Potential deleterious health effects to astronauts induced by space radiation is one of the most important long-term risks for human space missions, especially future planetary missions to Mars which require a return-trip duration of about 3 years with current propulsion technology. In preparation for future human exploration, the Radiation Assessment Detector (RAD) was designed to detect and analyze the most biologically hazardous energetic particle radiation on the Martian surface as part of the Mars Science Laboratory (MSL) mission. RAD has measured the deep space radiation field within the spacecraft during the cruise to Mars and the cosmic ray induced energetic particle radiation on Mars since Curiosity’s landing in August 2012. These first-ever surface radiation data have been continuously providing a unique and direct assessment of the radiation environment on Mars. We analyze the temporal variation of the Galactic Cosmic Ray (GCR) radiation and the observed Solar Energetic Particle (SEP) events measured by RAD from the launch of MSL until December 2020, i.e., from the pre-maximum of solar cycle 24 throughout its solar minimum until the initial year of Cycle 25. Over the long term, the Mars’s surface GCR radiation increased by about 50% due to the declining solar activity and the weakening heliospheric magnetic field. At different time scales in a shorter term, RAD also detected dynamic variations in the radiation field on Mars. We present and quantify the temporal changes of the radiation field which are mainly caused by: (a) heliospheric influences which include both temporary impacts by solar transients and the long-term solar cycle evolution, (b) atmospheric changes which include the Martian daily thermal tide and seasonal CO\(_2\) cycle as well as the altitude change of the rover, (c) topographical changes along the rover path-way causing addition structural shielding and finally (d) solar particle events which occur sporadically and may significantly enhance the radiation within a short time period. Quantification of the variation allows the estimation of the accumulated radiation for a return trip to the surface of Mars under various conditions. The accumulated GCR dose equivalent, via a Hohmann transfer, is about \(0.65 \pm 0.24\) sievert and \(1.59 \pm 0.12\) sievert during solar maximum and minimum periods, respectively. The shielding of the GCR radiation by heliospheric magnetic fields during solar maximum periods is rather efficient in reducing the total GCR-induced radiation for a Mars mission, by more than 50%. However, further contributions by SEPs must also be taken into account. In the future, with advanced nuclear thrusters via a fast transfer, we estimate that the total GCR dose equivalent can be reduced to about 0.2 sievert and 0.5 sievert during solar maximum and minimum periods respectively. In addition, we also examined factors which may further reduce the radiation dose in space and on Mars and discuss the many uncertainties in the interpreting the biological effect based on the current measurement.

空间辐射对宇航员健康造成的潜在有害影响是人类太空任务最重要的长期风险之一，特别是未来的火星行星任务，使用当前的推进技术需要大约 3 年的往返时间。为了为未来的人类探索做好准备，辐射评估探测器 (RAD) 旨在探测和分析火星表面最具生物危害性的高能粒子辐射，作为火星科学实验室 (MSL) 任务的一部分。 RAD 测量了火星巡航期间航天器内的深空辐射场以及自 2012 年 8 月好奇号着陆以来宇宙射线在火星上引起的高能粒子辐射。这些有史以来首次的表面辐射数据不断提供独特而直接的评估火星上的辐射环境。我们分析了从 MSL 发射到 2020 年 12 月期间，银河宇宙线 (GCR) 辐射和 RAD 观测到的太阳高能粒子 (SEP) 事件的时间变化，即从第 24 太阳周期前极大期到整个太阳活动期间的时间变化。直到第 25 周期的第一年才达到最小值。从长远来看，由于太阳活动减弱和日光层磁场减弱，火星表面 GCR 辐射增加了约 50%。在短期内的不同时间尺度上，RAD 还检测到了火星辐射场的动态变化。我们呈现并量化了辐射场的时间变化，这些变化主要是由以下原因引起的：（a）日光层影响，包括太阳瞬变的暂时影响和长期太阳周期演化，（b）大气变化，包括火星每日热量潮汐和季节性 CO \(_2\)循环以及漫游车的高度变化，(c) 漫游车路径沿线的地形变化导致额外的结构屏蔽，最后 (d) 偶发发生并可能显着增强的太阳粒子事件短时间内的辐射。对变化的量化可以估计在各种条件下返回火星表面的累积辐射。通过霍曼转移，累积的 GCR 剂量当量约为\(0.65 \pm 0.24\)西弗特和\(1.59 \pm 0.12\)分别在太阳极大期和极小期期间的西弗特。在太阳活动极大期期间，日光层磁场对 GCR 辐射的屏蔽相当有效，可以有效地将火星任务中由 GCR 引起的总辐射减少 50% 以上。然而，还必须考虑标准必要专利的进一步贡献。未来，通过快速转移的先进核推进器，我们估计在太阳极大期和太阳极小期期间，总 GCR 剂量当量可分别降至约 0.2 西弗和 0.5 西弗。此外，我们还研究了可能进一步减少太空和火星辐射剂量的因素，并讨论了根据当前测量结果解释生物效应的许多不确定性。