Explicit Constrained Terminal Acceleration Optimal Guidance for Three Dimensional Lunar Landing
About: The article was published on 2017-01-09. It has received 3 citations till now. The article focuses on the topics: Acceleration & Moon landing.
TL;DR: The proposed optimal trajectory technique satisfies the mission constraints in each phase and provides an overall fuel-minimizing guidance command history.
06 Nov 2020
TL;DR: In this article, an adaptive tracking control method based on traditional feedback control is designed to obtain that the control system works well under braking phase of lunar soft landing, where the high-thrust orbit-control engine works at maximum thrust, the interference and interferencetorque is in critical condition, and there is seriously attitude and orbit coupling situation.
Abstract: During braking phase of lunar soft landing, the high-thrust orbit-control engine works at maximum thrust, the interference and interference-torque is in critical condition, and there is seriously attitude and orbit coupling situation. In this paper we address the problem of braking phase of lunar soft landing. An adaptive tracking control method based on traditional feedback control is designed to obtain that the control system works well under braking phase of lunar soft landing. Taking the parameters of the Apollo in the simulation model, a comparison between the traditional control method and the adaptive tracking control method is undertaken. It is shown that the proposed controller copes with braking phase and shows faster convergence speed and higher stability precision.
Brown University1, Physical Research Laboratory2, Indian Space Research Organisation3, United States Geological Survey4, Jet Propulsion Laboratory5, Mount Holyoke College6, Johns Hopkins University Applied Physics Laboratory7, Goddard Space Flight Center8, College of Charleston9, Planetary Science Institute10, University of Maryland, College Park11, University of Tennessee12, DARPA13
TL;DR: Analysis of recent infrared mapping by Chandrayaan-1 and Deep Impact, and reexamining Cassini data obtained during its early flyby of the Moon, Pieters et al. reveal a noticeable absorption signal for H2O and OH across much of the surface, implying that solar wind is depositing and/or somehow forming water and OH in minerals near the lunar surface, and that this trapped water is dynamic.
Abstract: The search for water on the surface of the anhydrous Moon had remained an unfulfilled quest for 40 years. However, the Moon Mineralogy Mapper (M 3 ) on Chandrayaan-1 has recently detected absorption features near 2.8 to 3.0 micrometers on the surface of the Moon. For silicate bodies, such features are typically attributed to hydroxyl- and/or water-bearing materials. On the Moon, the feature is seen as a widely distributed absorption that appears strongest at cooler high latitudes and at several fresh feldspathic craters. The general lack of correlation of this feature in sunlit M 3 data with neutron spectrometer hydrogen abundance data suggests that the formation and retention of hydroxyl and water are ongoing surficial processes. Hydroxyl/water production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration.
TL;DR: In this paper, a multi-constrained suboptimal guidance method based on an improved zero-effort-miss/zeroeffortvelocity (ZEM/ZEV) algorithm and the recently developed model predictive static programming (MPSP) is presented for lunar pinpoint soft landing.
••08 Aug 2011
TL;DR: In this paper, the authors proposed a cost function that penalizes both the touchdown velocity and the fuel cost of the descent engine, and derived analytical expressions for the optimal thrust vector, touchdown velocity components, and other system variables.
Abstract: The landing of a crewed lunar lander on the surface of the Moon will be the climax of any Moon mission. At touchdown, the landing mechanism must absorb the load imparted on the lander due to the vertical component of the lander’s touchdown velocity. A large horizontal velocity must also be avoided because it could cause the lander to tip over, risking the life of the crew. To be conservative, the worst-case lander’s touchdown velocity is always assumed in designing the landing mechanism, making it very heavy. Fuel-optimal guidance algorithms for soft planetary landing have been studied extensively. In most of these studies, the lander is constrained to touchdown with zero velocity. With bounds imposed on the magnitude of the engine thrust, these optimal control solutions typically have a “bang-bang” thrust profile: the thrust magnitude “bangs” instantaneously between its maximum and minimum magnitudes. But the descent engine might not be able to throttle between its extremes instantaneously. There is also a concern about the acceptability of “bang-bang” control to the crew. In our study, the optimal control of a lander is formulated with a cost function that penalizes both the touchdown velocity and the fuel cost of the descent engine. In this formulation, there is not a requirement to achieve a zero touchdown velocity. Only a touchdown velocity that is consistent with the capability of the landing gear design is required. Also, since the nominal throttle level for the terminal descent sub-phase is well below the peak engine thrust, no bound on the engine thrust is used in our formulated problem. Instead of bang-bang type solution, the optimal thrust generated is a continuous function of time. With this formulation, we can easily derive analytical expressions for the optimal thrust vector, touchdown velocity components, and other system variables. These expressions provide insights into the “physics” of the optimal landing and terminal descent maneuver. These insights could help engineers to achieve a better “balance” between the conflicting needs of achieving a safe touchdown velocity, a low-weight landing mechanism, low engine fuel cost, and other design goals. In comparing the computed optimal control results with the preflight landing trajectory design of the Apollo-11 mission, we noted interesting similarities between their landing performance.
TL;DR: In this paper, the optimal control problem was restructured as a minimum-jerk problem to solve it and the new optimal guidance law obtained has no constraints on the initial conditions.
Abstract: An optimal guidance law derived by solving the minimum-acceleration problem has been reported for control of a lunar lander. In our past work, the guidance law was proved to enable vertical/soft landing. However, it was not robust against disturbance because there was a constraint condition relative to initial conditions in order to satisfy optimality. Therefore, if the constraint is not satisfied, the lunar lander must be controlled to track the reference trajectory generated by the optimal guidance law in order to be robust against disturbance. The control system makes the landing system complex and fuel consumption is increased in comparison to a guidance law without tracking control. Consequently, this study restructures the optimal control problem as a minimum-jerk problem to solve it. Jerk is a physical quantity defined as the time derivative of acceleration. The new optimal guidance law obtained has no constraints on the initial conditions. The results of computer simulation confirm the usefulness of the proposed guidance law.
TL;DR: In this paper, the authors present a novel analytic guidance law of the planetary landing mission by optimizing the control effort expenditure, where the control variable is expressed as a function of costate variables, and the problem is converted into a two-point boundary value problem.
Abstract: An optimal trajectory design of a module for the planetary landing problem is achieved by minimizing the control effort expenditure. Using the calculus of variations theorem, the control variable is expressed as a function of costate variables, and the problem is converted into a two-point boundary-value problem. To solve this problem, the performance measure is approximated by employing a trigonometric series and subsequently, the optimal control and state trajectories are determined. To validate the accuracy of the proposed solution, a numerical method of the steepest descent is utilized. The main objective of this paper is to present a novel analytic guidance law of the planetary landing mission by optimizing the control effort expenditure. Finally, an example of a lunar landing mission is demonstrated to examine the results of this solution in practical situations.
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