基于着陆器地基测量的火星定向参数确定

Mars orientation parameters determination based on direct-to-Earth measurement

火星定向参数的精确测定对约束火星内部结构以及极区干冰变化的建模具有重要意义.基于未来的火星着陆任务,仿真分析了利用双程多普勒与距离测量方法直接跟踪着陆器,解算火星定向参数所能达到的精度.结果表明,通过双程多普勒和双程测距直接跟踪火星着陆器超过200个工作日,将显著提高火星岁差、章动以及日长变化参数的精度,约800个工作日后,岁差参数精度可较目前提高5–10倍,章动参数精度可达到10–30 mas,日长变化与钱德勒摆动参数精度可收敛至5–10 mas,这一精度水平可以满足研究火星内部结构与大气物质交换的需要.通过分析不同纬度着陆器的解算结果,发现高纬度的着陆器有必要进行距离测量,以保持岁差和章动参数的解算精度.此外,研究还发现,当火星星历误差小于75 m时,双程多普勒数据解算火星定向参数的精度不受影响,而对于双程测距数据来说,只有当火星历表精度优于0.15 m时,定向参数的解算结果才具有可信性.

The Mars orientation parameters(MOPs)are important information for constraining Martian interior properties,ice caps sublimation,and condensation process.Considering the future Mars landing mission,we performed numerical simulations of MOP determination using direct-to-Earth radio signals.The results suggest that after 200 d of tracking using high-quality levels of both two-way Doppler and two-way range measurements,the MOP uncertainties will be significantly reduced.Then,after about 800 mission days the accuracy of precession parameters will be improved by 5–10 times compared with the present.Also,the accuracy of nutation parameters will reach 10–30 mas,and the accuracy of length-of-day and Chandler wobble parameters will reach 5–10 mas,which meets the need to investigate the internal structure of Mars and the dynamics of the atmosphere.By analyzing the solution results of different latitude landers,twoway range data can provide a good complement to two-way Doppler data.Therefore,it is necessary to perform a twoway range measurement for a high-latitude lander.In addition,the study has also found the limit of the ephemeris error of Mars for MOP determination.When using the two-way Doppler data,the ephemeris error should not be more than 75 m;and for the two-way range measurement,the error should be less than 0.15 m.