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NASA NTRS1987

Concept of adaptive structures

The concept of adaptive structures is brought up in connection with the need in ultra lightweight structural systems to maintain desired properties and configurations without human intervention when subjected to dynamic, thermal, and other environmental forces. Examples are large antenna structures and flexible robotic structures. In the both cases such adaptivity would allow less massive structural members to be employed under normal loading conditions. During special circumstances when unusually large loads are encountered, temporary stiffening would allow the use of less sturdy structures, resulting in large savings in their cost, and in increasing their mobility and efficiency. Within the framework of a finite-dimensional representation of structural dynamics, the adaptivity can be implemented by the dependence of the stiffness matrix (k) upon the expected load (Q), or expected (programmed) changes in configurations, i.e., (k) = (k(t)) where the dependence upon time is programmed in advance. In order to sustain unexpected loads the adaptive structure can be provided by feedback force control, or by a parametrical stiffness control.

Zak, Michail↗

NASA NTRS1994

Fabricating Structural Stiffeners By Superplastic Forming

Superplastic forming (SPF) of aluminum alloys effective technique for making strong, lightweight structural components conforming to close dimensional tolerances. Technique applied in experimental fabrication of prototypes of stiffening ribs for cylindrical tanks. When making structural panel, stiffening ribs spot-welded to metal skin. Use of discrete eliminates machining waste, and use of SPF. Cost of fabrication reduced.

Bales, Thomas T.↗

NASA NTRS1992

Development of a precision, six-axis laboratory dynamometer

This paper describes the design, fabrication, test, and operation of a unique six axis force/torque dynamometer The specimen table used to hold components under test is supported in a full six axis kinematic mount. Support struts fabricated from high strength steel with special integral two axis flexures link the specimen table to the load cell transducers. Realtime force/torque coordinate transform, root mean squared calculation, and data averaging, and color six axis display with controllable scaling are provided by a specially programmed desktop computer. The extensive structural analysis and design optimization required to obtain a stiff, well damped, lightweight structure is described in detail. Geometric optimization of the kinematic mount and fabrication details of the struts are also described.

P. J. Champagne↗

NASA NTRS1993

Machined Structural Panels With Integral End Fittings

Flat, cylindrical, or otherwise-shaped unitary machined corrugated metal panels used as structural skins, according to proposal. Machined plates offer advantages over such conventional lightweight structural components as formed corrugated sheets, composite panels, and honeycomb panels. Include integrally machined end fittings and are lighter, less prone to failure, easier to design and analyze, and offer greater stiffness. No additional stringers or frames needed for reinforcement.

Redmon, John W., Jr.↗

NASA NTRS2009

ATK Launch Vehicle (ALV-X1) Liftoff Acoustic Environments: Prediction vs. Measurement

The ATK Launch Vehicle (ALV-X1) provided an opportunity to measure liftoff acoustic noise data. NASA Marshall Space Flight Center (MSFC) engineers were interested in the ALV-X1 launch because the First Stage motor and launch pad conditions, including a relativity short deflector ducting, provide a potential analogue to future Ares I launches. This paper presents the measured liftoff acoustics on the vehicle and tower. Those measured results are compared to predictions based upon the method described in NASA SP-8072 "Acoustic Loads Generated by the Propulsion System" and the Vehicle Acoustic Environment Prediction Program (VAEPP) which was developed by MSFC acoustics engineers. One-third octave band sound pressure levels will be presented. This data is useful for the ALV-X1 in validating the pre-launch environments and loads predictions. Additionally, the ALV-X1 liftoff data can be scaled to define liftoff environments for the NASA Constellation program Ares vehicles. Vehicle liftoff noise is caused by the supersonic jet flow interaction with surrounding atmosphere or more simply, jet noise. As the vehicle's First Stage motor is ignited, an acoustic noise field is generated by the exhaust. This noise field persists due to the supersonic jet noise and reflections from the launch pad and tower, then changes as the vehicle begins to liftoff from the launch pad. Depending on launch pad and adjacent tower configurations, the liftoff noise is generally very high near the nozzle exit and decreases rapidly away from the nozzle. The liftoff acoustic time range of interest is typically 0 to 20 seconds after ignition. The exhaust plume thermo-fluid mechanics generates sound at approx.10 Hz to 20 kHz. Liftoff acoustic noise is usually the most severe dynamic environment for a launch vehicle or payload in the mid to high frequency range (approx.50 to 2000 Hz). This noise environment can induce high-level vibrations along the external surfaces of the vehicle and surrounding launch facility structures. The acoustic pressure fluctuations will induce severe vibrations in relatively large lightweight structures. Consequently, there is the potential for failure of the structure or attached electrical components. Due to these potential failures, the liftoff acoustic noise is one of the noise source inputs used to determine the vibro-acoustic qualification environment for a launch vehicle and its components.

Houston, Janice↗

NASA NTRS1992

Application of integrated structural analysis to the high speed civil transport

The Integrated Structural Analysis (ISA) system was developed in response to the need to define lightweight structures early in the design process for military aircraft. The objective of the ISA system is to permit rapid development of an optimized skin and big-bones structure that insures that the requirements of strength, dynamics, loads, and weight are met. While the system was originally developed for fighter aircraft, it is applicable to commercial transports or any other structures. The design requirements dictate the structural arrangement and sizing limitations to be imposed.

Saff, C. R.↗

NASA NTRS2001

Structural Dynamics Experimental Activities in Ultra-Lightweight and Inflatable Space Structures

This paper reports recently completed structural dynamics experimental activities with new ultra-lightweight and inflatable space structures (a.k.a., "Gossamer" spacecraft) at NASA Langley Research Center, NASA Marshall Space Flight Center, and NASA Goddard Space Flight Center. Nine aspects of this work are covered: 1) inflated, rigidized tubes, 2) active control experiments, 3) photogrammetry, 4) laser vibrometry, 5) modal tests of inflatable structures, 6) in-vacuum modal tests, 7) tensioned membranes, 8) deployment tests, and 9) flight experiment support. Structural dynamics will play a major role in the design and eventually in-space deployment and performance of Gossamer spacecraft. Experimental research and development such as this is required to validate new analysis methods. The activities discussed in the paper are pathfinder accomplishments. conducted on unique components and prototypes of future spacecraft systems.

Pappa, Richard S.↗

NASA NTRS1974

Advanced beaded and tubular structural panels. Volume 2: Fabrication

A study was conducted to exploit the efficiency of curved elements in the design of lightweight structural panels under combined loads of axial compression, inplane shear, and bending. A summary of the total program (analysis, fabrication and test) is presented in document NASA CR-2514. Detailed descriptions of the analysis effort and of the panel tests are contained in supplementary documents NASA CR-132460 and NASA-CR-132515 respectively. Data are also given on the development of economical fabrication techniques to minimize the effects of fabrication limitations on optimum panel designs.

Musgrove, M. D.↗

NASA NTRS1979

Space Construction Automated Fabrication Experiment Definition Study (SCAFEDS), part 3. Volume 3: Requirements

The performance, design and verification requirements for the space Construction Automated Fabrication Experiment (SCAFE) are defined. The SCAFE program defines, develops, and demonstrates the techniques, processes, and equipment required for the automatic fabrication of structural elements in space and for the assembly of such elements into a large, lightweight structure. The program defines a large structural platform to be constructed in orbit using the space shuttle as a launch vehicle and construction base.

Source record↗

NASA NTRS1987

Project CONDOR: Middle atmosphere wind structure obtained with lightweight inflatable spheres near the equatorial electrojet

Observed correlations between the atmospheric electric field and the neutral wind were studied using additional atmospheric measurements during Project CONDOR. Project CONDOR obtained measurements near the equatorial electrojet (12 S) during March 1983. Neutral atmosphere wind measurements were obtained using lightweight inflatable spheres and temperatures were obtained using a datasonde. The lightweight sphere technology, the wind structure, and temperature structure are described. Results show that the lightweight sphere gives higher vertical resolution of winds below 75 km compared with the standard sphere, but gives little or no improvement above 80 km, and no usable temperature and density data.

Schmidlin, F. J.↗

NASA NTRS2001

Detection of Micro-Leaks Through Complex Geometries Under Mechanical Load and at Cryogenic Temperature

Polymer Matrix Composite (PMC) hydrogen tanks have been proposed as an enabling technology for reducing the weight of Single-Stage-to-Orbit reusable launch vehicles where structural mass has a large impact on vehicle performance. A key development issue of these lightweight structures is the leakage of hydrogen through the composite material. The rate of hydrogen leakage can be a function of the material used, method of 6 fabrication used to manufacture the tank, mechanical load the tank must react, internal damage-state of the material, and the temperatures at which the tank must operate. A method for measuring leakage through a geometrically complex structure at cryogenic temperature and under mechanical load was developed, calibrated and used to measure hydrogen leakage through complex X-33 liquid-hydrogen tank structure sections.

Rivers, H. Kevin↗

NASA NTRS2016

Optimization of NTP System Truss to Reduce Radiation Shield Mass

The benefits of nuclear thermal propulsion are numerous and relevant to the current NASA mission goals involving but not limited to the crewed missions to mars and the moon. They do however also present new and unique challenges to the design and logistics of launching/operating spacecraft. One of these challenges, relevant to this discussion, is the significant mass of the shielding which is required to ensure an acceptable radiation environment for the spacecraft and crew. Efforts to reduce shielding mass are difficult to accomplish from material and geometric design points of the shield itself, however by increasing the distance between the nuclear engines and the main body of the spacecraft the required mass of the shielding is lessened considerably. The mass can be reduced significantly per unit length, though any additional mass added by the structure to create this distance serves to offset those savings, thus the design of a lightweight structure is ideal. The challenges of designing the truss are bounded by several limiting factors including; the loading conditions, the capabilities of the launch vehicle, and achieving the ideal truss length when factoring for the overall mass reduced. Determining the overall set of mass values for a truss of varying length is difficult since to maintain an optimally designed truss the geometry of the truss or its members must change. Thus the relation between truss mass and length for these loading scenarios is not linear, and instead has relation determined by the truss design. In order to establish a mass versus length trend for various truss designs to compare with the mass saved from the shield versus length, optimization software was used to find optimal geometric properties that still met the design requirements at established lengths. By solving for optimal designs at various lengths, mass trends could be determined. The initial design findings show a clear benefit to extending the engines as far from the main structure of the spacecraft as the launch vehicle's payload volume would allow when comparing mass savings verse the additional structure.

Scharber, Luke L.↗

NASA NTRS1974

Advanced beaded and tubular structural panels. Volume 1: Design and analysis

A study was conducted to exploit the efficiency of curved elements in the design of lightweight structural panels under combined loads of axial compression, inplane shear, and bending. Data cover analytical procedures for optimum panel design, static strength analyses, results of panel design studies, and correlation of theory with test results.

Greene, B. E.↗

NASA NTRS2011

Carbon Nanotubes on Titanium Substrates for Stray Light Suppression

A method has been developed for growing carbon nanotubes on a titanium substrate, which makes the nano tubes ten times blacker than the current state-of-the-art paints in the visible to near infrared. This will allow for significant improvement of stray light performance in scientific instruments, or any other optical system. Because baffles, stops, and tubes used in scientific observations often undergo loads such as vibration, it is critical to develop this surface treatment on structural materials. This innovation optimizes the carbon nano - tube growth for titanium, which is a strong, lightweight structural material suitable for spaceflight use. The steps required to grow the nanotubes require the preparation of the surface by lapping, and the deposition of an iron catalyst over an alumina stiction layer by e-beam evaporation. In operation, the stray light controls are fabricated, and nanotubes (multi-walled 100 microns in length) are grown on the surface. They are then installed in the instruments or other optical devices.

Hagopian, John↗

NASA NTRS1977

Method of making a composite sandwich lattice structure

A lattice type structural panel is described, which utilizes the unidirectional character of filamentary epoxy impregnated composites to produce stiff lightweight structural panels for use in constructing large area panels for space satellites and the like.

Rhodes, M. D.↗

NASA NTRS2012

Enhanced-Adhesion Multi-Walled Carbon Nanotubes on Titanium Substrates for Stray Light Control

Carbon nanotubes previously grown on silicon have extremely low reflectance, making them a good candidate for stray light suppression. Silicon, however, is not a good structural material for stray light components such as tubes, stops, and baffles. Titanium is a good structural material and can tolerate the 700 C nanotube growth process. The ability to grow carbon nanotubes on a titanium substrate that are ten times blacker than the current NASA state-of-the-art paints in the visible to near infrared spectra has been achieved. This innovation will allow significant improvement of stray light performance in scientific instruments or any other optical system. This innovation is a refinement of the utilization of multiwalled carbon nano tubes for stray light suppression in spaceflight instruments. The innovation is a process to make the surface darker and improve the adhesion to the substrate, improving robustness for spaceflight use. Bright objects such as clouds or ice scatter light off of instrument structures and components and make it difficult to see dim objects in Earth observations. A darker material to suppress this stray light has multiple benefits to these observations, including enabling scientific observations not currently possible, increasing observational efficiencies in high-contrast scenes, and simplifying instruments and lowering their cost by utilizing fewer stray light components and achieving equivalent performance. The prior art was to use commercially available black paint, which resulted in approximately 4% of the light being reflected (hemispherical reflectance or total integrated scatter, or TIS). Use of multiwalled carbon nanotubes on titanium components such as baffles, entrance aperture, tubes, and stops, can decrease this scattered light by a factor of ten per bounce over the 200-nm to 2,500-nm wavelength range. This can improve system stray light performance by orders of magnitude. The purpose of the innovation is to provide an enhanced stray light control capability by making a blacker surface treatment for typical stray light control components. Since baffles, stops, and tubes used in scientific observations often undergo loads such as vibration, it was critical to develop this surface treatment on structural materials. The innovation is to optimize the carbon nanotube growth for titanium, which is a strong, lightweight structural material suitable for spaceflight use. The titanium substrate carbon nanotubes are more robust than those grown on silicon and allow for easier utilization. They are darker than current surface treatments over larger angles and larger wavelength range. The primary advantage of titanium substrate is that it is a good structural material, and not as brittle as silicon.

Hagopian, John↗

NASA NTRS1991

Materials and light thermal structures research for advanced space exploration

The Light Thermal Structures Center at the University of Virginia sponsors educational and research programs focused on the development of reliable, lightweight structures to function in hostile thermal environments. Technology advances in materials and design methodology for light thermal structures will contribute to improved space vehicle design concepts with attendant weight savings. This paper highlights current research activities in three areas relevant to space exploration: low density, high temperature aluminum alloys, composite materials, and structures with thermal gradients. Advances in the development of new aluminum-lithium alloys and mechanically alloyed aluminum alloys are described. Material properties and design features of advanced composites are highlighted. Research studies in thermal structures with temperature gradients include inelastic panel buckling and thermally induced unstable oscillations. Current and future research is focused on the integration of new materials with applications to structural components with thermal gradients.

Thornton, Earl A.↗

NASA NTRS2015

Space Structure Development

The duration of my Summer 2015 Internship Tour at NASA's Johnson Space Center was spent working in the Structural Engineering Division's Structures Branch. One of the two main roles of the Structures Branch, ES2, is to ensure the structural integrity of spacecraft vehicles and the structural subsystems needed to support those vehicles. The other main objective of this branch is to develop the lightweight structures that are necessary to take humans beyond Low-Earth Orbit. Within ES2, my four projects involved inflatable space structure air bladder material testing; thermal and impact material testing for spacecraft windows; structural analysis on a joint used in the Boeing CST-100 airbag system; and an additive manufacturing design project.

Smith, Thomas↗