Space Shuttle Cargo Bay Research Articles

A Comparison between SISO and MIMO Modal Analysis Techniques on a Membrane Mirror Satellite

The future of space satellite technology lies in the development of ultra-large, ultra-lightweight space structures, orders of magnitude greater in size than the current satellites. Such large crafts will increase communication and imaging capabilities from orbits. Many such proposed ultra-flexible satellites are inflated structures. To get these ultra-large structures in space, they will have to be stored within the Space Shuttle cargo bay and then inflated on-orbit. However, the highly flexible and pressurized nature of these ultra-large spacecraft poses several daunting vibration and control problems. Disturbances (i.e., on-orbit maneuvering, guidance and attitude control, and the harsh environment of space) wreck havoc with the on-orbit stability, pointing accuracy, and surface resolution capability of the inflated satellite. Fortunately, recent advances in integrated smart material systems promise to provide solutions to these problems. Recent research into the use of Macro-Fiber Composite (MFC®) devices integrated into the dynamic measurement and vibration control of inflated structures has had promising results (Wilkie et al., 2000). These piezoelectric-based devices possess a superior electro-mechanical coupling coefficient making them superb actuators and decent sensors in dynamic analysis applications. Initially, research was performed on an inflated torus using single-input, single-output (SISO) testing techniques. Since then, steps have been taken to outline a new, multiple-input, multiple-output (MIMO) testing technique for these ultra-large structures. This study applies these results to an inflated torus with bonded membrane mirror to extract modal parameters, such as the damped natural frequencies, associated damping, and mode shapes within the frequency bandwidth of interest for these structures (5–200 Hz). Further, the nonlinear dynamic behavior of the inflated torus and membrane mirror is accentuated through a comparison of SISO and MIMO modal analysis techniques, and a discussion of the nonlinear results follows. The purpose of this work is to apply the results from prior works to an inflated torus with bonded membrane mirror to accomplish the following three goals: (1) to establish a baseline dynamic characterization of the test structure using SISO modal analysis techniques;(2) to perform a MIMO modal analysis of the test structure to identify natural frequencies, mode shapes, and damping ratios, and compare these MIMO results to the SISO analysis; and(3) to use the discrepancies between the two testing technique results as a platform for discussing the nonlinear nature of the test structure. In the future, the results of this work may form the premise for an autonomous, self-contained system that can both identify the vibratory characteristics of an ultra-large, inflated space craft and apply an appropriate control algorithm to suppress any unwanted vibration – all while on-orbit.

A Follow-the-Leader Approach to Serpentine Robot Motion Planning

Serpentine robots offer advantages over traditional mobile robots and robot arms because they have enhanced flexibility and reachability, especially in convoluted environments. These robots are well suited to inspect large space-fairing truss structures such as the future space station and can also be used to inspect the Space Shuttle cargo bay before launch. Serpentine mechanisms offer unique capabilities on Earth to applications such as bridge inspection, search and rescue, surface coating, and minimally invasive surgery. The work described in this paper will exploit a geometric structure, termed a roadmap, to guide the motions of a serpentine robot in highly convoluted spaces. This approach offers advantages over previous work with serpentine robots because it provides a general mathematical structure that is not mechanism specific, thereby having applications to a large class of problems.

Optimization of Space Station components using design code CometBoards

Weight minimization is an important requirement in the design of components of the Space Station, since it can directly save launch cost, reduce the number of space shuttle missions, and facilitate on orbit assembly and fabrication. Preliminary optimum designs for such flight components are obtained using a design tool, termed ‘CometBoards’ and utilizing an animation feature of PATRAN software. Salient features of CometBoards include multiple non-linear programming optimizers; industrial strength analyzers; component synthesis concepts through a design variable formulation; constraint grouping scheme; and substructuring optimization technique, etc. The optimum design capability of CometBoards is illustrated using two flight components: (a) a ‘spacer structure’ of the solar power module of the Space Station, and (b) a ‘support system’ for integration in the space shuttle cargo bay. Optimum designs for both components have been obtained for multiple pseudo-static flight loads for behavior constraints confirming to specifications of the Space Station. The design optimization process generated lighter structures, with a reduction in the weights of about one third those obtained by the traditional manual design. Brief organization of CometBoards, description of the Space Station components, their design environments, behavior limitations, dynamic animation via PATRAN, along with the optimum designs are presented in this paper.

Thermospheric connections

Many people believe that the region of space familiar for visions of astronauts floating about their work outside a space shuttle cargo bay is empty, nothing, a vacuum. Contrary to popular opinion, the Earth's atmosphere extends even beyond that place where shuttle crews release, repair, or retrieve satellites. Despite its comparative anonymity, this remote layer of the atmosphere, known as the thermosphere, contributes to the protection of life on Earth. This is humankind's fundamental connection to the thermosphere. For that reason alone, it is deserving of our attention. The thermosphere is, in turn, affected by our activities. It is physically connected to the sun, Earth, and the remainder of Earth's atmosphere. Important insight into this complicated physical system frequently emerges when thermospheric scientists connect their individual research interests. This report is about all of these thermospheric connections.

Deflection characteristics of some special configurations of snake-type robots

The redundant robots analyzed here have large numbers of degrees of freedom. Such robots are analogous to snake or tentacles and are useful for operation in highly constrained environments and novel forms of locomotion — here it has been defined as critical manipulation. In this paper the end-point deflection of hyper-redundant robots have been studied by parameterization of the flexible links of the robot manipulator. A number of planar configurations of the redundant manipulator were taken into consideration for the present study and the configuration which gives minimum end-point deflection has been recommended for the critical manipulation. This work is significant for some of the research activities recently going on in NASA's Kennedy Space Center towards the application of hyper-redundant robots for manipulation inside the space Shuttle Cargo Bay.

On the Development of Control Laws for an Orbiting Tethered Antenna / Reflector System Test Scale Model

Tethered systems can be used to change the geometry and inertial characteristics of space structural systems to meet the gravity gradient stability requirements. The control law design for an orbiting shallow spherical shell (antenna/reflector) system connected by a massive and flexible tether to a subsatellite is investigated in this article. The subsatellite is nominally deployed below the antenna along the yaw axis at a sufficient distance to provide a favorable composite moment of inertia ratio for gravitational stabilization. It is assumed that the tether would be deployed through the end of a rigid boom attached to the shell apex. The tension control strategy is used for stationkeeping and deployment and the control gains are obtained based on the structural data for a future proposed real space antenna/reflector. In order to prove the feasibility of this concept, a test scale model for an in-orbit experiment is also studied. The scale model should be small enough so that it could be accommodated within the volume and size limitations of the space shuttle cargo bay. Since the or bital angular velocity (determined by the orbital altitude of the space shuttle), tether diameter, etc. may not be directly scaled, the control gains will be adjusted to fit the requirements for the scale model. Furthermore, during the deployment, the real control gains will be adjusted to the change of the length of the tether and the deployed tether mass. Therefore, the control law gains for the pro posed in-orbit experiment scale model would be synthesized in a piece-wise adaptive manner. Nu merical results are presented both for the real antenna as well as for the proposed in-orbit (test) scale model.

Vibroacoustic analysis of a space shuttle payload

A Vibroacoustic payload environment prediction system (VAPEPS) has been developed to perform statistical energy analysis of spacecraft under acoustic excitation. VAPEPS was employed to analyze the random vibration response of the NASA Office of Space Science-1 (USS-1 Payload in the space shuttle cargo bay acoustic environment. The OSS-1 payload consists of various experimental hardwares mounted on a pallet. The pallet is constructed of a framework covered with face panels that is responsive to the acoustic pressure field. The entire pallet structure was modeled as an equivalent plate with the same dimension, stiffness, surface mass density, and longitudinal wavespeed. Detailed models were also constructed of the individual panels of honeycomb construction, which make up the overall face panels. The predicted acceleration power spectral density in third octave bands was compared with experimental data measured at system level acoustic test in a reverberant chamber. The agreement is good.

Signal acquisition and processing for autonomous Space Shuttle cargo bay acoustic measurements (NASA G‐313)

Abstract : A narrowband trigonal acoustic transducer array and digital signal processing software are described in support of Space Shuttle Vibroacoustic experiment (NASA G-313). The three co-planar, vibrationally isolated pressure- sensing microphones, the preamplifiers and the filters are designed to meet dynamic range and anti-aliasing requirements for the digitization and processing of recorded flight data with one Herty resolution within the 30-780 Hz baseband acoustic spectrum. The experiment is designed to operate in environments up to 160 dB SPL and provides model recognition and directional information to identify resonances and localize high intensity sound sources within the ambient launch environment of the Space Shuttle Cargo Bay. Also included in this thesis is a model of the empty Cargo Bay resonances and modal density calculations based on an adiabatic perturbations of a rigid, right circular cylindrical enclosure.

Vacuum Baking of Shuttle/Centaur Components

A variation of the Centaur launch vehicle will be used as a high-performance upper stage to launch spacecraft from the Space Shuttle cargo bay into geosynchronous orbit. As an element of the Shuttle payload, Centaur must be designed to avoid contaminating sensitive spacecraft surfaces. Nonmetallic materials used in structural and electronic applications can exhibit high rates of outgassing in a space vacuum and contaminate critical spacecraft surfaces of varying temperatures as condensation occurs. Judicious material selection, per NASA specifications, is used to control instances of such contamination. Vacuum baking is permitted by NASA Specification SP-R-0022 to "bake out" potential sources of organic contamination. Most Shuttle/Centaur missions are planned for spacecraft having surfaces of various temperatures in locations that are susceptible to condensation of organic outgassing products. To determine the extent of potential contamination, General Dynamics has initiated a test program with the White Sands Test Facility that is designed to measure outgassing and condensation rates of nonmetallic components in their use configuration. This paper reviews the tests, equipment requirements, sensor instrumentation, and some of the results to date.

Islamsat: A Technologically Advanced System For Efficient Charting Of Natural Resources

The landmasses encompassing the Muslim World have vast resources contained in every conceivable type of terrain, from forested mountains toplains and deserts. These landmasses enclose such valuable resources as fertilesoil and minerals and oil. Islamic countries also encompass numerous water bodies of lakes and rivers. However, except in a few cases, most of these resources have not been efficiently utilized.The scarcity or lack of basic data have hampered the effective utilization of these resources. First and foremost, accurate topographic maps and detailed photographs are required to survey, assess and develop these resources. Conventional methods ofphoto acquisition and map making are no longer viable because ofthe time and expense they require to do the job.In the meantime, space-age techniques offer new ways to reduce the time,cost and expertise that are required for the efficient charting of natural resources.It is here proposed that Islamic countries join together to initiate a plan to launch a resourcesurvey satellite withinfive years. The satellite here namedIslamsat is to obtain high resolution, stereo, mapping quality photographsfrom space. The most suitable photographic systems for such a satellite are:(I) a high resolution panoramic camera; (2) a topographic quality mapping camera; and (3) a six-lens multispectral camera. Such a complement of photographic systems can either be mounted on the Space Shuttle cargo bay or launched by the Shuttle as afree-flying satellite, withfilm return capability.The use of such technologically advanced methods and techniques assures the acquisition of the necessary data for development of the resources of Islamic countries in a timely and cost-effective manner.