Bronislaw K. Dichter

Preliminary comparison of dose measurements on CRRES to NASA model predictions

Measurements of proton and electron dose from the space radiation dosimeter on the CRRES satellite, in a 18.1 deg, 350 km by 33000km orbit, are compared to the NASA models for solar maximum conditions. Up to the time of the large, solar-initiated particle events near the end of March 1991, the results are similar to those previously reported for solar minimum at low altitudes. That is, prior to the March event, there is excellent agreement between model and measured values for protons and poor agreement for electrons. During the event period a second proton belt was formed at higher altitudes which is not contained in the proton models, and the electrons increased over an order of magnitude for the CRRES orbit. This resulted in poorer agreement between model and measured values for protons during and after the solar proton event and better agreement for electrons during the electron enhancement period. What the data show is that, depending on orbit, both the existing proton and electron models can give large errors in dose that can compromise space system performance and lifetime.

Compact environmental anomaly sensor (CEASE): a novel spacecraft instrument for in situ measurements of environmental conditions

A small, lightweight, and low power, spacecraft instrument, CEASE, has been designed to measure the local space radiation environment. The instruments on-board processing algorithms use the collected data to generate warnings of the space environment hazards of radiation damage, dielectric charging and single event effects (SEE). In addition, CEASE can provide detailed space environment data to aid in analysis of anomalies that may occur on the host spacecraft.

Energetic Proton Maps for the South Atlantic Anomaly

A new set of flux intensity maps for energetic protons in the South Atlantic Anomaly (SAA) region is presented for the epoch 2000-2006 based on data from the compact environment anomaly sensor (CEASE) flown onboard the tri-service experiment-5 (TSX-5) satellite in a 410 km x 1710 km, 69 degree inclination orbit. Maps for > 23 Mev, > 38 MeV, > 66 MeV and > 94 MeV protons have been constructed and boundary contours for 1/2 maximum, 1/10 maximum and 3 times the background standard deviation derived. Estimates are given of the integral energy spectra as a function of altitude from 400 km to 1650 km, an interval spanning the range where the controlling factor in the dynamics changes from the neutral density to the global magnetic field. The position of the maximum flux point is compared to that determined from earlier measurements in the 1994-1996 epoch and found to be consistent with the well-known westward drift.

Initial on-orbit results from the Compact Environmental Anomaly Sensor (CEASE)

The Compact Environmental Anomaly Sensor (CEASE) is an instrument designed to provide real-time space environment hazard warnings to the host spacecraft. In this paper, we report on the first year of on-orbit operation of this instrument and describe its performance with particular emphasis on its engineering, hazard-warning function.

Proton Flux Anisotropy in Low Earth Orbit

Proton flux anisotropy as a function of altitude in the South Atlantic Anomaly is investigated using data from the Compact Environment Anomaly Sensor (CEASE) flown onboard the tri-service experiment-5 (TSX-5) satellite from June 2000 to July 2006. In a 410 km times 1710 km, 69 degree inclination orbit, TSX-5 spanned a broad range of the low Earth orbit regime. Using measurements of total dose, integral energy flux >40 MeV and the differential flux at 40 MeV sorted into 3 degree latitude times 3 degree longitude times 50 km altitide bins and averaged over the entire mission, the components arising from eastward and westward traveling protons have been determined in areas of the SAA where CEASE detection efficiency is not compromised. For the first time, ratios of these components have been compared to predictions of east-west effect models above 400 km. There is good agreement in general with the anisotropy becoming apparent at approximately 1200 km (moving down) and increasing rapidly starting at approximately 1000 km, the magnitude and rate depending on location within the anomaly. Measurements of the differential flux at 40 MeV are compared to predictions of standard radiation belt models as a function of altitude and found to be substantially higher in magnitude than AP8, though a comprehensive survey has not yet been performed.

Grazing angle proton scattering: effects on Chandra and XMM-Newton X-ray telescopes

A proton scattering process resulted in damage to one of the Chandra X-ray telescopes focal plane detectors. In this process, incident protons were transmitted, by scattering off the telescope mirrors, to the focal plane. We identify the proton population responsible for the damage and, using a proper grazing angle formalism, we show that the standard calculations of grazing angle scattering will significantly under predict the expected proton flux at the focal plane.

Characterization of Teledyne microdosimeters for space weather applications

The Teledyne microdosimeter is a novel miniature dosimeter that has become recently available to satellite manufacturers and programs to provide awareness of the total radiation dose received by the satellite and its associated subsystems. A characterization of the response of the dosimeter to protons of energies from 30 - 200 MeV as a function of angle, energy and dose rate is presented in this paper. In addition, the response of the dosimeter to a simulated Solar proton event with several different levels of shielding has been measured. These results show that the dosimeter response is relatively uniform over a wide range of conditions for protons. Monte Carlo modeling of the dosimeter for isotropic particle fluxes (both electrons and protons) has also been accomplished. It is shown that a simplified model is appropriate in determining the response of the dosimeter when using it to design low cost, simple instruments for space weather and situational awareness applications.

The AFRL DSX Flight Experiment

The Deployable Structures Experiment (DSX) is a 2004 new-start AFRL Space Vehicles Flight Experiment. DSX is designed to perform four basic research experiments that coupled together provides DoD with the technological understanding needed to achieve transformational capability in space surveillance, microsats with large aperture and power, remediation of the effects of a high-altitude nuclear detonation (HAND), and radiationsurvivability design criteria for satellite systems planned for the highly desirable medium Earth orbit (MEO) regime. The four DSX experiments are fundamental research on large deployable space structures, Radiation Belt Remediation (RBR), thin-film photovoltaics (TFPV), and space particle measurement in the MEO environment. DSX is baselined to launch in 2008 to a 6000-km x 12000-km, 27 degree inclination MEO orbit.

Calibration of the Compact Environmental Anomaly Sensor (CEASE) for the DSX space weather mission

The CEASE instrument was designed to measure energetic electrons and protons in the space environment. It consists of two dosimeter detectors, a particle telescope and a Single Event Effect rate detector. CEASE was designed to be an engineering instrument providing real-time warnings of space weather hazards to the spacecraft operators. The Air Force Research Laboratory has flown CEASE instruments on two long term missions and is using the data as a part of its radiation belt model research. A third CEASE instrument will be flown on the Air Force Research Laboratory DSX mission. The method and results of the calibration of the particle telescope sensor on CEASE will be presented. An extensive program of telescope response simulation calculations has also been carried out using both simple analytical models and the Monte Carlo particle interaction codes, MCNPX and Integrated TIGER Series. Comparison of calculated telescope results to the measured calibration data will be presented.

Calibration of the High Energy Proton Spectrometer (HEPS) for the demonstration and science experiments (DSX) satellite space weather mission

HEPS was designed to measure high energy protons, with energies between 25 and 400 MeV, in the space environment. The instrument uses a collection of solid state Si particle detectors and Gadolinium Silicate (GSO) crystal scintillators to detect the protons and measure their energy. The sensors form a coaxial arrangement of four Si detectors, to provide an event trigger when struck by an incident proton. The energy measurement for each event is provided by the measurement of its energy losses in the two scintillator elements. Energy losses are determined by photodiodes that collect light produced in GSO by the protons. The HEPS flight unit was extensively calibrated in the 30-217 MeV energy range. The beam measurements were carried out at a series of angles in the instrument field-of-view as well as at larger angles to test its rejection capabilities. An extensive program of computer modeling of HEPS response has been carried out using the Monte Carlo particle interaction code MCNPX. Calibration data will be compared to the results of the calculations. Conclusions concerning the calibrated geometric factors will be discussed.