Observed and simulated LET spectra comparison for the CRaTER instrument on LRO

Abstract

The Lunar Reconnaissance Orbiter (LRO) was launched into lunar orbit in June 2009. Among its objectives are to find potential safe landing sites, locate potential resources, test new technologies, and characterize the lunar radiation environment. To accomplish the latter objective, the Cosmic Ray Telescope for the Effects of Radiation (CRaTER), a linear energy transfer (LET) spectrometer is mounted on the LRO. Its purpose is to measure the LET spectrum of the lunar radiation environment. LET is highly important in quantifying the biological and electronic effects of ionizing radiation. Although most of the particle fluence of importance consists of high energy protons from solar particle events (SPEs) and galactic cosmic rays (GCRs), the galactic cosmic ray spectrum also includes a significant component composed of high energy, heavy charged particles with high LET values. These particles are capable of fragmenting themselves and target materials, which causes large energy depositions capable of causing significant biological risk to lunar explorers. In this work, estimates of these LET values for the lunar environment, obtained using the HETC-HEDS (High Energy Transport Code — Human Exploration and Development in Space) are compared to observed CRaTER measurement results.