Journal of Aerospace Engineering

Recently, attention has been devoted to problems of construction of facilities on the lunar surface. Due to the unavailability of real lunar regolith, experimental studies have relied on the use of lunar soil simulants, with two of the more common simulants being Minnesota Lunar Simulant and a simulant produced in cooperation with the Johnson Space Center. Since various studies have used either simulant, it is important to be able to compare the engineering properties of these two simulants when comparing the results of various studies. The purpose of this paper is to compare the physical and mechanical properties of these two simulants. The load-settlement characteristics of the two materials are compared by examining data from centrifuge model foundation experiments. The two simulants are quite comparable in terms of physical and mechanical properties. Differences in the load-settlement behavior as seen in model foundation experiments are due to differences in the specific gravity of the two materials. The mechanical properties of the simulants pose significant problems when attempting to use conventional stability solutions for the design of lunar facilities.

Automation of excavation operations can be realized by an automatically controlled excavator system that is able to perform autonomously a planned digging work and to quickly comply to interacting forces experienced during excavation. The development of such an automated control system is usually based on a dynamic model of the system that describes the motion with time. A dynamic model for an excavator that is needed for the controller design can be derived by applying Newton-Euler equations to each link in succession. The model obtained describes the motion of the excavator. It corrects several shortcomings that appear in previously published excavator model. On the basis of the model derived, a proportional-differential controller is designed that makes the bucket to track a specified trajectory. It can be used to automate the machine operations, for example, for terrestrial and planetary excavations as well as for mining applications.

The ASCE Standard 7 and many other codes of practice now allow the use of wind tunnel model studies for developing wind loading information to supplement and, in some situations, replace code wind loads. As a result, it is important for the engineering community to be aware of the circumstances in which wind-tunnel model tests may be advantageous or even necessary and to become familiar with the underlying physical principles and procedures, which must be followed to ensure that meaningful information is obtained. The ASCE Manual 67 was published in 1987 to assist engineers, architects, and other users of wind-tunnel services. The wind-engineering field has been evolving rapidly, and members of the Aerospace Division have been busy in developing an update. This new manual is currently in the ASCE Blue Ribbon Review process and is scheduled to be published in 1996. The new edition of the Manual of Practice for Wind-Tunnel Studies of Buildings and Structures has two distinct parts. Part 1 is an expanded version of ASCE Manual 67, which has been updated to reflect changes in technology and which has additional information for model studies of atmospheric dispersion around buildings, quality control, and procedures for combining wind-tunnel findings with climatic wind data in order to provide statistical predictions of full-scale wind loads and wind-induced effects. Part 2 is a detailed commentary that provides explanations, supporting information on methodology, and examples of typical tests; it also includes an extensive bibliography. The material presented provides a preview of this new manual. Due to space limitations, only part 1 and the bibliography are included at this time. The full manual will be available in 1996 and interested readers can get further information from the ASCE.