The Water Electrolysis Hall Effect Thruster (WET-HET): Paving the Way to Dual Mode Chemical-Electric Propulsion

迄今为止，大多数人造卫星都使用两种截然不同的推进器和推进剂在太空中运行。高推力功能是由剧毒的化学燃料（肼）来满足的，这种燃料既昂贵又难以处理，因为短暂的接触对人类来说是致命的。在需要高燃油效率和可以接受低推力的地方，使用电力推进（EP）推进器，由昂贵的高纯度惰性气体（氙气）提供动力，储存在非常高的压力下。这两个完全独立的系统都存在于许多较大的航天器平台上，以满足推力和燃油效率的全部要求。小型卫星越来越多地采用了低成本和无毒的替代推进剂，其价格和操作优势具有特别大的影响。我们项目的最终目标是用水取代氙和肼，这是一种绿色、低成本的推进剂，用于大型卫星的化学和电力推进功能。提出的HYDRA系统概念是在任务期间按需将水电解成氧气和氢气。该项目的重点是EP子系统：水电解霍尔效应推进器（WET-HET）的开发，它将带正电的氧气电离并加速到燃油效率所需的非常高的速度。这与一个电子发射空心阴极装置相结合，该装置以氢气为燃料，以保持航天器的电荷中性。到目前为止，这两种装置都没有在太空飞行中与这些推进剂一起使用。对于卫星所需的更高推力脉冲，这两种气体还将用于化学双推进剂推进器ICE。这允许一个航天器用燃油效率高的电力和高推力化学推进选项飞行，但是一个单一的低压水推进剂罐，推进剂管理系统，和相关的硬件。这一全新的整体架构可以实现单靠任何一种技术都不可能实现的全谱任务场景，无需飞行两个完全独立的系统和推进剂的成本和质量损失，推进剂价格非常低，水的储存密度很高。该项目的重点是在技术和工程方面的挑战，将现有的霍尔效应推进器和中和器的技术概念应用于非常规的氧和氢燃料，并在原型中具有足够高的性能和寿命。工作将集中在这两个设备设计的各个方面，从材料选择到可制造性，并最终在真空室中进行广泛的测试活动，以模拟太空条件。

Most satellites built to date manoeuvre in space using two very different types of thrusters and propellants. High thrust functions are met by extremely toxic chemical fuels (Hydrazine) that are costly and challenging to handle as they are lethal to humans from brief exposure. Where high fuel efficiency is required and low thrust can be accepted, electric propulsion (EP) thrusters are used, fed by expensive high purity noble gas (Xenon), stored at very high pressure. These two entirely separate systems are both present on many larger spacecraft platforms to cover the full required ranges of thrust and fuel efficiency. Alternative low-cost and non-toxic propellants have been increasingly adopted for small satellites, where their price and handling advantages have a particularly high impact.Our project's ultimate goal is to replace both Xenon and Hydrazine with water, the ultimate green, low-cost propellant, for both chemical and electric propulsion functions in large satellites. The proposed HYDRA system concept electrolyses water on-demand during a mission into oxygen and hydrogen. The project is focussed on the EP sub-system: development of a Water ElecTrolysis Hall Effect Thruster (WET-HET), which ionises and accelerates positively charged oxygen to the very high speeds required for fuel efficiency. This is combined with an electron-emitting hollow cathode device, fed with hydrogen, required to keep the spacecraft charge-neutral. Both of these device types have not been used with those propellants in spaceflight to date. For the higher thrust impulses required by the satellite, these two gasses will in addition be used in a chemical bipropellant thruster, ICE. This allows a spacecraft to fly with both fuel efficient electrical and high thrust chemical propulsion options, but a single low pressure water propellant tank, propellant management system, and associated hardware. This completely novel overall architecture allows a full spectrum of mission scenarios that are not possible with either technology alone, without the cost and mass penalties of flying two completely separate systems and propellants, at the very low propellant price and high storage density of water.The project focusses on the technical and engineering challenge of adapting existing technology concepts of Hall Effect thrusters and neutralizers to run on the unconventional oxygen and hydrogen fuels, in prototypes with sufficiently high performance and lifetime. Work will focus on all aspects of these two device designs from material selection to manufacturability, and culminate in extensive test campaigns in vacuum chambers to simulate the conditions of space.