Radiation Exposures for Commercial Deep Space Missions: EM/L1, Lunar and NEO Scenarios

Radiation exposures to humans and onboard electronics systems are a major concern for commercial deep space missions, especially those mission scenarios that entail long durations. There are some mission planning considerations being given to use the EarthMoon libration point 1 (EM/L1) as an operations base for propellant depots and for staging missions to the Moon and Near Earth Objects (NEOs). These missions will subject crews and spacecraft systems to two sources of space radiation: the extremely energetic galactic cosmic radiation (GCR) and solar proton events (SPEs). Both of these radiation sources vary with the so-called 11-year solar cycle. The GCR environment, although at a low particle flux level, represents long-term biological effects to humans and short-term effects to onboard systems. Large solar proton events represent the single-most important source of acute space radiation exposure to humans and radio-sensitive spacecraft systems for deep space missions. In this paper, radiation exposures to humans and onboard systems are presented for several baseline design reference missions: the free-space environment for EM/L1, lunar surface, and NEO missions. For lunar surface and NEO missions the radiation exposures are approximately one-half the free-space exposures. The crew radiation exposures for each mission scenario are compared with the current astronaut radiation exposure limits. In addition, radiation effects on spacecraft systems, especially electronics, are discussed in detail.