is extremely sparse, and its sparseness increases rapidly with the number of objects in the catalog. Such equation systems require special methods for storing data on disks and in RAM, and for the choice of the techniques for their solving. Another specific feature of such systems is their high “stiffiness”, which also increases with the volume of a catalog. Special stable mathematical methods should be used in order not to lose precision when solving such systems of equations. We illustrate the problem by the example of photometric star catalogs, although similar problems arise in the case of positional, radial-velocity, and parallax catalogs.