The lunar landing stage can be divided into three phases: de-orbit, powered descent and terminal approach. Most fuel is consumed during the powered descent phase. Therefore, the optimization problem of minimum energy is typically focused on this phase. In this paper, a highly precise three-dimensional descent dynamics model is derived, and the main constraints for a manned lunar mission are presented. To solve this complex optimization problem with strict constraints, a hybrid optimization method which combines the collocation method-Gauss pseudospectral method (GPM) and shooting method is proposed. In this approach the GPM is used to provide an initial guess for the shooting method, which is then used to obtain the final optimal solution. The simulation results show that the proposed method can solve the lunar powered descent optimization problem effectively with the solution obtained satisfying all the input constraints and having high precision.
This study demonstrates the isolation performance of a non-linear passive isolator to enhance the pointing performance through isolating disturbances induced by a spaceborne cryogenic cooler. In this paper, a non-linear passive isolation system with varying stiffness under launching and under on-orbit conditions to attenuate the micro-vibration of the cooler is proposed. The isolation system provides low stiffness for small excitation of the cooler during on-orbit operation and high stiffness when the excitation range is relatively larger under the launch environment. The performance of the passive isolation system is investigated through both a launch environment test and a micro-vibration measurement test of the cooler combined with non-linear passive isolators.
This study establishes an efficient approach for sonic boom analysis under conditions of atmospheric uncertainty, such as temperature, density and wind velocity. This approach combines a non-intrusive polynomial chaos (NIPC) method, which approximates the statistical behavior of output function under conditions of uncertainty, with the sonic boom analysis method using an augmented Burgers' equation, which is able to account for the rise time of the sonic boom signature. The present simulations demonstrate the superior capability of NIPC, which can estimate the statistical signature of sonic boom under conditions of atmospheric uncertainty, while ensuring the same accuracy and much less computational time compared to the Monte Carlo (MC) method. The present simulation results indicate that temperature uncertainty has an impact on the local rise in sonic boom pressure, and atmospheric humidity uncertainty has an impact on the entire shape of the sonic boom signature, while wind uncertainty has almost no impact.
Receding horizon control is a feedback control approach that optimizes control performance over a finite horizon, and its performance index has moving initial and terminal times. Controlling the flow of fluids is a challenging problem that arises in many fields including aeronautical, biological and chemical engineering. The objective of this study is to provide a novel framework for designing a receding horizon controller for high-dimensional Burgers' equations used to describe fundamental flow phenomena. The advantage of our proposed method is that it can be applied to a wide class of optimization problems of high-dimensional Burgers' equations. The effectiveness of the proposed method is verified by numerical simulation.
This paper establishes a two-phase reacting flow model in the secondary combustor of a ducted rocket. The three-dimensional Favre-averaged compressible turbulent N-S equations are used as the governing equations of the reacting flow, the improved k ∼ ε two-equation turbulence model is used to simulate the turbulent flow, and the eddy break up model is used to simulate the gas combustion. The particle-phase solution is obtained using a well-established boron particle ignition and combustion model. Boron particles are ejected from the exit of the gas generator into a secondary combustor and their trajectories are traced through the reacting flowfield using discrete phase models. The secondary combustion in a cylindrical combustor for the ducted rocket is investigated preliminarily with tests conducted on a connected-pipe ramjet test bed. During the test, boron-based fuel-rich HTPB propellant is used. The effect of factors, such as air/fuel ratio, velocity of air injection and dome height on the performance of the combustor and the engine is examined. The work described in this paper represents an attempt to direct the design of the secondary chamber in order to increase combustion efficiency. The experimental results show that the reacting flow model established in this paper is correct.
The characteristics of decentralized air traffic control in a high-density corridor subject to separation control non-uniformity are discussed. A high-density corridor is expected to be a one-way air traffic route where only aircraft equipped with airborne surveillance systems are allowed to fly in order to achieve airborne self separation. The air traffic behavior in a high-density corridor under a decentralized control strategy that achieves safe and efficient operation of the air traffic flow with the maximum traffic volume is investigated through numerical simulations. Each simulation result is evaluated in terms of safety and workload. The numerical simulations reveal that some non-uniformity in the aircraft control parameters cause severe conflict situations. It is also found that the aircraft behave collaboratively for the conflict resolution when the uniform distance to begin separation control and the uniform maneuver swiftness are applied. It is concluded that such collaborative separation control is the key to safe operation.
A new class of lightweight carbon fiber reinforced plastic (CFRP)–-the lightweight ablator series for transfer vehicle systems (LATS)–-has recently been developed. The LATS is fabricated by heating and pressurizing a material in which resin is impregnated in the laminated carbon fiber felt. A characteristic required to ensure the excellence of a conventional lightweight CFRP ablator of the LATS is the simplicity of the resin impregnation process. Since dried bulk density can be easily controlled, this manufacturing method is beneficial for use in the aerospace industry. Here, the ablation characteristics of this material under high-enthalpy airflow are described by a recently developed computer code to simulate the one-dimensional transient thermal behavior. The validity of the mathematical model and the applicability of the ablation code are then discussed by comparing the simulated and experimental results of arc-heated tests with the LATS. A new index adopted in this study predicted the mass loss rate; the measured and estimated values of the total mass loss rate in various test conditions are in good agreement. Thus, a heated LATS material shows excellent performance characteristics for use in re-entry vehicles, and its surface and in-depth temperatures can be estimated using the developed analysis code.
Experiments using a pendulum thrust stand are performed to determine the dependences of the impulse on the laser wavelength and energy in a magnetic thrust chamber system for a laser fusion rocket. The impulse is generated by the interaction between a diamagnetic current in a laser-produced plasma and a magnetic field. The plasma is produced by irradiating a spherical polyacetal target with a single-beam glass laser (laser pulse duration: 1.3 ns; laser wavelengths: 1,053, 527 and 351 nm; laser energy: 30–900 J). The magnetic field is generated by a cylindrical neodymium permanent magnet (50 mm diameter and 40 mm long) placed in a position 33 mm from the target. Impulses in the range 0.02–10 mNs are measured using a pendulum thrust stand. The experiments reveal that the impulse for 2ω is similar to that for 3ω, and is larger than that for ω.