Engineering Commons^™

Defining An Abrasion Index For Lunar Surface Systems As A Function Of Dust Interaction Modes And Variable Concentration Zones, Ryan L. Kobrick, David M. Klaus, Kenneth W. Street Jr.

Publications

Unexpected issues were encountered during the Apollo era of lunar exploration due to detrimental abrasion of materials upon exposure to the fine-grained, irregular shaped dust on the surface of the Moon. For critical design features involving contact with the lunar surface and for astronaut safety concerns, operational concepts and dust tolerance must be considered in the early phases of mission planning. To systematically define material selection criteria, dust interaction can be characterized by two-body or three-body abrasion testing, and sub-categorically by physical interactions of compression, rolling, sliding and bending representing specific applications within the system. Two-body abrasion occurs when a …

Three-Body Abrasion Testing Using Lunar Dust Simulants To Evaluate Surface System Materials, Ryan L. Kobrick, Kenneth G. Budinski, Kenneth W. Street Jr., David M. Klaus

Publications

Numerous unexpected operational issues relating to the abrasive nature of lunar dust, such as scratched visors and spacesuit pressure seal leaks, were encountered during the Apollo missions. To avoid reoccurrence of these unexpected detrimental equipment problems on future missions to the Moon, a series of two- and three-body abrasion tests were developed and conducted in order to begin rigorously characterizing the effect of lunar dust abrasiveness on candidate surface system materials. Two-body scratch tests were initially performed to examine fundamental interactions of a single particle on a flat surface. These simple and robust tests were used to establish standardized measurement …

Scan Loss Pattern Synthesis For Adaptive Array Ground Stations, William C. Barott, Mary Ann Ingram, Paul G. Steffes

Publications

We present several techniques for maximizing the contact time between low Earth orbiting satellites (LEOs) and a ground station (GS). The GS comprises an adaptive array of electronically steered space-fed lenses (SFLs). Each SFL is manufactured as a low-cost printed circuit with the result that it exhibits scanning loss. By differently orienting the boresights of the SFLs in the adaptive array, the SFL's scanning losses can be made to optimally complement the path loss of the LEO, thereby reducing the cost of the GS while maximizing the download capacity of the satellite link. The optimization, implemented with a genetic algorithm …

A Design-Build-Test-Fly Project Involving Modeling, Manufacturing, And Testing, Scott Post, Shankar Seetharaman, Sree Abimannan

Publications

This paper describes a junior-level semester-long class project for students in Fluid Mechanics courses. The goals of the project are to introduce students to engineering design, project management, and to incorporate material from other courses in engineering graphics, numerical methods, instrumentation and measurements, and manufacturing processes in a single project. The project focuses on airfoil design using computational tools, and the main emphasis lies on verification of results obtained from computational methods with experimentally measured values. Students will use the airfoil shape they select to make wings to go on a model foam glider. The final part of the project …

Stability Of Fully Nonlinear Stokes Waves On Deep Water: Part 1. Perturbation Theory, Shahrdad Sajjadi, David L. Ross

Publications

We consider a full set of harmonics for the Stokes wave in deep water in the absence of viscosity, and examine the role that higher harmonics play in modifying the classical Benjamin-Feir instability. Using a representation of the wave coefficients due to Wilton, a perturbation analysis shows that the Stokes wave may become unbounded due to interactions between the N^th harmonic of the primary wave train and a set of harmonics of a disturbance. If the frequency of the n^th harmonic is denoted Ꙍ_n = Ꙍ(1 ± ꭉ) then instability will occur if

√2 k n^{n …}