Date of Completion

5-8-2015

Embargo Period

5-7-2015

Advisors

Jeong-Ho Kim, Kay Wille

Field of Study

Civil Engineering

Degree

Master of Science

Open Access

Open Access

Abstract

During the era of the Apollo missions, there was been a great deal of interest among scientists, engineers, and the general population regarding the Moon and Outer Space. That interest has cycled through the years since but still burns strongly today as evidenced by the National Space Policy of President Barack Obama in 2010. Within this document, six goals were stated dealing with advanced study of the universe, which likely leads to the necessity of lunar colonization; the focus of this thesis.

The lunar environment provides several extreme challenges that may place any long term mission and its crewmembers in severe danger. These challenges include, but not limited to, reduced gravity, lack of a significant atmosphere, high velocity micrometeoroid impacts, extreme high and low temperatures, and dangerous levels of ionizing radiation. This thesis discusses many of these challenges in brief detail but focuses primarily on the topic of extreme temperature variation. By using the principles of heat flow, it was determined that at the lunar equator, the expected surface temperature atop the lunar habitat ranges from 187.5 K at night to 470 K during the day. These temperatures require the use of a strong thermal shield to provide shelter for the crewmembers and shield the habitat itself from the potentially dangerous temperatures. By using a layer of lunar regolith one-meter thick housed within the depth of the aluminum frame, the interior of the habitat is adequately shielded from the surface temperatures. Using a numerical integration-based analysis, the high and low temperatures were found to dissipate within the outermost thirty centimeters, at which point the regolith temperature remained relatively constant throughout the entire lunar cycle.

This behavior is especially important due to the increased stress levels found within the aluminum frame members making up the structure of the habitat. After the application of the cold nighttime temperatures, the maximum Von Mises stress value within the outer chord members increased by 20% seeing the yield strength safety factor reduce from 2.2 prior to the thermal load to 1.82 after its application. Similarly, the high temperatures of the daytime resulted in a 35% stress increase with a safety factor equal to 1.63. The presence of a high quality thermal shield can help to minimize the exposure of the structural elements to this type of loading and therefore reduced the stresses and deflections within the habitat frame.

With respect to the habitat vibration, it was found that the attachment of the inflatable membrane helps to increase the natural frequency of the structure. However, without sufficient pre-stressing or applied pressure, highly localized vibrations with very low natural frequencies were seen within the individual membrane bays. As the temperature was increased this phenomena was less apparent due to the expansion of the frame members stretching and pre-stressing the membrane.

The idea of colonizing the lunar surface is often difficult one to grasp, especially due to the lack of real world knowledge and experience with its challenges. This thesis presents a study with the goal of lunar colonization in mind beginning with the many different design criteria and loading characteristics on the Moon. These are then considered, with a focus on thermal loading, to determine their effect on the lunar surface and ultimately on the structural behavior of a frame-membrane composite structure. The results of this study provide a great deal of valuable information regarding not only frame-membrane composite structures, but also the lunar surface and colonization as well.

Major Advisor

Ramesh B. Malla

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