During transit between the Earth and planetary destinations, spacecraft encounter conditions that are deleterious to the survival of terrestrial microorganisms. To model the resulting bioburden reduction, a Cruise-Phase Microbial Survival (CPMS) model was prepared based upon the Lunar Microbial Survival model, which considers the effects of temperature, vacuum, ultraviolet (UV), and ionizing radiation found in the space environment. As an example, the CPMS was used to determine the expected bioburden reductions on the Europa Clipper spacecraft upon arrival at Jupiter under two different transit scenarios. Under a direct trajectory scenario, exterior surfaces are rapidly sterilized with tens of thousands of lethal doses (LDs) absorbed to the spacecraft exterior and at least one LD to all interior spaces of the spacecraft heated to at least 240 K. Under a Venus-Earth-Earth gravity assist (VEEGA) trajectory, we find substantially higher bioburden reductions resulting from the spacecraft spending much more time near the Sun and more time in transit overall. With VEEGA, the exterior absorbs hundreds of thousands of LDs and interior surfaces heated above 230 K would absorb at least one LD. From these simulations, we are able to generalize about bioburden reduction in transit on spacecraft in general, finding that all spacecraft surfaces would sustain at least one LD in ≤38.5 years even if completely unheated. Temperature and vacuum synergy dominates surface reductions out to at most 3.3 AU (for gold multilayer insulation), UV irradiation and temperature between 3.3 and 600 AU, and past 600 AU the effect of vacuum acting alone is the primary factor for all exterior and interior surfaces. Even under the most conservative estimates, if the average interior temperature of the Cassini spacecraft exceeded 218 K, or the Galileo spacecraft interior exceeded 222 K, neither spacecraft would have likely had any viable bioburdens onboard at disposal.

中文翻译：

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一种巡航阶段微生物生存模型，用于计算过去或未来航天器在其整个任务中的生物负载减少，并应用于 Europa Clipper。

在地球和行星目的地之间的运输过程中，航天器遇到了对陆地微生物生存有害的条件。为了模拟由此产生的生物负载减少，基于月球微生物生存模型准备了巡航阶段微生物生存 (CPMS) 模型，该模型考虑了空间环境中发现的温度、真空、紫外线 (UV) 和电离辐射的影响。例如，CPMS 用于确定在两种不同的过境情景下到达木星时欧罗巴快船航天器的预期生物负载减少。在直接轨迹场景下，外表面被快速消毒，航天器外部吸收了数万个致死剂量 (LD)，航天器的所有内部空间至少吸收了一个致死剂量 (LD)，加热至至少 240 K。在金星-地球-地球重力辅助 (VEEGA) 轨迹下，我们发现由于航天器在太阳附近花费更多时间和整体运输时间更多，导致生物负载减少显着增加。使用 VEEGA，外部会吸收数十万个 LD，而加热到 230 K 以上的内表面将吸收至少一个 LD。从这些模拟中，我们能够概括总体上航天器运输过程中生物负载的减少，发现即使完全未加热，所有航天器表面也将在≤38.5 年内维持至少一个 LD。温度和真空协同控制表面减少至最多 3.3 AU（对于金多层绝缘），紫外线照射和温度在 3.3 到 600 AU 之间，超过 600 AU，真空单独作用的影响是所有外表面和内表面的主要因素.