Martin M. Mikulas

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.

Preliminary Design Considerations for 10-40 Meter-Diameter Precision Truss Reflectors

A simplified preliminary design capability for erectable precision segmented reflectors is presented. This design capability permits a rapid assessment of a wide range of reflector parameters as well as new structural concepts and materials. The preliminary design approach was applied to a range of precision reflectors from 10 meters to 100 meters in diameter while considering standard design drivers. The design drivers considered were: weight, fundamental frequency, launch packaging volume, part count, and on-orbit assembly time. For the range of parameters considered, on-orbit assembly time was identified as the major design driver. A family of modular panels is introduced which can significantly reduce the number of reflector parts and the on-orbit assembly time.

A Versatile Lifting Device for Lunar Surface Payload Handling, Inspection & Regolith Transport Operations

Devices for lifting and transporting payloads and material are critical for efficient Earth‐based construction operations. Devices with similar functionality will be needed to support lunar‐outpost construction, servicing, inspection, regolith excavation, grading and payload placement. Past studies have proposed that only a few carefully selected devices are required for a lunar outpost. One particular set of operations involves lifting and manipulating payloads in the 100 kg to 3,000 kg range, which are too large or massive to be handled by unassisted astronauts. This paper will review historical devices used for payload handling in space and on earth to derive a set of desirable features for a device that can be used on planetary surfaces. Next, an innovative concept for a lifting device is introduced, which includes many of the desirable features. The versatility of the device is discussed, including its application to lander unloading, servicing, inspection, regolith excavation and site preparation. A...

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.

POWERSAIL: THE CHALLENGES OF LARGE, PLANAR, SURFACE STRUCTURES FOR SPACE APPLICATIONS

Deployable surface structures, a subset of gossamer structures, are a near-term solution for producing large- area surfaces in orbit. These surfaces have a variety of applications, high stowed packing efficiency, and mass properties that increase flexibility in the overall system design. ABLE Engineerings SquareRigger, a major component of the Air Force Research Laboratory (AFRL) PowerSail program, is the first modular, large- scale, planar deployable surface structure intended for space applications. In developing and studying the basic module of this class of structure, a number of new challenges have arisen in ground testing and modeling. These challenges have led to changes in the modeling and testing procedures, resulting in an approach that closely ties finite element modeling with ground testing of modules and components. The approach is intended to generate increasingly accurate simulations of on- orbit behavior of surface structures unable to be completely tested on the ground.

Telescoping Solar Array Concept for Achieving High Packaging Efficiency

Lightweight, high-efficiency solar arrays are required for future deep space missions using high-power Solar Electric Propulsion (SEP). Structural performance metrics for stateof-the-art 30-50 kW flexible blanket arrays recently demonstrated in ground tests are approximately 40 kW/m3 packaging efficiency, 150 W/kg specific power, 0.1 Hz deployed stiffness, and 0.2 g deployed strength. Much larger arrays with up to a megawatt or more of power and improved packaging and specific power are of interest to mission planners for minimizing launch and life cycle costs of Mars exploration. A new concept referred to as the Compact Telescoping Array (CTA) with 60 kW/m3 packaging efficiency at 1 MW of power is described herein. Performance metrics as a function of array size and corresponding power level are derived analytically and validated by finite element analysis. Feasible CTA packaging and deployment approaches are also described. The CTA was developed, in part, to serve as a NASA reference solar array concept against which other proposed designs of 50-1000 kW arrays for future high-power SEP missions could be compared.

Design and Field Test of a Mass Efficient Crane for Lunar Payload Handling and Inspection: The Lunar Surface Manipulation System

Devices for lifting, translating and precisely placing payloads are critical for efficient Earthbased construction operations. Both recent and past studies have demonstrated that devices with similar functionality will be needed to support lunar outpost operations. Lunar payloads include: a) prepackaged hardware and supplies which must be unloaded from landers and then accurately located at their operational site, b) sensor packages used for periodic inspection of landers, habitat surfaces, etc., and c) local materials such as regolith which require grading, excavation and placement. Although several designs have been developed for Earth based applications, these devices lack unique design characteristics necessary for transport to and use on the harsh lunar surface. These design characteristics include: a) composite components, b) compact packaging for launch, c) simple in-field reconfiguration and repair, and d) support for tele-operated or automated operations. Also, in contrast to Earth-based construction, where special purpose devices dominate a construction site, a lunar outpost will require versatile devices which provide operational benefit from initial construction through sustained operations. This paper will detail the design of a unique, high performance, versatile lifting device designed for operations on the lunar surface. The device is called the Lunar Surface Manipulation System to highlight the versatile nature of the device which supports conventional cable suspended crane operations as well as operations usually associated with a manipulator such as precise positioning where the payload is rigidly grappled by a tool attached to the tip of the device. A first generation test-bed to verify design methods and operational procedures is under development at the NASA Langley Research Center and recently completed field tests at Moses Lake Washington. The design relied on non-linear finite element analysis which is shown to correlate favorably with laboratory experiments. A key design objective, reviewed in this paper, is the device s simplicity, resulting from a focus on the minimum set of functions necessary to perform payload offload. Further development of the device has the potential for significant mass savings, with a high performance device incorporating composite elements estimated to have a mass less than 3% of the mass of the maximum lunar payload lifted at the tip. The paper will conclude with future plans for expanding the operational versatility of the device.

Preliminary Structural Design Considerations and Mass Efficiencies for Lunar Surface Manipulator Concepts

‡The mass and sizing characteristics of manipulators for Lunar and Mars planetary surface applications are investigated by analyzing three structural configurations: a simple cantilevered boom with a square tubular cross-section; a hybrid cable/boom configuration with a square tubular cross-section support structure; and a hybrid cable/boom configuration with a square truss cross-section support structure. Design procedures are developed for the three configurations and numerical examples are given. A new set of performance parameters are developed that relate the mass of manipulators and cranes to a loading parameter. These parameters enable the masses of different manipulator configurations to be compared over a wide range of design loads and reach envelopes (radii). The use of these parameters is demonstrated in the form of a structural efficiency chart using the newly considered manipulator configurations. To understand the performance of Lunar and Mars manipulators, the design procedures were exercised on the three manipulator configurations assuming graphite/epoxy materials for the tubes and trusses. It is also assumed that the actuators are electric motor, gear reduction systems. Numerical results for manipulator masses and sizes are presented for a variety of manipulator reach and payload mass capabilities. Results are presented that demonstrate the sensitivity of manipulator mass to operational radius, tip force, and actuator efficiency. The effect of the value of gravitational force on the ratio of manipulator-mass to payload-mass is also shown. Finally, results are presented to demonstrate the relative mass reduction for the use of graphite/epoxy compared to aluminum for the support structure.

Space Structures on the Back of an Envelope: John Hedgepeth's Approach to Design

John M. Hedgepeth was among an elite group of engineers who were the main architects of NASA’s revolutionary research on large space structures during the 1970’s and 1980’s. He had an incisive ability to distill, for unique and complex structural design problems, a concise set of primary requirements and compact analytical expressions that relate key design parameters to critical performance metrics. Hedgepeth and his colleagues derived many such “back-of-theenvelope” expressions to facilitate the design of a wide variety of large space structures. Today, as a new generation of large space structures is being considered, it is timely to revisit Hedgepeth’s approach to the design of these structures. With this motivation, the present paper includes derivations of several “back-ofthe-envelope” solutions, some by the authors and one by Hedgepeth, to fundamental issues that must be addressed in the design of large space structures. Several conclusions are distilled from these analyses that have broad implication for space structure design. Nomenclature {AI} inertial acceleration vector AI magnitude of inertial acceleration vector {FI} D’Alembert inertial force vector {XI} displacement response vector {Xn} n th eigenvector (i.e., normal mode) [K] stiffness matrix [M] mass matrix { ˆ} N ordered set of unit normal vectors, nm, m=1,2,...M, from surface nodes {U} ordered set of nodal displacement vectors, um, m=1,2,...M, from member length errors * Chief Engineer, Associate Fellow AIAA † Associate Professor, Associate Fellow AIAA ‡ Professor Emeritus, Fellow AIAA Copyright

Preliminary design of a large tetrahedral truss/hexagonal panel aerobrake structural system

This paper introduces an aerobrake structural concept consisting of two primary components: (1) a lightweight erectable tetrahedral support truss, and (2) a heatshield composed of individual sandwich hexagonal panels which, when attached to the truss, function as a continuous aerobraking surface. A general preliminary analysis procedure to design the aerobrake components is developed, and values of the aerobrake design parameters which minimize the mass and packaging volume for a 120-foot-diameter aerobrake are determined. Sensitivity of the aerobrake design to variations in design parameters is also assessed.