Russian, US, Chinese hypersonic arms lack treaty curbs

Significance Russia and China have several hypersonic weapons in service or near readiness. This class of weapon is raising concerns in the conventional and strategic realms, where security tensions are already high. A Chinese weapon tested this year created new concerns by reportedly spending time in near-earth orbit. Impacts Governments will review the survivability of their nuclear forces as a hypersonic arms race develops. The reported Chinese test of an orbital system will increased US call to bring hypersonic technologies into arms control discussions. Chinese advances will spur Washington and some of its regional allies to develop defensive and offensive options to counter such systems.

An Improved Equivalent Squint Range Model and Imaging Approach for Sliding Spotlight SAR Based on Highly Elliptical Orbit

As an emerging orbital system with flexibility and brand application prospects, the highly elliptical orbit synthetic aperture radar (HEO SAR) can achieve both a low orbit detailed survey and continuous earth surface observation in high orbit, which could be applied to marine reconnaissance and surveillance. However, due to its large eccentricity, two challenges have been faced in the signal processing of HEO SAR at present. The first challenge is that the traditional equivalent squint range model (ESRM) fails to accurately describe the entire range for the whole orbit period including the perigee, the apogee, and the squint subduction section. The second one is to exploit an efficient HEO SAR imaging algorithm in the squinted case which solves the problem that traditional imaging algorithm fails to achieve the focused imaging processing of HEO SAR during the entire orbit period. In this paper, a novel imaging algorithm for HEO SAR is presented. Firstly, the signal model based on the geometric configuration of the large elliptical orbit is established and the Doppler parameter characteristics of SAR are analyzed. Secondly, due to the particularity of Doppler parameters variation in the whole period of HEO, the equivalent velocity and equivalent squint angle used in MESRM can no longer be applied, a refined fourth-order equivalent squint range model(R4-ESRM) that is suitable for HEO SAR is developed by introducing fourth-order Doppler parameter into Modified ESRM (MESRM), which accurately reconstructs the range history of HEO SAR. Finally, a novel imaging algorithm combining azimuth resampling and time-frequency domain hybrid correlation based on R4-ESRM is derived. Simulation is performed to demonstrate the feasibility and validity of the presented algorithm and range model, showing that it achieves the precise phase compensation and well focusing.

Bandgap tunability from synergistic mixture of Pandanus amaryllifolius and Curcuma longa as photo-absorber candidates

The application of natural plant-derived dyes to replace ruthenium-based material as photo-absorber in solar cells application, have been extensively studied. Several advantages such as low cost, abundant in supply, sustainability and environmentally-safe make natural materials as current favourite photo-absorber. Natural plant-derived dyes are known containing natural compounds (e.g. carotenoids, chlorophylls, anthocyanins) that have the characteristics of electronic delocalization in extended ?-orbital system involving in electronic transfer mechanism. To date, massive investigations were done to exploit this system to be used as a potential photo-absorber in solar cells. Due to this matter, the hybrid dyes from the mixture of Pandanus amaryllifolius (pandan, P) and Curcuma longa (turmeric, T) were successfully prepared and several physical characterizations were carried out to analyse the photo-absorber (sensitizer) properties. From the results obtained, the ratios of P:T was varied into 1:2, 1:4, 4:1, and 8:1. This ratio has changed the wavelength of absorbers that were slightly shifted and the indirect bandgap (Eg) also were significantly changed. With this new approach, the bandgap of the hybrid dyes as core point in modulating electrical conductivity of photo-absorber can be simply tuned. By implying two different extract dyes to form hybrid dyes, the bandgap was found decreased with higher ratio of T used. Overall results suggesting that by adjusting the ratio of hybrid dyes, the photo-absorber properties and the Eg values were differed and with slightly modification, better electrical conductivity can be expected for solar cells application.

Method for Estimating the Efficiency of Small Orbital Spacecraft Systems for Optoelectronic Surveillance

The paper presents the results of analysing existing approaches to estimating how efficient small orbital spacecraft systems are for the purpose of optoelectronic surveillance, including determining their shortcomings. We simulated employing an orbital system required to ensure surveying the earth surface at various latitudes, accounting for sunrise and sunset time on the winter and summer solstice days, and discovered that the following parameters show low sensitivity: average daily object sighting number at a preset latitude and maximum time delay between object sightings at a preset latitude. We propose a new efficiency factor reflecting a confidence interval regarding the object sighting time delay. We developed a procedure utilising the factor proposed, expanding the scientific methodology in terms of estimating how efficient small orbital spacecraft systems are for optoelectronic surveillance. We obtained object sighting time delays at a preset latitude as functions of the probability of these delays occurring. We recommend using this procedure to estimate the efficiency of jointly employing several small orbital spacecraft systems and incomplete composition systems, as well as to state and solve the problem of synthesising the ballistic structure of an orbital system intended to improve the efficiency of earth surveillance.

Analytical determination of motion parameters of the center of mass of an uncooperative orbiter on the basis of measurement information provided by on-board systems of a space robot in a coplanar orbit

An analytical solution to the problem of determining the parameters of motion of an orbiter’s center of mass is presented on the basis on the results of measurements carried out using the optical system of a space robot located in orbit coplanar to that of the orbiter. The “space robot-orbiter” line-of-sight angle and the line-of-sight rate in the moving orbital system of coordinates of the space robot are selected as initial parameters that are measured by the space robot’s on-board optical system. Along with the known orbital parameters of the space robot they are used to solve the problem of determining the parameters of motion of the orbiter’s center of mass. When solving this task, assumptions are introduced concerning the central gravitational field of the Earth, the coplanarity of the orbits of the space robot and of the orbiter, absence of influence of the atmosphere, the moon's attraction and the pressure of the solar wind on the motion of the space robot and of the orbiter, absence of errors in the results of measurements performed by the space robot’s on-board optics. Analytical expressions are obtained to determine the unknown parameters of motion of the orbiter’s center of mass. The results presented can be used to develop methods allowing standalone determination of parameters of the orbit of unknown orbiters using on-board optics of a space robot.

Co-orbital exoplanets from close-period candidates: the TOI-178 case

Despite the existence of co-orbital bodies in the solar system, and the prediction of the formation of co-orbital planets by planetary system formation models, no co-orbital exoplanets (also called trojans) have been detected thus far. Here we study the signature of co-orbital exoplanets in transit surveys when two planet candidates in the system orbit the star with similar periods. Such a pair of candidates could be discarded as false positives because they are not Hill-stable. However, horseshoe or long-libration-period tadpole co-orbital configurations can explain such period similarity. This degeneracy can be solved by considering the transit timing variations (TTVs) of each planet. We subsequently focus on the three-planet-candidate system TOI-178: the two outer candidates of that system have similar orbital periods and were found to have an angular separation close to π∕3 during the TESS observation of sector 2. Based on the announced orbits, the long-term stability of the system requires the two close-period planets to be co-orbital. Our independent detrending and transit search recover and slightly favour the three orbits close to a 3:2:2 resonant chain found by the TESS pipeline, although we cannot exclude an alias that would put the system close to a 4:3:2 configuration. We then analyse the co-orbital scenario in more detail, and show that despite the influence of an inner planet just outside the 2:3 MMR, this potential co-orbital system could be stable on a gigayear time-scale for a variety of planetary masses, either on a trojan or a horseshoe orbit. We predict that large TTVs should arise in such a configuration with a period of several hundred days. We then show how the mass of each planet can be retrieved from these TTVs.