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This report is the result of the Space Station Redesign Team's activity. Its purpose is to present without bias, and in appropriate detail, the characteristics and cost of three design and management approaches for the Space Station Freedom. It was presented to the Advisory Committee on the Redesign of the Space Station on 7 Jun. 1993, in Washington, D.C.
Given a desired output trajectory, inversion-based techniques find input-state trajectories required to exactly track the output. These inversion-based techniques have been successfully applied to the endpoint tracking control of multijoint flexible manipulators and to aircraft control. The specified output trajectory uniquely determines the required input and state trajectories that are found through inversion. These input-state trajectories exactly track the desired output; however, they might not meet acceptable performance requirements. For example, during slewing maneuvers of flexible structures, the structural deformations, which depend on the required state trajectories, may be unacceptably large. Further, the required inputs might cause actuator saturation during an exact tracking maneuver, for example, in the flight control of conventional takeoff and landing aircraft. In such situations, a compromise is desired between the tracking requirement and other goals such as reduction of internal vibrations and prevention of actuator saturation; the desired output trajectory needs to redesigned. Here, we pose the trajectory redesign problem as an optimization of a general quadratic cost function and solve it in the context of linear systems. The solution is obtained as an off-line prefilter of the desired output trajectory. An advantage of our technique is that the prefilter is independent of the particular trajectory. The prefilter can therefore be precomputed, which is a major advantage over other optimization approaches. Previous works have addressed the issue of preshaping inputs to minimize residual and in-maneuver vibrations for flexible structures; Since the command preshaping is computed off-line. Further minimization of optimal quadratic cost functions has also been previously use to preshape command inputs for disturbance rejection. All of these approaches are applicable when the inputs to the system are known a priori. Typically, outputs (not inputs) are specified in tracking problems, and hence the input trajectories have to be computed. The inputs to the system are however, difficult to determine for non-minimum phase systems like flexible structures. One approach to solve this problem is to (1) choose a tracking controller (the desired output trajectory is now an input to the closed-loop system and (2) redesign this input to the closed-loop system. Thus we effectively perform output redesign. These redesigns are however, dependent on the choice of the tracking controllers. Thus the controller optimization and trajectory redesign problems become coupled; this coupled optimization is still an open problem. In contrast, we decouple the trajectory redesign problem from the choice of feedback-based tracking controller. It is noted that our approach remains valid when a particular tracking controller is chosen. In addition, the formulation of our problem not only allows for the minimization of residual vibration as in available techniques but also allows for the optimal reduction fo vibrations during the maneuver, e.g., the altitude control of flexible spacecraft. We begin by formulating the optimal output trajectory redesign problem and then solve it in the context of general linear systems. This theory is then applied to an example flexible structure, and simulation results are provided.
The Space Station Program was initiated in 1984 to provide for permanent human presence in an orbiting laboratory. This program evolved into Space Station Freedom, later identified as a component to facilitate a return of astronauts to the Moon, followed by the exploration of Mars. In March 1993 the Clinton Administration directed NASA to undertake an intense effort to redesign the space station at a substantial cost savings relative to Space Station Freedom. The Advisory Committee on the Redesign of the Space Station was established in March 1993 to provide independent assessment of the advantages and disadvantages of the redesign options. The results of the Committee's work is described. Discussion describes the mission that the Administration has articulated for the Space Station Program and the scientific and technical characteristics that a redesigned station must possess to fulfill those objectives. A description of recommended management, operations, and acquisition strategies for the redesigned program is provided. The Committee's assessment of the redesign options against five criteria are presented. The five criteria are technical capabilities, research capabilities, schedule, cost, and risk. A discussion of general mission risk is included.
A low-boom supersonic transport was generated in a previous low-boom multidisciplinary optimization (MDO) study that used computational fluid dynamics (CFD) off-body pressure to compute the undertrack sonic boom ground signature and calibrated low-fidelity aerodynamics analyses to compute the mission performance metrics. This low-boom aircraft, referred to as the Mach 1.7 40-PAX concept, can carry 40 passengers for a low-boom overland mission with cruise Mach 1.7 for the airport pairs over the continental US and has the potential to achieve an undertrack sonic boom ground noise level below 70 perceived level of decibels at the start of overland cruise (SOC). The engine for the Mach 1.7 40-PAX concept was designed using the Numerical Propulsion System Simulation (NPSS) for the mission analysis and modeled as a flow-through nacelle for CFD-based sonic boom analysis. To understand how the engine plume affects the undertrack ground signature, the Mach 1.7 40-PAX concept is redesigned in this paper after replacing the flow-through nacelles by CFD engines for sonic boom analysis using aeropropulsive CFD simulation. A process is developed for approximation of the NPSS engine at SOC by a CFD engine for aeropropulsive CFD simulation. The generated CFD engine has the identical nozzle boundary conditions and approximately the same mass flow and thrust as those of the NPSS engine at SOC. Then, the outer mold line of the configuration with the CFD engines is redesigned to approximately restore the low-boom characteristics of the Mach 1.7 40-PAX concept at SOC. Finally, the CFD simulation data for the redesigned concept with the CFD engines is used to calibrate the low-fidelity aerodynamic analyses for mission analysis of this concept. The cyclic dependency of the involved disciplinary analyses is resolved using an iteration method for a consistent coupling of the mission analysis, NPSS engine analysis, and low-boom redesign using the aeropropulsive CFD simulation. This low-boom redesign study is used as an example to demonstrate how the propulsion-airframe integration could be implemented for conceptual design of supersonic transports that satisfy both the low-boom and mission performance requirements.
The procedures, performance, and results obtained from the Thiokol Corporation/Wasatch Redesigned Field Joint Protection System (FJPS) Installation Evaluation are documented. The purpose of the evaluation was to demonstrate and develop the procedures required to install two different concepts (referred to as Concepts 1 and 3) of the redesigned FJPS. The processing capability of each configuration was then evaluated and compared. The FJPS is installed on redesigned solid rocket motors (RSRM) to protect the field joints from rain intrusion and to maintain the joint temperature sensor measurement between 85 and 122 F while the boosters are on the launch pad. The FJPS is being redesigned to reduce installation timelines at KSC and to simplify or eliminate installation processing problems related to the present design of an EPDM moisture seal/extruded cork combination. Several installation techniques were evaluated, and a preferred method of application was developed for each concept. The installations were performed with the test article in the vertical (flight) position. Comparative timelines between the two concepts were also developed. An additional evaluation of the Concept 3 configuration was performed with the test article in the horizontal position, to simulate an overhead installation on a technical evaluation motor (TEM).
The Mixed Mode Bending (MMB) test uses a lever to simultaneously apply mode I and mode II loading to a split beam specimen. An iterative analysis that accounts for the geometric nonlinearity of the MMB test was developed. The analysis accurately predicted the measured load displacement response and the strain energy release rate, G, of an MMB test specimen made of APC2 (AS4/PEEK). The errors in G when calculated using linear theory were found to be as large as thirty percent in some cases. Because it would be inconvenient to use a nonlinear analysis to analyze MMB data, the MMB apparatus was redesigned to minimize the nonlinearity. The nonlinear analysis was used as a guide in redesigning the MMB apparatus. With the redesigned apparatus, loads were applied through a roller attached to the level and loaded just above the midplane of the test specimen. The redesigned apparatuus has geometric nonlinearity errors of less than three percent, even for materials substantially tougher than APC2. This apparatus was demonstrated by measuring the mixed mode delamination fracture toughness of APC2.
The mixed-mode bending (MMB) test uses a lever to simultaneously apply mode I and mode II loading to a split-beam specimen. A nonlinear, iterative analysis that accurately predicts the measured load-displacement response and the strain energy release rate, G, of an MMB test, has shown that the errors in G calculated using linear theory can be quite large. The nonlinear analysis was used as a guide in redesigning the MMB apparatus. With the redesigned apparatus, loads are applied through a roller attached to the lever and loaded just above the midplane of the test specimen. The redesigned MMB apparatus has geometric nonlinearity errors of less than 3 percent, even for materials substantially tougher than APC2 (AS4/PEEK). This apparatus was demonstrated by measuring the mixed-mode delamination fracture toughness of APC2. The data from the redesigned MMB apparatus were analyzed with a linear analysis which yielded results similar to those found with the original apparatus and the nonlinear analysis.
The purpose of this summer project was to develop a set of schematic drawings for redesign of the Space Shuttle flight deck from which three dimensional computer drawings can be built and viewed in a virtual environment. In order to achieve this goal, first recommendations for overall redesign of Space Shuttle previously made by experts in the field were reviewed and relevant information was extracted and delineated. Original drawings of the Space Shuttle made by Rockwell were obtained and carefully examined. In order to implement and assess any modifications in terms of space saving parameters, it was determined that the drawings alone could not achieve this objective. As a complement, physical measurements of the mockup of Space Shuttle flight deck were made and the information was categorized and properly labeled on the original drawings. Then, spacesaving redesign ideas, as motivated by expert recommendations on such things as information display panel upgrade by technologically advanced flat display units, were implemented. Next, the redesign ideas were executed on the Forward flight deck, Overhead Console, Right and Left Console, and Center Console. A new 3-D computer drawing of this was developed by modifying the existing drawing on the in-house developed software (PLAID). Finally, the drawing was transported to a Virtual Environment and observed.
This paper describes the efforts to redesign, fabricate, assemble and test the wrist actuators on the Automated Tile Processing System (ATPS). The ATPS is a robotic system being developed at Kennedy Space Center to inspect and rewaterproof thermal protection tiles on the space shuttle orbiter prior to launch. The objective of the redesign was to eliminate backlash and provide adequate pitch and yaw actuator force. The wrist actuators have been successfully redesigned, fabricated, tested, and installed. The redesigned wrist actuators meet or exceed all design requirements. The wrist has been reinstalled on the tile processing robot and will be further evaluated during operational testing of the system.
The Space Shuttle Main Engine Liquid Air Insulation redesign was required to prevent the reoccurance of the STS-111 High Pressure Speed Sensor In-Flight Anomaly. The STS-111 In-Flight Anomaly Failure Investigation Team's initial redesign of the High Pressure Fuel Turbopump Pump End Ball Bearing Liquid Air Insulation failed the certification test by producing Liquid Air. The certification test failure indicated not only the High Pressure Fuel Turbopump Liquid Air Insulation, but all other Space Shuttle Main Engine Liquid Air Insulation. This paper will document the original Space Shuttle Main Engine Liquid Air STS-111 In-Flight Anomaly investigation, the heritage Space Shuttle Main Engine Insulation certification testing faults, the techniques and instrumentation used to accurately test the Liquid Air Insulation systems on the Stennis Space Center SSME test stand, the analysis techniques used to identify the Liquid Air Insulation problem areas and the analytical verification of the redesign before entering certification testing, Trade study down selected to three potential design solutions, the results of the development testing which down selected the final Liquid Air Redesign are also documented within this paper.
To design a more realistic low-boom supersonic demonstrator concept, theoretical engines were replaced with F-100 type engines. The original nacelle for the theoretical engine is replaced with a larger nacelle that is assumed adequate to house the F-100 engine. The process to redesign the configuration is then described and the rationales for design changes are given in some detail. Computational fluid dynamics (CFD) analysis was used to compute the equivalent area (A(sub e)) of the configuration during the redesign process. The goal of redesigning the configuration to match the CFD Ae of the configuration to a low-boom target was accomplished. The ground signature for CFD A(sub e) of the redesigned configuration has similar low-boom characteristics as that of the original low-boom configuration with theoretical engines.
NASA has conducted an extensive redesign effort for the Space Shutle in the aftermath of the STS 51-L Challenger accident, encompassing not only Shuttle vehicle and booster design but also such system-wide factors as organizational structure, management procedures, flight safety, flight operations, sustainable flight rate, and maintenance safeguards. Attention is presently given to Solid Rocket Booster redesign features, the Shuttle Main Engine's redesigned high pressure fuel and oxidizer turbopumps, the Shuttle Orbiter's braking and rollout (landing gear) system, the entry control mode of the flight control system, a 'split-S' abort maneuver for the Orbiter, and crew escape capsule proposals.
As a part of the redesign of the Space Shuttle Solid Rocket Motor, the field and nozzle-to-case joints were redesigned to minimize the dynamic flexure caused by internal motor pressurization during ignition. The O-ring seals and glands for the joints were designed to accommodate both structural deflections and to promote pressure assistance. A test program was conducted to determine if a fluorocarbon elastomeric O-ring could meet this criteria in the redesigned gland. Resiliency tests were used to investigate the O-ring response to gap motion while static seal tests were used to verify design criteria of pressure assistance for sealing. All tests were conducted in face seal fixtures mounted in servo-hydraulic test machines. The resiliency of the O-ring was found to be extremely sensitive to the effects of temperature. The External Tank/Solid Rocket Booster attach strut loads had a negligible affect on the ability of the O-ring to track the simulated SRB field joint deflection. In the static pressure-assisted seal tests, as long as physical contact was maintained between the O-ring and the gland sealing surface, pressure assistance induced instantaneous sealing.
A new digital redesign technique is developed for determining the digital version of an optimal momentum management controller previously designed by the authors for the Space Station Freedom. The technique matches all the states at all sampling instants to find a pseudo-continuous time quadratic regulator. It is shown that the redesigned digital states closely match the continuous time optimal states. It is also shown how the redesign technique can be applied to a state estimator.
The redesigned solid rocket motor of the Space Shuttle is described. Improvements over the model that led to the loss of the Space Shuttle Challenger are outlined. Scale and full-size tests carried out to verify the quality of the redesign are described. A unique feature of the test program is the introduction of deliberate flaws into some test articles. Post-flight evaluation of the redesigned boosters show excellent results.
In structural redesign, two structural states are involved; the baseline (known) State S1 with unacceptable performance, and the objective (unknown) State S2 with given performance specifications. The difference between the two states in performance and design variables may be as high as 100 percent or more depending on the scale of the structure. A Perturbation Approach to Redesign (PAR) is presented to relate any two structural states S1 and S2 that are modeled by the same finite element model and represented by different values of the design variables. General perturbation equations are derived expressing implicitly the natural frequencies, dynamic modes, static deflections, static stresses, Euler buckling loads, and buckling modes of the objective S2 in terms of its performance specifications, and S1 data and Finite Element Analysis (FEA) results. Large Admissible Perturbation (LEAP) algorithms are implemented in code RESTRUCT to define the objective S2 incrementally without trial and error by postprocessing FEA results of S1 with no additional FEAs. Systematic numerical applications in redesign of a 10 element 48 degree of freedom (dof) beam, a 104 element 192 dof offshore tower, a 64 element 216 dof plate, and a 144 element 896 dof cylindrical shell show the accuracy, efficiency, and potential of PAR to find an objective state that may differ 100 percent from the baseline design.
Engineers regularly analyze SSME ground test and flight data with respect to engine systems performance. Recently, a redesigned SSME powerhead was introduced to engine-level testing in part to increase engine operational margins through optimization of the engine internal environment. This paper presents an overview of the MSFC personnel engine systems analysis results and conclusions reached from initial engine level testing of the redesigned powerhead, and further redesigns incorporated to eliminate accelerated main injector baffle and main combustion chamber hot gas wall degradation. The conclusions are drawn from instrumented engine ground test data and hardware integrity analysis reports and address initial engine test results with respect to the apparent design change effects on engine system and component operation.
In early 1993, President Clinton mandated that NASA look at lower cost alternatives to Space Station Freedom. He also established an independent advisory committee - the Blue Ribbon Panel - to review the redesign work and evaluate alternatives. Daniel Goldin, NASA Administrator, established a Station Redesign Team that began operating in late March from Crystal City, Virginia. NASA intercenter teams - one each at Marshall Space Flight Center, Johnson Space Center, and Langley Research Center provided engineering and other support. The results of the Option A study done at Marshall Space Flight Center are summarized. Two configurations (A-1 and A-2) are covered. Additional data is provided in the briefing package MSFC SRT-001, Final System Review to SRT-002, Space Station Option A Modular Buildup Concept, Volumes 1-5, Revision B, June 10, 1993. In June 1993, President Clinton decided to proceed with a modular concept consistent with Option A, and asked NASA to provide an Implementation Plan by September. All data from the Option A redesign activity was provided to NASA's Transition Team for use in developing the Implementation Plan.