Martin Mikulas

Carbon Fiber Reinforced Shape Memory Polymer Composites

In this paper we present results on the deformation of carbon fiber reinforced shape memory polymer matrix composites for deployable space structure applications. The composites were processed using resin transfer molding or a pre-impregnated (pre-preg) laminate press, with both satin and plain weave fiber architectures. The polymer matrix glass transition temperature, T g , was approximately 95°C. Composite specimens were bent to specific radii at T = 120°C, and cooled while constrained to a temperature of 25°C, which left them frozen in the bent state. Heating the specimens above T g caused the composites to return to their original unbent shape with up to 95% recovery based on bend angle. The effect of constraint hold times up to 350 hours on the recoverability was found to be negligible. Microscopic investigations revealed that the dominant local deformation mode of the composites was buckling of the carbon fibers on the inner surface of the bend. Localized buckling out of the material plane lead to detrimental interfacial matrix failure while dispersed in-plane buckling was elastic and non-damaging. A clear path for tailoring the shape memory polymer composites to facilitate in-plane elastic buckling is presented and tested. The improved materials can bend to local radii of curvature, R, of 1.6 mm with full recoverability and negligible local damage.

Geometry attained by pressurized membranes

An intensive investigation has been carried out to study the surface profiles obtained as a result of the large deformations of pressurized membranes. The study shows that the inflated membrane shapes may have the requisite surface accuracy for use in future large space apertures. Both analytical and experimental work have been carried out. On the analytical side, the classical work of Hencky on flat circular membranes was extended to eliminate the limitations it imposed; namely a lateral non-follower pressure with no pre-stress. The result is a computer program for the solution of the pressurized circular membrane problem. The reliability of the computer program is demonstrated via verification against FAIM, a nonlinear finite element solver developed primarily for the analysis of inflated membrane shapes. The experimental work includes observations made by Veal on the (W-shaped) deviations between the membrane deflected shape and the predicted profile. More recent measurements have been made of the deformations of pressurized flat circular and parabolic membranes using photogrammetric techniques. The surface error quantification analyses include the effect of material properties, geometric properties, loading uncertainties, and boundary conditions. These effects are very easily handled by the special FEM code FAIM which had recently been enhanced to predict the on-orbit dynamics, RF, and solar concentration characteristics of inflatable parabolic antennas/reflectors such as the IAE that flew off the space shuttle Endeavour in May 1996. The results of measurements have been compared with analyses and their ramifications on precision-shape, large-aperture parabolic space reflectors are discussed. Results show that very large space apertures with surface slope error accuracies on the order to space reflectors are discussed. Results show that very large space apertures with surface slope error accuracies on the order of 1 milliradian or less are feasible. Surface shape accuracies of less than 1 mm RMS have been attained on ground measurements.

Tension Aligned Deployable Structures for Large 1-D and 2-D Array Applications

A concept is presented for the packaging and deployment of large tension aligned 1-D and 2-D arrays composed of hard panels with a finite thickness. The concept involves three novel features which together act to provide an array with unique packaging, deployment, and operational capabilities. First, a linear array of panels are supported only at the ends and require no continuous attachment along the support truss. This simplifies integration and enables modular development and use of heritage hardware. Also, since the panels are only supported at the ends and are aligned by tension, the array is isolated from the mechanical and thermal distortions of the truss. Second, the panels are attached to each other with revolute joints to simplify deployment and required mechanisms. Third, a pattern of hinges has been developed that allows a direct extension of the concept to a 2-D array of hard panels. Simple models are presented that demonstrate the 2-D array folding and deployment concept. Frequency analyses are presented of the 1-D and 2-D arrays that provide a perspective of their structural performance.

Torus-Less Inflated Membrane Reflector with an Exact Parabolic Center

A possible alternative to the lenticular configuration, the concept of a torus-less pressurized membrane antenna with an exact parabolic center, is introduced. For a characteristic symmetric configuration, three membrane regions are identified: the parabolic reflector center, the (wrinkled) perimeter that suspends it, and a transition zone between. Via an analysis of the pressurization kinematics, the last of the three is seen as critical. Structural economy and optimization are considered, and a design paradigm is established and demonstrated. It is also shown that there can exist mechanically sound pressurized membrane shapes for which no strain-free initial configurations correspond. The study is restricted to the pressurized membrane itself: no application-specific system integration issues are addressed.

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

Automation of a Versatile Crane (the LSMS) for Lunar Outpost Construction, Maintenance and Inspection

Devices for lifting, translating and precisely placing payloads are critical for efficient Earth-based construction operations. Both recent and past studies have demonstrated that devices with similar functionality will be needed to support lunar outpost operations. The first generation test-bed of a new high performance device, the Lunar Surface Manipulation System (LSMS) has been designed, built and field tested. The LSMS has many unique features resulting in a mass efficient solution to payload handling on the lunar surface. Typically, the LSMS device mass is estimated at approximately 3% of the mass of the heaviest payload lifted at the tip, or 1.8 % of the mass of the heaviest mass lifted at the elbow or mid-span of the boom for a high performance variant incorporating advanced structural components. Initial operational capabilities of the LSMS were successfully demonstrated during field tests at Moses Lake, Washington using a tele-operated approach. Joint angle sensors have been developed for the LSMS to improve operator situational awareness. These same sensors provide the necessary information to support fully automated operations, greatly expanding the operational versatility of the LSMS. This paper develops the equations describing the forward and inverse relation between LSMS joint angles and Cartesian coordinates of the LSMS tip. These equations allow various schemes to be used to optimize LSMS maneuvers. One such scheme will be described in detail that eliminates undesirable swinging of the payload at the conclusion of a maneuver, even when the payload is suspended from a passive rigid link. The swinging is undesirable when performing precision maneuvers, such as aligning an object for mating or positioning a camera. Use of the equations described here enables automated control of the LSMS greatly improving its operational versatility.

A Modular, Reusable Latch and Decking System for Securing Payloads During Launch and Planetary Surface Transport

Efficient handling of payloads destined for a planetary surface, such as the moon or Mars, requires robust systems to secure the payloads during transport on the ground, in-space and on the planetary surface. In addition, mechanisms to release the payloads need to be reliable to ensure successful transfer from one vehicle to another. An efficient payload handling strategy must also consider the devices available to support payload handling. Cranes used for overhead lifting are common to all phases of payload handling on Earth. Similarly, both recent and past studies have demonstrated that devices with comparable functionality will be needed to support lunar outpost operations. A first generation test-bed of a new high performance device that provides the capabilities of both a crane and a robotic manipulator, the Lunar Surface Manipulation System (LSMS), has been designed, built and field tested and is available for use in evaluating a system to secure payloads to transportation vehicles. National Institute of Aerospace, Hampton Va 23662 A payload handling approach must address all phases of payload management including: ground transportation, launch, planetary transfer and installation in the final system. In addition, storage may be required during any phase of operations. Each of these phases requires the payload to be lifted and secured to a vehicle, transported, released and lifted in preparation for the next transportation or storage phase. A critical component of a successful payload handling approach is a latch and associated carrier system. The latch and carrier system should minimize requirements on the: payload, carrier support structure and payload handling devices as well as be able to accommodate a wide range of payload sizes. In addition, the latch should; be small and lightweight, support a method to apply preload, be reusable, integrate into a minimal set of hard-points and have manual interfaces to actuate the latch should a problem occur. A latching system which meets these requirements has been designed and fabricated and will be described in detail. This latching system works in conjunction with a payload handling device such as the LSMS, and the LSMS has been used to test first generation latch and carrier hardware. All tests have been successful during the first phase of operational evaluations. Plans for future tests of first generation latch and carrier hardware with the LSMS are also described.

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.