Novel Four-Cell Lenticular Honeycomb Deployable Boom with Enhanced Stiffness

Composite thin-walled booms can easily be folded and self-deployed by releasing stored strain energy. Thus, such booms can be used to deploy antennas, solar sails, and optical telescopes. In the present work, a new four-cell lenticular honeycomb deployable (FLHD) boom is proposed, and the relevant parameters are optimized. Coiling dynamics analysis of the FLHD boom under a pure bending load is performed using nonlinear explicit dynamics analysis, and the coiling simulation is divided into three consecutive steps, namely, the flattening step, the holding step, and the hub coiling step. An optimal design method for the coiling of the FLHD boom is developed based on a back propagation neural network (BPNN). A full factorial design of the experimental method is applied to create 36 sample points, and surrogate models of the coiling peak moment (Mpeak) and maximum principal stress (Smax) are established using the BPNN. Fatigue cracks caused by stress concentration are avoided by setting Smax to a specific constraint and the wrapping Mpeak and mass of the FLHD boom as objectives. Non-dominated sorting genetic algorithm-II is used for optimization via ISIGHT software.

Ideals and ideologies

In response to Ling Xin’s news analysis article “Tibet seen as ideal stargazing spot” in which she reports that Chinese astronomer Licai Deng has found that Saishiteng Mountain in the Tibetan Plateau has ideal conditions for future gigantic optical telescopes.

LONG-TERM PHOTOMETRY WITH SKYNET ROBOTIC TELESCOPE NETWORK

In this paper, we describe the Skynet Robotic Telescope Network, a network of about 2 dozen small optical telescopes spanning four continents. For a prospective user of the network, we provide details on its operation and mention certain caveats potentially affecting observations taken under the control of Skynet software. The actual performance of the network is demonstrated by long-term observations of two blazars: OJ 49 and 3C 279. We show their photometric light curves acquired with a subset of Skynet telescopes in the 2018/19 observing seasons. Preliminary results of the analysis of the variability of these two targets are given, including the quantitative properties of light variations and the periods of possible Quasi Periodic Oscillations (QPOs) found in the seasonal light curves.

Compensation Techniques Aimed at Mitigating Vibrations in Optical Ground-Based Telescopes: A Systematic Review

The objective of this study was to evaluate the performance of the different systems and techniques aimed at suppressing vibrations on optical ground-based telescopes. We identified the studies by searching three electronic databases (Science Direct, IEEE library and Web of Science) from the year 2000 to December 2020. The studies were eligible if they proposed systems focused on mitigating the effects of vibrations in optical telescopes and brought performance data. A total of nine studies met our eligibility criteria. Current evidence confirms the feasibility of adaptative optics (AO) systems based on closed-loop control to mitigate vibrations, although variations and additions should be made depending on their nature and characteristics in order to improve the performance of the proposed techniques. This systematic review was conducted to provide a state-of-the-art of the methods and techniques that have been developed over the past two decades. The review also points out some issues that demand future research.

Axisymmetric Loading of a Plate on a Local Support in the Framework of the Rodionova-Titayev-Chernykh Theory

The problem of an axisymmetric bending of a plate with constant thickness under its own weight is considered. The plate has a circular support. The problem is solved in an axisymmetric statement using a nonclassical shell theory of Rodionova-Titaev-Chernykh (RTCh), which takes plate compression in thickness into account. The solution for this theory is obtained using Godunov's orthogonal sweep method. This solution is compared with the solution obtained using the general three-dimensional theory of elasticity, implemented in an open-source package Code_Aster using axisymmetric finite elements. The motivation for this study is the description of a stress-strain state of some variants of primary mirrors of large optical telescopes under the action of gravity. The obtained results characterizing the optical quality of the mirror surface are: the peak value (PV) and the root-mean square (RMS) of its displacement. A parametric study was carried out, i.e., the thickness of the plate and the half-width of the support were varied. The two methods were compared. It is shown that, as the plate thickness increases or the half-width of the support decreases, non-physical behaviour of the mirror surface takes place within the limits of the nonclassical theory of RTCh. A criterion of its applicability is therefore proposed.

Prevention of NEO hazard: the Russian approach

Russian Academy of Sciences (RAS) is actively working to solve the problem of preventing Near-Earth Object (NEO) hazard. The article provides the goals and objectives of preventing NEO hazard, as well as ways to achieve them. The described ways of achieving the goal are applied in RAS best. The current state and prospects of the Russian contribution to the prevention of NEO hazard are considered. Statistical data on the dynamics of observation of minor planets by Russian telescopes is presented. The structure of the NEO part of hazardous situations classifier developed by Keldysh Institute of Applied Mathematics (KIAM RAS) and structure of perspective National System Security of space activities in outer space are presented, including the system’s response to event classified as dangerous. The article is accompanied by illustrations of potentially hazardous objects in the sky, made by telescopes of the International Network of Optical Telescopes (ISON), coordinated by the KIAM RAS.