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NASA NTRS2002

The Dusk Flank of Jupiter's Magnetosphere

Limited single-spacecraft observations of Jupiter's magnetopause have been used to infer that the boundary moves inward or outward in response to variations in the dynamic pressure of the solar wind. At Earth, multiple-spacecraft observations have been implemented to understand the physics of how this motion occurs, because they can provide a snapshot of a transient event in progress. Here we present a set of nearly simultaneous two-point measurements of the jovian magnetopause at a time when the jovian magnetopause was in a state of transition from a relatively larger to a relatively smaller size in response to an increase in solar-wind pressure. The response of Jupiter's magnetopause is very similar to that of the Earth, confirming that the understanding built on studies of the Earth's magnetosphere is valid. The data also reveal evidence for a well-developed boundary layer just inside the magnetopause.

Kurth, W. S.↗
NASA NTRS1991

An SEU immune logic family

A new logic family, which is immune to single event upsets, is described. Members of the logic family are capable of recovery, regardless of the shape of the upsetting event. Glitch propagation from an upset node is also blocked. Logic diagrams for an Inverter, Nor, Nand, and Complex Gates are provided. The logic family can be implemented in a standard, commercial CMOS process with no additional masks. DC, transient, static power, upset recovery and layout characteristics of the new family, based on a commercial 1 micron CMOS N-Well process, are described.

Canaris, J.↗
NASA NTRS2010

The Infrared-Optical Telescope (IRT) of the Exist Observatory

The IRT is a 1.1m visible and infrared passively cooled telescope, which can locate, identify and obtain spectra of GRB afterglows at redshifts up to z 20. It will also acquire optical-IR, imaging and spectroscopy of AGN and transients discovered by the EXIST (The Energetic X-ray Imaging Survey Telescope). The IRT imaging and spectroscopic capabilities cover a broad spectral range from 0.32.2m in four bands. The identical fields of view in the four instrument bands are each split in three subfields: imaging, objective prism slitless for the field and objective prism single object slit low resolution spectroscopy, and high resolution long slit on single object. This allows the instrument, to do simultaneous broadband photometry or spectroscopy of the same object over the full spectral range, thus greatly improving the efficiency of the observatory and its detection limits. A prompt follow up (within three minutes) of the transient discovered by the EXIST makes IRT a unique tool for detection and study of these events, which is particularly valuable at wavelengths unavailable to the ground based observatories.

Kutyrev, Alexander↗
NASA NTRSDate not supplied

Failure Modes and Mitigation Strategies for a Turboelectric Aircraft Concept with Turbine Electrified Energy Management

The electrification of gas turbine engines represents a major step-change in aircraft propulsion systems commonly known as Electrified Aircraft Propulsion (EAP). EAP involves the integration of electric machines potentially functioning as generators for large scale power extraction, as motors providing electrical augmentation of the engine spools, and even as a means of driving propulsors beyond the immediate scope of the engine. It may also include the use of energy storage. These and other characteristics of hybrid electric propulsion systems are relatively new to aircraft propulsion. The expanded propulsion architecture can be leveraged to improve propulsive efficiency and achieve better vehicle aerodynamics and controllability. It can also allow for additional benefits such as those enabled through Turbine Electrified Energy Management (TEEM). As the propulsion system and its functions expand, new failure modes are introduced. Due to the highly coupled nature of the propulsion system, failures could propagate throughout the system in ways that are unique to the new EAP architectures. To build confidence in the safety and practicality of EAP concepts, these failure modes need to be identified, explored, and addressed through mitigation strategies. This paper seeks to evaluate failure modes and failure mitigation strategies for the EAP concept known as the Single aisle Turboelectric AiRCaft with Aft Boundary Layer propulsor (STARC-ABL). The TEEM control concept is applied to improve transient operability. Several failure modes are considered and control based failure mitigation strategies are proposed with the goal of retaining operability and overall thrust. The results demonstrate the ability to maintain operability and a substantial amount of thrust in the event of various types of failures. Some challenges are also identified and discussed.

Turbine Electrified Energy Management↗
NASA NTRS1985

1985 Annual Conference on Nuclear and Space Radiation Effects, 22nd, Monterey, CA, July 22-24, 1985, Proceedings

Basic mechanisms of radiation effects in structures and materials are discussed, taking into account the time dependence of interface state production, process dependent build-up of interface states in irradiated N-channel MOSFETs, bias annealing of radiation and bias induced positive charges in n- and p-type MOS capacitors, hole removal in thin-gate MOSFETs by tunneling, and activation energies of oxide charge recovery in SOS or SOI structures after an ionizing pulse. Other topics investigated are related to radiation effects in devices, radiation effects in integrated circuits, spacecraft charging and space radiation effects, single-event phenomena, hardness assurance and radiation sources, SGEMP/IEMP phenomena, EMP phenomena, and dosimetry and energy-dependent effects. Attention is given to a model of the plasma wake generated by a large object, gate charge collection and induced drain current in GaAs FETs, simulation of charge collection in a multilayer device, and time dependent dose enhancement effects on integrated circuit transient response mechanisms.

Jones, C. W.↗
NASA NTRS2016

Post Launch Calibration and Testing of the Geostationary Lightning Mapper on GOES-R Satellite

The Geostationary Operational Environmental Satellite R (GOES-R) series is the planned next generation of operational weather satellites for the United States National Oceanic and Atmospheric Administration (NOAA). The National Aeronautics and Space Administration (NASA) is procuring the GOES-R spacecraft and instruments with the first launch of the GOES-R series planned for October 2016. Included in the GOES-R Instrument suite is the Geostationary Lightning Mapper (GLM). GLM is a single-channel, near-infrared optical detector that can sense extremely brief (800 s) transient changes in the atmosphere, indicating the presence of lightning. GLM will measure total lightning activity continuously over the Americas and adjacent ocean regions with near-uniform spatial resolution of approximately 10 km. Due to its large CCD (1372x1300 pixels), high frame rate, sensitivity and onboard event filtering, GLM will require extensive post launch characterization and calibration. Daytime and nighttime images will be used to characterize both image quality criteria inherent to GLM as a space-based optic system (focus, stray light, crosstalk, solar glint) and programmable image processing criteria (dark offsets, gain, noise, linearity, dynamic range). In addition ground data filtering will be adjusted based on lightning-specific phenomenology (coherence) to isolate real from false transients with their own characteristics. These parameters will be updated, as needed, on orbit in an iterative process guided by pre-launch testing. This paper discusses the planned tests to be performed on GLM over the six-month Post Launch Test period to optimize and demonstrate GLM performance.

validation↗
NASA NTRS2016

Post Launch Calibration and Testing of the Geostationary Lightning Mapper on the GOES-R Satellite

The Geostationary Operational Environmental Satellite R (GOES-R) series is the planned next generation of operational weather satellites for the United States National Oceanic and Atmospheric Administration (NOAA). The National Aeronautics and Space Administration (NASA) is procuring the GOES-R spacecraft and instruments with the first launch of the GOES-R series planned for October 2016. Included in the GOES-R Instrument suite is the Geostationary Lightning Mapper (GLM). GLM is a single-channel, near-infrared optical detector that can sense extremely brief (800 microseconds) transient changes in the atmosphere, indicating the presence of lightning. GLM will measure total lightning activity continuously over the Americas and adjacent ocean regions with near-uniform spatial resolution of approximately 10 km. Due to its large CCD (1372x1300 pixels), high frame rate, sensitivity and onboard event filtering, GLM will require extensive post launch characterization and calibration. Daytime and nighttime images will be used to characterize both image quality criteria inherent to GLM as a space-based optic system (focus, stray light, crosstalk, solar glint) and programmable image processing criteria (dark offsets, gain, noise, linearity, dynamic range). In addition ground data filtering will be adjusted based on lightning-specific phenomenology (coherence) to isolate real from false transients with their own characteristics. These parameters will be updated, as needed, on orbit in an iterative process guided by pre-launch testing. This paper discusses the planned tests to be performed on GLM over the six-month Post Launch Test period to optimize and demonstrate GLM performance.

validation↗
NASA NTRSDate not supplied

A Combined Al-Mg/Pb-Pb Age of the Solar System

Astrophysical models of planet formation and protoplanetary disk evolution demand precise and accurate timing of the sequence of events in the solar nebula, relative to a time t=0, usually taken to be during the short epoch of CAI (Ca-rich, Al-rich inclusion) formation. Most CAIs formed withlive26Al (mean-life τ26= 1.034 Myr [1]), with an abundance 26Al/27Al ≈ (26Al/27Al)SS= 5.23 × 10-5[2]. We adopt this as the widespread level of 26Al in the solar nebula at t=0. Assuming spatial homogeneity of 26Al, an inclusion that had less 26Al, (26Al/27Al)0, formed a time Δt26= τ26ln[(26Al/27Al)SS/ (26Al/27Al)0] after t=0.These ages are typical precise to within ±0.1 Myr. Igneous bulk meteorites and inclusions can be relatively dated by the Al-Mg chronometer, but only ifΔt26<6 Myr. The Pb-Pb system is useful as a longer relative chronometer. It yields absolute ages tPb using 207Pb/206Pb, 206Pb/204Pb, and 238U/235U ratios measured indifferent portions of a sample, assuming certain half-lives [4]. These absolute ages are uncertain to within ±9 Myr due to uncertainties in the 235U half-life[3], but times of formation ΔtPb= tCAI–tPb relative to t=0, are more precise(±0.5Myr),iftCAI can be found. Here, tCAI means the Pb-Pb age that would be measured in CAIs using the half-lives the community typically uses, if they achieved isotopic closure at t=0. Unfortunately, direct Pb-Pb dating of CAIs has not definitively determined tCAI. Based on four CAIs with canonical (26Al/27Al)0,[5,6] found tPb= 4567.30 ± 0.16 Myr. No other CAI ages with measured 238U/235U have been reported in the refereed literature, but there are hints of other CAIs with ages tPb= 4568.0 ± 0.2 Myr [7] and tPb= 4568.3 ± 0.2 Myr [8].It is unclear whether anyof these igneous type B CAIs isotopically closed at t=0 or represents tCAI. Instead of measurements, we advocate finding tCAI by minimizing the discrepancies between the Al-Mg and Pb-Pb chronometers. Assuming Δt26=ΔtPb, we find the implied t’CAI= tPb+Δt26, then define t*CAIas the weighted mean of the t’CAI. t*CAIis the best guess for the Pb-Pb age of t=0; the assumption of homogeneity is justified if the t’CAI cluster within errors around t*CAI. This statistical approach is similar to, but improves on, that of[9]. We find t*CAI= 4568.73 ± 0.16 Myr. Below we discuss our methodology and the implications of this age for CAIs, 1.4 Myr older than the reported and typically used age 4567.30±0.16 Myr. Methods: We base our estimate of t*CAIon five achondrites for which published (26Al/27Al)0and Pb-Pb ages exist: the quenched angrites D’Orbigny, Sahara 99555 (SAH 99555), and Northwest Africa (NWA) 1670; the pseudo-eucrite Asuka 881394; and the inner disk achondrite. All are “NC” (non-carbonaceous) achondrites that likely cooled quickly enough that the Al-Mg and Pb-Pb systems achieved isotopic closure simultaneously. We also considered the “CC” (carbonaceous chondrite-like) achondrites NWA 2796 and NWA 6704, butdo not include them in our fit. Al-Mg and Pb-Pb seem not to have closed simultaneously, possibly because formation in the outer disk from volatile-rich composition led to slower cooling. Of the 8 chondrules from NWA 5697 measured by [20,21], we also consider the 4 for which 238U/235U was measured: 2-C1, 5-C2, 3-C5, 11-C1.Depending on their post-formation thermal histories, the Al-Mg and Pb-Pb systems in chondrules may or may not have closed simultaneously. Table 1: (26Al/27Al)0, Pb-Pb ages of selected samplesSample(26Al/27Al)0/ 10-6RefPb-PbRefD’Orbigny3.98±0.15104563.43±0.19♮10-12SAH 995553.64±0.18104563.88±0.2712NWA16705.92±0.59104564.39±0.24*10Asuka 88139413.1±0.5613-154564.98±0.1715NWA 73253.03±0.14164563.4±2.616NWA 27963.94±0.16174562.89±0.5917NWA 67043.03±0.14184562.76±0.26192-C17.56±1.53204567.57±0.56*215-C27.04±1.51204567.54±0.52*213-C58.85±1.83204566.20±0.63*2111-C15.55±1.84204565.84±0.72*21*regression based on one subset of data points ♮weighted mean of two datasets Pb-Pb ages are proportional to the intercept of the line formed by linear regression of 207Pb/206Pb vs. 206Pb/204Pb data from various washes, leachates and residues of acid dissolution of a sample. Because contamination by terrestrial or primordial Pb is pervasive, some fractions must be excluded from regressions to ensure a fit with acceptable mean squares weighted deviation (MSWD). Usually points are excluded based on low [Pb], or low 206Pb/204Pb ratio(low radiogenic component), with single outliers identified [11,12,15,16,17]. In the starred examples (Table 1)and the case of 3 CAI Pb-Pb ages [5], up to half the points were excluded solely because did not fit a pre-determined line. This approach is vulnerable to confirmation bias and produces fits with low MSWD and too-low Pb-Pb age uncertainty. Regressing the same data points as [10], were produce the Pb-Pb age of NWA 1670 of 4564.39±0.24 Myr. But selecting other combinations of data points, other, equally valid, isochrons yield ages from 4563.77±0.21 Myr to 4564.64±0.23 Myr. Similar arguments apply to the Pb-Pb isochrons built by [21] for chondrules 2-C1 (we find 4567.33±0.44 to 4567.85±0.46 Myr), 5-C2 (4566.84±0.53 to 4567.70±0.44 Myr), 3-C5 (4565.84±0.54to 4567.04±0.54)and 11-C1 (4565.36±0.51 to 4565.74±0.45 Myr). Our adopted ages for these and NWA 1670 are listed in Table 2.Table 2. tCAI estimated from various components, using our regressions for the chondrules & NWA 1670.SampleΔt26(Myr)tPb(Myr)t’CAI(Myr)D’Orbigny5.05±0.044563.43±0.194568.48±0.19SAH 995555.14±0.054563.88±0.274569.02±0.27NWA16704.64±0.104564.21±0.634568.85±0.67Asuka 8813943.81±0.044564.98±0.174568.79±0.17NWA 73255.33±0.054563.4±2.64568.7±2.6NWA 27965.06±0.044562.89±0.594567.95±0.59NWA 67045.29±0.134562.76±0.264568.05±0.292-C12.00±0.214567.59±0.704569.59±0.725-C22.07±0.224567.23±0.914569.30±0.933-C51.84±0.214566.44±1.124568.28±1.1411-C12.32±0.344565.52±0.664567.84±0.73achondrite4568.72±0.16chondrules4568.76±0.58combined4568.73±0.16A weighted average of the five NC achondrites(or just D’Orbigny, SAH 99555 and Asuka 881394)yields t*CAI= 4568.72 ± 0.16Myr. All are consistent with this value to within 1.8σ, and MSWD=1.5. Including the 4 U-corrected chondrules, t*CAI= 4568.73± 0.16Myrwith MSWD=1.66, which is statistically significant. All chondrules and NC achondrites are consistent with this to within 1.8σ, (Figure 1).Figure 1. Al-Mg formation times after t=0 vs. Pb-Pb ages. The five NC achondrites and four chondrules are consistent with a Pb-Pb age of t=0 of 4568.7 Myr. Discussion: The data from achondrites and chondrules are consistent with a single Pb-Pb age at t=0, justifying the assumption of 26Al homogeneity. The age, 4568.7 Myr, is ≈1.4 Myr older than the commonly accepted Pb-Pb age of CAIs that formed with canonical 26Al/27Al at t=0 [3]. Others have interpreted the discrepancy to signify 26Al heterogeneity in the CAI-forming region[5,21]. We suggest instead that CAIs were exposed to transient heating events that reset the Pb-Pb system without disturbing the Al-Mg system. Notably, chondrules typically experienced transient heating at these times in the nebula [22]. If so, direct measurements of CAIs will not yield as reliable a Pb-Pb age of t=0 as statistical approaches like this and that of [9].References:[1] Auer et al. 2009. [2] Jacobsen, B et al. 2008, EPSL 272, 353-364. [3] Tissot, Fet al. 2017, GCA 213, 593-617.[4] Villa, I et al. 2016, GCA 172, 387-392.[5] Amelin, Y et al. 2010, EPSL 300, 343-350.[6] Connelly, Jet al. 2012, Science 338, 651.[7] Bouvier, Aet al. 2011, LPICo 1639, 9054. [8] Bouvier, Aand Wadhwa, M2010, Nat Geosci 3, 637-641.[9] Nyquist, Let al. 2009, GCA 73, 5115-5136.[10] Schiller et al. 2015. [11] Wadhwa & Brennecka 2012. [12] Tissot et al. 2017. [13] Nyquist et al. 2003. [14] Wadhwa et al. 2009. [15] Wimpenny et al. 2019, GCA 244, 478-501.[16] Koefoed et al. 2016, GCA 183, 31-45. [17] Bouvier, A et al. 2011, GCA 75, 5310-5323. [18] Sanborn, Met al. 2019, GCA 245, 577-596. [19] Amelin, Yet al. 2019, GCA 245, 628-642.[20] Bollard, Jet al. 2017, Sci Adv 3 ,e1700407. [21] Bollard, Jet al. 2019, GCA 260, 62-83.[22] Villeneuve, J et al. 2009, Science 325, 985

S. J. Desch↗
NASA NTRS2005

Single Particle Damage Events in Candidate Star Camera Sensors

Si charge coupled devices (CCDs) are currently the preeminent detector in star cameras as well as in the near ultraviolet (uv) to visible wavelength region for astronomical observations in space and in earth-observing space missions. Unfortunately, the performance of CCDs is permanently degraded by total ionizing dose (TID) and displacement damage effects. TID produces threshold voltage shifts on the CCD gates and displacement damage reduces the charge transfer efficiency (CTE), increases the dark current, produces dark current nonuniformities and creates random telegraph noise in individual pixels. In addition to these long term effects, cosmic ray and trapped proton transients also interfere with device operation on orbit. In the present paper, we investigate the dark current behavior of CCDs - in particular the formation and annealing of hot pixels. Such pixels degrade the ability of a CCD to perform science and also can present problems to the performance of star camera functions (especially if their numbers are not correctly anticipated). To date, most dark current radiation studies have been performed by irradiating the CCDs at room temperature but this can result in a significantly optimistic picture of the hot pixel count. We know from the Hubble Space Telescope (HST) that high dark current pixels (so-called hot pixels or hot spikes) accumulate as a function of time on orbit. For example, the HST Advanced Camera for Surveys/Wide Field Camera instrument performs monthly anneals despite the loss of observational time, in order to partially anneal the hot pixels. Note that the fact that significant reduction in hot pixel populations occurs for room temperature anneals is not presently understood since none of the commonly expected defects in Si (e.g. divacancy, E center, and A-center) anneal at such a low temperature. A HST Wide Field Camera 3 (WFC3) CCD manufactured by E2V was irradiated while operating at -83C and the dark current studied as a function of temperature while the CCD was warmed to a sequence of temperatures up to a maximum of +30C. The device was then cooled back down to -83 and re-measured. Hot pixel populations were tracked during the warm-up and cool-down. Hot pixel annealing began below 40C and the anneal process was largely completed before the detector reached +3OC. There was no apparent sharp temperature dependence in the annealing. Although a large fraction of the hot pixels fell below the threshold to be counted as a hot pixel, they nevertheless remained warmer than the remaining population. The details of the mechanism for the formation and annealing of hot pixels is not presently understood, but it appears likely that hot pixels are associated with displacement damage occurring in high electric field regions.

Marshall, Paul↗
NASA NTRS1988

Heavy ion induced Single Event Phenomena (SEP) data for semiconductor devices from engineering testing

The accumulation of JPL data on Single Event Phenomena (SEP), from 1979 to August 1986, is presented in full report format. It is expected that every two years a supplement report will be issued for the follow-on period. This data for 135 devices expands on the abbreviated test data presented as part of Refs. (1) and (3) by including figures of Single Event Upset (SEU) cross sections as a function of beam Linear Energy Transfer (LET) when available. It also includes some of the data complied in the JPL computer in RADATA and the SPACERAD data bank. This volume encompasses bipolar and MOS (CMOS and MHNOS) device data as two broad categories for both upsets (bit-flips) and latchup. It also includes comments on less well known phenomena, such as transient upsets and permanent damage modes.

Nichols, Donald K.↗
NASA NTRS1995

A theoretical analysis of steady-state photocurrents in simple silicon diodes.

A theoretical analysis solves for the steady-state photocurrents produced by a given photogeneration rate function with negligible recombination in simple silicon diodes, consisting of a uniformly doped quasi-neutral region (called "substrate" below) between a p-n junction depletion region (DR) and an ohmic contact (electrode). Special attention is given to conditions that produce "funneling" (a term used by the single-event-effects community) under steady-state conditions. Funneling occurs when carriers are generated so fast that the DR becomes flooded and partially or completely collapses. Some or nearly all of the applied voltage plus built-in potential normally across the DR is now across the substrate. This substrate voltage drop affects substrate currents. The steady-state problem can provide some qualitative insights into the more difficult transient problem. Chapter 6 discusses some similarities between the steady-state and transient problems...

Edmonds, Larry↗
NASA NTRS2011

Multiple-Beam Detection of Fast Transient Radio Sources

A method has been designed for using multiple independent stations to discriminate fast transient radio sources from local anomalies, such as antenna noise or radio frequency interference (RFI). This can improve the sensitivity of incoherent detection for geographically separated stations such as the very long baseline array (VLBA), the future square kilometer array (SKA), or any other coincident observations by multiple separated receivers. The transients are short, broadband pulses of radio energy, often just a few milliseconds long, emitted by a variety of exotic astronomical phenomena. They generally represent rare, high-energy events making them of great scientific value. For RFI-robust adaptive detection of transients, using multiple stations, a family of algorithms has been developed. The technique exploits the fact that the separated stations constitute statistically independent samples of the target. This can be used to adaptively ignore RFI events for superior sensitivity. If the antenna signals are independent and identically distributed (IID), then RFI events are simply outlier data points that can be removed through robust estimation such as a trimmed or Winsorized estimator. The alternative "trimmed" estimator is considered, which excises the strongest n signals from the list of short-beamed intensities. Because local RFI is independent at each antenna, this interference is unlikely to occur at many antennas on the same step. Trimming the strongest signals provides robustness to RFI that can theoretically outperform even the detection performance of the same number of antennas at a single site. This algorithm requires sorting the signals at each time step and dispersion measure, an operation that is computationally tractable for existing array sizes. An alternative uses the various stations to form an ensemble estimate of the conditional density function (CDF) evaluated at each time step. Both methods outperform standard detection strategies on a test sequence of VLBA data, and both are efficient enough for deployment in real-time, online transient detection applications.

Thompson, David R.↗
NASA NTRS2012

A VLA (Very Large Array) Search for 5 GHz Radio Transients and Variables at Low Galactic Latitudes

We present the results of a 5GHz survey with the Very Large Array (VLA) and the expanded VLA, designed to search for short-lived (approx < 1 day) transients and to characterize the variability of radio sources at milli-Jansky levels. A total sky area of 2.66 sq. deg, spread over 141 fields at low Galactic latitudes (b approx equals 6 - 8 deg) was observed 16 times with a cadence that was chosen to sample timescales of days, months and years. Most of the data were reduced, analyzed and searched for transients in near real time. Interesting candidates were followed up using visible light telescopes (typical delays of 1 - 2 hr) and the X-Ray Telescope on board the Swift satellite. The final processing of the data revealed a single possible transient with a flux density of f(sub v) approx equals 2.4mJy. This implies a transients sky surface density of kappa(f(sub v) > 1.8mJy) = 0.039(exp +0.13,+0.18) (sub .0.032,.0.038) / sq. deg (1, 2 sigma confidence errors). This areal density is consistent with the sky surface density of transients from the Bower et al. survey extrapolated to 1.8mJy. Our observed transient areal density is consistent with a Neutron Stars (NSs) origin for these events. Furthermore, we use the data to measure the sources variability on days to years time scales, and we present the variability structure function of 5GHz sources. The mean structure function shows a fast increase on approximately 1 day time scale, followed by a slower increase on time scales of up to 10 days. On time scales between 10 - 60 days the structure function is roughly constant. We find that approx > 30% of the unresolved sources brighter than 1.8mJy are variable at the > 4-sigma confidence level, presumably due mainly to refractive scintillation.

Ofek, E. O.↗
NASA NTRS2005

Space-Borne Observations of Intense Gamma-Ray Flashes Above Thunderstorms

Intense millisecond flashes of MeV photons were discovered with the space-borne detectors of the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory (CGRO). These flashes originate at altitudes above at least 30 km, in order to be observable by the orbiting detectors. Over the entire CGRO mission, from 1991 until 2000, about 70 of these events were observed. Nearly all TGFs had short (millisecond) durations and sub-ms rise-times and fall-times, however a small fraction of them had longer timescales associated with them. Most were single pulses, but about a dozen had double pulses and a few had more than two pulses. The TGFs are observed in a photon-by-photon recording mode, with each photon from eight independent detectors being tagged to the nearest two microseconds in four energy channels. The TGFs show very hard spectra, in most cases there are more photons recorded above 300 keV than below. Several of the TGFs were also recorded by the thicker (but smaller area) spectroscopy detectors that provided improved spectral resolution than the large area detectors. The temporal and spectral characteristics of the events and the capabilities of the detectors will be described in more detail than the in the original paper. The association of TGFs with thunderstorms is primarily statistical; the TGFs show a strong correlation with the global distribution of lightning, as observed with recent satellites. There has also been an association based upon coincidences with spheric events, however, this association is debatable due to the high spherics rate and the non-directionality of the detectors. This talk gives an update of the BATSE observations of TGFs were published by the BATSE instrument team over ten years ago.

Fishman, Jerry↗
NASA NTRS1991

Structure and evolution of compound streams at not greater than 1 AU

Two cases of compound stream formation and evolution at heliocentric distances of not greater than 1 AU have been studied using simultaneous data from both multipoint in situ and global sources. The sequences of events analyzed occurred around December 16, 1978, and February 19, 1979, respectively. The sources of the multipoint observations were Helios A, Helios B, IMP 8, and ISEE 3. The global observations were obtained by interplanetary scintillation analysis of radio sources. It was found that the radio and in situ data complemented each other and that both were needed for a unique interpretation of complex, time-dependent flows. The cases studied show that a single corotating stream can interact with different transient flows at different times, and a single transient flow can interact with different corotating streams at different times. In each instance, a compound stream is formed. This work further shows that the cosmic ray intensity at a point depends on the global compound stream configuration in the vicinity of the point.

Burlaga, L. F.↗
NASA NTRS1983

High throughput non-dispersive hard X-ray spectrograph with angular resolution for cosmic bursts, transients, and sources

An instrument concept which offers high throughput nondispersive spectroscopy in the 35-150 keV band for measuring line intensities and widths of faint supernovae is described. The design is based on existing xenon filled, two-dimensional, position sensitive, multiwired proportional counters. Effective detector areas of 1000 sq cm are readily achievable, and expansion to 10,000 sq cm per unit is feasible. Either single-unit or array operation to provide all-sky coverage with one arcmin resolution is possible. The instrument could be used to record gamma ray bursts and would have the capability of distinguishing particle events. Observations could also be made of X ray cyclotron lines and the Ti-44 lines expected to issue from a supernova explosion.

Gorenstein, P.↗
NASA NTRS2016

The Effect of Dust on the Martian Polar Vortices

The influence of atmospheric dust on the dynamics and stability of the martian polar vortices is examined, through analysis of Mars Climate Sounder observations and MarsWRF general circulation model simulations. We show that regional and global dust storms produce transient vortex warming events that partially or fully disrupt the northern winter polar vortex for brief periods. Increased atmospheric dust heating alters the Hadley circulation and shifts the downwelling branch of the circulation poleward, leading to a disruption of the polar vortex for a period of days to weeks. Through our simulations, we find this effect is dependent on the atmospheric heating rate, which can be changed by increasing the amount of dust in the atmosphere or by altering the dust optical properties (e.g., single scattering albedo). Despite this, our simulations show that some level of atmospheric dust is necessary to produce a distinct northern hemisphere winter polar vortex.

Guzewich, Scott D.↗
NASA NTRS1985

Impacts in Ice: Commissions of Solar System Crater Populations

The classical phases of cratering are compression, excavation, and modification. Recent theory, however, supports and alternative sequence of physical events: (1) coupling - energy and momentum are transferred, and the cratering flow field is set up; (2) power-law-growth the flow field expands, with transient cavity dimensions expressible as a simple power law function of time; and (3) late phase - some combination of gravity, strength, and viscosity limits cavity growth, initially causing a deviation from power-law behavior and eventually determining the size and shape of the final (transient) crater. The dominant mechanism that limits cavity growth defines a cratering regime and a single variable, the coupling parameter, determines the scaling laws in the various regimes. The coupling parameter is intermediate in dimensionality between energy and momentum and its exact form is determined. For simple materials with rate and scale independent strength, the transition crater diameter between the strength and gravity regimes is, within reasonable bounds, independent of velocity. Even the smallest craters observed by Voyager appear to be gravity dominated.

Mckinnon, W. B.↗