Journal of Aerospace Engineering

Effects of orbital and structural initial conditions, such as initial structural axial deformation, pitch (attitude) angle, and orbit altitude have been investigated on the subsequent orbital motion (time variation of orbit radius), attitude or pitch motion (time variation of pitch angle), and axial motion (time variation of axial length) of a large space structure in low earth orbit (LEO) and geosynchronous earth orbit (GEO). The space structure is assumed to be only axially flexible and executing a planar motion under the action of the earth's gravitational force. In LEO it is observed that the initial values of the axial deformation and pitch angle have appreciable effects on the structure's subsequent axial and attitude motions, whereas they have negligible effects on the structure's orbital motion. In GEO, the effects are found similar to those in LEO, except that the initial values of pitch angle have no effect on axial deformation. Furthermore, the investigation shows that the response of the space structure is greatly affected by the change in the orbit altitude. The study also indicates that flexibility of the structure has significant influence on its pitch librational motion.

In simple terms, value engineering (VE) identifies the function of a system with a verb/noun and assigns it a value. This paper provides a background phase that briefly identifies the Soviet's launching capability. A lesson has been learned from the former U.S.S.R.'s success with massive booster rockets. Their version of the shuttle has been tested and will become an integral part of their fleet. The use of VE concepts for spaceport launching will allow existing facilities to be converted for handling a new generation of expendable launch vehicles (ELV). The paper postulates that not all ELVs have to be assembled in buildings. It also suggests that the hoisting system used for vehicle assembly does not have to be 300–500 ft off the ground. The VE proposal identifies mobility as the key factor for elimination of space‐aged dinosaurs. Modular construction can permit support services and equipment to be mounted on large crawler transporters and be able to move with ground support. A mobile spaceport launching system could traverse up and down Cape Canaveral or Vandenberg AFB at about one‐half the present launch support cost.

Automation of excavation work calls for a robotic system able to perform the planned digging work that is responsive to interaction forces experienced during excavation. The development of automated excavation control methods requires a dynamic model to describe the evolution of the excavator motion with time. The joint torques of the boom mechanism are generated by hydraulic rams that also affect the torques at other joints. Analyzing each link in succession as a free body and applying the Newton‐Euler formulation in the local coordinate frame, a dynamic model for an excavator can be derived in a straightforward manner. The model presented in this paper is intended for further development of an automated excavation control system for terrestrial, lunar, and planetary excavation.

One of the high‐volume and repetitive construction operations on earth is the excavation of soil. Automation of planetary excavation work requires a system that is able to perform the planned digging work that is responsive to interaction forces experienced during excavation. The conditions and importance of excavation motivates the goal of having a robot excavator that would be given the location and dimensions of a desired excavation and would plan the excavation process, sense the environment, react to changes as excavation proceeds, and accomplish the desired excavation with almost no external or human intervention. Cognitive robots require information for modeling, planning, and acting at different levels. The development of such a control system requires a dynamic model to describe the evolution of the excavator motion with time. In planetary digging, the regolith resists bucket movements, demanding the excavator to be able to comply with the restrictions imposed by the environment. A control system that is able to perform a preplanned digging work while complying with the regolith restrictions is described in the present paper.

Typical tasks in construction engineering that can be performed by robots include the spraying or cleaning of surfaces. Both applications require that the external force at the end effector of the manipulator be properly controlled. In this paper, the force‐control problem in spraying is analyzed. The paper shows that an unpredictable jet force causes the end effector to diverge from its desired trajectory. The interface between the end effector of the robot and the jet force is modeled as soft contact because both force error and displacement of the end effector are measurable. Therefore, the force‐control problem is simplified to the position‐control problem. The proposed control scheme, using a position‐force adaptive controller, is applied to counterbalancing a jet force. Computer simulation demonstrates that the scheme works well. The maximal position error can be controlled to within 4 mm with the new controller.

A computational technique for incorporating stability and strength into the analysis of plane frameworks is presented. The procedure for computing critical and/or collapse loads and for identifying the corresponding failure mode is outlined. The analysis is based on nonlinear kinematic relations and linearly elastic material behavior except at the plastic hinges—concentrated plasticity. The connections can be treated either as rigid or as flexible. The supports, in general, contain rotational restraints. The developed solution methodology is applicable to all multistory‐multibay orthogonal frames. The examples analyzed in the paper include: (1) A single‐story‐two‐bay frame with rigid joint connections; (2) a single‐story‐three‐bay frame with flexible joint connections; (3) a two‐story‐single‐bay frame with both rigid and flexible joint connections; and (4) a three‐story‐two‐bay frame with rigid joint connections. In all cases the loading consists of a symmetric distribution of concentrated loads on the beams, applied at the midspan positions and at or near the beam‐to‐column joints. The effect of several geometric and structural parameters is assessed.

Graphite/epoxy laminates with and without a softening strip around a hole were investigated. The softening strip is a portion of the graphite critical ply, which is replaced by a glass/epoxy composite. Analysis was conducted with finite element methods: The in‐plane stress distribution was found using a planform two‐dimensional model and interlaminar stress distributions around a hole were obtained from a through‐thickness quasi‐three‐dimensional model. The variation of strain‐energy release rate for a delamination occurring at the critical interface was investigated. The finite element results indicate that the inplane and interlaminar stress distributions, as well as the strain‐energy release rates, are significantly reduced for laminates with a softening strip.