Experimental investigations have been conducted in hydrogen-oxygen mixtures with equivalence ratio of 1.5 at cryogenic temperature (77 K) and initial pressure (P0) from 0.2 to 0.5 atm. The sensors optical fibers are used measure the overpressure flame velocity, respectively. precursor shock wave is formed by combination 1st 2nd waves. When catches up wave, detonation occurs. Strong acceleration was observed all tested conditions, which can be well characterized predicted Zel'dovich number...

The satellite clocks used in the BeiDou-2 navigation System (BDS) are Chinese self-developed Rb atomic clocks, and their performances stabilities worse than GPS Galileo clocks. Due to special periodic noises nonlinear system errors existing BDS clock offset series, ultra-rapid model, which uses a simple quadratic polynomial plus one is not suitable for BDS. Therefore, an improved prediction model proposed order enhance precision of predicted offsets. First, basic fit rubidium (Rb)...

Precise ionospheric total electron content (TEC) is critical for many aerospace applications, and forecasting TEC of great significance to it. Besides, short-term prediction values fills the gap between product latency precision. The machine learning-based approaches are promising in solving nonlinear issues, particularly suitable global positioning system due its complex temporal spatial variation. In this article, four different learning models, i.e., artificial neural network, long memory...

A new precise point positioning (PPP)-B2b augmentation service broadcast by the BeiDou Navigation Satellite System (BDS-3) geosynchronous Earth orbit (GEO) satellite can provide real-time and high-precision clock offset corrections for global navigation system (GNSS) users in China its surrounding areas. It has great significance research value applications. First, orbit, offset, differential code bias (DCB) of PPP-B2b products are evaluated. Second, influence on enhanced single-frequency...

Low Earth Orbit (LEO) satellite for navigation augmentation applications can significantly reduce the precise positioning convergence time and attract increasing attention recently. A few LEO Navigation Augmentation (LEO-NA) constellations have been proposed, while corresponding constellation design methodologies not systematically studied. The LEO-NA generally consists of a huge number satellites it strives multiple optimization purposes. It is essentially different from communication or...

As China's Beidou satellite navigation system (Beidou system) achieves a primary global coverage, the low earth orbiter augmentation (LEO-NA) technique becomes hot research topic, since it can easily cooperate with to improve precision for autonomous and extend application market of systems (GNSS). This paper analyzed demand status LEO-NA technique, focused on in-orbit validation key techniques "Luojia-1A" satellite. It also studied challenges faced by system, including interoperability...

As the deployment of large Low Earth Orbiters (LEO) communication constellations, navigation from LEO satellites becomes an emerging opportunity to enhance existing satellite systems. The augmentation (LEO-NA) systems require a centimeter decimeter accuracy broadcast ephemeris support high positioning applications. Thus, how design key issue for LEO-NA In this paper, temporal variation characteristics orbit elements were analyzed via spectrum analysis. A non-singular element set fitting was...

Luojia-1A is a scientific experimental satellite operated by Wuhan University, which the first low earth orbiter (LEO) navigation signal augmentation satellite. The precise orbit prerequisite of augmenting existing Global Navigation Satellite System (GNSS) performance and improves users’ positioning accuracy. Meanwhile, LEO determination (POD) with BeiDou-2 observations particularly challenging since it only provides regional service. In this study, we investigated method for onboard BeiDou...

A series of experiments were carried out in a closed tube at cryogenic temperature (77 K) for hydrogen-oxygen mixtures. Flame propagation speed and overpressure measured by optical fibers pressure sensors, respectively. The first second shock waves captured the experiments, although always precede flames all cases indicating absence stable detonation. However, strong flame acceleration was observed situations, which is consistent with prediction expansion ratio Zeldovich number. Besides,...

The third generation of the BeiDou navigation satellite system (BDS-3) can transmit five-frequency signals. real-time clock offset BDS-3 is typically generated utilizing B1I/B3I combination with ambiguity-float solutions. By conducting ambiguity resolution (AR), reliability be improved. However, performance ambiguity-fixed B1C/B2a signals remains unknown and unrevealed. In this contribution, new investigated. One week observation data from 85 stations was used to perform estimation. For...

The indoor positioning system is now an important technique as part of the Internet-of-Things (IoT) ecosystem. Among techniques, multiple Wi-Fi Access Points (APs)-based systems have been researched a lot. There lack research focusing on scene where only one AP available. This work proposes hybrid that takes advantage Fine-Timing Measurements (FTM) IEEE 802.11mc standard, introduced back in 2016. uses single FTM and built-in inertial sensors smartphone to estimate device's position. We...

Real-time satellite clock offset is a crucial element for real-time precise point positioning (RT-PPP). However, the elapsed time undifferenced (UD) multi-global navigation system (GNSS) estimation at each epoch increased with growth of stations, which may fall short application requirements. Therefore, rapid method UD multi-GNSS proposed to improve computation efficiency, in both dimension normal equation (NEQ) and number redundant observations are calculated before adjustment; if these two...

The predicted navigation satellite clock offsets are crucial to support real-time global system (GNSS) precise positioning applications, especially for those applications difficult access the data stream, such as low earth orbit (LEO) autonomous determination. Currently, prediction Chinese BeiDou is still challenging meet requirement. onboard clocks of satellites provided by different manufacturers, and clocks’ switch events more frequent. Considering satellite-specified temporal variation...