低轨卫星肼推进剂泄漏估计

Estimation of hydrazine propellant leakage for LEO satellite

针对空间环境对低轨卫星推进系统的影响,以某卫星超寿命运行下的肼推进剂泄漏为例,在讨论卫星轨道倾角、光照角、降交点地方时等参数漂移的基础上,详细分析卫星无姿态控制下的俯仰角速度遥测参数加速变化与干扰力矩来源,随后根据气态方程建立模型,估计质量泄漏率、气体泄漏率、干扰力矩、比冲等参数,最后利用姿态角速度、储箱温度与压力等遥测数据进行检验。结果表明,干扰力矩具有分段线性变化特征,极大值约为3.4μN·m,极小值约0.9μN·m;肼推进剂的质量泄漏率在7.4~13.4μg·s^-1之间变化,初始值相对较大,随后下降并逐渐稳定在8.0μg·s^-1附近;对应的气体泄漏率在0.56~1.18 Pa·L·s^-1之间变化,稳定值约为0.60 Pa·L·s^-1;比冲在121~249 m·s^-1之间,稳定值接近200 m·s^-1。温度对漏气比冲的影响较为明显,温度高则比冲相对较大,反之亦然;温度对干扰力矩也有相应影响,但对质量泄漏率的影响并不明显。泄漏由密封材料性能下降所致,温度对材料老化的影响是其中的关键因素,但肼推进剂的质量泄漏率相对较小,推进系统的产品质量相对较优,能够满足长寿命低轨卫星应用需求。

The propulsion system of a satellite is influenced by the in-flight environment in space.Consequently,to investigate the leakage of propellant from a monopropellant hydrazine propulsion system,a Low Earth Orbit(LEO)satellite is sampled over its devised life.Details regarding orbit shifting,inclination,solar shining angle,and Local Time of Descending Node(LTDN)are discussed.The cause of leakage is attributed to acceleration in the pitch velocity of the satellite when it has no attitude control.A model is presented using the gaseous equation to estimate the parameters of leakage,including mass and gas leakage rates,disturbing torque,and specific impulse.From validation using satellite telemetry data,such as angular velocity and the temperature and pressure of the propellant tank,the estimation results show that the disturbing torque is periodically linear,with maximum and minimum values of approximately 3.4μN·m and 0.9μN·m,respectively.Furthermore,the mass leakage rate of the hydrazine propellant,which varies between 7.4μg·s^-1 and 13.4μg·s^-1,is originally at a high level and then decreases gradually to a relatively stable value of approximately 8.0μg·s^-1.The gas leakage rate varies from 0.56 Pa·L·s^-1 to 1.18 Pa·L·s^-1,stabilizing at 0.60 Pa·L·s^-1,and the specific impulse varies between 121 m·s^-1 and 249 m·s^-1,finally closing at 200 m·s^-1.The temperate of the environment has a relatively stronger influence on the specific impulse and disturbing torque,but not on the mass and gas leakage rates.The specific impulse increases with an increase in the temperature,and vice versa.The leakage is possibly caused by the degradation of the elastomeric seal,mainly due to the ageing of the material,which in turn stems from the varying thermal environment.With a low mass leakage rate,the propulsion system is relatively more reliable and life-sustaining in LEO satellites.It is possible to prolong the dump period of the momentum by avoiding the leakage of the hydrazine propellant,if the environmental temperature is decreased.