Development of an artificial radio transmitter on the Moon for precise measurement of lunar physical librations, tides and gravity fields

为了精确测量月球物理振动和月球潮汐，我们研制了一种用于差分VLBI的人工无线电发射机。我们于1992年底完成了2.2GHz发射机、电池包、定时器和天线的整体系统，并证实了系统的频率稳定性优于10 ^<-6>，并能在10000 g （1g=9.8ms ^<-2>）加速度下存活，这相当于从200Km高度的月球轨道飞行器上坠落的发射机撞击月球表面时所接收到的加速度。我们制备了与月球风化层具有相似电学特性的沙子，并通过改变天线表面与沙子表面之间的深度和距离，测量了埋在沙子中的发射机发出的连续波无线电信号的辐射模式和强度。由此得出了发射机在月球上应满足的条件。本研究的特点是：1)研制了能承受月球表面硬着陆的无线电发射机；2)研制了一种差分VLBI方法，该方法可以精确测量月球上两个射电源之间的角距离，消除了大气波动的影响。我们证实，差分VLBI可以确定月球物理振动的振幅，精度为10 ^<-5>，比以前的结果提高了10倍，月球潮汐的精度为10 ^<-1>。这种无线电发射机将在行星科学中具有巨大的功率和可能性和广泛的应用。建立了在月球表面硬着陆设置无线电发射机的方法，为研究行星科学开辟了一条新的途径。

We have developed an artificial radio transmitter for differential VLBI in order to measure lunar physical librations and lunar tides precisely. We completed the total aystem including a 2.2GHz transmitter, a battery package, a timer and an antenna by the end of 1992, and confirmed that the frequency stability is better than 10 ^<-6> and that the system can survive under acceleration of 10,000g (1g=9.8ms ^<-2>), which is equivalent to that received when the transmitter dropped from a lunar orbiter on the altitude of 200Km collides to the lunar surface. We prepared sands which have similar electrical properties to the lunar regolith, and measured radiation patterns and intensities of CW radio signals emitted from the transmitter buried in the sands by changing the depth and the agale between the anttena surafce and the sand surface. As the results, we could obtain the condition which the transmitter should satisfy on the Moon.This research is characterized by 1)development of the radio transmitter tolerating a hard landing on the lunar surface and 2)development of a method of the differential VLBI which can measure an angular distance between two radio sources on the Moon precisely, eliminating the effect of atmospheric fluctuation. We confirmed that the differential VLBI can determine the amplitude of the lunar physical librations with an accuracy of 10 ^<-5>, which is 10 times better than the previous results, and that of the lunar tides with an accuracy of 10 ^<-1>, respectively.This radio transmitter will have great power and possibilities and wide applications in planetary science. The method of setting the radio transmitter on the lunar surface by hard landing has been established and a new approach into the planetary science has been prospected through this research.