Predicting residual friction angle of lunar regolith based on Chang'e-5 lunar samples.

With the rapid development of human lunar exploration projects, the lunar base establishment and resource utilization are on the way, and hence it is urgent and significant to reasonably predict engineering properties of the lunar regolith, which remains to be unclear due to limited lunar samples currently accessible for geotechnical tests. In this contribution, we aim to address this outstanding challenge from the perspective of granular material mechanics. To this end, the 3D multi-aspect geometrical characteristics and mechanical properties of Chang'e-5 lunar samples are for the first time evaluated with a series of non-destructive microscopic tests. Based on the measured particle surface roughness and Young's modulus, the interparticle friction coefficients of lunar regolith particles are well predicted through an experimental fitting approach using previously published data on terrestrial geomaterials or engineering materials. Then the residual friction angle of the lunar regolith under low confining pressure is predicted as 53° to 56° according to the particle overall regularity and interparticle friction coefficients of Chang'e-5 lunar samples. The presented results provide a novel cross-scale method to predict engineering properties of the lunar regolith from particle scale information to serve for the future lunar surface engineering construction.

First measurements of low-energy cosmic rays on the surface of the lunar farside from Chang'E-4 mission.

Human activities on the lunar surface are severely constrained by the space radiation dominated by cosmic rays (CRs). Here, we report the first measurements of the low-energy (about 10 to 100 MeV/nuc) CR spectra on the lunar surface from China's Chang'E-4 (CE-4) mission around the solar minimum 24/25. The results show that for the proton, helium, CNO, and heavy-ion groups, the ratios (ratio errors) of the CE-4 fluxes to those from the near-earth spacecraft are 1.05 (0.15), 1.30 (0.18), 1.08 (0.16), and 1.24 (0.21), respectively, and to those predicted by the models [CRÈME96 and CRÈME2009] are instead [1.69 (0.17), 2.25 (0.23)], [1.66 (0.17), 1.76 (0.18)], [1.08 (0.11), 1.07 (0.11)], and [1.33 (0.18), 1.17 (0.15)]. Moreover, a notable enhancement of 3He/4He ratio is observed at ~12 MeV/nuc, and the CR dawn-dusk symmetry is confirmed. These results provide valuable insights into the CRs on the lunar farside surface and will benefit future lunar exploration.

Drop tower tests of Taiji-1 inertial sensor substitute.

Taiji-1, which is the first technical verification satellite of China's Space Gravitational Wave Detection Program, was successfully launched on August 31, 2019. The mission aimed to investigate the key technologies used in space gravitational wave detection. The inertial sensor, which was one of the main payloads, measured the residual acceleration of the satellite, and verified the drag-free control technology. Its performance was crucial to the success of the Taiji-1 mission. To ensure its performance in orbit, the inertial sensor was fully evaluated prior to launch. Owing to the gravitational acceleration on the ground, it is impossible to verify all the properties of the inertial sensor in a routine laboratory. A feasible method to conduct such tests is to use a drop tower. To guarantee the safety of the inertial sensor, a substitute was used with similar structure and circuit design. A total of 20 falls in three groups were completed, a set of research methods was established, and the importance of conducting simulations before the drop tests was verified. For the first time, the switch of different circuit gains in a drop tower test has been achieved and the National Microgravity Laboratory of China (NMLC) drop tower's residual accelerations in three dimensions were measured. The results demonstrated that the microgravity level of the drop tower can reach about 58 µg0 in the fall direction and 13 µg0 along the horizontal axes.

Optimized sleeve monopole antenna for detection of electrostatic discharge radiation of spacecraft solar array.

The spacecraft operating on a geosynchronous orbit (GEO) is affected by the plasma environment and is prone to electrostatic discharges (ESD) that affect the safe operation of the spacecraft, especially solar array, radiating electromagnetic (EM) signals of a few MHz to tens of MHz. The capture of radiated EM signals helps to better study the characteristics and suppress the occurrence of ESD. In this paper, based on the frequency band characteristics of the EM wave signal radiated by ESD in space, a novel optimized compact sleeve monopole antenna is designed by using three-dimensional EM field simulation software High Frequency Structure Simulator. The length of the proposed antenna is only about 52 mm and its center frequency is 30 MHz. The frequency band of the voltage standing wave ratio (VSWR) less than 2 is 28.8-31.1 MHz and that of less than 5 is 26.8 MHz-33.2 MHz, and the bandwidth is 21.3%. The sample preparation and VSWR test by using the vector network analyzer were carried out. Finally, the sensitivity test was carried out in an EM shielding room by the piezoelectric ceramic ESD simulation experiment. The test results show that the designed antenna can receive the EM wave signal radiated by the ESD stably and can be used for spacecraft discharge detection.