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NASA NTRS2000

Transient Flows in the Magnetospheric Cusp: Ground Satellite Correlations

We first identified conjunctions of the POLAR magnetic footprint and the MACCS ground-based magnetometer array during intervals when the POLAR orbit was near the noon meridian and then searched the ground based data for transient events (i.e. large rapid changes in the magnetic field). This resulted in the identification of several tens of possible events, but we decided to limit ourselves to the study of three particularly good examples. The examples we chose were all cases where the ionospheric convection, as deduced from the MACCS observations, changed significantly in a few minutes. We then looked for signatures of these flow changes and for other corresponding changes in the POLAR data. We found that: a) the fast irregular flows seen in the POLAR electric field and plasma data completely mask the slower more steady flows seen in the ionosphere. The mapped ionospheric flows are an order of magnitude slower than the irregular flows at POLAR. b) the changes in magnetic field direction at POLAR did correlate very well with the required field stresses needed to move the flux tubes through the resistive ionosphere, so the effects of the ionospheric flow changes are seen at POLAR. c) the plasma fluxes seen at POLAR varied with the north-south component of the IMF on a minute time scale, and also correlated very well with the ionospheric flow changes.

Hughes, W. Jeffrey↗
NASA NTRS2000

Observations of Leonid Meteors Using a Mid-Wave Infrared Imaging Spectrograph

We report broadband 3-5.5 micrometer detections of two Leonid meteors observed during the 1998 Leonid Multi-Instrument Aircraft Campaign. Each meteor was detected at only one position along their trajectory just prior to the point of maximum light emission. We describe the particular aspects of the Aerospace Corp. Mid-wave Infra-Red Imaging Spectrograph (MIRIS) developed for the observation of short duration transient events that impact its ability to detect Leonid meteors. This instrument had its first deployment during the 1998 Leonid MAC. We infer from our observations that the mid-infrared light curves of two Leonid meteors differed from the visible light curve. At the points of detection, the infrared emission in the MIRIS passband was 25 +/- 4 times that at optical wavelengths for both meteors. In addition, we find an upper limit of 800 K for the solid body temperature of the brighter meteor we observed, at the point in the trajectory where we made our mid-wave infrared detection.

Rossano, G. S.↗
NASA NTRS2001

FPGAs in Space Environment and Design Techniques

This viewgraph presentation gives an overview of Field Programmable Gate Arrays (FPGA) in the space environment and design techniques. Details are given on the effects of the space radiation environment, total radiation dose, single event upset, single event latchup, single event transient, antifuse technology and gate rupture, proton upsets and sensitivity, and loss of functionality.

Katz, Richard B.↗
NASA NTRS2000

On the Stability of Liquid Water on Present Day Mars

The mean annual surface pressure and temperature on present day Mars do not allow for the long term stability of liquid water on the surface. However, theoretical arguments have been advanced that suggest liquid water could form in transient events even though it would not be in equilibrium with the environment. Using a Mars General Circulation Model, we calculate where and for how long the surface pressure and surface temperature meet the minimum requirements for this metastability of liquid water. These requirements are that the pressure and temperature must be above the triple point of water, but below its boiling point. We find that there are five regions on Mars where these requirements are periodically satisfied: in the near equatorial regions of Amazonis, Arabia, and Elysium, and in the Hellas and Argyre impact basins. Whether liquid water ever forms in these regions depends on the availability of ice and heat, and on the evaporation rate. The latter is poorly understood for low pressure CO2 environments, but is likely to be so high that melting occurs rarely, if at all. However, in the relatively recent past, surface pressures may have been higher than they are today perhaps by as much as a factor of 2 or 3. Under these circumstances melting would have been easier to achieve. We plan to undertake laboratory experiments to better understand the potential for melting in low pressure environments.

Haberle, Robert M.↗
NASA NTRS2001

Vorticity and Wave Motion in a Compressible Protoplanetary Disk

The impact of an isolated vortex in a compressible Keplerian disk is examined using higher order numerical solutions of the Euler and entropy-conserving Energy equations. The vortex is stretched by the background shear flow with longer lasting anticyclonic vortices persisting for about 10 vortex revolutions. Simultaneously, the vortex emits transient radial waves consisting mainly of axisymmetrical weak shock waves and a slower, nonaxisymmetric Rossby wave. These waves may contribute to certain transient events in protoplanetary disks. The vortex stretching and waves were found to have little long-term feedback on the baseline 'standard solar nebula' disk structure and confirm the extremely stable structure of non self-gravitating disks.

Davis, Sanford S.↗
NASA NTRS1996

SOFIA: The Next Airborne Observatory

SOFIA (Stratospheric Observatory for Infrared Astronomy) will be a telescope with 2.5 m effective aperture operating at altitudes of 12.5 to 13.7 km in a Boeing 747 aircraft. It will enable astronomers on board to make observations which are impossible from the ground at wavelengths between 0.3 microns and 1.5 mm. Diffraction-limited imaging will be possible at wavelengths beyond about 10 microns. SOFIA's mobility will assure all-sky coverage and access to transient events from anywhere in the world. Some of the science topics to be studied will be star and planet formation, origin and evolution of biogenic materials, comets and planetary atmospheres in the solar system, the interstellar media of other galaxies, and phenomena at our galactic center. The SOFIA concept is based on 21 years of experience with NASA's Kuiper Airborne Observatory (KAO), which has been retired to help fund the project. As with the KAO, state-of-the-art focal plane instruments and a vigorous educational outreach program will be features of this new airborne astronomy facility. A more intensive flight program, approximately 150 flights per year, will accommodate many more guest investigators however. Planned as a collaboration between the United States and Germany, SOFIA is scheduled to begin a 20 year operating lifetime in 2001.

Erickson, E. F.↗
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 NTRS2002

How Sample Completeness Affects Gamma-Ray Burst Classification

Unsupervised pattern recognition algorithms support the existence of three gamma-ray burst classes; class I (long, large fluence bursts of intermediate spectral hardness), Class II (short, small fluence, hard bursts), and class III (soft bursts of intermediate durations and fluences). The algorithms surprisingly assign larger membership to class III than to either of the other two classes. A known systematic bias has been previously used to explain the existence of class III in terms of class I; this bias allows the fluences and durations of some bursts to be underestimated. We show that this bias primarily affects only the longest bursts and cannot explain the bulk of the class III properties. We resolve the question of class III existence by demonstrating how samples obtained using standard trigger mechanisms fail to preserve the duration characteristics of small peak flux bursts: (Sample incompleteness is thus primarily responsible for the existence of class III.) In order to avoid this incompleteness, we show how a new dual timescale peak flux can be defined in terms of peak flux and fluence. The dual timescale peak flux reserves the duration distribution of faint bursts and correlates either with spectral hardness (and presumably redshift) than either peak flux or fluence. The techniques presented here are generic and have applicability to the studies of other transient events. The results also indicate that pattern recognition algorithms are sensitive to sample completeness; this can influence the study of large astronomical databases such as those found in a Virtual Observatory.

Hakkila, Jon↗
NASA NTRS2003

Multi-Satellite Observations of Oceanic Lightning

This paper will present several case studies of active oceanic lightning storms. Measurements by instruments on the Tropical Rainfall Measuring Mission (TRMM) and Fast On-orbit Recording of Transient Events (FORTE) platforms demonstrate that the two sets of sensors reinforce and complement one another. There is spatial and temporal coincidence between the optical data sets from Lightning Imaging Sensor (LIS) on TRMM and the photo-diode detector on FORTE. The LIS flash analysis provides a framework to interpret the stroke level data from FORTE. For these cases, the VHF receiver on FORTE is slaved to the optical system to provide stroke level radio frequency (RF) diagnostics. The occasions when TRMM and FORTE simultaneously have a lightning storm in their overlapping fields of view are extremely rare. One case study in the Gulf of Mexico is within range of land based sensor networks. These networks confirm the interpretation of satellite data and well as provide context for the storm conditions.

Boeck, W. L.↗
NASA NTRS2003

How Sample Completeness Affects Gamma-Ray Burst Classification

Unsupervised pattern-recognition algorithms support the existence of three gamma-ray burst classes: class 1 (long, large-fluence bursts of intermediate spectral hardness), class 2 (short, small-fluence, hard bursts), and class 3 (soft bursts of intermediate durations and fluences). The algorithms surprisingly assign larger membership to class 3 than to either of the other two classes. A known systematic bias has been previously used to explain the existence of class 3 in terms of class 1 ; this bias allows the fluences and durations of some bursts to be underestimated, as recently shown by Hakkila et al. We show that this bias primarily affects only the longest bursts and cannot explain the bulk of the class 3 properties. We resolve the question of class 3's existence by demonstrating how samples obtained using standard trigger mechanisms fail to preserve the duration characteristics of small-peak flux bursts. Sample incompleteness is thus primarily responsible for the existence of class 3. In order to avoid this incompleteness, we show how a new, dual-timescale peak flux can be defined in terms of peak flux and fluence. The dual-timescale peak flux preserves the duration distribution of faint bursts and correlates better with spectral hardness (and presumably redshift) than either peak flux or fluence. The techniques presented here are generic and have applicability to the studies of other transient events. The results also indicate that pattern recognition algorithms are sensitive to sample completeness; this can influence the study of large astronomical databases, such as those found in a virtual observatory.

Hakkila, Jon↗
NASA NTRS2004

A Study on the Requirements for Fast Active Turbine Tip Clearance Control Systems

This paper addresses the requirements of a control system for active turbine tip clearance control in a generic commercial turbofan engine through design and analysis. The control objective is to articulate the shroud in the high pressure turbine section in order to maintain a certain clearance set point given several possible engine transient events. The system must also exhibit reasonable robustness to modeling uncertainties and reasonable noise rejection properties. Two actuators were chosen to fulfill such a requirement, both of which possess different levels of technological readiness: electrohydraulic servovalves and piezoelectric stacks. Identification of design constraints, desired actuator parameters, and actuator limitations are addressed in depth; all of which are intimately tied with the hardware and controller design process. Analytical demonstrations of the performance and robustness characteristics of the two axisymmetric LQG clearance control systems are presented. Takeoff simulation results show that both actuators are capable of maintaining the clearance within acceptable bounds and demonstrate robustness to parameter uncertainty. The present model-based control strategy was employed to demonstrate the tradeoff between performance, control effort, and robustness and to implement optimal state estimation in a noisy engine environment with intent to eliminate ad hoc methods for designing reliable control systems.

DeCastro, Jonathan A.↗
NASA NTRS2004

Virtex-II Pro SEE Test Methods and Results

The Xilinx Virtex-II Pro is a platform FPGA that embeds multiple microprocessors within the fabric of an SRAM-based reprogrammable FPGA. The variety and quantity of resources provided by this family of devices make them very attractive for spaceflight applications. However, these devices will be susceptible to single event effects (SEE), which must be mitigated. To use the Virtex-II Pro reliably in space applications, these devices must first be tested to determine if they are susceptible to single event latchup (SEL), the degree to which they are susceptible to single event upsets (SEU) and single event transients (SET), and how these effects are manifested in the device. With this information, mitigations schemes can be developed and tested that address the specific susceptiblities of these devices. This initial SEE test uses a commercial off the shelf Virtex-II Pro evaluation board, with a single processor XC2VP7 FPGA. The FPGA on this board is an acid etched device, which can be partially covered with a shield. The shield covers a portion of the logic, routing, and memory resources along with some of the RocketIO transceivers. The processor, along with a large portion of logic, routing, memory, and transceivers are left exposed. This test will be performed at the Cyclotron Laboratories at Texas A&M University and Michigan State University using ions of varying energy levels and fluencies.

Petrick, David↗
NASA NTRS2000

Surge Flow in a Centrifugal Compressor Measured by Digital Particle Image Velocimetry

A planar optical velocity measurement technique known as Particle Image Velocimetry (PIV) is being used to study transient events in compressors. In PIV, a pulsed laser light sheet is used to record the positions of particles entrained in a fluid at two instances in time across a planar region of the flow. Determining the recorded particle displacement between exposures yields an instantaneous velocity vector map across the illuminated plane. Detailed flow mappings obtained using PIV in high-speed rotating turbomachinery components are used to improve the accuracy of computational fluid dynamics (CFD) simulations, which in turn, are used to guide advances in state-of-the-art aircraft engine hardware designs.

Wernet, Mark P.↗
NASA NTRS2006

The Effectiveness of TAG or Guard-Gates in SET Suppression Using Delay and Dual-Rail Configurations at 0.35 microns

Design options for decreasing the susceptibility of integrated circuits to Single Event Upset (SEU) fall into two categories: (1) increasing the critical charge to cause an upset at a particular node, and (2) employing redundancy to mask or correct errors. With decreasing device sizes on an Integrated Circuit (IC), the amount of charge required to represent a logic state has steadily reduced. Critical charge methods such as increasing drive strength or increasing the time required to change state as in capacitive or resistive hardening or delay based approaches extract a steadily increasing penalty as a percentage of device resources and performance. Dual redundancy is commonly assumed only to provide error detection with Triple Modular Redundancy (TMR) required for correction, but less well known methods employ dual redundancy to achieve full error correction by voting two inputs with a prior state to resolve ambiguity. This requires special circuits such as the Whitaker latch [1], or the guard-gate [2] which some of us have called a Transition AND Gate (TAG) [3]. A 2-input guard gate is shown in Figure 1. It is similar to a Muller Completion Element [4] and relies on capacitance at node "out" to retain the prior state when inputs disagree, while eliminating any output buffer which would be susceptible to radiation strikes. This paper experimentally compares delay based and dual rail flip-flop designs wherein both types of circuits employ guard-gates to optimize layout and performance, and draws conclusions about design criteria and suitability of each option. In both cases a design goal is protection against Single Event Transients (SET) in combinational logic as well as SEU in the storage elements. For the delay based design, it is also a goal to allow asynchronous clear or preset inputs on the storage elements, which are often not available in radiation tolerant designs.

Shuler, Robert L.↗
NASA NTRS2002

Ka-band and X-band observations of the solar corona acquired during the Cassini 2001 superior conjunction

Simultaneous dual-frequency Ka-band (32 GHz) and X-band (8.4 GHz) carrier signal data have been acquired during the superior conjunction of the Cassini spacecraft June 2001, using the NASA Deep Space Network's facilities located in Goldstone, California. The solar elongation angle of the observations varied from -4.1 degrees (-16 solar radii) to -0.6 degrees (-2.3 solar radii). The observed coronal and solar effects on the signals include spectral broadening, amplitude scintillation, phase scintillation, and increased noise. The measurements were generally consistent with existing solar models, except during solar transient events when the signatures of the measurements were observed to increase significantly above the quiet background levels. This is the second solar conjunction of Cassini for which simultaneous X/Ka data were acquired. Both solar conjunctions, conducted in May 2000 and June 2001, occurred near the peak of the current 11 year solar cycle.

propagation scintillation spectral broadening↗
NASA NTRS2006

SEU and Test Considerations for FPGA Devices

This viewgraph presentation provides an overview of Field Programmable Gate Arrays (FPGAs), what they are, implementations in space missions, and current available technologies. Single Event Upsets (SEUs) and Single Event Transients (SETs) are discussed in relation to their effects on FPGAs. Testing goals, considerations, and data analysis are reviewed.

Berg, Malanie↗
NASA NTRS2008

Exploiting the Photoelectric effect for X-ray Polarimetry using Time Projection Chamber

The promise of photoelectric X-ray polarimetry has now been realized in laboratory demonstrations and may soon be used for astrophysical observations. Photoelectric polarimetry in gas filled proportional counters achieves high sensitivity through a combination of broad band width and good modulation. The band can be tuned by careful choice of gas composition and pressure. The measurements rely on imaging the tracks of photoelectrons. The initial direction of each track carries information about the electric field of the X-ray photon, and an ensemble of such measurements thus measures the net polarization of the source. A novel readout geometry using time projection chambers (TPC) allows deep (i.e. high efficiency) detectors, albeit without the ability to image the sky. Polarimeters which exploit the TPC geometry can be optimized for use behind telescopes, to study faint persistent sources, or as wide field of view instruments, designed to study bright transient events such as gamma-ray bursts or solar flares. We present the conceptual design of both types of TPC polarimeter. Recent laboratory results demonstrate that these polarimeters can achieve substantial gains in the polarization sensitivity achievable in experiments of modest size.

Jahoda, Keith↗
NASA NTRS2007

Total Dose Effects on Error Rates in Linear Bipolar Systems

The shapes of single event transients in linear bipolar circuits are distorted by exposure to total ionizing dose radiation. Some transients become broader and others become narrower. Such distortions may affect SET system error rates in a radiation environment. If the transients are broadened by TID, the error rate could increase during the course of a mission, a possibility that has implications for hardness assurance.

Buchner, Stephen↗