Assessment of Propellant Droplet Contamination Effects on the Europa Clipper Spacecraft

NASA's Europa Clipper spacecraft will carry nine science instruments to investigate whether Jupiter’s moon Europa has an environment that could support life. Europa Clipper is the largest spacecraft NASA has flown for a planetary mission. With solar arrays fully extended the spacecraft spans over 30 meters. At launch, nearly half of Europa Clipper’s mass is propellant which will be consumed during travel to Jupiter, inserting the spacecraft into orbit around Jupiter, and to perform almost 50 flybys of Europa. Europa Clipper’s propulsion system has 24 bipropellant engines which will process nearly 2750 kg of fuel and oxidizer during the course of the mission. During propulsion system operation liquid droplets of unburned fuel and oxidizer are expelled from the engines. An empirical bipropellant plume contamination model that was originally developed for International Space Station thrusters was applied to investigate droplet effects on the Europa Clipper spacecraft. Unburned propellant droplets can cause damage to spacecraft materials by chemical reactions and mechanical damage exhibited by pitting surfaces. Bounding estimates for propellant droplet fluxes to Europa Clipper surfaces were obtained using the empirical model. Based on material testing results, estimates of damage to materials used for thermal blankets, solar arrays, and instruments were assessed to determine the impact to spacecraft thermal, power and science systems. Where needed, design changes were made to mitigate deleterious effects caused by propulsion system operation.

NASA的欧罗巴快船（Europa Clipper）探测器将搭载九台科学探测载荷，开展探测研究以确认木星卫星欧罗巴是否具备可支持生命存活的环境。欧罗巴快船是NASA执行行星探测任务以来发射的最大型航天器。其太阳能帆板（solar arrays）完全展开后，整机跨度超过30米。发射阶段，欧罗巴快船的总质量近半数为推进剂，这些推进剂将在前往木星的航程、木星轨道捕获以及近50次欧罗巴飞掠任务中被逐步消耗。
欧罗巴快船的推进系统搭载24台双组元发动机（bipropellant engines），整个任务周期内将消耗近2750千克的燃料与氧化剂。推进系统工作时，未完全燃烧的燃料与氧化剂液滴会从发动机喷口排出。本研究采用了最初为国际空间站（International Space Station）推力器开发的经验式双组元羽流污染模型，以探究此类液滴对欧罗巴快船探测器的影响。未燃烧的推进剂液滴可通过化学反应以及表面点蚀等机械损伤形式，对航天器材料造成损毁。
研究团队通过该经验模型，估算出了抵达欧罗巴快船各表面的推进剂液滴通量的边界范围。结合材料测试结果，研究人员对热控毯（thermal blankets）、太阳能帆板及科学载荷所用材料的受损情况进行了评估，以此分析其对探测器热控、电源及科学载荷系统的影响。针对识别出的风险点，团队已开展针对性设计改进，以缓解推进系统运行所带来的有害影响。