Journal of Aerospace Engineering

The establishment of an efficient transportation system is key to any human development on Earth or in space. Different technologies for transporting humans and goods have been developed, the diversity of which indicates that individual concepts have specific strengths and weaknesses. So far, transportation on the Moon has utilized a wheel‐based vehicle, the lunar rover. Present concepts for transporting goods and people in a lunar base of the future are generally based on using wheels and traction. While such systems have many advantages for a variety of applications, the hauling of heavy goods will require the preparation of stable and trafficable roadways, a challenging and potentially expensive undertaking. This paper presents an alternative based on using one of the fundamental means to move objects, namely ropes and cables. Because of their inherent characteristics, ropes have been used to lift and haul heavy loads for long distances with high levels of reliability. This mature and constantly perfected technology, not well known in this car‐oriented society, has been investigated for its use as a true alternative to the traditional wheel‐based transportation systems. As will be shown, innovative applications of cable‐based technologies may in effect provide many opportunities to leverage the differences between the Earth and the Moon for the purpose of creating efficient engineering products.

To use construction machines effectively in the dark, severe weather, or hazardous and/or unhealthy environments, their operations should be controlled automatically. It can be realized if the kinematics and dynamics of the machine are understood. To help achieve this goal, the kinematics of specific construction machines—excavators (backhoes and loaders)—are investigated here. A systematic procedure is presented to assign Cartesian coordinate frames for the links (joints) of an excavator. Then, the homogeneous transformation matrices that relate two adjacent coordinate frames are given. The kinematic relations of the pose (position and orientation) of the bucket, the joint shaft angles, and the lengths of the cylinder rods in the hydraulic actuators for an excavator are studied. Explicit expressions for the forward and backward (inverse) kinematic relations are presented. Then, the corresponding kinematic velocity relations for the excavators are developed. The kinematic relations presented provide the foundation for engineers to realize the automatic computer‐controlled operations of the machine.

Basic surface treatment tasks on construction sites that can be performed by robots include the spraying, cleaning, and finishing of surfaces. In the present paper, a construction robot is proposed for accomplishing a variety of cleaning tasks in construction. Specifically, the force‐control problem in cleaning a surface is studied. The paper shows that a force sensor can be used not only to monitor the force acting at the contact points, but also to identify the uncertainties of the unstructured construction environment. A different formulation for the external force is presented. With this formulation, the external force on the end‐effector is presented as a function of the contact force, contact torque, and constraint conditions, but not the actuated torque in the joint space. Therefore, the force‐control problem is simplified to compensate for the external force and to exert a desired force. One advantage of this approach is that the original PID position control loop of an industrial robot is retained so that the time‐consuming computed torque method is avoided. The proposed control scheme can be applied to numerous cleaning tasks with hard contact regardless of the different nature of the surface.

A thermoviscoplastic finite element method employing the Bodner‐Partom constitutive model is used to investigate the response of simplified thermal‐structural models to intense local heating. The computational method formulates the problem in rate form and advances the solution in time by numerical integration. The thermoviscoplastic response of simplified structures with prescribed temperatures is investigated. With rapid rises of temperature, the nickel alloy structures display initially higher yield stresses due to strain rate effects. As temperatures approach elevated values, yield stress and stiffness degrade rapidly and pronounced plastic deformation occurs.

Deployable structures can be stored in a compact, folded configuration and are easily deployed into load‐bearing, open forms. Hence, they are suitable for applications where speed and ease of erection and reusability are desired. The structures investigated here are prefabricated space frames made of so called scissor‐like elements, sets of two straight bars connected to each other by a pivot. These structures are stress‐free and self‐standing in both their folded and deployed configurations, thus overcoming major disadvantages of previous designs. This study deals with deployable structures that are flat and subjected to normal loads in their deployed configuration. Although the behavior for that loading case is linear, the availability of an equivalent continuum model for stiffness prediction is desirable because it can significantly reduce the computational effort during preliminary design. The derivation of such a model is not straightforward because of the unorthodox geometry and the rotations allowed by the hinged and pivotal connections. This problem is addressed by first applying the direct stiffness method within a symbolic manipulation framework to transform the lattice structure to an equivalent single‐layer grid, and then using existing expressions to obtain the desired equivalent plate. The model exhibits good accuracy and convergence characteristics for uniform loads.

The orbital recovery of the external tank (ET), backbone of the U.S. space transportation system, can be considered enormously important for the future development and colonization of space. America's ability to respond to the many space opportunities on the horizon of research, commercialization and planetary science depend on the resiliency of the space transportation system, and especially on the use of the external tank in space. The use of ETs—as launch stages for planetary exploration, as large platforms in either low Earth orbit or geosynchronous Earth orbit to coorbit with other payloads requiring human interaction, or as an element of support for the next part of space station Freedom—could be of fundamental importance. The purpose of this paper is to describe a method for the orbital construction of the device and the corresponding recovery of the ET.

This paper presents a robust hybrid genetic algorithm for optimization of space structures using the augmented Lagrangian method. An attractive characteristic of genetic algorithm is that there is no line search and the problem of computation of derivatives of the objective function and constraints is avoided. This feature of genetic algorithms is maintained in the hybrid genetic algorithm presented in this paper. Compared with the penalty function‐based genetic algorithm, only a few additional simple function evaluations are needed in the new algorithm. Furthermore, the trial and error approach for the starting penalty function coefficient and the process of arbitrary adjustments are avoided. There is no need to perform extensive numerical experiments to find a suitable value for the penalty function coefficient for each type or class of optimization problem. The algorithm is general and can be applied to a broad class of optimization problems.

Mathematical optimization of space trusses in a vector/parallel processing environment is the subject of this paper. Parallel processing is achieved through microtasking and the use of the CRAY CFT77 compiler directives. Speedup results are presented for four space‐truss examples. It is concluded that the speedup due to microtasking is improved substantially with an increase in the size of the problem.