Pre-engineering spaceflight validation of environmental models and the 2005 HZETRN simulation code J.E. Nealy a , F.A. Cucinotta b , J.W. Wilson c, * , F.F. Badavi d , Ts.P. Dachev e , B.T. Tomov e , S.A. Walker a , G. De Angelis a,f , S.R. Blattnig c , W. Atwell g a Old Dominion University, Norfolk, VA 23508, USA b NASA Johnson Space Center, Houston, TX 77058, USA c NASA Langley Research Center, Hampton, VA 23681, USA d Christopher Newport University, Newport News, VA 23606, USA e Bulgarian Academy of Science, Acad. Georgi Bonchev St., Block 3, 1113 Sofia, Bulgaria f Istituto Superiore di Sanita ` , Viale Regina Elena 299, I-00161 Rome, Italy g The Boeing Company, Houston, TX 77058, USA Received 31 October 2006; received in revised form 18 December 2006; accepted 19 December 2006 Abstract The HZETRN code has been identified by NASA for engineering design in the next phase of space exploration highlighting a return to the Moon in preparation for a Mars mission. In response, a new series of algorithms beginning with 2005 HZETRN, will be issued by correcting some prior limitations and improving control of propagated errors along with established code verification processes. Code validation processes will use new/improved low Earth orbit (LEO) environmental models with a recently improved International Space Station (ISS) shield model to validate computational models and procedures using measured data aboard ISS. These validated models will provide a basis for flight-testing the designs of future space vehicles and systems of the Constellation program in the LEO environment. Published by Elsevier Ltd. on behalf of COSPAR. Keywords: Space radiation; Shielding; Models; Measurements 1. Introduction Improved spacecraft shield design requires early entry of radiation constraints into the design process to maximize performance and minimize costs. As a result, we have been investigating computational procedures to allow shield analysis starting with preliminary design concepts through high-fidelity final design models (Wilson et al., 2003). Of particular importance is the need to implement probabilis- tic models to account for design uncertainties (Wilson et al., 2004) in the context of optimal design processes (Qualls et al., 2003). These requirements need supporting tools with high computational efficiency to enable appro- priate design methods. Only the HZETRN code has so far been identified for this purpose. As a result, Wilson et al. (2005) have prepared a review of past HZETRN code development, verification, and validation. Although there has been sporadic research to generalize this code over the last ten years, evaluation of code status among princi- pal users demonstrated drift in the various code versions and databases. As a result of this renewed interest in HZETRN for future space systems design, there is now a systematic effort to advance, verify, and validate these codes in preparation to integrating them into engineering design processes. The present paper will describe the first several months of this renewed systematic effort. As NASA’s newly defined technology development spirals are now progressing, there is a need to identify a 0273-1177/$30 Published by Elsevier Ltd. on behalf of COSPAR. doi:10.1016/j.asr.2006.12.029 * Corresponding author. Tel.: +1 757 864 1414; fax: +1 757 864 8094. E-mail address: john.w.wilson@nasa.gov (J.W. Wilson). www.elsevier.com/locate/asr Available online at www.sciencedirect.com Advances in Space Research 40 (2007) 1593–1610