Electromagnetic compatibility (EMC) evaluation of the SELENE spacecraft for the lunar radar sounder (LRS) observations

In order to achieve the lunar subsurface sounding and planetary radio wave observations by the Lunar Radar Sounder (LRS) onboard the SELENE spacecraft, strict electromagnetic compatibility (EMC) requirements were applied for all instruments and the whole system of the spacecraft. In order to detect the lunar subsurface echoes from a depth of 5 km, the radiated emission (RE) limit was determined to be -10 dBμV/m and the commonmode (CM) current limit to be 20 dBμA. The EMC performance of the spacecraft was finally evaluated in the system EMC test held from Oct. 20 to Oct. 22, 2005. There is no broadband noise but some narrowband noises at a level above the CM-current limit in a frequency range from 4 to 6 MHz, in which radar soundings are operated. Based on the noise spectrum within 4-6 MHz, the noise level of FMCW radar sounder is estimated to be 14 dB lower than the CM-current limit. In the SELENE EMC test, the following new techniques were introduced: (1) systematic control and evaluation of CM-current noises were first performed to improve the spacecraft EMC performance; (2) onboard battery operation was utilized for reduction of ambient broadband noises during EMC measurements.