Abstract
Abstract. The radiation data collected by the Standard Radiation Environment Monitor (SREM) aboard ESA missions INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory), Rosetta, Herschel, Planck and Proba-1, and by the high-energy neutron detector (HEND) instrument aboard Mars Odyssey, are analysed with an emphasis on characterising galactic cosmic rays (GCRs) in the inner heliosphere. A cross calibration between all sensors was performed for this study, which can also be used in subsequent works. We investigate the stability of the SREM detectors over long-term periods. The radiation data are compared qualitatively and quantitatively with the corresponding solar activity. Based on INTEGRAL and Rosetta SREM data, a GCR helioradial gradient of 2.96 % AU−1 is found between 1 and 4.5 AU. In addition, the data during the last phase of the Rosetta mission around comet 67P/Churyumov–Gerasimenko were studied in more detail. An unexpected yet unexplained 8 % reduction of the Galactic Comic Ray flux measured by Rosetta SREM in the vicinity of the comet is noted.
Highlights
The space radiation environment affects both manned and unmanned missions outside the Earth’s protecting atmosphere and its magnetic field
The variation in galactic cosmic ray intensity depends on different physical processes: inward diffusion in the interplanetary magnetic field (IMF), adiabatic cooling, outward convection and deceleration in the solar wind plasma, drift along the heliospheric current sheet, and interaction with magnetic structures in shocks and in interplanetary coronal mass ejections (e.g. Potgieter, 2013; Moraal, 2013; Alania et al, 2014; Kozai et al, 2014; Giseler and Heber, 2016)
This was achieved with several gravity-assist fly-bys, which are indicated on the plot by vertical lines: three Earth gravity assists on 4 March 2005, 13 November 2007 and 13 November 2009 and a Mars gravity assist on 25 February 2007, which all had a significant impact on the trajectory of the spacecraft
Summary
The space radiation environment affects both manned and unmanned missions outside the Earth’s protecting atmosphere and its magnetic field. Energetic particles can penetrate living tissue and a spacecraft’s component materials, causing damage due to the deposition of energy Major sources of this radiation are solar energetic particles (SEPs) and galactic cosmic rays (GCRs). While INTEGRAL, Herschel, Planck and Proba-1 are located at around 1 AU from the Sun and HEND orbits Mars with an average heliocentric distance of 1.5 AU, Rosetta’s heliocentric distance varied from 1 to 4.5 AU during its mission lifetime. Of special interest are the Rosetta measurements close to comet 67P/Churyumov–Gerasimenko
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