低温推进剂无损贮存技术试验研究进展

液氢/液氧等低温推进剂,由于其高性能优势被作为深空探索使用推进剂,但低温推进剂长时间在轨应用,主要受限于低沸点的推进剂受热蒸发所带来的贮箱压力控制和蒸发损失等一系列问题,需要发展低温推进剂无损贮存技术来解决。文章介绍了应用低温制冷机结合换热技术实现贮箱内低温推进剂无损贮存的试验情况,总结其发展趋势和展望。     

低温推进剂的温度控制

通过对低温火箭三子级地面试验和多次飞行试验的分析及国外有关资料的报导，总结出影响低温推进剂温度的相关因素及控制方法，对新型的增压系统及温控技术进行了展望。     

低温推进剂在轨压力控制方法及效能对比分析

针对液氢、液氧低温推进剂在轨贮存时长及排气量,建立了直接排气和热力排气数学模型。在0.13—0.14 MPa和0.2—0.3 MPa两种控压区间分析了40 W和100 W漏热环境下的贮箱排气量的对比分析,结果表明液氧易于实现长期无损贮存,而液氢在轨无损贮存时间相对较短,若要实现10天或更长时间的空间任务,有必要对液氢贮箱采用热力学排气技术进行压力控制,降低液氢蒸发量。对基于热力学排气技术的液氢在不同工况下的排气量进行了计算,根据液氢在轨任务时长的要求给出了合适的控压方式选择方向。     

低温推进剂贮箱大面积冷屏热分析及成本优化

运载火箭低温贮箱采用大面积冷屏与多层隔热材料组成的复合结构可以有效减少低温推进剂蒸发损耗,延长低温推进剂在轨贮存时间。通过建立多层隔热材料耦合90 K大面积冷屏的传热模型,获得了引入大面积冷屏后对多层隔热材料层间温度分布及热流密度影响的变化规律,对比了采用冷屏技术和直接对液氢采用主动制冷两种方式,同等条件下采用冷屏在主动制冷系统重量和功耗方面可分别节省60%和64%。研究了低温推进剂不同在轨贮存时间和冷屏安装在多层隔热材料中不同位置时热管理系统重量和功耗成本,以成本最小为目标获得了90 K冷屏布局最优化设计方法。     

火箭低温上面级流体管理技术研究进展

对比了国内外火箭低温上面级的主要技术特征,梳理了关键流体管理技术,对低温推进剂空间热防护技术、在轨气液分离技术、在轨排气技术开展了调研与进展分析。指出新型被动热防护技术应用于上面级可显著拓展上面级的适用范围。热防护技术与上面级结构优化、空间流体管理集成使用可显著降低低温推进剂蒸发损失。金属网幕表面张力式气液分离装置在实现低温推进剂,尤其是液氢全液获取领域具有显著优势。热力学排气系统可实现无夹液排气,但会增大蒸发损失,被动式热力学排气系统可节省推进剂消耗量。我国应重视液氢空间流体科学与管理技术,尽早开发基于液氢/液氧推进剂组合的上面级平台。     

低温推进剂地面加注停放阶段蒸发量分析

建立了一种可以描述低温推进剂加注、停放过程的计算模型,分析了影响低温推进剂加注停放阶段蒸发的主要因素。研究表明:为缩短发射组织时间、优化加注流程、提升推进剂品质,在全系统能力范畴内,低温推进剂加注过程应提高推进剂加注速度,降低推进剂加注温度,尽量减小外界环境漏热率,并适当增加系统排气能力。     

空间低温技术的进展

综合介绍国外，主要是美国、西欧空间低温技术的最新进展。论述超流氦冷却技术及空间飞行中的液氦再供给等在轨机载验证、低温风洞技术、氢浆的制备和应用前景等。重点讨论目前在空间探测过程中最具竞争性的斯特林制冷机和脉管制冷机的最新发展。对可望在空间中应用的毫开（ｍＫ）级３Ｈｅ—４Ｈｅ稀释制冷机和绝热退磁制冷机及其它制冷技术也作简要介绍。最后对发展我国空间低温技术提出了建议。     

火星探测任务中低温推进剂弹性保障策略

为确保在当年发射窗口内具备多次组织加注、发射的机会,成功实施火星探测任务,亟需解决低温推进剂弹性保障问题。结合任务特点,分析了第一窗口准时发射、未加注前推迟发射、加注后推迟发射和加注泄回后重新组织发射4种发射情况;据此建立了低温推进剂筹措模型,识别了推进剂保障关键点;结合生产实际制定了多窗口保障策略,即通过统筹推进剂筹措计划、优化系统准备工作和提升筹措过程可靠性,实现低温推进剂弹性保障。实践证明,弹性保障策略实现了低温推进剂的有效、可靠保障。     

低温推进剂火箭发动机泵出口密度、温度计算的一种新方法

对补燃循环和使用低温推进剂的液体火箭发动机，需要考虑泵出口温度、密度变化对发动机动、静态特性的影响，目前计算泵出口温度、密度的方法存在一定的局限性，本文提出了一种新的计算方法，它根据泵出口推进剂的压力和比焓，利用推进剂的有关热力状态方程来迭代计算泵出口推进剂的密度与温度，具有使用方便，适用范围广和计算精度高的优点，采用最小二乘法拟合了低温推进剂火箭发动机泵出口温度、密度计算所需的热力状态方程，利用本文的方法对低温发动机泵出口密度、温度进行了计算，计算结果与实测值吻合很好。     

低温液体运载火箭推进剂加注过程分析

介绍了国外运载火箭典型低温贮箱的推进剂加注流程,讨论了影响低温推进剂加注特性的主要因素,建立了一种可以描述低温推进剂加注过程的计算模型,结合试验数据验证了模型预示加注过程贮箱推进剂平均温度、气枕压力等关键参数的准确性,进一步依据仿真和试验结果分析了低温推进剂加注过程的典型特性。     

Passive ZBO storage of liquid hydrogen and liquid oxygen applied to space science mission concepts

Liquid hydrogen and oxygen cryogenic propulsion and storage were recently considered for application to Titan Explorer and Comet Nuclear Sample Return space science mission investigations. These missions would require up to 11 years of cryogenic storage. We modeled and designed cryogenic propellant storage concepts for these missions. By isolating the propellant tank’s view to deep space, we were able to achieve zero boil-off for both liquid hydrogen and oxygen propellant storage without cryocoolers. Several shades were incorporated to protect the tanks from the sun and spacecraft bus, and to protect the hydrogen tank from the warmer oxygen tank. This had a dramatic effect on the surface temperatures of the propellant tank insulation. These passive storage concepts for deep space missions substantially improved this application of cryogenic propulsion. It is projected that for missions requiring larger propellant tank sizes, the results would be even more dramatic.     

低温推进剂蒸发量主动控制实验研究

以液氮为研究工质,基于研制的低温推进剂蒸发量主动控制实验平台开展了"零蒸发"贮存实验研究。该实验平台以G-M制冷机作为冷源,通过换热器对500 L液氮贮存容器内部输入冷量,以此控制液氮的蒸发速率,实现液氮的"零蒸发"贮存。实验研究表明,对于液氮贮存空间气相区和液相区分别输入冷量,均能抑制系统压力上升趋势,实现"零蒸发"贮存的目的,其中对于液相区输入冷量效率更高,能够在较短时间内降低系统压力。通过该实验平台上还进行了蒸汽冷却屏控制液氮蒸发速率研究,实验证明通过蒸汽冷却屏可以降低液氮蒸发速率。     

NASA cryocooler technology developments and goals to achieve zero boil-off and to liquefy cryogenic propellants for space exploration

NASA’s interest in human exploration of Mars has driven it to invest in 20 K cryocooler technology to achieve zero boil-off of liquid hydrogen and 90 K cryocooler technology to achieve zero boil-off liquid oxygen or liquid methane as well as to liquefy oxygen or methane that is produced on the surface of Mars. These investments have demonstrated efficiency progress, mass reductions, and integration insights. A history of the application of cryocooler technology to zero boil-off propellant storage is presented. A trade space on distributed cooling is shown, along with the progress of reverse turbo-Brayton cycle cryocoolers, where the specific power and specific mass have dropped, decreasing the mass and power of these cryocoolers. Additionally, the cryocooler technology advancements of recuperators and compressors are described. Finally, NASA’s development ideas with respect to zero boil-off technology are discussed.     

环境压力对低温容器蒸发流量的理论分析和试验验证

建立了用于计算低温容器蒸发流量的数学模型,得出了蒸发流量与环境温度、环境压力之间的关系。结果显示,瞬时蒸发流量变化不但受到环境压力影响,同时还受到环境压力变化率以及容器内液体量的影响。提出了衡量环境压力变化对蒸发流量影响程度的无因次量,讨论了在不同漏热、不同装载量情况下环境压力变化的影响程度。以液氮为工质,对35立方米高真空多层绝热低温容器在不同地点进行了试验,试验结果与计算结果符合较好。     

A new experiment for investigating evaporation and condensation of cryogenic propellants

Passive and active technologies have been used to control propellant boil-off, but the current state of understanding of cryogenic evaporation and condensation in microgravity is insufficient for designing large cryogenic depots critical to the long-term space exploration missions. One of the key factors limiting the ability to design such systems is the uncertainty in the accommodation coefficients (evaporation and condensation), which are inputs for kinetic modeling of phase change.A novel, combined experimental and computational approach is being used to determine the accommodation coefficients for liquid hydrogen and liquid methane. The experimental effort utilizes the Neutron Imaging Facility located at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland to image evaporation and condensation of hydrogenated propellants inside of metallic containers. The computational effort includes numerical solution of a model for phase change in the contact line and thin film regions as well as an CFD effort for determining the appropriate thermal boundary conditions for the numerical solution of the evaporating and condensing liquid. Using all three methods, there is the possibility of extracting the accommodation coefficients from the experimental observations. The experiments are the first known observation of a liquid hydrogen menisci condensing and evaporating inside aluminum and stainless steel cylinders. The experimental technique, complimentary computational thermal model and meniscus shape determination are reported. The computational thermal model has been shown to accurately track the transient thermal response of the test cells. The meniscus shape determination suggests the presence of a finite contact angle, albeit very small, between liquid hydrogen and aluminum oxide.     

Study on effect of liquid level on the heat leak into vertical cryogenic vessels

The diminishing of heat leak into cryogenic vessels can prolong the storage time of cryogenic liquid. With the storage of cryogenic liquid reducing, the heat leak decreases, while the actual storage time increases. Compared with the theoretical analysis, the numerical simulation can more accurately calculate the heat transfer and temperature distribution in the vessel with complex structure. In this paper the steady state heat leak into cryogenic vessels with different liquid level height is analyzed using a finite element model. And liquid nitrogen boil-off method was adopted in experiments to validate the result of numerical simulation. Experimental results indicate favorable agreement with numerical simulation by ANSYS software. The effect of liquid level on heat leak into the cryogenic vessel can be considered in calculation of storage time and structure design.     

Theory to boil-off gas cooled shields for cryogenic storage vessels

An intermediate refrigeration with boil-off gas cooled shields using the boil-off gas stream is an alternative method to the conventional intermediate refrigeration with a cryogenic liquid.By using an analytical calculation method relations are derived, which enable complete predictions about the effectiveness of an intermediate refrigeration with boil-off gas cooled shields as a function of the number of shields for the different stored cryogenic liquids. For this theoretical derivation however, the restrictive assumption must be made that the thermal conductivity of the used insulation material has a constant value between the considered temperature boundaries.For purposes of a more exact calculation a numerical method is therefore suggested, which takes into consideration that the thermal conductivity is temperature-dependent. For a liquid hydrogen storage vessel with a perlite-vacuum insulation e.g., the effectiveness of one shield and its equilibrium temperature are given as a function of the position of the shield in the insulation space.     

Integrated Resonant Self-Pumped Loop and pulse tube cryocooler for cryogenic cooling distribution

Cooling distribution is a vital technology concerning cryogenic thermal management systems for many future space applications, such as in-space, zero boil-off, long-term propellant storage, cooling infrared sensors at multiple locations or at a distance from the cryocooler, and focal-plane arrays in telescopes. These applications require a cooling distribution technology that is able to efficiently and reliably deliver cooling power (generated by a cryocooler) to remote locations and uniformly distribute it over a large-surface area. On-going efforts by others under this technology development area have not shown any promising results.This paper introduces the concept of using a Resonant Self-Pumped Loop (RSPL) integrated with the proven, highly efficient pulse tube cryocooler. The RSPL and pulse tube cryocooler combination generates cooling power and provides a distributive cooling loop that can be extended long distances, has no moving parts, and is driven by a single linear compressor. The RSPL is fully coupled with the oscillating flow of the pulse tube working fluid and utilizes gas diodes to convert the oscillating flow to one-directional (DC) steady flow that circulates through the cooling loop. The proposed RSPL is extremely simple, lightweight, reliable, and flexible for packaging. There are several requirements for the RSPL to operate efficiently. These requirements will be presented in this paper. Compared to other distributive cooling technologies currently under development, the RSPL technology is unique.