Judith J. Watson

Truss Performance and Packaging Metrics

In the present paper a set of performance metrics are derived from first principals to assess the efficiency of competing space truss structural concepts in terms of mass, stiffness, and strength, for designs that are constrained by packaging. The use of these performance metrics provides unique insight into the primary drivers for lowering structural mass and packaging volume as well as enabling quantitative concept performance evaluation and comparison. To demonstrate the use of these performance metrics, data for existing structural concepts are plotted and discussed. Structural performance data is presented for various mechanical deployable concepts, for erectable structures, and for rigidizable structures.

A history of astronaut construction of large space structures at NASA Langley Research Center

During the 1970s through the early 1990s, NASA Langley Research Center (LaRC) conducted studies for the design and construction of large space structures in Low Earth Orbit (LEO). The Langley studies focused on the design and construction of erectable space structures. The construction studies evaluated assembly methods using astronauts with and without mechanized foot-restraints. Astronaut construction was shown to be very effective and efficient when the structure and the construction methods were developed in parallel. This paper presents an overview of the LaRC astronaut construction studies of erectable structures, including a database of assembly rates and lessons learned. In addition this paper presents potential applications of erectable structure assembly methods using EVA astronauts and a suggested integrated approach for construction of large space structures.

Finite Element Modeling and Analysis of Large Pretensioned Space Structures

Pretensioned structures have great potential for providing the required size, stiffness, and packaging efficiency for large deployable space structures such as radio antenna, radar, and solar reflectors. These structures, however, are difficult tomodel correctly using standard numerical techniques, such as finite element analysis, and the current lack of literature on a robust modeling methodology can lead to analysis errors and wasted time. This paper details the static and dynamic behavior of pretensioned systems in their analytical forms and demonstrates how that behavior can be characterized using commercially available finite element software. This study was performed using ABAQUS Standard/CAE, but the methodology could be applied to any of the major finite element packages. A simple cable–beam system and a pretensioned truss structure are analyzed to verify the methodology and illustrate its suitability tomodeling the behavior of complex pretensioned structures. This paper provides an introduction and overview to modeling and analyzing pretensioned space structures for analysts and engineers familiar with modern finite element methods.

In-Space Structural Assembly: Applications and Technology

As NASA exploration moves beyond earths orbit, the need exists for long duration space systems that are resilient to events that compromise safety and performance. Fortunately, technology advances in autonomy, robotic manipulators, and modular plug-and-play architectures over the past two decades have made in-space vehicle assembly and servicing possible at acceptable cost and risk. This study evaluates future space systems needed to support scientific observatories and human/robotic Mars exploration to assess key structural design considerations. The impact of in-space assembly is discussed to identify gaps in structural technology and opportunities for new vehicle designs to support NASAs future long duration missions.

Space Assembly of Large Structural System Architectures (SALSSA)

Developing a robust capability for Space Assembly of Large Spacecraft Structural System Architectures (SALSSA) has the potential to drastically increase the capabilities and performance of future space missions and spacecraft while significantly reducing their cost. Currently, NASA architecture studies and space science decadal surveys identify new missions that would benefit from SALSSA capabilities, and the technologies that support SALSSA are interspersed throughout the fourteen NASA Technology Roadmaps. However, a major impediment to the strategic development of cross-cutting SALSSA technologies is the lack of an integrated and comprehensive compilation of the necessary information. This paper summarizes the results of a small study that used an integrated approach to formulate a SALSSA roadmap and associated plan for developing key SALSSA technologies.

Design and Analysis of Tension -Aligned Large Aperture Sensorcraft

Advances in materials, manufacturing and structural design have led to the realization of v ery large, highl y compactable space structures. These structures provide the support required for a variety of volumetrically large payloads, such as antennas, reflectors and radar arrays. Typically, the sensor surface is directly attached to the support s tructure and must therefore be precisely integrated into the folding and deployment scheme of the entire system. This requires numerous and often complex attachment points to maintain a viable and compact packaging arrangement. The support structure must a lso deploy into, and maintain a highly precise state to attain a high degree of surface accuracy and minimize the need for ancillary corrections. A study has been performed to explore a new class of structures that offer a solution to these issues. The se nsor surface in the conceptual study is attached to the ends of the support structure in the manner of a bow and string . A small number of intermediary supports are added to represent locations at which con trol elements, such as actuators or dampers c ould be added. The fundamental frequency of the system with the surface directly attached to the support structure is taken as the baseline requirement for the new concept. The tension in the surface is adjusted in the new concept until the system frequency mat ches the baseline. The analyses result in a distinctly nonlinear relationship between the required tension level and the mass of the radar array, which is dependent on the coupled interactions of the frequency, mass, member stiffnesses and number of inte rmediary connections. Additional studies demonstrate that the bending deformation induced in the base structure can be reduced or removed by the addition of an appropriately tensioned upper cable, attached to a small central support column. Previous approa ches to Large Space Structures with attached surfaces are discussed followed by an explanation of the fundamental mechanics of the Tension -Ali gned Large Aperture Sensorcraft. A series of parametric analyses are then presented that demonstrate how the stiff ness of the structure can be tailored to meet a given requirement by variation of the key system parameters. Engineering impli cations are summarized and some concluding remarks are offered

Mars surface tunnel element concept

When the first human visitors on Mars prepare to return to Earth, they will have to comply with stringent planetary protection requirements. Apollo Program experience warns that opening an EVA hatch directly to the surface will bring dust into the ascent vehicle. To prevent inadvertent return of potential Martian contaminants to Earth, careful consideration must be given to the way in which crew ingress their Mars Ascent Vehicle (MAV). For architectures involving more than one surface element - such as an ascent vehicle and a pressurized rover or surface habitat - a retractable tunnel that eliminates extravehicular activity (EVA) ingress is an attractive solution. Beyond addressing the immediate MAV access issue, a reusable tunnel may be useful for other surface applications, such as rover to habitat transfer, once its primary mission is complete. A National Aeronautics and Space Administration (NASA) team is studying the optimal balance between surface tunnel functionality, mass, and stowed volume as part of the Evolvable Mars Campaign (EMC). The study team began by identifying the minimum set of functional requirements needed for the tunnel to perform its primary mission, as this would presumably be the simplest design, with the lowest mass and volume. This Minimum Functional Tunnel then becomes a baseline against which various tunnel design concepts and potential alternatives can be traded, and aids in assessing the mass penalty of increased functionality. Preliminary analysis indicates that the mass of a single-mission tunnel is about 237 kg, not including mass growth allowance.

Non-Axisymmetric Inflatable Pressure Structure (NAIPS) Full-Scale Pressure Test

Inflatable space structures have the potential to significantly reduce the required launch volume for large pressure vessels required for exploration applications including habitats, airlocks and tankage. In addition, mass savings can be achieved via the use of high specific strength softgoods materials, and the reduced design penalty from launching the structure in a densely packaged state. Large inclusions however, such as hatches, induce a high mass penalty at the interfaces with the softgoods and in the added rigid structure while reducing the packaging efficiency. A novel, Non-Axisymmetric Inflatable Pressure Structure (NAIPS) was designed and recently tested at NASA Langley Research Center to demonstrate an elongated inflatable architecture that could provide areas of low stress along a principal axis in the surface. These low stress zones will allow the integration of a flexible linear seal that substantially reduces the added mass and volume of a heritage rigid hatch structure. This paper describes the test of the first full-scale engineering demonstration unit (EDU) of the NAIPS geometry and a comparison of the results to finite element analysis.

Non-Axisymmetric Inflatable Pressure Structure (NAIPS) Concept that Enables Mass Efficient Packageable Pressure Vessels with Sealable Openings

Achieving minimal launch volume and mass are always important for space missions, especially for deep space manned missions where the costs required to transport mass to the destination are high and volume in the payload shroud is limited. Pressure vessels are used for many purposes in space missions including habitats, airlocks, and tank farms for fuel or processed resources. A lucrative approach to minimize launch volume is to construct the pressure vessels from soft goods so that they can be compactly packaged for launch and then inflated en route or at the final destination. In addition, there is the potential to reduce system mass because the packaged pressure vessels are inherently robust to launch loads and do not need to be modified from their in-service configuration to survive the launch environment. A novel concept is presented herein, in which sealable openings or hatches into the pressure vessels can also be fabricated from soft goods. To accomplish this, the structural shape is designed to have large regions where one principal stress is near zero. The pressure vessel is also required to have an elongated geometry for applications such as airlocks.

Structural concepts for a lunar transfer vehicle aerobrake which can be assembled on orbit

A multidisciplinary conceptual study was conducted to define a reusable lunar transfer vehicle (LTV) aerobrake which could be launched on a Space Shuttle of Titan 4 and assembled on orbit at Space Station Freedom. A major objective was to design an aerobrake, with integrated structure and thermal protection systems, which has a mass less than 20 percent (9040 lb) of the LTV lunar return mass. The aerobrake segmentation concepts, the structural concepts, a joint concept for assembly, and a structural design with analysis of the aerobrake are described. Results show that a 50-foot diameter LTV aerobrake can be designed for on-orbit assembly which will achieve the 20 percent mass budget.