Space-based Navigation Research Articles

Study of Power Density Transmitted from Cellular Base Station Towers of Nepal Telecom in Biratnagar Sub-Metropolitan City

Background: In this present world, human beings are being exposed directly or indirectly to some kind of ionizing and non-ionizing radiations with the development of recent scientific technologies or by natural phenomena. The study of the measurement of power density (PD) or Radio Frequency (RF) radiated from cellular Base Station Towers (BSTs) is seemed to be important in Nepal like other countries because of its various health effects. In this study, the authors measured the PD radiated from mobile base station towers in Biratnagar sub-metropolitan city, Morang. Methods and Methodology: All together 18 BSTs were selected within Biratnagar for the study purpose. Tenmars TM-196 which is a non-ionizing radiation detector was used to measure the power density. The Global Positioning System (GPS), a space-based satellite navigation system was used to locate the Maximum Peak Point (MPP) from the BSTs. Result: The maximum power density (PD) was observed near Jogbani boarder i.e. 3781.0 µW/m2 which was 0.63% of the NTA guidelines. Similarly, the minimum power density was observed near Rani BRT i.e 1549.3 µW/m2which was 0.26% of the NTA guidelines. Conclusion: From the survey it can be concluded that there is no significant health hazard to the general people due to non-ionizing radiation radiated from Base Station Towers in Biratnagar. Int J Appl Sci Biotechnol, Vol 4(3): 338-345

Mercury Ion Clock for a NASA Technology Demonstration Mission.

There are many different atomic frequency standard technologies but only few meet the demanding performance, reliability, size, mass, and power constraints required for space operation. The Jet Propulsion Laboratory is developing a linear ion-trap-based mercury ion clock, referred to as DSAC (Deep-Space Atomic Clock) under NASA's Technology Demonstration Mission program. This clock is expected to provide a new capability with broad application to space-based navigation and science. A one-year flight demonstration is planned as a hosted payload following an early 2017 launch. This first-generation mercury ion clock for space demonstration has a volume, mass, and power of 17 L, 16kg, and 47W, respectively, with further reductions planned for follow-on applications. Clock performance with a signal-to-noise ratio (SNR)*Q limited stability of 1.5E-13/τ(1/2) has been observed and a fractional frequency stability of 2E-15 at one day measured (no drift removed). Such a space-based stability enables autonomous timekeeping of with a technology capable of even higher stability, if desired. To date, the demonstration clock has been successfully subjected to mechanical vibration testing at the 14 grms level, thermal-vacuum operation over a range of 42(°)C, and electromagnetic susceptibility tests.

Has GPS Made the Adequate Enforcement of Privacy Laws in the United States a Luxury of the Past?

In today’s society, nearly everyone uses a piece of technology that allows them to be tracked by a Global Navigation Satellite System and rarely do we even consider the ramifications of using these devices. When a person uses an iPhone to get directions via Google Maps they may not realize that while they are gaining information from the website, they are also allowing their movements to be tracked. It may seem like only a paranoid person would worry about being tracked when they are going from their house to work, but the fact that there has not been a line drawn between what tracking information the government may or may not use against you creates a serious problem. This paper argues that due to the increasing use and development of the Global Positioning System’s tracking abilities, the government must make it a priority to develop new privacy laws and clarifications. Because most of the privacy laws and amendments were created decades before Global Positioning System technologies existed, there is a clash between tracking and privacy that is difficult for the courts to decide without updated laws.This paper begins with an introduction of Global Navigation Satellite Systems and the Global Positioning System. The historical section of the paper gives an overview of the Soviet Union’s attack on Korean Air 007 and its importance on the future use of GPS by civilians. Next, this paper thoroughly explains the complex technologies involved in GPS tracking. The fourth section summarizes the three main parts of the United States Code that apply to GPS and the U.S. Space-Based Positioning, Navigation, and Timing Policy. Fifth, the paper discusses where privacy laws conflict with certain uses of GPS tracking, which leads into the in depth review of the leading case in this area, United States v. Jones (2013). Finally, this paper concludes with a summary of current, proposed legislation on this topic and suggestions for future legislation.

Ionospheric precursors to scintillation activity

<p>Ionospheric scintillation is the rapid fluctuation of both phase and amplitude of trans-ionospheric radio waves due to small scale electron density irregularities in the ionosphere. Prediction of the occurrence of scintillation at L band frequencies is needed to mitigate the disruption of space-based communication and navigation systems. The purpose of this paper is to present a method of using tomographic inversions of the ionospheric electron density obtained from ground-based GPS data to infer the location and strength of the post-sunset plasma drift vortex. This vortex is related to the pre-reversal enhancement in the eastwards electric field which has been correlated to the subsequent occurrence of scintillation.</p>

Total electron content of the ionosphere at two stations in East Africa during the 24–25 October 2011 geomagnetic storm

The equatorial ionosphere has been known to become highly disturbed and thus rendering space-based navigation unreliable during space weather events, such as geomagnetic storms. Modern navigation systems, such as the Global Positioning System (GPS) use radio-wave signals that reflect from or propagate through the ionosphere as a means of determining range or distance. Such systems are vulnerable to effects caused by geomagnetic storms, and their performance can be severely degraded. This paper analyses total electron content (TEC) and the corresponding GPS scintillations using two GPS SCINDA receivers located at Makerere University, Uganda (Lat: 0.3o N; Lon: 32.5o E) and at the University of Nairobi, Kenya (Lat: 1.3o S; Lon: 36.8o E), both in East Africa. The analysis shows that the scintillations actually correspond to plasma bubbles. The occurrence of plasma bubbles at one station was correlated with those at the other station by using observations from the same satellite. It was noted that some bubbles develop at one station and presumably “die off” before reaching the other station. The paper also discusses the effects of the geomagnetic storm of the 24–25 October 2011 on the ionospheric TEC at the two East African stations. Reductions in the diurnal TEC at the two stations during the period of the storm were observed and the TEC depletions observed during that period showed much deeper depletions than on the non-storm days. The effects during the storm have been attributed to the uplift of the ionospheric plasma, which was then transported away from this region by diffusion along magnetic field lines.

Mapping Autonomous Constellation Design Spaces Using Numerical Continuation

In response to an anticipated need for space-based navigation and communication infrastructure in the larger cislunar region, this research explores the use of numerical-continuation techniques to support the design of autonomous Earth–moon constellations. Based on the Linked Autonomous Interplanetary Satellite Orbit Navigation technique, the design of such architectures is a challenging task, due in part to the computational effort required to analyze a single-spacecraft configuration. Although an optimization formulation coupled with a continuation-based method was previously developed by the authors to tackle such issues, the direct application of this technique still remained computationally expensive and was only demonstrated using a heuristically reduced cost function. This paper both simplifies and extends the previous approach by carefully studying the spacecraftplacement problem and decoupling the continuation methods into tractable subproblems. Using this decoupling strategy, exhaustive computational bottlenecks are relieved, and a deeper insight into the global behavior of solution manifolds is achieved. Results from two case studies are presented for the halo and axial periodic orbit families in the restricted Earth–moon system.

A new global TEC model for estimating transionospheric radio wave propagation errors

Space-based navigation and radar systems operating at single frequencies of <10 GHz require ionospheric corrections of the signal delay or range error. Because this ionospheric propagation error is proportional to the total electron content of the ionosphere along the ray path, a user friendly TEC model covering global scale and all levels of solar activity should be helpful in various applications. Since such a model is not available yet, we present an empirical model approach that allows determining global TEC very easily. Although the number of model coefficients and parameters is rather small, the model describes main ionospheric features with good quality. Presented is the empirical approach describing dependencies on local time, geographic/geomagnetic location and solar irradiance and activity. The non-linear approach needs only 12 coefficients and a few empirically fixed parameters for describing the broad spectrum of TEC variation at all levels of solar activity. The model approach is applied on high-quality global TEC data derived by the Center for Orbit Determination in Europe (CODE) at the University of Berne over more than half a solar cycle (1998–2007). The model fits to these input data with a negative bias of 0.3 TECU and a RMS deviation of 7.5 TECU. As other empirical models too, the proposed Global Neustrelitz TEC Model NTCM-GLis climatological, i.e. the model describes the average behaviour under quiet geomagnetic conditions. During severe space weather events the actual TEC data may deviate from the model values considerably by more than 100%. A preliminary comparison with independent data sets as TOPEX/Poseidon altimeter data reveals similar results for NeQuick and NTCM-GL with RMS deviations in the order of 5 and 11 TECU (1 TECU = 1016 electrons/m2) for low and high-solar activity conditions, respectively. The more extended data base of ionosphere information that accumulates in the coming years will help in further improving the set of coefficients of the model.

Technology, security, and policy implications of future transatlantic partnerships in space: Lessons from Galileo

Policy makers seek to identify an institutional framework that facilitates the commercialization of publicly funded R&D, while simultaneously addressing innovation market failure. In the space industry, the formation of such a framework is complicated by national security considerations and the fact that numerous sovereign nations are often included in the commercialization process. This paper analyses how multi-public partnerships with industry can promote commercially viable space programs, resolve market failures, and address transatlantic security concerns. The benefits and policy implications of the formation of such transatlantic multi-public–private partnerships (TMP 3) are illustrated based on a case study of the design of a major European public–private project in the space industry: the Galileo space-based navigation system.

Space Weather and the Global Positioning System

Space Weather and the Global Positioning System

An Assessment of Anti-Satellite Capabilities and their Strategic Implications

ABSTRACT The success of space-based communications, navigation and reconnaissance programs – in both the commerical and military arenas – presents a significant vulnerability. Intuitively, as the economic importance and military indispensability of space systems grows, so will their attractiveness as targets. Although attacks against satellites would involve significant operational challenges, economic costs and diplomatic risks, it is well within the realm of technological possibility. For example, China's decision to research ASATs is an indication of its long-term strategic goal of weakening America's monopoly on military space capabilities. This essay describes the current capabilities of anti-satellite (ASAT) technology, assesses its military impact and considers its broader policy and security implications. In light of the broad implications of ASAT weapons on the debate about missile defense in particular and space weaponization in general, the author concludes that the best way to protect America's space-related economic and military functions is to avoid ASATs development.

The Military Capabilities and Implications of China's Indigenous Satellite-Based Navigation System

China has orbited a three-satellite constellation for space-based navigation known as Beidou. This article uses the constellation geometry, as determined by the NORAD space-surveillance system and publicly available from NASA, to estimate the accuracy available to a user of the Beidou system. Limited in terrestrial coverage to roughly the Asian subcontinent, this system requires a user either to go through an iterative procedure ill-suited to most military applications or to provide his or her own standard of time by carrying a high-precision clock. The iterative method does provide accuracies comparable to NAVSTAR/GPS over a restricted area of the Earth. Carrying an atomic clock, however, allows the system to be used in a mode that can provide sufficient accuracy to be used on MIRVed Chinese ICBMs en route to the United States and make a significant improvement in accuracy. Surprisingly, those modes of operation do not provide sufficient accuracy for most conventional military users.

Enhanced space integrated GPS/INS (SIGI)

Safe, reliable, and low cost space-based navigation is being provided with embedded INS/GPS systems such as the space integrated GPS/INS (SIGI). The SIGI is being used for various space vehicle applications such as launch vehicles, orbital vehicles, and re-entry vehicles. This paper describes current space vehicle navigation capabilities. The SIGI is being enhanced to provide additions to these existing capabilities with such items as higher processing and a commercial-off-the-shelf operating system. This will allow hosting of various software applications such as advanced navigation functions, flight control, guidance and vehicle management algorithms. The SIGI can host redundancy management functions by incorporating a cross channel data link card (CCDL) using a high speed firewire bus. The SIGI can then be used as a redundancy management platform which has application to current space vehicle avionics topologies incorporating distributed processing architectures.

GPS in Agriculture – A Growing Market!

This paper, and the paper which follows it, were first presented at the IBC '98 Conference ‘Space-Based Navigation Industry’, which was held in London, 11–12 June 1998.In conventional arable agriculture, position within the field was usually irrelevant! However, the advent of precision agriculture, wherein inputs are targeted according to locally-determined requirements within the field, has opened up a potentially large market for GPS. Indeed, it was the availability of GPS which permitted the development and implementation of precision agriculture – a concept which holds the promise of significant economic and environmental benefits to the farmer. This paper indicates the technical requirements for GPS and presents three case studies where a positioning system is required.