Implications for space radiation environment models from CREAM & CREDO measurements over half a solar cycle C.S. Dyer a, *, P.R. Truscott a , C.L. Peerless a , C.J. Watson a , H.E. Evans a , P. Knight a , M. Cosby a , C. Underwood b , T. Cousins c , R. Noulty d , C. Maag e a Space Department, DERA Farnborough, Hampshire, GU14 0LX, UK b Centre for Satellite Engineering Research, University of Surrey, Guildford, Surrey, UK c Defence Research Establishment, Ottawa, Ontario, Canada d Bubble Technology Industries, Chalk River, Ontario, Canada e T&M Engineering, Cape Canaveral, Florida, USA Received 8 May 1998; received in revised form 18 June 1999 Abstract Flight data obtained between 1990 and 1997 from the Cosmic Radiation Environment Monitors CREAM & CREDO carried on UoSAT-3, Space Shuttle, STRV-1a (Space Technology Research Vehicle) and APEX (Advanced Photovoltaic and Electronics Experiment Spacecraft) provide coverage over half a solar cycle. The modulation of cosmic rays and evolution of the South Atlantic Anomaly are observed, the former comprising a factor of three increase at high latitudes and the latter a general increase accompanied by a north-westward drift. Comparison of particle ¯uxes and linear energy transfer (LET) spectra is made with improved environment & radiation transport calculations which account for shield distributions and secondary particles. While there is an encouraging convergence between predictions and observations, signi®cant improvements are still required, particularly in the treatment of locally produced secondary particles. Solar-particle events during this time period have LET spectra signi®cantly below the October 1989 event which has been proposed as a worst case model.. Crown Copyright # 1999 Published by Elsevier Science Ltd. All rights reserved. Keywords: Cosmic rays; Inner-belt protons; Solar particle event; South Atlantic Anomaly; Shielding; Secondaries; Neutrons; Dose; Single event eects; Linear energy transfer spectra; Space shuttle; MIR 1. Introduction The temporal evolution of the space radiation en- vironment continues to provide a challenge to models used to predict eects in electronics and hazards to astronauts. In particular, the increasing use of com- mercial-o-the-shelf components in future space sys- tems means that more accurate assessment must be made of the hazards arising from single event eects (SEE). Improvements to the space environment models for cosmic rays, trapped protons and solar particles are required. In addition the deployment of large space structures, such as the International Space Station, require the application of sophisticated radiation trans- port tools which account for the generation of second- ary particles by nuclear interactions. Finally, validation of these models is required by comparison with controlled ¯ight experiments. In previous papers (Dyer et al., 1996a,b) results Radiation Measurements 30 (1999) 569±578 1350-4487/99/$ - see front matter. Crown Copyright # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S1350-4487(99)00236-X www.elsevier.com/locate/radmeas * Corresponding author.