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At least 235 records · Page 13

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NASA NTRS2011

Explosive Bolt Dual-Initiated from One Side

An explosive bolt has been developed that has a one-sided dual initiation train all the way down to the pyro charge for high reliability, while still allowing the other side of the bolt to remain in place after actuation to act as a thermal seal in an extremely high-temperature environment. This lightweight separation device separates at a single fracture plane, and has as much redundancy/reliability as possible. The initiation train comes into the explosive bolt from one side.

Snow, Eric↗

NASA NTRS2012

Hypervelocity Impact Initiation of Explosive Transfer Lines

The Gemini, Apollo and Space Shuttle spacecraft utilized explosive transfer lines (ETL) in a number of applications. In each case the ETL was located behind substantial structure and the risk of impact initiation by micrometeoroids and orbital debris was negligible. A current NASA program is considering an ETL to synchronize the actuation of pyrobolts to release 12 capture latches in a contingency. The space constraints require placing the ETL 50 mm below the 1 mm thick 2024-T72 Whipple shield. The proximity of the ETL to the thin shield prompted analysts at NASA to perform a scoping analysis with a finite-difference hydrocode to calculate impact parameters that would initiate the ETL. The results suggest testing is required and a 12 shot test program with surplused Shuttle ETL is scheduled for February 2012 at the NASA White Sands Test Facility. Explosive initiation models are essential to the analysis and one exists in the CTH library for HNS I, but not the HNS II used in the Shuttle 2.5 gr/ft rigid shielded mild detonating cord (SMDC). HNS II is less sensitive than HNS I so it is anticipated that these results using the HNS I model are conservative. Until the hypervelocity impact test results are available, the only check on the analysis was comparison with the Shuttle qualification test result that a 22 long bullet would not initiate the SMDC. This result was reproduced by the hydrocode simulation. Simulations of the direct impact of a 7 km/s aluminum ball, impacting at 0 degree angle of incidence, onto the SMDC resulted in a 1.5 mm diameter ball initiating the SMDC and 1.0 mm ball failing to initiate it. Where one 1.0 mm ball could not initiate the SMDC, a cluster of six 1.0 mm diameter aluminum balls striking simultaneously could. Thus the impact parameters that will result in initiating SMDC located behind a Whipple shield will depend on how well the shield fragments the projectile and spreads the fragments. An end-to-end simulation of the impact of an aluminum ball onto a Whipple shield covering SMDC is problematic due to the hydrocode fracture models. Regardless, two simulations were performed resulting in a 5 mm ball initiating the SMDC and a 4 mm ball failing to initiate the SMDC.

Bjorkman, Michael D.↗

NASA NTRS2012

Detection of Chemical Precursors of Explosives

Certain selected chemicals associated with terrorist activities are too unstable to be prepared in final form. These chemicals are often prepared as precursor components, to be combined at a time immediately preceding the detonation. One example is a liquid explosive, which usually requires an oxidizer, an energy source, and a chemical or physical mechanism to combine the other components. Detection of the oxidizer (e.g. H2O2) or the energy source (e.g., nitromethane) is often possible, but must be performed in a short time interval (e.g., 5 15 seconds) and in an environment with a very small concentration (e.g.,1 100 ppm), because the target chemical(s) is carried in a sealed container. These needs are met by this invention, which provides a system and associated method for detecting one or more chemical precursors (components) of a multi-component explosive compound. Different carbon nanotubes (CNTs) are loaded (by doping, impregnation, coating, or other functionalization process) for detecting of different chemical substances that are the chemical precursors, respectively, if these precursors are present in a gas to which the CNTs are exposed. After exposure to the gas, a measured electrical parameter (e.g. voltage or current that correlate to impedance, conductivity, capacitance, inductance, etc.) changes with time and concentration in a predictable manner if a selected chemical precursor is present, and will approach an asymptotic value promptly after exposure to the precursor. The measured voltage or current are compared with one or more sequences of their reference values for one or more known target precursor molecules, and a most probable concentration value is estimated for each one, two, or more target molecules. An error value is computed, based on differences of voltage or current for the measured and reference values, using the most probable concentration values. Where the error value is less than a threshold, the system concludes that the target molecule is likely. Presence of one, two, or more target molecules in the gas can be sensed from a single set of measurements.

Li, Jing↗

NASA NTRS2014

An Experimental Study of Unconfined Hydrogen/Oxygen and Hydrogen/Air Explosions

Development tests are being conducted to characterize unconfined Hydrogen/air and Hydrogen/Oxygen blast characteristics. Most of the existing experiments for these types of explosions address contained explosions, like shock tubes. Therefore, the Hydrogen Unconfined Combustion Test Apparatus (HUCTA) has been developed as a gaseous combustion test device for determining the relationship between overpressure, impulse, and flame speed at various mixture ratios for unconfined reactions of hydrogen/oxygen and hydrogen/air. The system consists of a central platform plumbed to inject and mix component gasses into an attached translucent bag or balloon while monitoring hydrogen concentration. All tests are ignited with a spark with plans to introduce higher energy ignition sources in the future. Surrounding the platform are 9 blast pressure "Pencil" probes. Two high-speed cameras are used to observe flame speed within the combustion zone. The entire system is raised approx. 6 feet off the ground to remove any ground reflection from the measurements. As of this writing greater than 175 tests have been performed and include Design of Experiments test sets. Many of these early tests have used bags or balloons between approx. 340L and approx. 1850L to quantify the effect of gaseous mixture ratio on the properties of interest. All data acquisition is synchronized between the high-speed cameras, the probes, and the ignition system to observe flame and shock propagation. Successful attempts have been made to couple the pressure profile with the progress of the flame front within the combustion zone by placing a probe within the bag. Overpressure and impulse data obtained from these tests are used to anchor engineering analysis tools, CFD models and in the development of blast and fragment acceleration models.

Richardson, Erin↗

NASA NTRS2014

Constraints on the Progenitor System of the Type Ia Supernova 2014J from Pre-Explosion Hubble Space Telescope Imaging

We constrain the properties of the progenitor system of the highly reddened Type Ia supernova (SN Ia) 2014J in Messier 82 (M82; d (is) approx. 3.5 Mpc). We determine the supernova (SN) location using Keck-II K-band adaptive optics images, and we find no evidence for flux from a progenitor system in pre-explosion near-ultraviolet through near-infrared Hubble Space Telescope (HST) images. Our upper limits exclude systems having a bright red giant companion, including symbiotic novae with luminosities comparable to that of RS Ophiuchi. While the flux constraints are also inconsistent with predictions for comparatively cool He-donor systems (T (is) approximately 35,000 K), we cannot preclude a system similar to V445 Puppis. The progenitor constraints are robust across a wide range of RV and AV values, but significantly greater values than those inferred from the SN light curve and spectrum would yield proportionally brighter luminosity limits. The comparatively faint flux expected from a binary progenitor system consisting of white dwarf stars would not have been detected in the pre-explosion HST imaging. Infrared HST exposures yield more stringent constraints on the luminosities of very cool (T (is) less than 3000 K) companion stars than was possible in the case of SN Ia 2011fe.

RS Ophiuchi↗

NASA NTRS2014

SN 2010j1: Optical to Hard X-Ray Observations Reveal an Explosion Embedded in a Ten Solar Mass Cocoon

Some supernovae (SNe) may be powered by the interaction of the SN ejecta with a large amount of circumstellar matter (CSM). However, quantitative estimates of the CSM mass around such SNe are missing when the CSM material is optically thick. Specifically, current estimators are sensitive to uncertainties regarding the CSM density profile and the ejecta velocity. Here we outline a method to measure the mass of the optically thick CSM around such SNe. We present new visible-light and X-ray observations of SN 2010jl (PTF 10aaxf), including the first detection of an SN in the hard X-ray band using NuSTAR. The total radiated luminosity of SN 2010jl is extreme atleast 9 1050 erg. By modeling the visible-light data, we robustly show that the mass of the circumstellar material within 1016 cm of the progenitor of SN 2010jl was in excess of 10M_. This mass was likely ejected tens of years prior to the SN explosion. Our modeling suggests that the shock velocity during shock breakout was 6000 km s1, decelerating to 2600 km s1 about 2 yr after maximum light. Furthermore, our late-time NuSTAR and XMM spectra of the SN presumably provide the first direct measurement of SN shock velocity 2 yr after the SN maximum light measured to be in the range of 2000-4500 km s1 if the ions and electrons are in equilibrium, and_2000 km s1 if they are not in equilibrium. This measurement is in agreement with the shock velocity predicted by our modeling of the visible-light data. Our observations also show that the average radial density distribution of the CSM roughly follows an r2 law. A possible explanation for the _10M_ of CSM and the wind-like profile is that they are the result of multiple pulsational pair instability events prior to the SN explosion, separated from each other by years.

circumstellar matter (CSM)↗

NASA NTRS2015

Ti-44 Gamma-Ray Emission Lines from SN1987A Reveal an Asymmetric Explosion

In core-collapse supernovae, titanium-44 (Ti-44) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32-kilo-electron volt emission lines from decay of Ti-44 produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.

44Ti gamma-ray emission lines↗

NASA NTRS2018

SAPS-Associated Explosive Brightening on the Duskside: A New Type of Onset- Like Disturbance

Quasi-periodic energetic particle injections have been observed at geosynchronous orbit on the dusk-side during a steady magnetospheric convection event. We examine high-resolution auroral imager data and ground magnetometer data associated with the first of these injections and conclude that it was not associated with classical sub-storm signatures. It is proposed that these injections are caused by the explosive nonlinear growth of a shear flow-ballooning instability in the region where sub-auroral polarization streams (SAPS) also occur. It is suggested that interchange will occur preferentially in the low-conductivity SAPS region since the magnetic Richardson number is lowest there and the "line-tying" effect will also be least stabilizing there. We propose that the observed particle injection signatures and auroral morphology constitute a new type of SAPS-associated explosive "onset-like" disturbance that can occur during intervals of strong convection.

Henderson, M. G.↗

NASA NTRS2019

Onset of the Magnetic Explosion in On-Disk Solar Coronal Jets

In our recent studies of ~10 quiet region and ~13 coronal hole coronal jets, we found that flux cancelation is the fundamental process in the buildup and triggering of the minifilament eruption that drives the production of the jet. Here, we investigate the onset and growth of the ten on-disk quiet region jets, using EUV images (304, 171, 193, and 94 Å) from SDO/AIA and magnetograms from SDO/HMI. We find that: (i) in all ten events the minifilament starts to rise at or before the onset of the signature of internal or external reconnection; (ii) in two out of ten jets brightening from the external reconnection starts at the same time as the slow rise of the minifilament and (iii) in six out of ten jets brightening from the internal reconnection starts before the start of the brightening from external reconnection. These observations show that the magnetic explosion in coronal jets begins in the same way as the magnetic explosion in filament eruptions that make solar flares and coronal mass ejections (CMEs). Our results indicate (1) that coronal jets are miniature versions of CME-producing eruptions and flux cancelation is the fundamental process that builds and triggers both the small-scale and the large-scale eruptions, and (2) that, contrary to the view of Moore et al (2018), the current sheet at which the external reconnection occurs in coronal jets usually starts to form at or after the onset of (and as a result of) the slow rise of the minifilament flux-rope eruption, and so is seldom of appreciable size before the onset of the slow rise of the minifilament flux-rope eruption.

Panesar, Navdeep K.↗

NASA NTRS2019

Evidence for Late-stage Eruptive Mass Loss in the Progenitor to SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient

We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising (1.4 ± 0.1 mag/hr) and luminous (M(g,peak) = -20 mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity (L(bol) ≳ 3 x 10^(44) erg/s), the short rise time (t = 3 days rise in g band), and the blue colors at peak (g–r ~ -0.4) all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign, including the highest-temperature (T(eff) ≳ 40,000 K) spectra of a stripped-envelope SN. A retrospective search revealed luminous (M(g) ~ M(r) ≈ -14 mag) emission in the days to weeks before explosion, the first definitive detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release E(γ,iso) < 4.9 x 10^(48) erg, a limit on X-ray emission L(X) < 10^(40) erg/s, and a limit on radio emission vL(v) ≲ 10^(37) erg/s. Taken together, we find that the early (<10 days) data are best explained by shock breakout in a massive shell of dense circumstellar material (0.02 Mꙩ) at large radii (3 x 10^(14) cm) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time (>10 days) light curve requires an additional energy source, which could be the radioactive decay of Ni-56.

Anna Y. Q. Ho↗

NASA NTRS2022

Major Scientific Challenges and Opportunities in Understanding Magnetic Reconnection and Related Explosive Phenomena in Heliophysics and Beyond

Magnetic reconnection underlies many explosive phenomena in the heliosphere and in laboratory plasmas. New research capabilities in theory/simulations, observations, and laboratory experiments provide the opportunity to solve the grand scientific challenges summarized in this white paper. Success will require enhanced and sustained investments from relevant funding agencies, increased interagency/international partnerships, and close collaborations among the heliophysics, astrophysics, and laboratory plasma communities. These investments will deliver transformative progress in understanding magnetic reconnection and related explosive phenomena including space weather events.

H. Ji↗

NASA NTRS2021

Spitzer’s Last Look at Extragalactic Explosions: Long-Term Evolution of Interacting Supernovae

Here we present new, yet final, mid-infrared (mid-IR) data for supernovae (SNe) based on measurements with the Spitzer Space Telescope. Comparing our recent 3.6 and 4.5 μm photometry with previously published mid-IR and further multiwavelength data sets, we were able to draw some conclusions about the origin and heating mechanism of the dust in these SNe or in their environments, as well as about possible connection with circumstellar matter (CSM) originating from pre-explosion mass-loss events in the progenitor stars. We also present new results regarding both certain SN classes and single objects. We highlight the mid-IR homogeneity of SNe Ia-CSM, which may be a hint of their common progenitor type and of their basically uniform circumstellar environments. Regarding single objects, it is worth highlighting the late-time interacting Type Ib SNe 2003gk and 2004dk, for which we present the first-ever mid-IR data, which seem to be consistent with clues of ongoing CSM interaction detected in other wavelength ranges. Our current study suggests that long-term mid-IR follow-up observations play a key role in a better understanding of both pre- and post-explosion processes in SNe and their environments. While Spitzer is not available anymore, the expected unique data from the James Webb Space Telescope, as well as long-term near-IR follow-up observations of dusty SNe, can bring us closer to the hidden details of this topic.

Supernovae↗

NASA NTRS1963