Home

Lightweight Solar Sail for a Spacecraft Flying Near the Sun

A report proposes a high-temperature- resistant solar sail with an areal mass density less than 1 g/m2, for a spacecraft that would approach the Sun to within a distance of 0.2 astronomical unit (≈3 × 107 km). The sail would be made in multiple segments of a carbon microtruss fabric held in a network of tensioned lines. The segments and network would be designed to minimize tension in the fabric. The porosity of the fabric would be tailored so that to photons, the fabric would behave as though it were solid. Reflective metal surface films could be attached to the fabric. In advanced versions, the fabric could be directly coated with metal, or, alternatively, the fabric surface would be the sail surface and there would be no metal layer. The sail fabric would be wrapped around a sail cylinder and deployed by use of centrifugal force. A separate structure next to the sail cylinder would contain most of the deployment hardware and would be ejected after deployment of the sail to reduce the mass staying with the sail.

Posted in: Briefs, TSP, Materials

Read More >>

Fabricating Better PSSA-PVDF-Based MEAs for Fuel Cells

Changes in the fabrication process enhance electrochemical performance. Some changes have been made in the fabrication of PSSA/ PVDF-based membrane/electrode assemblies for direct methanol fuel cells. The effect of the changes is to improve the electrochemical performances of the cells.

Posted in: Briefs, TSP, Materials

Read More >>

Making Hydrophobic Cathodes for MEAs in Fuel Cells

Poly(tetra- fluoroethylene) powder is added to catalytic inks used to make electrodes. The fabrication of membrane/electrode assemblies (MEAs) for direct methanol fuel cells can be modified to make the cathodes hydro- phobic. These mod- ifications improve the performances of the fuel cells, as explained below.

Posted in: Briefs, TSP, Materials

Read More >>

Improved Polymer/Solid-Electrolyte Membranes for Fuel Cells

Because water would be unnecessary for proton conductivity, operating temp- eratures could be increased. A class of devel- opmental membrane electrolyte materials for methanol/air and hydrogen/air fuel cells is exemplified by a composite of (1) a melt-processable polymer [in particular, poly(vinylidene fluoride) (PVDF)] and (2) a solid proton conductor (in particular, cesium hydrogen sulfate). In comparison with previously tested membrane electrolyte materials, including those described in the two preceding articles, these developmental materials offer potential advantages of improved performance, lower cost, and greater amenability to manufacturing of fuel cells.

Posted in: Briefs, TSP, Materials

Read More >>

Nontoxic X-Ray-Absorbing Windows

Tantalum oxide/ polymer composites are molded into light-transparent plates. Windows that absorb x rays and are transparent to visible light can be made by compression molding of tantalum oxide/polymer com- posite materials. The main xray-absorbing medium in these windows is tantalum instead of lead, which is the traditional main x-ray-absorbing medium. These composite windows have been developed to replace lead-filled glass and lead-filled polymer x-ray-absorbing windows, which are unsuitable for use in some environments because of the toxicity of lead.

Posted in: Briefs, TSP, Materials

Read More >>

Research on Life-Prediction Methods for MMCs— Phase I

A report describes the completed first phase of a NASA/industry cooperative program of research on metal-matrix composites (MMCs) as lightweight, strong, high- temperature-resistant materials for use in future aircraft engines. The first phase of the research included assessment of life- and fracture-prediction methods, determination of fracture strengths and fatigue lives, and experiments in nondestructive evaluation. The metal-matrix composite specimens used in these studies were rings made of silicon-carbide-based fibers in a titanium-alloy matrix. The particular composite material was chosen because extensive data on the material were already available and the material is representative of composites that would be used in aircraft engines. Five fracture- and lifeprediction analysis methods were applied to the rings; their predictions were compared with each other and with experimental data on fracture of the rings. Manufacturing defects prevented the researchers from conducting planned cyclic tests. Fatigue-life predictions ranged from 1,000 to 15,000 cycles. Fracture-stress predictions were less scattered, ranging from 25 to 40.1 kpsi (172 to 276 MPa). Low-resolution x-ray computed tomography proved to be an effective nondestructiveevaluation technique.

Posted in: Briefs, TSP, Materials

Read More >>

Internal-Combustion Engines With Ringless Carbon Pistons

Efficiencies would be higher and weights lower than those of conventional engines. Internal-combustion engines would be constructed with cylinders and ringless pistons made of lightweight carbon/carbon composite materials, according to a proposal. This proposal is a logical extension of previous research that showed that engines that contain carbon/carbon pistons with conventional metal piston rings running in conventional metal cylinders perform better than do engines with conventional aluminum-alloy pistons. The observed performance improvement (measured as increased piston life during high-performance operation) can be attributed mainly to the low thermal expansion of the carbon-carbon composite. Carbon-carbon pistons can continue to operate under thermal loads that cause aluminum pistons to seize or sustain scuffing damage due to excessive thermal growth and thermal distortion.

Posted in: Briefs, Materials

Read More >>

The U.S. Government does not endorse any commercial product, process, or activity identified on this web site.