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At least 397 records · Page 22

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NASA NTRS1989

SPAN security policies and guidelines

A guide is provided to system security with emphasis on requirements and guidelines that are necessary to maintain an acceptable level of security on the network. To have security for the network, each node on the network must be secure. Therefore, each system manager, must strictly adhere to the requirements and must consider implementing the guidelines discussed. There are areas of vulnerability within the operating system that may not be addressed. However, when a requirement or guideline is discussed, implementation techniques are included. Information related to computer and data security is discussed to provide information on implementation options. The information is presented as it relates to a VAX computer environment.

Sisson, Patricia L.↗

NASA NTRS1991

Hardening communication ports for survival in electrical overstress environments

Greater attention is being focused on the protection of data I/O ports since both experience and lab tests have shown that components at these locations are extremely vulnerable to electrical overstress (EOS) in the form of transient voltages. Lightning and electrostatic discharge (ESD) are the major contributors to these failures; however, these losses can be prevented. Hardening against transient voltages at both the board level and system level has a proven record of improving reliability by orders of magnitude. The EOS threats, typical failure modes, and transient voltage mitigation techniques are reviewed. Case histories are also reviewed.

Clark, O. Melville↗

NASA NTRS1991

Lightning protection for shuttle propulsion elements

The results of lightning protection analyses and tests are weighed against the present set of waivers to the NASA lightning protection specification. The significant analyses and tests are contrasted with the release of a new and more realistic lightning protection specification, in September 1990, that resulted in an inordinate number of waivers. A variety of lightning protection analyses and tests of the Shuttle propulsion elements, the Solid Rocket Booster, the External Tank, and the Space Shuttle Main Engine, were conducted. These tests range from the sensitivity of solid propellant during shipping to penetration of cryogenic tanks during flight. The Shuttle propulsion elements have the capability to survive certain levels of lightning strikes at certain times during transportation, launch site operations, and flight. Changes are being evaluated that may improve the odds of withstanding a major lightning strike. The Solid Rocket Booster is the most likely propulsion element to survive if systems tunnel bond straps are improved. Wiring improvements were already incorporated and major protection tests were conducted. The External Tank remains vulnerable to burn-through penetration of its skin. Proposed design improvements include the use of a composite nose cone and conductive or laminated thermal protection system coatings.

Goodloe, Carolyn C.↗

NASA NTRS1991

Lightning protection of full authority digital electronic systems

Modern electronic systems are vulnerable to transient and they now provide safety critical functions such as full authority digital electronic control (FADEC) units for fly by wire aircraft. Of the traditional suppression technologies available diodes have gained the wider acceptance, however, they lack the current handling capacity to meet existing threat levels. The development of high speed fold back devices where, at a specified voltage, the off state resistance switches to a very low on state one has provided the equivalent to a semiconductor spark gap. The size of the technology enables it to be integrated into connectors of interconnection cables. To illustrate the performance the technology was developed to meet the Lightning Protection requirements for FADEC units within aeroengines. Work was also carried out to study switching behavior with the waveform 5, the 500 us, 10 kA pulse applied to cable assemblies. This test enabled all the switches in a connector to be fired simultaneously.

Crofts, David↗

NASA NTRS1991

Moessbauer spectra of olivine-rich achondrites - Evidence for preterrestrial redox reactions

Moessbauer spectral measurements at 4.2 K were made on several ureilites and the two shergottites found in Antarctica, as well as two ureilite falls, three SNC meteorite falls, and two finds in order to distinguish products of preterrestrial redox reactions from phases formed during oxidative weathering on the earth. The spectra indicated that several ureilites contain major proportions of metallic iron, much of which resulted from preterrestrial carbon-induced reduction of ferrous iron in the outermost 10-100 microns of olivine grains in contact with carbonaceous material in the ureilites. The cryptocrystalline nature of these Fe inclusions in olivine renders the metal extremely vulnerable to aerial oxidation, even in ureilites collected as falls. It is inferred that the nanophase ferric oxides or oxyhydroxides identified in Brachina and Lafayette were produced by terrestrial weather of olivines before the meteorites were found. The absence of goethite in two olivine-bearing Antarctic shergottites suggests that the 2 percent ferric iron determined in their Moessbauer spectra also originated from oxidation on Mars.

Burns, R. G.↗

NASA NTRS1992

Robust Method For Robotic Mapping

Robot constructs map from experience. Topological model consists of nodes and arcs corresponding to distinctive places and local travel edges linking nearby distinctive places. Model created by linking places and edges. Enables accumulation of metrical information with reduced vulnerability to metrical errors. Applications include robotic sentires, robotic delivery trucks, robotic floor cleaners, and robotic lawnmowers.

Kuipers, Benjamin J.↗

NASA NTRS1992

Rugged Noncontact Backshorts For Waveguides

Improved adjustable noncontact backshort for waveguide easily scaled to any frequency from 1 to 1,000 GHz, not vulnerable to wear, oxidation, or corrosion of contacts, and stronger and easier to fabricate. Will allow development of waveguide mixer and oscillator circuits at frequencies approaching 1,000 GHz, for atmospheric and astrophysical remote-sensing programs.

Mcgrath, William R.↗

NASA NTRS1992

Notch Charge-Coupled Devices

Notch charge-coupled devices are imaging arrays of photodetectors designed to exhibit high charge-transfer efficiencies necessary for operation in ultra-large array, and less vulnerable to degradation by energetic protons, neutrons, and electrons. Main channel of horizontal register includes deep narrow inner channel (notch). Small packets of charge remain confined to notch. Larger packets spill into rest of channel; transferred in usual way. Degradation of charge-transfer efficiency by energetic particles reduced.

Janesick, James↗

NASA NTRS1992

Radar Altimetry For Topographical Mapping

Two altimeter concepts based on spaceborne synthetic-aperture-radar (SAR) proposed to gather global, uniformly sampled, high-resolution, topographical data on land and ice. Wide swath and high pulse rate of SAR makes possible to acquire spatially contiguous data over large areas in reasonable amount of time, and time needed for altimetric processing of SAR data considerably less than that needed to generate topographical maps from stereoscopic photographs. Radar less vulnerable to cloud cover and other weather conditions than optical techniques.

Im, Eastwood↗

NASA NTRS1991

Design of joint source/channel coders

The need to transmit large amounts of data over a band limited channel has led to the development of various data compression schemes. Many of these schemes function by attempting to remove redundancy from the data stream. An unwanted side effect of this approach is to make the information transfer process more vulnerable to channel noise. Efforts at protecting against errors involve the reinsertion of redundancy and an increase in bandwidth requirements. The papers presented within this document attempt to deal with these problems from a number of different approaches.

Source record↗

NASA NTRS1992

Atomic oxygen undercutting of LDEF aluminized-Kapton multilayer insulation

Atomic oxygen undercutting is a potential threat to vulnerable spacecraft materials which have atomic oxygen protective coatings. Such undercutting is due to atomic oxygen attack of oxidizable materials at microscopic defects in the protective coatings. These defects occur during fabrication and handling, or from micrometeoroid and debris bombardment in space. An aluminized-polyimide Kapton multilayer insulation sample that was located on the leading edge of the Long Duration Exposure Facility (LDEF) was used to study low Earth orbit directed ram atomic oxygen undercutting. Cracks in the aluminized coatings located around vent holes provided excellent defect sites for evaluation of atomic oxygen undercutting. The experimentally observed undercutting profiles were compared to predictions from Monte Carlo models for normal incident ram atomic oxygen attack. The shape of the undercut profile was found to vary with crack width, which is proportional to the number of oxygen atoms entering the crack. The resulting profiles of atomic oxygen which occurred on LDEF indicated wide undercut cavities in spite of the fixed ram orientation. Potential causes of the observed undercutting are presented. Implications of the undercutting profiles relevant to the Space Station Freedom are also discussed.

Degroh, Kim K.↗

NASA NTRS1992

An overview of the first results on the solar array materials passive LDEF experiment (sample), A0171

Power degradation in the solar cells was consistent with the exposure environment and appears to be produced principally by the radiation and atomic oxygen environments. Atomic oxygen erosion was generally as expected; atomic oxygen effects dominated for the most part in materials that were both atomic oxygen and ultraviolet vulnerable. Silicone coatings appear to protect Kapton, and adhesive systems contained under photon opaque materials were surprisingly environmentally resistant. A high density of small micro-meteroid/space debris impacts were observed on mirrors, protective coatings, paints, and composites. New synergistic effects of the space environment were noted in the interaction of atomic oxygen and copious amounts of contamination and in the induced luminescence of many materials.

Ann F Whitaker↗

NASA NTRS1992

Rates of oxidative weathering on the surface of Mars

Implicit in the mnemonic 'MSATT' (Mars surface and atmosphere through time) is that rates of surface processes on Mars through time should be investigated, including studies of the kinetics and mechanism of oxidative weathering reactions occurring in the Martian regolith. Such measurements are described. Two major elements analyzed in the Viking Lander XRF experiment that are most vulnerable to atmospheric oxidation are iron and sulfur. Originally, they occurred as Fe(2+)-bearing silicate and sulfide minerals in basaltic rocks on the surface of Mars. However, chemical weathering reactions through time have produced ferric- and sulfate-bearing assemblages now visible in the Martian regolith. Such observations raise several question about: (1) when the oxidative weathering reactions took place on Mars; (2) whether or not the oxidized regolith is a fossilized remnant of past weathering processes; (3) deducting chemical interactions of the ancient Martian atmosphere with its surface from surviving phases; (4) possible weathering reactions still occurring in the frozen regolith; and (5) the kinetics and mechanism of past and present-day oxidative reactions on Mars. These questions may be addressed experimentally by studying reaction rates of dissolution and oxidation of basaltic minerals, and by identifying reaction products forming on the mineral surfaces. Results for the oxidation of pyrrhotite and dissolved ferrous iron are reported.

Burns, Roger G.↗

NASA NTRS1991

An overview of computer viruses in a research environment

The threat of attack by computer viruses is in reality a very small part of a much more general threat, specifically threats aimed at subverting computer security. Here, computer viruses are examined as a malicious logic in a research and development environment. A relation is drawn between the viruses and various models of security and integrity. Current research techniques aimed at controlling the threats posed to computer systems by threatening viruses in particular and malicious logic in general are examined. Finally, a brief examination of the vulnerabilities of research and development systems that malicious logic and computer viruses may exploit is undertaken.

Bishop, Matt↗

NASA NTRS1993

Single-Fiber Optical Link For Video And Control

Single optical fiber carries control signals to remote television cameras and video signals from cameras. Fiber replaces multiconductor copper cable, with consequent reduction in size. Repeaters not needed. System works with either multimode- or single-mode fiber types. Nonmetallic fiber provides immunity to electromagnetic interference at suboptical frequencies and much less vulnerable to electronic eavesdropping and lightning strikes. Multigigahertz bandwidth more than adequate for high-resolution television signals.

Galloway, F. Houston↗

NASA NTRS1992

Advanced stitching technology

In the design of textile composites, the selection of materials and constructional techniques must be matched with product performance, productivity, and cost requirements. Constructional techniques vary. A classification of various textile composite systems is given. In general, the chopped fiber system is not suitable for structural composite applications because of fiber discontinuity, uncontrolled fiber orientation and a lack of fiber integration or entanglement. Linear filament yarn systems are acceptable for structural components which are exposed to simple tension in their applications. To qualify for more general use as structural components, filament yarn systems must be multi-directionally positioned. With the most sophisticated filament winding and laying techniques, however, the Type 2 systems have limited potential for general load-bearing applications because of a lack of filament integration or entanglement, which means vulnerability to splitting and delamination among filament layers. The laminar systems (Type 3) represented by a variety of simple fabrics (woven, knitted, braided and nonwoven) are especially suitable for load-bearing panels in flat form and for beams in a roled up to wound form. The totally integrated, advanced fabric system (Type 4) are thought to be the most reliable for general load-bearing applications because of fiber continuity and because of controlled multiaxial fiber orientation and entanglement. Consequently, the risk of splitting and delamination is minimized and practically omitted. Type 4 systems can be woven, knitted, braided or stitched through with very special equipment. Multiaxial fabric technologies are discussed.

Scardino, Frank L.↗

NASA NTRS1993

NASA's Advanced solid rocket motor

The Advanced Solid Rocket Motor (ASRM) will not only bring increased safety, reliability and performance for the Space Shuttle Booster, it will enhance overall Shuttle safety by effectively eliminating 174 failure points in the Space Shuttle Main Engine throttling system and by reducing the exposure time to aborts due to main engine loss or shutdown. In some missions, the vulnerability time to Return-to-Launch Site aborts is halved. The ASRM uses case joints which will close or remain static under the effects of motor ignition and pressurization. The case itself is constructed of the weldable steel alloy HP 9-4-0.30, having very high strength and with superior fracture toughness and stress corrosion resistance. The internal insulation is strip-wound and is free of asbestos. The nozzle employs light weight ablative parts and is some 5,000 pounds lighter than the Shuttle motor used to date. The payload performance of the ASRM-powered Shuttle is 12,000 pounds higher than that provided by the present motor. This is of particular benefit for payloads delivered to higher inclinations and/or altitudes. The ASRM facility uses state-of-the-art manufacturing techniques, including continuous propellant mixing and direct casting.

Mitchell, Royce E.↗

NASA NTRS1993

Fullerenes formation in flames

Fullerenes are composed of carbon atoms arranged in approximately spherical or ellipsoidal cages resembling the geodesic domes designed by Buckminster Fuller, after whom the molecules were named. The approximately spherical fullerene, which resembles a soccer ball and contains sixty atoms (C60), is called buckminsterfullerene. The fullerene containing seventy carbon atoms (C70) is approximately ellipsoidal, similar to a rugby ball. Fullerenes were first detected in 1985, in carbon vapor produced by laser evaporation of graphite. The closed shell structure, which has no edge atoms vulnerable to reaction, was proposed to explain the observed high stability of certain carbon clusters relative to that of others at high temperatures and in the presence of an oxidizing gas.

Howard, Jack B.↗