Journal of Aerospace Engineering

Explicit algebraic expressions needed to compute element stiffness matrices using procedural (FORTRAN) and object oriented $\left({\mathrm{C}}^{++}\right)$ computer programs are presented. Numerical illustrations for a convex quadrilateral and a triangle with a side node are included. The wide controversy due to conventional element level approximate numerical quadrature within the computational square domain in $\eta$ and $\xi$ coordinates is completely resolved here by the closed form analytical integration within the physical element, in $x$ and $y$ coordinates.

Flight in all weather conditions has necessitated correctly detecting icing and taking reasonable measures against it. This work aims at the detection and identification of airframe icing based on statistical properties of aircraft dynamics and reconfigurable control protecting aircraft from hazardous icing conditions. A Kalman filter is used for the data collection for the detection of icing, which aerodynamically deteriorates flight performance. A neural network process is applied for the identification of icing model of the aircraft, which is represented by five parameters based on past experiments for iced wing airfoils. Icing is detected by a Kalman filtering innovation sequence approach. A neural network structure is embodied such that its inputs are the aircraft estimated measurements and its outputs are the parameters affected by ice, which corresponds to the aircraft inverse dynamic model. The necessary training and validation set for the neural network model of the iced aircraft are obtained from the simulations of nominal model, which are performed for various icing conditions. In order to decrease noise effects on the states and to increase training performance of the neural network, the estimated states by the Kalman filter are used. A suitable neural network model of aircraft inverse dynamics is obtained by using system identification methods and learning algorithms. This trained model is used as an application for the control of the aircraft that has lost its controllability due to icing. The method is applied to F16 military and A340 commercial aircraft models and the results seem to be good enough.

The parameter dependency of large space structures on the coupling among attitude motion, structural vibration, and orbital motion has been investigated, particularly for structures such as tethered satellite systems. Tethered satellites are noticed for their possible applications. From space solar power systems to deorbit system, the applications of tethered satellites spread out over various fields. In this paper, we investigate planar motion of a satellite model, which consists of two tip particles and a massless spring. For such a space structure, the characteristics of the planar motion are shown to be determined by the mass ratio of tip particles, the natural frequency ratio of axial vibration to orbital motion, and the axial length ratio of the spring to the orbital radius. Among these three parameters, the natural frequency ratio has the greatest influence on the coupling phenomenon. Furthermore, the parameter range over which the coupling phenomenon occurs is specified.

The moon has recently regained the interest of many of the world’s space agencies. Lunar missions are the first steps in expanding manned and unmanned exploration inside our solar system. The moon represents various options; it can be used as a laboratory in low gravity, it is the closest and most accessible planetary object from the Earth, and it possesses many resources that humans could potentially exploit. This paper has two objectives: to review the current status of the knowledge of lunar environmental requirements for future lunar structures, and to attempt to classify different future lunar structures based on the current knowledge of the subject. The paper divides lunar development into three phases. The first phase is building shelters for equipment only; in the second phase, small temporary habitats will be built, and finally in the third phase, habitable lunar bases will be built with observatories, laboratories, or production plants. Initially, the main aspects of the lunar environment that will cause concerns will be lunar dust and meteoroids, and later will include effects due to the vacuum environment, lunar gravity, radiation, a rapid change of temperature, and the length of the lunar day. This paper presents a classification of technical requirements based on the current knowledge of these factors, and their importance in each of the phases of construction. It gives recommendations for future research in relation to the development of conceptual plans for lunar structures, and for the evolution of a lunar construction code to direct these structural designs. Some examples are presented along with the current status of the bibliography of the subject.

Lunar in situ resource utilization (ISRU) processes require thermal energy at various temperatures. Chemical recovery processes (pyrolysis, gas-solid reactions, gas-liquid or three-phase reactions and desorption) require thermal energy at temperatures from $\mathrm{1,000}\mathrm{K}\text{to}\mathrm{2,500}\mathrm{K}$ . Manufacturing processes (hot liquid processing, sinter forming, composite forming, welding, etc.) can be accomplished with thermal energy at temperatures $\mathrm{1,200}\mathrm{K}–\mathrm{1,800}\mathrm{K}$ . For these materials, process applications or solar thermal power can be effectively utilized. Physical Sciences Inc. has been developing an innovative solar power system in which solar radiation is collected by the concentrator, which transfers the concentrated solar radiation to the optical waveguide transmission line made of low loss optical fiber. In this paper, we will review our work on the development of the solar thermal power system and its application to a lunar ISRU process.

Libration orbit stationkeeping controls are designed based on selected reference quasi-periodic orbit trajectories. The baseline trajectory is designed to meet science requirements and in the same time achieve minimum fuel consumptions. The success of finding libration point reference orbits is based on accurate numerical computation, dynamics, and space environment modeling. The linear quadratic regulator controller has been developed widely for maintaining a spacecraft in such libration orbit reference trajectories as close as possible. However, any dynamics models, including the circular restricted three-body dynamics, space environment, sensor, and actuator, are only approximations of real physical systems. Any noise and uncertainties can cause spacecraft’ motion to diverge due to the high instability region around libration points. This study investigates the modeling and designing of a passive robust $\mathbf{\mu }$ controller and an active adaptive linear quadratic regulator in libration point stationkeeping controls around ${\mathrm{L}}_1$ . The adaptive law in the linear quadratic regulator is used to estimate unknown gains of spacecraft’ subsystems. The results are compared for a family of libration orbits with reasonable $\mathrm{\Delta }V$ yearly budgets under the influence of perturbations, noise, and unmodeled dynamics. The comparison with a publicly accessible work indicates that the controller developed in this work can provide comparable annual cost by nearly even including the worst case of perturbations.