Long Term Trend in the LEO Radiation Environment as Measured by the Radiation Monitors On-Board Three UoSAT-Class Micro-Satellites

Details Long Term Trend in the LEO Radiation Environment as Measured by the Radiation Monitors On-Board Three UoSAT-Class Micro-Satellites Long Term Trend in the LEO Radiation Environment as Measured by the Radiation Monitors On-Board Three UoSAT-Class Micro-Satellites

Dec 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996esasp.392...37u&link_type=abstract

Environment Modelling for Space-based Applications, Symposium Proceedings (ESA SP-392). ESTEC Noordwijk, 18-20 September 1996. E

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Radiation environment monitoring payloads developed by DRA Farnborough and the University of Surrey have been flown on-board three low-Earth orbiting (LEO) microsatellites: UoSAT-3, KITSAT-1 and PoSAT-1. These have provided near-continuous sampling of the cosmic-ray and trapped proton environment inside the spacecraft since May 1990 - a period covering half a solar cycle {1,2,3,4}. This paper provides an analysis of the data from the payloads, and in particular examines the long term trends in the galactic cosmic-ray (GCR) background and trapped proton environment as experienced in LEO. These are then compared with predictions made using the standard environmental models available in the SPACE RADIATION code, together with our own PRISM code {5} to model particle transport and detector response. The results show good inter-correlation between the instruments, which were calibrated independently prior to flight using ion-beams, fission-fragments and alpha-sources. The trend in cosmic-ray background over the period has been generally upwards (as expected), and particle fluxes have doubled (in the LET-range of the instruments) over the six-year period. Fluxes are well correlated with the phase of the solar cycle. However, shorter-term features are observed which are not included in standard models. For example, there was a significant decrease in GCR following the major solar particle events of June 1991. This decrease persisted until late 1991. All the instruments showed a significant low-LET enhancement over the predictions made on the basis of standard models. The trapped proton environment shows long-term dynamics which are significantly out of phase with the solar cycle. The particle flux detected in the heart of the South-Atlantic anomaly reached a minimum in early-to-mid 1992, and has been increasing since then. This suggests that the phase of the trapped proton environment cycle might be better modelled on the basis of atmospheric density. Maps of the observed particle environment have been constructed from the data for comparison to standard models.
C.S. Dyer, A.J. Sims, J. Farren, J. Stephen, C. Underwood, "Radiation Environment Measurements & Single-Event Upset Observations in Sun-Synchronous Orbit", IEEE Trans. Nucl. Sci., NS-37, No. 6, pp.1700-1707, Dec 1991.
C.S. Dyer, A.J. Sims, P.R. Truscott, J. Farren, C. Underwood, "Radiation Measurements on Shuttle Missions Using the CREAM Experiment", IEEE Trans. Nucl.Sci., NS-39, No.6, pp.1809-1816, Dec 1992.
C.S. Dyer, A.J. Sims, P.R. Truscott, J. Farren, C. Underwood, "The Low Earth Radiation Environment and its Evolution from Measurements Using the CREAM and CREDO Experiments", IEEE Trans. Nucl. Sci., NS-39, No.6, pp.1471-1478, Dec 1993.
C.I. Underwood, D.J. Brock, P.S. Williams, S. Kim, R. Dilao, P.R. Santos,M.C. Brito, C.S. Dyer, A.J. Sims, "Radiation Environment Measurements with the Cosmic-Ray Experiments On-Board the KITSAT-1 and PoSAT-1 Micro-Satellites",IEEE Trans. Nucl. Sci., NS-40, No.6, Dec. 1994.
M.K. Oldfield and C.I. Underwood "PRISM - A Tool for Modelling Proton Energy Deposition in Semi-Conductor Materials", paper to be presented at IEEE NSREC 1996.

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