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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

A hypervelocity launcher for simulated large fragment space debris impacts at 10 km/s

The background, design, and testing of two explosive launchers for simulating large fragment space debris impacts are presented. The objective was to develop a launcher capable of launching one gram aluminum fragments at velocities of 10 km/s. The two launchers developed are based on modified versions of an explosive shaped charge, common in many military weapons. One launcher design has yielded a stable fragment launch of approximately one gram of aluminum at 8.93 km/s velocity. The other design yielded velocities in excess of 10 km/s, but failed to produce a cohesive fragment launch. This work is ongoing, and future plans are given.

Tullos, R. J.↗
NASA NTRS1990

Jam-Resistant Cutters For Emergency Separation

Pyrotechnic emergency-separation system includes shaped explosive charges that sever pair of hinges. System ensures reliable opening of escape hatch. Two pairs of cutters provided for each hinge so if one pair of cutters fails, other completes job. Pressure of explosions vented to prevent charge holders from fragmenting and forming sharp edges around open hatch. Exit slide deployed without tearing. Before detonation L-shaped retainers bear on hinge. After denonation, retainers fold outward to facilitate egress of severed hinges.

Ordonez, Arturo C.↗
NASA NTRS1989

Role of dust to gas production rate ratio in cometary physics

According to results of Earth based observations and in situ measurements cometary nuclei are intensive sources of both the gaseous and the dusty matter. Investigations of the interaction between gas-dust cometary atmospheres and dust grains of the Zodiacal dust cloud reveals the presence of two principally possible mechanisms: meteor-like and explosive-type ones. The meteor-like mechanism is connected with bombardment of zodiacal dust particles by cometary molecules when the temperatures T = 2000 to 3000 K are developed. This mechanism can create over-saturated vapors of refractory elements (Fe, Si, C etc.) in cometary heads. The explosion-type mechanism is connected with high-velocity impacts between cometary and zodiacal dust particles resulting in the generation of high-temperature plasma (T = 10(exp 5) to 10(exp 7) K) and, hence, of x ray radiation and multicharged ions, i.e., with the processes not yet realized in the laboratory conditions.

Ibadov, S.↗
NASA NTRS1989

Albedo estimates for debris

The albedo of upper-stage breakup debris is proposed as an accurate discriminator among the various possible causes of breakup, which encompass residual fuel explosions and hypervelocity particle impacts. The fragments from an impact are covered with a thin layer of soot deposited from the destruction of polymeric circuit boards, while pressure vessel explosion fragments can be expected to remain soot-free. Albedo also facilitates the interpretation of small-debris optical telescope measurements.

Potter, A. E.↗
NASA NTRS1989

Ariane-related debris in deep-space orbit

A group of data bases for deep-space artificial satellites has been analyzed for orbital element sets exhibiting mean motions within 1.5 rev/day of 2.2 rev/day, eccentricity within 0.3 of 0.73, and inclination within 3 deg of 6.2 deg, as would be expected of Ariane upper stage explosion debris. The rapid growth of objects in these Ariane-type orbits is consistent with the two recorded explosions of Ariane launch vehicle upper stage elements. About 250 objects are currently being tracked.

Taff, L. G.↗
NASA NTRS1990

Convective instabilities in SN 1987A

Following Bandiera (1984), it is shown that the relevant criterion to determine the stability of a blast wave, propagating through the layers of a massive star in a supernova explosion, is the Schwarzschild (or Ledoux) criterion rather than the Rayleigh-Taylor criterion. Both criteria coincide only in the incompressible limit. Results of a linear stability analysis are presented for a one-dimensional (spherical) explosion in a realistic model for the progenitor of SN 1987A. When applying the Schwarzschild criterion, unstable regions get extended considerably. Convection is found to develop behind the shock, with a characteristic growth rate corresponding to a time scale much smaller than the shock traversal time. This ensures that efficient mixing will take place. Since the entire ejected mass is found to be convectively unstable, Ni can be transported outward, even into the hydrogen envelope, while hydrogen can be mixed deep into the helium core.

Benz, Willy↗
NASA NTRS1990

Synoptic/planetary-scale interactions and blocking over the North Atlantic Ocean

Work was completed on the height tendency diagnoses of two extratropical cyclones that occurred upstream from the blocking event studied previously. One developed explosively over water 60 to 36 hours before the block first appeared, while the second developed explosively over the southeastern United States during the time of block formation. In both cases, both vorticity and temperature advection were consistently important forcing mechanisms. This is in contrast to the block itself, in which vorticity advection was easily the dominant forcing mechanism. Latent heat release was also significant, accounting for about 50 percent of the total height falls in the cyclone below 850 mb. Estimates of latent heat release were greatly enhanced by coupling parameterized estimates with values derived from GOES IR data using an algorithm developed by Marshall's F. R. Robertson. Among the difficulties encountered in this work was the identification of an appropriate lower boundary condition for the solution of the height tendency equation. The zero value currently used tends to yield underestimates of the lower troposphere height tendencies. To address this problem a new diagnostic technique was developed in cooperation with Dr. Peter Zwack of the University of Quebec at Montreal. Based on an equation Dr. Zwack had previously developed (the Zwack-Okossi development equation), researchers now have a relationship that is completely consistent with the height tendency equation and provides estimates of lower boundary geostrophic vorticity or height tendencies. Finally, comparison of the SAT (satellite data) and NOSAT (no satellite data) analyses is progressing well. The present focus is on both the new diagnostic technique and the SAT/NOSAT comparisons. The former is being tested on the southeastern United States cyclone case previously mentioned and compared with the height tendency diagnoses already completed. The latter are being examined for the blocking case described in the publications cited in this summary. In addition to obtaining statistics that will allow general comparison of the two analyses, it will be possible to determine whether conclusions about the dynamics of the block development are influenced by the analysis set used.

Smith, Phillip J.↗
NASA NTRS1990

A limit on the production of Ni-56 in a type I supernova

The data from the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite have been searched for evidence of gamma-ray line emission from the decay of Co-56 in the type Ia SN, 1986G. No significant flux at either 847 or 1238 keV, the energies of the two strongest decay lines is found. Based on the data, a 3-sigma upper limit of 0.4 solar masses (D/3 Mpc)-squared on the amount of Ni-56 produced in the explosion is set. This value is consistent with radioactive models of type I light curves. For distances less than 3 Mpc, the limit is inconsistent with most models of SN Ia as thermonuclear explosions of white dwarfs.

Matz, Steven M.↗
NASA NTRS1991

Conditions for accretion-induced collapse of white dwarfs

Recent discovery of an unexpectedly large number of low-mass binary pulsars (LMBPs) in globular clusters has instigated active discussions on the evolutionary origin of binary pulsars. Prompted by the possibility that at least some of LMBPs originate from accretion-induced collapse (AIC) of white dwarfs, a reexamination is conducted as to whether or not AIC occurs for the new models of O + Ne + Mg white dwarfs and solid C + O white dwarfs that can ignite explosive nuclear burning at significantly lower central densities than in the previous models. Even with low critical densities, AIC is still much more likely than explosion for both types of white dwarfs. Possible regions for AIC are presented in a diagram of mass accretion rate vs initial mass of the white dwarfs.

Nomoto, Ken'ichi↗
NASA NTRS1991

Co-57 and Ti-44 production in SN 1987A

A survey of parameterized explosive silicon burning is carried out in order to limit the range of allowed masses of Co-57 produced by SN 1987A. The most likely value is between 0.5 and 2.5 times that implied by a solar ratio for Fe-57/Fe-56. Values more than four and less than one-third times the solar ratio would pose very severe problems for the theory of stellar nucleosynthesis, implying, for example, that Fe-56 was not the dominant iron group isotope or that no electron capture occurred during oxygen burning. Though dependent somewhat on the neutron excess, the Fe-57 yield is most sensitive to the occurrence of an alpha-rich freeze-out. An accurate measurement of the Fe-57 yield, as reflected observationally by the current abundance of radioactive Co-57, is thus an important constraint upon the supernova explosion mechanism. The abundance of Ti-44, another nucleus produced exclusively in the alpha-rich freeze-out, cannot be much greater than that implied by the solar ratio of Ca-44/Fe-56.

Woosley, S. E.↗
NASA NTRS1991

Hydrodynamical instabilities and mixing in SN 1987A - Two-dimensional simulations of the first 3 months

Results are presented from numerical simulations of the early stages of the explosion of SN 1987A. Using a two-dimensional cylindrical geometry version of a smooth particle hydrodynamics code, the explosion is followed for three months to investigate both the early hydrodynamical instabilities and the effect of the subsequent radioactive decay of Ni-56 and Co-56 with half-lives of 6.1 and 77.8 days, respectively. It is shown that the mixing induced by hydrodynamical instabilities occurring during the first few hours is substantially modified at later time by the radioactive decay of Ni-56 and Co-56. The inner cavity of the expanding supernova remnant fills up with nickel, its decay products thus forming a giant 'nickel bubble'. The peak velocity of the nickel increases by approximately 30 percent after the decays. While these results adequately model the core of the observed Fe line profiles, they fail to reproduce the high velocity wings of the spectra.

Herant, Marc↗
NASA NTRS1990

Helicopter in-flight stores jettison

A helicopter emergency external-stores jettison system accommodating an experimental simplified mounting system is presented. The system's conceptual approach is described, including store interface, attachment, functional mechanisms, and system initiation. It is novel both in the stores' mounting interface logic and in the modifications to existing technology for the components. Two nonfragmenting 'ridge cut' explosive bolts were mounted in each 600-pound store to interface with a simple plate on the aircraft. Starting designs with proven technology and functional margins were demonstrated by analysis and test through the design and development. Design details of the system's components, from the explosive bolt to the initiation handle, are described.

Bement, Laurence J.↗
NASA NTRS1990

Techniques for capturing expert knowledge - An expert systems/hypertext approach

The knowledge-acquisition strategy developed for the Explosive Hazards Classification (EHC) Expert System is described in which expert systems and hypertext are combined, and broad applications are proposed. The EHC expert system is based on rapid prototyping in which primary knowledge acquisition from experts is not emphasized; the explosive hazards technical bulletin, technical guidance, and minimal interviewing are used to develop the knowledge-based system. Hypertext is used to capture the technical information with respect to four issues including procedural, materials, test, and classification issues. The hypertext display allows the integration of multiple knowlege representations such as clarifications or opinions, and thereby allows the performance of a broad range of tasks on a single machine. Among other recommendations, it is suggested that the integration of hypertext and expert systems makes the resulting synergistic system highly efficient.

Lafferty, Larry↗
NASA NTRS1992

Blast-Absorbing Bag

Proposed expandable bag contains debris from explosion. Permanently surrounds vessel or devices prone to explosive disintegration or slipped around small bomb. Finned cells shaped like outward-opening cups. Cells built up from overlapped sheets of fabric and stitched together to form expandable polyhedral bag. Cells pentagonal, triangular or square.

Kahn, Jon B.↗
NASA NTRS1991

Load limiting energy absorbing lightweight debris catcher

In the representative embodiment of the invention disclosed, a load limiting, energy absorbing net is arranged to overlay a normally-covered vent opening in the rear bulkhead of the space orbiter vehicle. Spatially-disposed flexible retainer straps are extended from the net and respectively secured to bulkhead brackets spaced around the vent opening. The intermediate portions of the straps are doubled over and stitched together in a pattern enabling the doubled-over portions to progressively separate at a predicable load designed to be well below the tensile capability of the straps as the stitches are successively torn apart by the forces imposed on the retainer members whenever the cover plate is explosively separated from the bulkhead and propelled into the net. By arranging these stitches to be successively torn away at a load below the strap strength in response to forces acting on the retainers that are less than the combined strength of the retainers, this tearing action serves as a predictable compact energy absorber for safely halting the cover plate as the retainers are extended as the net is deployed. The invention further includes a block of an energy-absorbing material positioned in the net for receiving loose debris produced by the explosive release of the cover plate.

Kahn, Jon B.↗
NASA NTRS1991

Management of the orbital environment

Data regarding orbital debris are presented to shed light on the requirements of environmental management in space, and strategies are given for active intervention and operational strategies. Debris are generated by inadvertent explosions of upper stages, intentional military explosions, and collisional breakups. Design and operation practices are set forth for minimizing debris generation and removing useless debris from orbit in the low-earth and geosynchronous orbits. Self-disposal options include propulsive maneuvers, drag-augmentation devices, and tether systems, and the drag devices are described as simple and passive. Active retrieval and disposition are considered, and the difficulty is examined of removing small debris. Active intervention techniques are required since pollution prevention is more effective than remediation for the problems of both earth and space.

Loftus, Joseph P., Jr.↗
NASA NTRS1991

Collisional cascading - The limits of population growth in low earth orbit

Random collisions between made-made objects in earth orbit will lead to a significant source of orbital debris, but there are a number of uncertainties in these models, and additional analysis and data are required to fully characterize the future environment. However, the nature of these uncertainties are such that while the future environment is uncertain, the fact that collisions will control the future environment is less uncertain. The data that already exist is sufficient to show that cascading collisions will control the future debris environment with no, or very minor increases in the current low-earth-orbit population. Two populations control this process: explosion fragments and expended rocket bodies and payloads. Practices are already changing to limit explosions in low earth orbit; it is necessary to begin limiting the number of expended rocket bodies and payloads in orbit.

Kessler, Donald J.↗
NASA NTRS1992

Global tracking of the SO2 clouds from the June, 1991 Mount Pinatubo eruptions

The explosive June 1991 eruptions of Mount Pinatubo produced the largest sulfur dioxide cloud detected by the Total Ozone Mapping Spectrometer (TOMS) during its 13 years of operation: approximately 20 million tons of SO2, predominantly from the cataclysmic June 15th eruption. The SO2 cloud observed by the TOMS encircled the earth in about 22 days (about 21 m/s); however, during the first three days the leading edge of the SO2 cloud moved with a speed that averaged about 35 m/s. Compared to the 1982 El Chichon eruptions, Pinatubo outgassed nearly three times the amount of SO2 during its explosive phases. The main cloud straddled the equator within the first two weeks of eruption, whereas the El Chichon cloud remained primarily in the Northern Hemisphere. The measurements indicate that Mount Pinatubo has produced a much larger and perhaps longer-lasting SO2 cloud; thus, climatic responses to the Pinatubo eruption can exceed those of El Chichon.

Bluth, Gregg J. S.↗