Manufacturing & Prototyping

Venting Closed-Cell Foam Panels

Stresses caused by differential gas pressures are reduced.

A technique for reducing in-flight loss of closed-cell foam insulation has been devised. In the original application, foam is used for thermal insulation on the external tank of the space shuttle. As the space shuttle ascends, aerodynamic effects cause an increase in surface temperature of the foam. This heating increases the internal cell gas pressure and reduces cell wall strength. The difference between the increasing pressure of the gases trapped in the foam cells and the decreasing pressure of the ambient air contribute to stresses that can break off pieces of foam during flight. Perforating the foam with small holes makes it possible for some trapped gases to escape, reducing the stresses sufficiently to keep the foam intact during ascent. This technique reduced in-flight foam loss by more than 95 percent. The vent holes could offer similar benefits in other applications where materials are subjected to thermal and pressure gradients.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Thermodynamics, Foams, Insulation, Spacecraft

Chemical Machining of Microscopic Holes and Grooves in Glass

This technique overcomes disadvantages of conventional macro- and micromachining.

A technique for making precise, microscopic holes and grooves in glass workpieces has been invented. The technique differs from both (1) traditional macroscopic mechanical drilling and milling and (2) conventional micromachining that involves etching through photolithographically patterned masks. The technique can be used, for example, to make holes between 20 µm and 1 mm in diameter.

Posted in: Briefs, Manufacturing & Prototyping, Machining processes, Manufacturing equipment and machinery, Chemicals, Glass, Nozzles

Two Concepts for Deployable Trusses

Thermal-actuation and misalignment-tolerant double-pivot designs are proposed.

Two concepts that could be applied separately or together have been suggested to enhance the utility of deployable truss structures. The concepts were intended originally for application to a truss structure to be folded for compact stowage during transport and subsequently deployed in outer space. The concepts may also be applicable, with some limitations, to deployable truss structures designed to be used on Earth.

Posted in: Briefs, Manufacturing & Prototyping, Aircraft structures, Design processes, Spacecraft

Use of Nanofibers to Strengthen Hydrogels of Silica, Other Oxides, and Aerogels

Research has shown that including up to 5 percent w/w carbon nanofibers in a silica backbone of polymer crosslinked aerogels improves its strength, tripling compressive modulus and increasing tensile stress-at-break fivefold with no increase in density or decrease in porosity. In addition, the initial silica hydrogels, which are produced as a first step in manufacturing the aerogels, can be quite fragile and difficult to handle before cross-linking. The addition of the carbon nanofiber also improves the strength of the initial hydrogels before cross-linking, improving the manufacturing process. This can also be extended to other oxide aerogels, such as alumina or aluminosilicates, and other nanofiber types, such as silicon carbide.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Fabrication, Nanomaterials, Polymers

Improved Attachment in a Hybrid Inflatable Pressure Vessel

Care is taken to distribute loads and maintain desired shapes.

Some modifications that could be made, separately or together, have been conceived as improvements of the generic design of a structure of the type described in “Hybrid Inflatable Pressure Vessel” (MSC-23024/92), NASA Tech Briefs, Vol. 28, No. 4 (April 2004), page 44. To recapitulate: The vessel is a hybrid that comprises an inflatable shell attached to a rigid structure. The inflatable shell is, itself, a hybrid that comprises (1) a pressure bladder restrained against expansion by (2) a restraint layer that comprises a web of straps made from high-strength polymeric fabrics. The present improvements are intended to overcome deficiencies in those aspects of the original design that pertain to attachment of the inflatable shell to the rigid structure. In a typical intended application, such attachment(s) would be made at one or more window or hatch frames to incorporate the windows or hatches as integral parts of the overall vessel.

Posted in: Briefs, TSP, Manufacturing & Prototyping

Electrostatic Separator for Beneficiation of Lunar Soil

Process complexity may be significantly reduced.

A charge separator has been constructed for use in a lunar environment that will allow for separation of minerals from lunar soil. Any future lunar base and habitat must be constructed from strong, dense materials to provide for thermal and radiation protection. It has been proposed that lunar soil may meet this need, and sintering of full-scale bricks has been accomplished using lunar simulant. In the present experiments, whole lunar dust as received was used. The approach taken here was that beneficiation of ores into an industrial feedstock grade may be more efficient. Refinement or enrichment of specific minerals in the soil before it is chemically processed may be more desirable as it would reduce the size and energy requirements necessary to produce the virgin material, and it may significantly reduce the process complexity.

The principle is that minerals of different composition and work function will charge differently when tribocharged against different materials, and hence be separated in an electric field. The charge separator is constructed of two parallel copper plates separated by a variable distance in a vacuumcompatible box. The top and bottom of the box are designed so that the separation and angle between the plates can be varied. The box has a removable front plate for access, and each plate is connected to a high-voltage, vacuumcompatible connector that connects to feedthroughs in a vacuum chamber. Each plate is respectively powered by positive and negative high-voltage regulated DC power modules. Tribocharged dust is fed into the top through a small hole, where it is subjected to an intense electric field generated between the plates. Positively charged particles will be attracted to the negative plate, while negatively charged particles will be attracted to the positive plate. Dust collected on each plate and on filter paper in the collection box at the bottom of the plates can then be weighed to determine the mass-fraction separation.

Because this device is meant for use in a lunar environment, much higher voltages can be used where there is no gas breakdown. Special care was taken in the design of the high-voltage connections to the separator plates. Pure copper plates and other materials were chosen for their low outgassing properties. Modeling of particle trajectories within the plates showed that for the Q/M (charge to mass ratio) measurements of the charged particles in vacuum, a smaller, more compact separator can be used on the Moon compared to the same device on Earth. Another advantage of this design is that, in the lower gravity environment of the Moon, particles will spend more time falling between the plates. Again, a smaller device and higher voltages can use this advantage to increase the efficiency of the lunar soil beneficiation process.

This work was done by Jacqueline Quinn, and Ellen Arens of NASA Kennedy Space Center, Steve Trigwell of ASRC Aerospace, and James Captain of the University of Central Florida. For more information, download the Technical Support Package (free white paper) at under the Manufacturing & Prototyping category. KSC-13007

Posted in: Briefs, TSP, Manufacturing & Prototyping, Soils, Chemicals, Materials properties, Construction vehicles and equipment, Spacecraft

Bonded Invar Clip Removal Using Foil Heaters

A new process uses local heating and temperature monitoring to soften the adhesive under Invar clips enough that they can be removed without damaging the composite underneath or other nearby bonds. Two 1×1 in. (≈2.5×2.5 cm), 10-W/in.2 (≈1.6-W/cm2), 80-ohm resistive foil Kapton foil heaters, with pressure-sensitive acrylic adhesive backing, are wired in parallel to a 50-V, 1-A limited power supply. At 1 A, 40 W are applied to the heater pair. The temperature is monitored in the clip radius and inside the tube, using a dual thermocouple readout. Several layers of aluminum foil are used to speed the heat up, allowing clips to be removed in less than five minutes. The very local heating via the foil heaters allows good access for clip removal and protects all underlying and adjacent materials.

Posted in: Briefs, Manufacturing & Prototyping, Heat treatment, Adhesives and sealants, Fasteners

Gratings Fabricated on Flat Surfaces and Reproduced on Non-Flat Substrates

A method has been developed for fabricating gratings on flat substrates, and then reproducing the groove pattern on a curved (concave or convex) substrate and a corresponding grating device. First, surface relief diffraction grating grooves are formed on flat substrates. For example, they may be fabricated using photolithography and reactive ion etching, maskless lithography, holography, or mechanical ruling. Then, an imprint of the grating is made on a deformable substrate, such as plastic, polymer, or other materials using thermoforming, hot or cold embossing, or other methods. Interim stamps using electroforming, or other methods, may be produced for the imprinting process or if the same polarity of the grating image is required. The imprinted, deformable substrate is then attached to a curved, rigid substrate using epoxy or other suitable adhesives. The imprinted surface is facing away from the curved rigid substrate.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Fabrication, Manufacturing equipment and machinery, Stamping

Fabricating Radial Groove Gratings Using Projection Photolithography

Projection photolithography has been used as a fabrication method for radial grove gratings. Use of photolithographic method for diffraction grating fabrication represents the most significant breakthrough in grating technology in the last 60 years, since the introduction of holographic written gratings. Unlike traditional methods utilized for grating fabrication, this method has the advantage of producing complex diffractive groove contours that can be designed at pixel-by-pixel level, with pixel size currently at the level of 45×45 nm. Typical placement accuracy of the grating pixels is 10 nm over 30 nm. It is far superior to holographic, mechanically ruled or direct e-beam written gratings and results in high spatial coherence and low spectral cross-talk. Due to the smooth surface produced by reactive ion etch, such gratings have a low level of randomly scattered light. Also, due to high fidelity and good surface roughness, this method is ideally suited for fabrication of radial groove gratings.

Posted in: Briefs, Manufacturing & Prototyping, CAD, CAM, and CAE, Lasers, Fabrication, Finishing

Discrete Fourier Transform Analysis in a Complex Vector Space

Alternative computational strategies for the Discrete Fourier Transform (DFT) have been developed using analysis of geometric manifolds. This approach provides a general framework for performing DFT calculations, and suggests a more efficient implementation of the DFT for applications using iterative transform methods, particularly phase retrieval. The DFT can thus be implemented using fewer operations when compared to the usual DFT counterpart. The software decreases the run time of the DFT in certain applications such as phase retrieval that iteratively call the DFT function. The algorithm exploits a special computational approach based on analysis of the DFT as a transformation in a complex vector space. As such, this approach has the potential to realize a DFT computation that approaches N operations versus Nlog(N) operations for the equivalent Fast Fourier Transform (FFT) calculation.

Posted in: Briefs, Manufacturing & Prototyping

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