Donald Brautigam

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.

Specification of the radiation belt slot region: comparison of the NASA AE8 model with TSX5/CEASE data

The NASA AE8 models are compared with 4 years of CEASE data from the TSX-5 satellite, with a focus on the radiation belt slot region. The current 4 years of the TSX5 mission is divided into solar cycle phase, with CEASE models developed for the solar maximum and declining phases. It is found that the AE8 models predict slot fluxes that are orders of magnitude less than that observed by TSX5/CEASE.

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.