The deep space galactic cosmic ray lineal energy spectrum at solar minimum

Abstract

[1] The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument is an energetic particle telescope on board the Lunar Reconnaissance Orbiter spacecraft. CRaTER measures energetic charged particles that have sufficient energy to penetrate the outer shielding of the instrument (about 12 MeV/nucleon). Galactic cosmic rays (GCR) with these energies are the primary radiation concern for spacecraft and astronauts outside of the Earth's magnetosphere during times of minimal solar activity. These particles can easily penetrate typical shielding and damage electronics, causing increased electronics failure rates and single event upsets. When this radiation impacts biological cells, it causes an increased risk of cancer. The CRaTER instrument was built to characterize the radiation dose and lineal energy with unprecedented time and energy resolution and was fortuitously flown during a period of time that coincided with the highest GCR fluxes in the modern space age. We report here this worst-case GCR lineal energy spectrum. Observations are made behind a thin aluminum window and different thicknesses of tissue-equivalent plastic. These measurements provide important observational data points to compare with current model predictions of the dose deposited by energetic particles within a tissue-like material.

Does the worsening galactic cosmic radiation environment observed by CRaTER preclude future manned deep space exploration?

“…The second consideration is the conversion from dose to dose equivalent using linear energy transfer (LET) spectra. We estimate the dose equivalent using the observed LET spectra by LRO/CRaTER [ Case et al , ] in its almost unshielded zenith‐facing detectors (D1/D2) and by Mars Science Laboratory/Radiation Assessment Detector (MSL/RAD) during the MSL cruise to Mars [ Zeitlin et al , ], in addition to using results from models. In the case of CRaTER and RAD, we first convert the measured LET spectrum in Si to the LET spectrum in water [ Benton et al , ].…”

Measurements of galactic cosmic ray shielding with the CRaTER instrument

“…At Δ E values above this the data have been averaged over bins that are 4 MeV wide, whereas at lower values the bins are 1 MeV wide. An alternate way of handling the binning is given by [ Case et al ., ].…”

Feasibility study of astronaut standardized career dose limits in LEO and the outlook for BLEO

“…The Moon is generally seen to provide the first step, building on lessons learned aboard the International Space Station/ISS and aboard the Russian Space Station MIR. In situ measurements currently being made by the Cosmic Ray Telescope for the Effects of Radiation/ CRaTER instrument aboard the Lunar Reconnaissance Orbiter/LRO spacecraft already provide a useful, incrementing, data set with which to test predictive particle modeling for the Moon [6]. An idea to, thereafter, send astronauts to the Earth-Moon-Lagrange point (EM-L2) has recently emerged in the United States.…”