Gregory P. Ginet

CRRES observations of radiation belt protons 1. Data overview and steady state radial diffusion

The Proton Telescope (PROTEL) instrument on the CRRES satellite made measurements of omnidirectional differential proton flux in the energy range 1-100 MeV, with full pitch angle resolution. An overview of the equatorially mirroring particle data is presented for the entire CRRES mission. We then consider the equatorially mirroring particle distribution in terms of steady state radial diffusion theory. The outer zone, 1.7 ≤ L ≤ 3, is shown to have deviated drastically from steady state profiles both before and after the magnetic storm of March 24, 1991, which rearranged the outer zone but left the inner zone, L ≤ 1.7, largely unaffected. Time-averaged measurements are compared to theoretical steady state diffusion profiles of the inner zone, which are calculated using several different, previously introduced models of the plasmaspheric electron density and cosmic ray albedo neutron decay (CRAND). For each combination of models, a four-parameter (electrostatic plus magnetic) radial diffusion coefficient is sought which minimizes the difference between the measurements and calculated flux values. While the best fit values found are physically implausible, nearly equally good results are obtained for values only moderately adjusted from standard, consensus values.

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.

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.

SEE relative probability maps for space operations

Normalized flux and dose data for protons with energies >50 MeV are used to produce contour maps of relative probabilities of experiencing Single Event Effects (SEEs) in the Earths inner radiation belt. The data were taken on the APEX and CRRES satellites. To make the maps, the data are averaged in 3/spl deg/ by 3/spl deg/ bins in geographic latitude and longitude, and in 50 km steps in altitude. All geographic longitudes, and latitudes between /spl les/70/spl deg/ are covered. The altitude range extends from 350 km to 14,000 km. This geographic range includes the complete region of inner belt >50 MeV protons, except in the area of the South Atlantic Anomaly below 350 km. The maps easily locate regions of high risk for SEEs and are designed primarily for use in space mission planning and operations. The data base includes the added proton peak following the March 1991 magnetic storm, but does not include SEE probabilities in the polar cap regions associated with high energy solar particle events.

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.

Correction to "The Trapped Proton Environment in Medium Earth Orbit (MEO)" [Dec 10 3135-3142]

Due to a combination of conversion factor and spreadsheet format errors, Table II in the original paper (ibid., vol. 57, no. 6, pp. 3135-3142, Dec. 2010) is incorrect. A corrected version of Table II is presented here. Also, the last sentence in Section IV should read: Not surprisingly, Composite Model 2, which weighs the CRRES results more heavily, predicts a dose ~3-8 times higher than the NASA models while Composite Model 1 is in the range of ~0.5 - 1.8 times the NASA models.

Release of AE9/AP9/SPM Radiation Belt and Space Plasma Model Version 1.20.002

An update of the AE9/AP9/SPM radiation belt and space plasma specification model, Version 1.20.002, has been released. As in the prior releases in 2012 and 2013, this model suite provides estimates of trapped energetic electrons, energetic protons, and plasma, for use in space system design, mission planning, and other applications of climatological specification. It is based on 37 satellite-based data sets processed to create maps of the particle fluxes along with estimates of uncertainties from both imperfect measurements and space weather variability. These uncertainty estimates can be obtained as statistical confidence intervals, e.g. the median and 95 percentile, for fluxes and derived quantities, supporting design trades. Implementations of the legacy AE8/AP8 and CRRESELE/CRRESPRO models are available within the model suite. The SHIELDOSE2 code is used for dose estimation from the calculated fluxes. Orbit ephemeris may be generated using one of three orbit propagators, or may be directly supplied. The self-contained software package includes a Windows-based executable version of the model suite, accessible either by command line or graphical user interface, plus supporting documentation such as the users’ guide, validation results, and software license information.

Overview of the AFRL's Demonstration and Science Experiments (DSX) Program

Abstract : The Air Force Research Laboratory (AFRL) Space Vehicles Directorate has developed the Demonstration and Science Experiments (DSX) mission to research technologies needed to significantly advance Department of Defense (DoD) capability to operate spacecraft in the harsh radiation environment of medium-earth orbits (MEO). The ability to operate effectively in the MEO environment significantly increases the DoDs capability to field space systems that provide persistent global targeting-grade space surveillance, high-speed satellite-based communication, lower-cost GPS navigation, and protection from space weather on a responsive satellite platform. The three DSX physics-based research areas are: 1. Wave Particle Interaction Experiment (WPIx): Researching the physics of very-low-frequency (VLF) transmissions in the magnetosphere and characterizing the feasibility of natural and man-made VLF waves to reduce space radiation; 2. Space Weather Experiment (SWx): Characterizing and modeling the space radiation environment in MEO, an orbital regime attractive for future DoD and commercial missions; 3. Space Environmental Effects (SFx): Researching and characterizing the space weather effects on spacecraft electronics and materials. DSX uses a modular design that allows for launch either as a primary satellite on a conventional launcher, such as a Minotaur, or as a secondary payload on a larger rocket, such as the Evolved Expendable Launch Vehicle (EELV). Another key feature is the use of a dedicated payload computer, which unburdens the avionics of the need to conform to custom payload data interfaces, enabling the rapid procurement of a standard spacecraft bus. An overview of the DSX science experiments, payload design, spacecraft subsystems, and engineering approach will be described.

MEO Wave-Particle Interaction, Space Weather, and Environmental Effects Payloads on AFRL's Demonstration and Science Experiments (DSX)

The Air Force Research Laboratory (AFRL) Space Vehicles Directorate has developed the Demonstration and Science Experiments (DSX) mission to research technologies needed to significantly advance Department of Defense (DoD) capability to operate spacecraft in the harsh radiation environment of medium-earth orbits (MEO). The ability to operate effectively in the MEO environment significantly increases the DoDs capability to field space systems that provide persistent global targeting-grade space surveillance, high-speed satellite-based communication, lower-cost GPS navigation, and protection from space weather on a responsive satellite platform. The three DSX physics- based research areas are: 1. Wave Particle Interaction Experiment (WPIx): Researching the physics of very- low-frequency (VLF) transmissions in the magnetosphere and characterizing the feasibility of natural and man-made VLF waves to reduce space radiation; 2. Space Weather Experiment (SWx): Characterizing and modeling the space radiation environment in MEO, an orbital regime attractive for future DoD and commercial missions; 3. Space Environmental Effects (SFx): Researching and characterizing the space weather effects on spacecraft electronics and materials.