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Decreasing Proton Single Event Effects in CubeSats with Shielding

Shields-1, NORAD ID 43850,has been operating in polar low earth orbit since December 2018. The shielding has resulted in a lower total ionizing dose over time than typical aluminum thin-walled CubeSat structures. The reduced ionizing dosage caused by Shields-1 increases the reliability of commercial parts and reduces internal charging. Furthermore, the Shields-1 shielding reduces the ionizing particle fluence inside the spacecraft that contributes to the ionizing dose. NOVICE Sigma shielding software, using the (Aerospace Proton) AP8 –(Aerospace Electron) AE8 solar minimum trapped belt environment for a 1-year mission, estimates a 21.3 g/cm2 aluminum effective shielding for the Shields-1 electronics enclosure. This high areal density reduces not only the total number of energetic protons, but also reduces the number of ionizing particles over all modeled energies from the estimated shielded fluence for a 1-year mission. NOVICE Adjoint CAD modeling of the Shields-1 structure, with the detector located within the electronics enclosure, estimates that the total number of particles is reduced from 2.20x 10exp9 protons/cm2 to 1.52x 10exp8 protons/cm2, which represents 6.90% of the remaining particles(figure 1). By slowing down approximations of the integral proton fluence, a minimum proton threshold is estimated at 151 MeV. In comparison, a 0.204-cm aluminum thin-walled 3-unit (U) structure, with a 0.907 g/cm2 effective shielding, has 25.0% remaining particles and a minimum proton threshold of 36.2 MeV(figure 1). Proton energies that contribute to single event effects in radiation tolerant or higher semiconductor hardness are typically 100 MeV and higher. The Shields-1 electronics enclosure is estimated to attenuate energies: 100 MeV by 76.5%, 200 MeV by 61.7%, and 500 MeV by 63.0%(figure 2), when comparing the space environment proton differential fluence with the shielded differential fluence. The aluminum thin-walled structure is estimated to attenuate proton energies: 100 MeV by 13.7%, 200 MeV by 12.4%, and 500 MeV by 12.6%(figure 2), which are lower than for the Shields-1 electronics enclosure. The significant differences in attenuation between the Shields-1 electronics enclosure and aluminum thin-walled 3U structure show the additional utility of increasing shielding effectiveness for reducing the numbers of energetic protons that contribute to single event effects.

Larry Thomsen↗

NASA NTRS1978

Radiation Hazard Detector

NASA technology has made commercially available a new, inexpensive, conveniently-carried device for protection, of people exposed to potentially dangerous levels of microwave radiation. Microwaves are radio emissions of extremely high frequency. They can be hazardous but the degree of hazard is not yet well understood. Generally, it is believed that low intensity radiation of short duration is not harmful but that exposure to high levels can induce deep internal burns, affecting the circulatory and nervous systems, and particularly the eyes. The Department of Labor's Occupational Safety and Health Administration (OSHA) has established an allowable safe threshold of exposure. However, people working near high intensity sources of microwave energy-for example, radar antennas and television transmitters-may be unknowingly exposed to radiation levels beyond the safe limit. This poses not only a personal safety problem but also a problem for employers in terms of productivity loss, workman's compensation claims and possible liability litigation. Earlier-developed monitoring devices which warn personnel of dangerous radiation levels have their shortcomings. They can be cumbersome and awkward to use while working. They also require continual visual monitoring to determine if a person is in a dangerous area of radiation, and they are relatively expensive, another deterrent to their widespread adoption. In response to the need for a cheaper and more effective warning system, Jet Propulsion Laboratory developed, under NASA auspices, a new, battery-powered Microwave Radiation Hazard Detector. To bring the product to the commercial market, California Institute Research Foundation, the patent holder, granted an exclusive license to Cicoil Corporation, Chatsworth, California, an electronic components manufacturer.

Source record↗

NASA NTRS1991

Advanced Ge detectors for gamma-ray astronomy

Externally segmented coaxial detectors are fabricated for high efficiency in detecting gamma rays from cosmic sources with good sensitivities. The external background is reduced by enclosing the Ge detector array inside a thick active shield. The outer electrode of the coaxial detectors is subdivided into five segments, and internal beta activity is rejected by operating the segmented detector in a multisegment mode. The multisegment mode requires that events be detected in two or more segments before they are recorded. The full-energy-peak (FEP) efficiency of the unit is tested as a function of the incident gamma-ray energy and of the discriminator threshold of the segments. Measurements of beta-rejection and FEP efficiency are compared with Monte Carlo calculations, and good agreement is noted.

Varnell, Larry S.↗

NASA NTRS1999

Inferring Selected Cloud Properties from Satellite Lightning Data

The recent advent of satellite lightning detection programs has introduced a new potential for obtaining global information about other (hard to measure) cloud properties. We have made use of observations together with numerical model studies to show that positive correlations exist between: (1) lightning flashrate (F) and vertical velocity (w); and (2) flashrate (F) and the amount of condensate (water and ice) lofted through the -10 C isotherm (C(sub u)). The lightning flashrate appears to be very sensitive to the magnitude of the updraft velocity, with F increasing rapidly with w above a threshold of w approx. = 5-10 m/s. By contrast, we have found that the flashrate/condensate relationship appears to be approximately linear. We are currently refining the F-updraft and F-condensate relationships with further model studies before applying them to lightning data from the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS). We hope, with this method, to provide estimates of the large scale vertical water transport by continental convective systems over seasonal timescales.

Schroeder, Vicki↗

NASA NTRS2004

Central Stars of Planetary Nebulae in the SMC

In FUSE cycle 3's program C056 we studied four Central Stars of Planetary Nebulae (CSPN) in the Small Magellanic Could. All FUSE observations have been successfully completed and have been reduced and analyzed. The observation of one object (SMP SMC 5) appeared to be off-target and no useful stellar flux was gathered. For another observation (SMP SMC 1) the voltage problems resulted in the loss of data from one of the SiC detectors, but we were still able to analyze the remaining data. The analysis and the results are summarized below. The FUSE data were reduced using the latest available version of the FUSE calibration pipeline (CALFUSE v2.4). The flux of these SMC post-AGB objects is at the threshold of FUSE S sensitivity, and the targets required many orbit-long exposures, each of which typically had low (target) count-rates. The background subtraction required special care during the reduction, and was done in a similar manner to our FUSE cycle 2 BOO1 objects. The resulting calibrated data from the different channels were compared in the overlapping regions for consistency. The final combined, extracted spectra of each target was then modeled to determine the stellar and nebular parameters. The FUSE spectra, combined with archival HST spectra, have been analyzed using stellar atmospheres codes such as TLUSTY and CMFGEN to derive photospheric and wind parameters of the central stars, and with ISM models to determine the amount and temperature of the surrounding atomic and molecular hydrogen. We have combined these results with those of our cycle 4 (D034) program (CSPN of the LMC) in Herald & Bianchi 2004a (paper in preparation, will be submitted to ApJ in June 2004). Two of the three SMC objects analyzed were found to have significantly lower stellar temperatures than had been predicted using nebular photoionization models, indicating either a hotter ionizing companion or the existence of strong shocks in the nebular environment. The analysis also revealed that some objects are surrounded by significant quantities of hot (e.g., 1000- 2000 K) molecular H2, similar to what we found for some LMC and Galactic CSPN (Herald & Bianchi 2002, 2003a, b, 2004b, c, d).

Bianchi, Luciana↗

NASA NTRS1985

Measurement of energy muons in EAS at energy region larger thean 10(17) eV

A measurement of low energy muons in extensive air showers (EAS) (threshold energies are 0.25, 0.5, 0.75 and 1.38 GeV) was carried out. The density under the concrete shielding equivalent to 0.25 GeV at core distance less than 500 m and 0.5 GeV less than 150 m suffers contamination of electromagnetic components. Therefore the thickness of concrete shielding for muon detectors for the giant air shower array is determined to be 0.5 GeV equivalence. Effects of photoproduced muons are found to be negligible in the examined ranges of shower sizes and core distances. The fluctuation of the muon density in 90 sq m is at most 25% between 200 m and 600 m from the core around 10 to the 17th power eV.

Matsubara, Y.↗

NASA NTRS1981

Solar radiation monitoring for high altitude aircraft

Ground-based and satellite-based ionizing radiation monitoring systems are considered as alternative methods for ensuring safe radiation levels for high-altitude aircraft. It is found that ground-based methods are of limited accuracy due to insensitivity to solar particles of energies between the riometer upper cutoff of about 50 MeV and the neutron monitor threshold of about 450 MeV. This energy range is demonstrated to be essential for atmospheric radiation monitoring at high altitude, and must be covered by satellite measurement. On the basis of presently available data, the accuracy to which the incident solar particle flux must be measured by satellite-borne detectors is examined and recommendations are made to establish minimum requirements.

Wilson, J. W.↗

NASA NTRS1986

An intermediate-sensitivity survey at high Galactic latitude with HEAO A-1

A 314 square degree region of sky at high galactic latitude was mapped in 0.5-20 keV X-rays using summed data from the HEAO A-1 experiment. 21 sources are detected above a 5 sigma threshold corresponding to a limiting flux of about 0.2 UFU. This limit is at a decade intermediate to those achieved in the full-sky surveys, Uhuru, Ariel 5, and the HEAO A-2 experiment, and to those achieved in the Einstein partial-sky surveys. The HEAO A-1 detectors also complement these other instruments in terms of spectral response characteristics. A table of source intensities and positional error boxes for the 21 source detections is presented. A graphical representation of the positional error boxes is also presented. Identifications for 14 sources are proposed. A number-flux curve representing all high galactic latitude X-ray sources detected with HEAO A-1 has been constructed. The number-flux curve appears to be consistent with d log N/d log S = -1.5.

Shrader, C. R.↗

NASA NTRS1988

Simulated performance of an order statistic threshold strategy for detection of narrowband signals

The application of order statistics to signal detection is becoming an increasingly active area of research. This is due to the inherent robustness of rank estimators in the presence of large outliers that would significantly degrade more conventional mean-level-based detection systems. A detection strategy is presented in which the threshold estimate is obtained using order statistics. The performance of this algorithm in the presence of simulated interference and broadband noise is evaluated. In this way, the robustness of the proposed strategy in the presence of the interference can be fully assessed as a function of the interference, noise, and detector parameters.

Satorius, E.↗

NASA NTRS2003

Vertical Distribution of Shallow Water in the Distinguishable Regions at Low and High Latitudes of Mars: Neutron Data Deconvolution of HEND

High Energy Neutron Detector (HEND) is the part of Gamma-Ray Spectrometer suite onboard NASA Mars Odyssey orbiter [1-4]. During 16 months of mapping stage of Odyssey mission HEND has accumulated the set of maps of neutron emission of Mars at more than seven decades of energies range from the Cadmium threshold of 0.4 eV up to 15 MeV. These maps present very large variations of neutrons at different regions of Mars and they also show quite strong changes along Martian seasons.

I G Mitrofanov↗

NASA NTRS2004

Prototype Test Results for the Single Photon Detection SLR2000 Satellite Laser Ranging System

NASA's aging Satellite Laser Ranging (SLR) network is scheduled to be replaced over the next few years with a fully automated single photon detection system. A prototype of this new system, called SLR2000, is currently undergoing field trials at the Goddard Space Flight Center in Greenbelt, Maryland to evaluate photon counting techniques and determine system hardware, software, and control algorithm performance levels and limitations. Newly developed diode pumped microchip lasers and quadrant microchannel plate-based photomultiplier tubes have enabled the development of this high repetition rate single photon detection SLR system. The SLR2000 receiver threshold is set at the single photoelectron (pe) level but tracks satellites with an average signal level typically much less than 1 pe. The 2 kHz laser fire rate aids in satellite acquisition and tracking and will enable closed loop tracking by accumulating single photon count statistics in a quadrant detector and using this information to correct for pointing errors. Laser transmitter beamwidths of 10 arcseconds (FWHM) or less are currently being used to maintain an adequate signal level for tracking while the receiver field of view (FOV) has been opened to 40 arcseconds to accommodate point ahead/look behind angular offsets. In the near future, the laser transmitter point ahead will be controlled by a pair of Risley prisms. This will allow the telescope to point behind and enable closure of the receiver FOV to roughly match the transmitter beam divergence. Bandpass filters (BPF) are removed for night tracking operations while 0.2 nm or 1 nm filters are used during daylight operation. Both day and night laser tracking of Low Earth Orbit (LEO) satellites has been achieved with a laser transmitter energy of only 65 microjoules per pulse. Satellite tracking is presently limited to LEO satellites until the brassboard laser transmitter can be upgraded or replaced. Simultaneous tracks have also been observed with NASA s SLR standard, MOBLAS 7, for the purposes of data comparison and identification of biases. Work continues to optimize the receive optics; upgrade or replace the laser transmitter; calibrate the quadrant detector, the point ahead Risley prisms, and event timer verniers; and test normal point generation with SLR2000 data. This paper will report on the satellite tracking results to date, issues yet to be resolved, and future plans for the SLR2000 system.

Zagwodzki, Thomas W.↗

NASA NTRS1989

Positron line radiation from halo WIMP annihilations as a dark matter signature

We suggest a new signature for dark matter annihilation in the halo: high energy positron line radiation. Because the cosmic ray positron spectrum falls rapidly with energy, e+'s from halo WIMP annihilations can be a significant, clean signal for very massive WIMP's (approx. greater than 30 GeV). In the case that the e+e- annihilation channel has an appreciable branch, the e+ signal should be above background in a future detector, such as have been proposed for ASTROMAG, and of potential importance as a dark matter signature. A significant e+e- branching ratio can occur for neutralinos or Dirac neutrinos. High-energy, continuum positron radiation may also be an important signature for massive neutralino annihilations, especially near or above the threshold of the W+W- and ZoZo annihilation channels.

Turner, Michael S.↗

NASA NTRS2020

Advanced Silicon Avalanche Photodiodes on NASA's Global Ecosystem Dynamics Investigation (GEDI) Mission

Silicon Avalanche Photodiodes (APDs) are used in NASA’s Global Ecosystem Dynamics Investigation (GEDI) which was launched in December 2018 and is currently measuring the Earth’s vegetation vertical structure from the International Space Station. The APDs were specially made for space lidar with a much lower hole-to-electron ionization coefficient ratio (k-factor ~0.008) than that of commercially available silicon APDs in order to reduce the APD excess noise from the randomness of the avalanche gain. A silicon heater resistor was used under the APD chip to heat the device up to 70°C and improve its quantum efficiency at 1064 nm laser wavelength while maintaining a low dark current such that the overall signal to noise ratio is improved. Special APD protection circuits were used to raise the overload damage threshold to prevent device damage from strong laser return by specular surfaces, such as still water bodies, and space radiation events. The APD and a hybrid transimpedance amplifier circuit were hermetically sealed in a package with a sufficiently low leak rate to ensure multi-year operation lifetime in space. The detector assemblies underwent a series of pre-launch tests per NASA Goddard Environmental Verification Standard for space qualification. They have performed exactly as expected with GEDI in orbit. A detailed description of the GEDI detector design, signal and noise model, and test results are presented in this paper.

Sun, Xiaoli↗

NASA NTRS1993

Three Alternative Symbol-Lock Detectors

Three symbol-lock detectors proposed as alternatives in advanced receivers processing non-return-to-zero binary data signals. Two perform operations similar to those of older square-law and absolute-value types. However, integrals computed during nonoverlapping symbol periods and, therefore, only one integrator needed in each such detector. Proposed detectors simpler, but performances worse because noises in overlapping samples correlated, whereas noises in nonoverlapping samples not correlated. Third detector is signal-power-estimator type. Signal integrated during successive half symbol cycles, and therefore only one integrator needed. Half-cycle integrals multiplied to eliminate effect of symbol polarity, and products accumulated during M-cycle observation period to smooth out estimate of signal power. If estimated signal power exceeds threshold, delta, then lock declared.

Shihabi, Mazen M.↗

NASA NTRS1994

An analysis of carrier phase jitter in an MPSK receiver utilizing map estimation

The use of 8 and 16 PSK TCM to support satellite communications in an effort to achieve more bandwidth efficiency in a power-limited channel has been proposed. This project addresses the problem of carrier phase jitter in an M-PSK receiver utilizing the high SNR approximation to the maximum aposteriori estimation of carrier phase. In particular, numerical solutions to the 8 and 16 PSK self-noise and phase detector gain in the carrier tracking loop are presented. The effect of changing SNR on the loop noise bandwidth is also discussed. These data are then used to compute variance of phase error as a function of SNR. Simulation and hardware data are used to verify these calculations. The results show that there is a threshold in the variance of phase error versus SNR curves that is a strong function of SNR and a weak function of loop bandwidth. The M-PSK variance thresholds occur at SNR's in the range of practical interest for the use of 8 and 16-PSK TCM. This suggests that phase error variance is an important consideration in the design of these systems.

Osborne, William P.↗

NASA NTRS2004

Central Stars of Planetary Nebulae in the LMC

In FUSE cycle 2's program B001 we studied Central Stars of Planetary Nebulae (CSPN) in the Large Magellanic Could. All FUSE observations have been successfully completed and have been reduced, analyzed and published. The analysis and the results are summarized below. The FUSE data were reduced using the latest available version of the FUSE calibration pipeline (CALFUSE v2.2.2). The flux of these LMC post-AGB objects is at the threshold of FUSE's sensitivity, and thus special care in the background subtraction was needed during the reduction. Because of their faintness, the targets required many orbit-long exposures, each of which typically had low (target) count-rates. Each calibrated extracted sequence was checked for unacceptable count-rate variations (a sign of detector drift), misplaced extraction windows, and other anomalies. All the good calibrated exposures were combined using FUSE pipeline routines. The default FUSE pipeline attempts to model the background measured off-target and subtracts it from the target spectrum. We found that, for these faint objects, the background appeared to be over-estimated by this method, particularly at shorter wavelengths (i.e., < 1000 A). We therefore tried two other reductions. In the first method, subtraction of the measured background is turned off and and the background is taken to be the model scattered-light scaled by the exposure time. In the second one, the first few steps of the pipeline were run on the individual exposures (correcting for effects unique to each exposure such as Doppler shift, grating motions, etc). Then the photon lists from the individual exposures were combined, and the remaining steps of the pipeline run on the combined file. Thus, more total counts for both the target and background allowed for a better extraction.

Bianchi, Luciana↗

NASA NTRS2011

On the Sensitivity of the HAWC Observatory to Gamma-Ray Bursts

We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very high-energy gamma-ray observatory currently under construction in Mexico at an altitude of 4100 m. It will observe atmospheric air showers via the water Cherenkov method. HAWC will consist of 300 large water tanks instrumented with 4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main DAQ system reads out coincident signals in the tanks and reconstructs the direction and energy of individual atmospheric showers. The scaler DAQ counts the hits in each photomultiplier tube (PMT) in the detector and searches for a statistical excess over the noise of all PMTs. We show that HAWC has a realistic opportunity to observe the high-energy power law components of GRBs that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The two DAQ systems have an energy threshold that is low enough to observe events similar to GRB 090510 and GRB 090902b with the characteristics observed by Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs which in turn will lead to understanding about e-pair attenuation in GRB jets, extragalactic background light absorption, as well as establishing the highest energy to which GRBs accelerate particles.

Hays, E.↗

NASA NTRS2012

Limits on Achievable Dimensional and Photon Efficiencies with Intensity-Modulation and Photon-Counting Due to Non-Ideal Photon-Counter Behavior

An ideal intensity-modulated photon-counting channel can achieve unbounded photon information efficiencies (PIEs). However, a number of limitations of a physical system limit the practically achievable PIE. In this paper, we discuss several of these limitations and illustrate their impact on the channel. We show that, for the Poisson channel, noise does not strictly bound PIE, although there is an effective limit, as the dimensional information efficiency goes as e[overline] e PIE beyond a threshold PIE. Since the Holevo limit is bounded in the presence of noise, this illustrates that the Poisson approximation is invalid at large PIE for any number of noise modes. We show that a finite transmitter extinction ratio bounds the achievable PIE to a maximum that is logarithmic in the extinction ratio. We show how detector jitter limits the ability to mitigate noise in the PPM signaling framework. We illustrate a method to model detector blocking when the number of detectors is large, and illustrate mitigation of blocking with spatial spreading and altering. Finally, we illustrate the design of a high photon efficiency system using state-of-the-art photo-detectors and taking all these effects into account.

quantum limited communications↗