Michoud Assembly Facility

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

During the past few years, pultrusion of thermoplastic composites has shown the promise of becoming a major new force in the pultrusion industry. Advantages of thermoplastic pultrusion are the improved toughness, higher service temperature, and post-process formability that these advanced composite systems offer over thermosetting systems. However, the pultrusion of thermoplastics is much different from that of thermo setting materials, and much work remains before the processing of these materials becomes as well understood as that for thermosetting materials. This paper will describe the results of an experimentally based statistical study to determine the critical process pa rameters of the pultrusion of a thermoplastic material and how those parameters interact to affect the quality, integrity, and cost of the pultruded components.

Abstract A method for determining the aluminum oxide and aluminum metal atomic concentrations on complex aluminum alloy surfaces using a high‐energy Mg/Zr x‐ray source (1253.6 and 2042.4 eV, respectively) was discussed. XPS analysis of chemically processed aluminum surfaces using an Mg or Mg/Al anode limits the analysis of aluminum to the Al 2s and Al 2p photoelectron lines. Analysis of aluminum surfaces using the Al KLL Auger transition and the Mg or Mg/Al x‐ray source is accomplished with the bremsstrahlung radiation. The utility of the high‐energy Mg/Zr x‐ray anode is realized by offering the ability to qualitatively and quantitatively analyze aluminum using the Al KLL Auger region at 1374–1405 eV kinetic energy. The Al KLL Zr excited Auger transition provides a clear separation between the aluminum oxide and metal transitions (6.0 eV).

The application of a robot runaway protection system (RRPS) is discussed. The RRPS uses a triaxial accelerometer which is mounted on the robot's end effectors. The accelerometer signals are sampled, digitized and stored in computer memory during an initial system data acquisition mode. The stored data forms the reference signature which is associated with a specified cycle of robot motion. Once the reference signature is acquired, the system protection mode engages and guards against robot runaway. A mismatch between the real-time acceleration signal and the stored reference signature generates an abort command if threshold limits are exceeded.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hydrochlorofluorocarbons (HCFCs) have been widely adopted as an interim blowing agent in urethane insulations. Due to their scheduled phase-out, research efforts are being devoted to the identification and development of alternatives with zero ozone depletion potential. Physical blowing agents identified have included hydrocarbons, fluorocarbons, hydrofluoroethers, and more predominantly, hydrofluorocarbons (HFCs). The majority of the HFC evaluations have focused on the more readily available, low boiling candidates such as HFC 134a. Higher boiling HFC candidates that could be handled at ambient conditions and use current processing equipment would be more desirable. This paper will describe results from a research program of two such candidate HFCs performed as a cooperative effort between the Environmental Protection Agency, Oak Ridge National Laboratory and Martin Marietta Manned Space Systems. The purpose of this effort was to perform a limited evaluation of the developmental HFCs 245ca and 236ea as blowing agents in urethane based insulations. These two materials were selected from screening tests of 37 C 2 , C 3 and C 4 isomers based on physical properties, atmospheric lifetime, flammability, estimated toxicity, difficulty of synthesis, suitability for dual use as a refrigerant and other factors. Solubility of the two materials in typical foam components was tested, pour foaming trials were performed and preliminary data were gathered regarding foam insulation performance.

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

A Fortran IV computer program has been developed to design integrally stiffened two-panel boxes subject to fatigue-crack growth and fracture as well as side constraints, displacements, yielding, and local and general buckling. For crack growth and fracture, stress-intensity factors are compounded from available solutions, and final crack sizes are estimated using R-curve methods for the fracture constraints. An average and integrate strategy is employed for life prediction. Mathematical programming is used for design optimization, and approximation concepts reduce the constraint calculation effort. In the design procedure, multilayered constraint deletion and replacement of original constraint analyses by approximate substitutes define a sequence of approximate subproblems for design solution. For each subproblem, an extended Fiacco-McCormick penalty function is used with a modified Davidon-Fletcher-Powell deflected gradient algorithm for the unconstrained minimizations. The effective slope of crack growth with respect to stress-intensity factor is central to the success of procedures developed. This slope provides a normalizing exponent for the design constraints and a weighting exponent for efficient interpolation and quadrature to predict crack-growth lives. Probabilistic treatment of identified uncertainties in the crack growth ahd fracture analysis, in place of across the board safety factors, has improved design efficiency.

A numerical model was developed, with the SINDA'85/FLUINT program, for calculating the thermal and hydrodynamic transients that occur during the chilldown of a cryogenic transfer line, using a well documented test case to validate the modeling process. Using this model, a total of ten cases were analyzed to evaluate the effects of variable inlet valve position, inlet pressures, and the use of an internal flow liner to promote nucleate boiling. It was found that an efficient transfer line cooldown can be achieved if the inlet flow is throttled, to reduce the flow rate and quality, and an internal flow liner such as Teflon is used.

External Tanks (ET's) for Space Shuttle missions are coated with isocyanurate foams. These materials must perform as an insulator for cryogenic propellants and as an ablator during ascent conditions. Because of the limited high- temperature stability of conventional urethane foams, qualification of Spray-On Foam Insulation (SOFI) systems was undertaken early in the Shuttle program. The criteria used to chemically evaluate the individual components of the in sulation and the flame retardancy tests correlating composition, radiant reces sion rate and bond tension of the finished product are described in this paper. Laboratory methods to measure and control predefined component ratios for production units are also discussed.

Small amplitude, linearized wave theory is used to derive a differential equation for the sloshing wave height under conditions in which a sloshing liquid drains out of a tank of circular but variable cross sectional area, allowing for changes of effective gravity with time. A few illustrative examples are given in which analytical results can be displayed and interpreted. Numerical integrations are presented for various examples of interest with respect to slosh behavior in the bottom dome of the Space Shuttle External Tank during thrust termination, particularly as this bears on scavenging of cryogens.

The coupling of data and knowledge has a synergistic effect when building an intelligent data base. The goal is to integrate the data and knowledge almost to the point of indistinguishability, permitting them to be used interchangeably. Examples given in this paper suggest that Case-Based Reasoning is a more integrated way to link data and knowledge than pure rule-based reasoning.

Payload enclosures subjected to high energy acoustical environments may have high transmissability due to coupling between structural and acoustical modes. Reducing transmissability by mass attenuation, increased absorption or damping causes undesirable weight increases. Decoupling of the dynamic modes can be achieved without increasing weight by introducing a different gas (helium [HP] inside the enclosure from the ambient gas (air) outside the enclosure. For a certain frequency range, analytical studies of the External Tank Aft Cargo Carrier (ET/ACC) show nearly zero sound reduction through the structure. Various means were investigated to decrease sound transmission into the ACC compartment. Due to the large attenuation required, the only system that would work with air or nitrogen was a complicated, double wall acoustic liner with a limp mass barrier and absorption material. This system was heavy on the order of 2 lb/sq ft and expensive. Analysis showed that using He as a purge gas would only require a simple absorption layer to obtain the desired acoustical reduction. This system would be much lighter and cheaper than the double walled barrier. The sound attenuation capability of He was verified by testing a 4 ft x 6 ft panel. This test panel was designed to represent the anticipated structural characteristics of the ACC payload shroud. Transmission losses in the chamber were determined for air and various percentages of He. Test data verified that He would decouple structural and acoustical effects and decrease transtransmissibility of the panel.

Fracture toughness and cyclic crack propagation data for Ti-5A1-2.5Sn extra-low interstitial (ELI) castings, 0.51 and 2.54 cm (0.20 and 1.00 in.) thick, at 394, 294, 77, and 20 K (250, 70, −320, and −423° F), are presented. Both surface flaw and compact tension geometries were tested. Comparison is made with other titanium alloys in both wrought and cast forms. Crack propagation resistance is comparable to wrought Ti-5A1-2.5Sn ELI, even with the extremely coarse as-cast grain size encountered.

The history of the engineering and manufacturing requirements leading to the final Thermal Protection System (TPS) for the External Tank (ET) is presented. The thermal design for the ET must be optimized, based on considerations of cost, weight, and application of the TPS. The significant thermal requirements include the structural and component temperature limits, the propellant quality, the minimization of ice and frost, no air liquefaction, and no film boiling. The TPS materials selected to meet the requirements are a low density closed cell foam (CPR-488) and two light-weight ablators (SLA-56 and MA-25s). The first four flights of the Space Shuttle (1981) will measure and evaluate external environmental, structural, propulsion, electrical, and engine performance data. The ET will be instrumented to measure acoustics, pressures, heat transfer, vibration, temperatures, and structural strains. TPS weight reductions are planned for future ETs through the use of a comprehensive thermal instrumentation system.

Attention is given to the design parameters of the LH2/LO2 system in a description of the development of the external tank for the Space Shuttle Main Propulsion System (MPS). Design and functional changes for the MPS are reviewed, including: improvement of the vibroacoustic environment through the adaptation of a two-stage pilot to the existing basic valve design, a redesign of the GH2 vent line to accommodate increased deflections and loads, and the minimization of ice formation through slide joint insulation. The anti-geyser splash plate for the LO2 system is outlined in terms of fuel flow parameters under varying conditions of temperature and pressure, and test results for individual components are presented.

Welding processes and assembly techniques used in the fabrication of the external tank of the Space Shuttle are discussed. Each external tank consists of one liquid oxygen tank and one liquid hydrogen tank connected by an intertank skirt which is mechanically assembled; the fabrication of the external tank pressure vessel involves about 36,000 linear inches of weld required to join 138 pieces of 2219 aluminum. The discussion includes several innovations, such as building domes using the 1/4 panel assembly technique, which have been used in the fabrication of the tank.

An overview is presented of current studies that will permit more robust designs and reduce the safety hazards of maximum dynamic pressure during launches. Key considerations in the assessment of future operable launch capabilities are the dynamics problems that arise during the initial minutes of transition from the static configuration on the launch pad to the attainment of orbital velocity. Attention is given to a typical attempt to achieve robustness that involves creating a design in which the first bending mode will have a high enough frequency to allow decoupling between the autopilot design and the flexible body dynamics.

&lt;div class="htmlview paragraph"&gt;THE SPACE SHUTTLE EXTERNAL FUEL TANK (ET) is covered with a Thermal Protection System (TPS). The TPS materials are designed to prevent structural overheating during ascent/descent and maintain good quality cryogenic propellents until main engine cut off.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;The primary TPS materials consist of a nonmetallic rigid foam and a composite ablator. These materials and processes were developed through an evolutionary procedure, driven by changing requirements, definitions, and progressively increasing delivery rates. The evolution, from contract start in 1973 to the present, is reviewed.&lt;/div&gt;

The Oak Ridge National Laboratory has conducted treatability studies on clay soils taken from the Rinsewater Impoundment at the National Aeronautics and Space Administration Michoud Assembly Facility. The soils are contaminated with up to 3000 mg/kg of trichloroethylene and cis-1,2-dichloroethylene, less than 10 mg/kg of trans-1,2-DCE, and less than 10 mg/kg of vinyl chloride. The goal of the study described in this report was to identify and test in situ technologies and/or develop a modified treatment regime to remove or destroy volatile organic compounds from the contaminated clay soils. Much of the work was based upon previous experience with mixed-region vapor stepping and mixed-region peroxidation. Laboratory treatments were performed on intact soil cores that were taken from contaminated areas at the Rinsewater Impoundment at MAF. Treatability studies were conducted on soil that was close to in situ conditions in terms of soil structure and contaminant concentrations.

The marker and cell technique is applied to three idealized hydrodynamic situations of interest to the Space Shuttle External Tank (ET). These applications illustrate the versatility of this technique as well as its usefulness in solving similar problems in the aerospace industry. The codes used are the simplified marker and cell (SMAC) code and the variable grid simplified marker and cell code named ERIE. The examples focus on the dropout height in the LH2 tank, the slosh behavior of propellant in the bottom dome of the ET during thrust termination, both of which are required to accurately determine the amount of usable propellants, and the effect on liquid surface due to LO2 tank wall motions occurring during Space Shuttle lift-off. Comparisons with experimental results and linear theory are also presented.