Power Descent Research Articles

Soft Landing Parameter Measurements for Candidate Navigation Trajectories Using Deep Learning and AI-Enabled Planetary Descent

Smart instruments, sensors, and AI technologies are playing an important role in many fields such as medical science, Earth science, astronomy physics, and space study. This article attempts to study the role of sensors, instruments, and AI (artificial intelligence) based smart technologies in lunar missions during navigation of trajectories. Lunar landing missions usually divide the power descent phase into three to four sub-phases. Each sub-phase has its own set of initial and final constraints for the desired system state. The landing systems depend on human competencies for making the most crucial landing decisions. Trajectory planning and designing are very significant in lunar missions, and it requires inputs with precision. The manual systems may be prone to errors. In contrast, AI and smart sensor-based measurements give an accurate idea about the trajectory paths and make appropriate decisions where manual systems may turn into disasters. The manual systems are either pre-fed or have manual controls to guide the trajectory. For autonomous landing problems, trajectory design is a very crucial task. The automated trajectories play a vital role in the measurement and prediction of landing state parameters of the space rocket. Nowadays, sensors, intelligent instruments, and the latest technologies go hand in hand to devise measurement methods for accurate calculations and make appropriate decisions during landing space rockets at the designated destination. Space missions are very expensive and require huge efforts to design smart systems for navigation trajectories. This paper attempts to design all possible candidates of reference navigation trajectories for autonomous lunar descent by employing 3D non-linear system dynamics with randomly chosen initial state conditions. The generated candidates do not rely on multiple hops and thus exhibit an ability to serve autonomous missions. This research work makes use of smart sensors and AI federated techniques for smartly training the system to serve the ultimate purpose. The trajectories are simulated in an automated simulating environment to perform exhaustive analyses. The results accurately approximate the trajectories analogous to their numerical counterparts and converge to their measured final state estimates. The generation rate of feasible trajectories measures the accuracy of the algorithm. The algorithm’s accuracy is near 0.87 for 100 sec flight time, which is reasonable.

Simulation and Analysis of Multiphase Flow in a Novel Deepwater Closed-Cycle Riserless Drilling Method With a Subsea pump+gas Combined Lift

Recently, deepwater resource exploration has grown rapidly. Because the conditions of marine environment and seabed geology are more complex, deepwater drilling needs to numerous confront challenges, such as more complicated wellbore situations, low drilling efficiency, and high cost. Advanced novel drilling methods serve as significant impetus to facilitate the rapid advancement in deepwater oil-and-gas exploration and development. However, adopting riserless drilling methods may pollute marine environment and yield poor wall protective effects, while drilling methods with risers may suffer from relatively high cost and risk. Based on these dilemmas, in this study, a novel deepwater closed-cycle riserless drilling method with a subsea pump + gas combined lift is proposed. The proposed novel closed-cycle method has also established a multiphase flow drilling model and analyzed the effects of drilling fluid displacement, gas injection displacement, gas injection site and seawater depth on the multiphase flow in the wellbore. The simulation results revealed the following: As the gas migrates upward along the pipeline, its flow velocity first increases slowly and then rapidly owing to the volume expansion of gas. Larger displacement of drilling fluid demands greater working power of the subsea lifting pump, which is characterized by a nonlinear relationship. The gas injection displacement can effectively mitigate the load-bearing capacity of the pump, and increasing gas injection displacement leads to a decreased subsea lifting pump working power requirement; the decreasing effect on pump power load is more significant in the case of low gas injection displacement. Increasing the depth of gas injection sites reduces the subsea pump working with a decreasing slope with respect to the power descent. Finally, the subsea pump lifting power demand increases approximately linearly with an increasing seawater depth. Subsequently, an optimization method of hydraulic parameters for deepwater closed-cycle riserless drilling was proposed, which provides a theoretical foundation for the selection of subsea pumping power as well as the optimization of gas injection sites and displacement.

Evaluation of Fundamental Characteristics of High Functional Direct Carbon Fuel Cell Using Wood Pellet as Fuel

After the Great East Japan Earthquake, because the power supply of Japan shifted from nuclear power generation to thermal power generation, the exhaust amount of CO2 as the greenhouse gas increased drastically. On the other hand, Japan has a lot of organic wastes such as a food waste and unused biomass. To solve these problems, we have been developing High Functional Direct Carbon Fuel Cell (HF-DCFC) composed of molten salts gasification system and tubular molten carbonate fuel cell (T-MCFC) since 2012. Molten salts gasification is a technology to produce H2 and CO for T-MCFC from organic wastes. Our previous study obtained the fundamental characteristics of HF-DCFC using soy sauce cake as fuel. Generally, because the operating condition of HD-DCFC depends on a fuel type, we examine the fuel diversity of HF-DCFC. Therefore, this paper aimed to evaluate the fundamental characteristics of HF-DCFC using wood pellet made of unused timber. Moreover, because the performance of T-MCFC depends on the electrolyte loading ratio of both electrodes, this paper also examined the optimum electrolyte loading ratio. In the results of the optimum electrolyte loading ratio, although the performances of the cell to which electrolyte of 45% or more was impregnated were very low under 650℃ of the cell temperature, it has been improved when the cell temperature was raised to 750℃ which was the operating temperature of HF-DCFC. Especially, the diffusion overpotential of each cell was improved greatly by the cell temperature rise. Generally, about three days are required so that the electrolyte is normally distributed to each cell component of a plate type MCFC. Although the distribution of T-MCFC was worse than that of a plate type MCFC because of the difference of the pore structure, it was improved by the decrease in the viscosity of electrolyte by the cell temperature rise. Consequently, we confirmed that the optimum electrolyte loading ratio was in about 25%. On the HF-DCFC experiment, the fundamental characteristic of HF-DCFC was evaluated by the cell voltage change when the wood pellet of 3g was supplied to HF-DCFC generating electricity by a constant current density of 100mA/cm2. The fuel gas utilization was changed from 40% to 80% to evaluate the influence of the gasification gas from the wood pellet on the cell performance. Although the cell power decreases rapidly immediately after the supplying of the wood pellet, thereafter it increases significantly. This tendency becomes large with the increase of the fuel gas utilization. The power descent immediately after the supplying of wood pellet originates to the influence of the air that mixed at the pellet supplying. The cell power descent immediately after the supplying of the pellet originates to the decrease of the partial pressure of hydrogen because of the combustion of air that mixes at the pellet supplying and the T-MCFC fuel gas. Thereafter, the cell power increases rapidly by the increase of fuel gas produced by gasification of the wood pellet. The ratio of the gasification gas in the anode gas increases so that the supply flow rate decreases as the fuel gas utilization increases. Therefore, this tendency increases with the increase of the fuel gas utilization. Consequently, we were able to confirm that HF-DCFC is effective enough as the distributed power source and the waste disposal equipment if wood pellet was supplied to HF-DCFC continuously. Figure 1

Infinite-dimensional gradient-based descent for alpha-divergence minimisation

This paper introduces the $(\alpha, \Gamma)$-descent, an iterative algorithm which operates on measures and performs $\alpha$-divergence minimisation in a Bayesian framework. This gradient-based procedure extends the commonly-used variational approximation by adding a prior on the variational parameters in the form of a measure. We prove that for a rich family of functions $\Gamma$, this algorithm leads at each step to a systematic decrease in the $\alpha$-divergence and derive convergence results. Our framework recovers the Entropic Mirror Descent algorithm and provides an alternative algorithm that we call the Power Descent. Moreover, in its stochastic formulation, the $(\alpha, \Gamma)$-descent allows to optimise the mixture weights of any given mixture model without any information on the underlying distribution of the variational parameters. This renders our method compatible with many choices of parameters updates and applicable to a wide range of Machine Learning tasks. We demonstrate empirically on both toy and real-world examples the benefit of using the Power descent and going beyond the Entropic Mirror Descent framework, which fails as the dimension grows.

Precise power descent control of a lunar lander using a single thruster

This paper addresses the problem of powered descent control of a lunar lander during its final landing phase, where soft and precise landing at the target cite is required. In the literature, this problem has been solved considering a fully actuated lunar lander. Recently, landers are designed as complex systems with several onboard payloads and subsystems for completing demanding mission tasks. There are increasing constraints on mass budget and space availability onboard a lander. In order to meet these requirements, a novel controller using a single thruster is proposed. The proposed controller has three control inputs (thrust and two gimbaled angles) to control the six degrees of motion of a lander; these control inputs are non-affine. The proposed controller is designed based on variable structure control technique augmented with a high order filter, an immersion and invariance-based mass estimator and a sliding mode angular velocity observer. The stability analysis using Lyapunov theory and the results of the numerical simulations along with Monte Carlo simulations of the system show that the precise landing of the lunar lander using a single thruster is feasible.

Three-dimensional transient analysis for control rods drop into CSR1000 core

Transient performance of China supercritical water-cooled reactor (SCWR) with the rated electric power of 1000MWe (CSR1000) core during the control rods (CR) drop into the core is analyzed and evaluated with the coupled three- dimensional neutronics and thermal-hydraulics SCWR transient analysis method. The 3-D CR drop transient analysis shows that while the high worth CR drop into the core, the core power in the initial stage of the CR drop process decreases rapidly. The core power descent rate exceeds the shutdown setting value, which will trigger the protection shutdown. While the low worth CR drop into the core, due to the reactivity feedback of the water density, the core power decreases slowly, and the core power descent rate cannot reach the shutdown setting value, which will not trigger the protection shutdown. In the transient process, the peak value of maximum cladding surface temperature (MCST) remains lower than the transient safety limit of 850 °C, whether it is a high worth CR drop or a low worth CR drop. The safety performance of CSR1000 core can be ensured in the process of CR drop into the core under the salient reactivity feedback of water density and the essential reactor protection system.

MACV/Radio integrated navigation for Mars powered descent via robust desensitized central difference Kalman filter

An innovative integrated navigation scheme based on MCAV/Radio measurement information during Mars powered descent phase, and a robust desensitized central difference Kalman filter (DCDKF) for systems with uncertain parameters or biases are proposed to improve the navigation descent accuracy. Based on the altitude and velocity information of the Miniature Coherent Altimeter and Velocimeter (MCAV), the radio-range information is added into the integrated navigation system to correct the horizontal position error of the vehicle during the Mars powered descent phase. Based the central difference transform, the sensitivity propagation of the state estimate errors in the DCDKF is described, and a designed desensitized cost function is minimized to obtain the gain matrix of the DCDKF. The performances of the innovative navigation scheme and the proposed DCDKF are all demonstrated by two Monte Carlo simulations with the Inertial Measurement Unit biases during the Mars power descent phase.

Correction to: Power Quadratic Diophantine Equations and Descent

Correction to: Power Quadratic Diophantine Equations and Descent