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Large satellite constellations in low-Earth orbit seek to be the infrastructure for global broadband Internet and other telecommunication needs. We briefly review the impacts of satellite constellations on astronomy and show that the Internet service offered by these satellites will primarily target populations where it is unaffordable, not needed, or both. The harm done by tens to hundreds of thousands of low-Earth orbit satellites to astronomy, stargazers worldwide, and the environment is not acceptable.
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In this work we apply generalized A. Sparavigna method (use of freely available softwares (programs), e.g. http://www.sollumis.com/, http://suncalc.net/#/44.557,22.0265,13/2014.12.29/09:22, http://universimmedia.pagesperso-orange.fr/geo/loc.htm, http://www.spectralcalc.com/solar_calculator/solar_position.php and http://www.fourmilab.ch/cgi-bin/Yourhorizon) for analysis of possible astronomical characteristics of three remarkable Giza, i.e. Cheops, Chephren and Mikerin pyramids. Concretely, we use mentioned programs for determination of the Giza plateau longitude and latitude, moments of the sunrise and sunset for any day at the Giza plateau, and, simulation of the sky horizon above Giza plateau in any moment of any day, respectively. In this way we obtain a series of the figures which unambiguously imply the following original results. Any of three remarkable Giza pyramids (Cheops, Chephren and Mikerin) holds only one characteristic edge between apex and north-west vertex of the base so that sunrise direction overlap almost exactly this edge during 28. October. (There is a small declination of the overlap date by Chephren pyramid by which overlap date is approximately 23. or 24. October.) Simultaneously, in the sunset moment for the same day, Taurus constellation (corresponding to holly bull in ancient Egypt mythology) appears at a point at the very eastern boundary of the sky horizon.
In this paper we use a variation of simulated annealing algorithm for optimizing two-dimensional constellations with 32 signals. The main objective is to maximize the symmetric pragmatic capacity under the peak-power constraint. The method allows the joint optimization of constellation and binary labeling. We also investigate the performance of the optimized constellation over nonlinear satellite channel under additive white Gaussian noise. We consider the performance over systems with and without pre-distorters. In both cases the optimized constellations perform considerably better than the conventional Amplitude Phase Shift Keying (APSK) modulations, used in the current digital video broadcasting standard (DVB-S2) on satellite channels. Based on our optimized constellations, we also propose a new labeling for the 4+12+16-APSK constellation of the DVB-S2 standard which is Gray over all rings.
We argue that light sails that are rapidly accelerated to relativistic velocities by lasers must be significantly curved in order to reduce their mechanical stresses and avoid tears. Using an integrated opto-thermo-mechanical model, we show that the diameter and radius of curvature of a circular light sail should be comparable in magnitude, both on the order of a few meters in optimal designs for gram-scale payloads. Moreover, when sufficient laser power is available, a sails acceleration length decreases and its chip payload capacity increases as its curvature increases. Our findings provide guidance for emerging light sail design programs, which herald a new era of interstellar space exploration.
Millisecond pulsars (MSPs) have a great potential to set standards in timekeeping, positioning and metadata communication.
Parabolic flights provide cost-effective, time-limited access to weightless or reduced gravity conditions experienced in space or on planetary surfaces, e.g. the Moon or Mars. These flights facilitate fundamental research - from materials science to space biology - and testing/validation activities that support and complement infrequent and costly access to space. While parabolic flights have been conducted for decades, reference acceleration profiles and processing methods are not widely available - yet are critical for assessing the results of these activities. Here we present a method for collecting, analyzing, and classifying the altered gravity environments experienced during a parabolic flight. We validated this method using a commercially available accelerometer during a Boeing 727-200F flight with $20$ parabolas. All data and analysis code are freely available. Our solution can be easily integrated with a variety of experimental designs, does not depend upon accelerometer orientation, and allows for unsupervised and repeatable classification of all phases of flight, providing a consistent and open-source approach to quantifying gravito-intertial accelerations (GIA), or $g$ levels. As academic, governmental, and commercial use of space increases, data availability and validated processing methods will enable better planning, execution, and analysis of parabolic flight experiments, and thus, facilitate future space activities.
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