In this paper, in situ synthesis of 3D-graphene/MnO2 foam composite using the combination of chemical vapor deposition and hydrothermal method was reported for producing highly efficient graphene/metal oxide-based hybrid supercapacitors. The in situ conformal growth of 3D-graphene/MnO2 composite exhibited high crystallinity and low contact resistance, thereby improving the charge transport efficiency of the electrolyte. Compared with the previously described MnO2-based counterparts, the porous structure of the 3D conductive graphene foam permitted electrolyte ions to rapidly move around the surface of MnO2. In the supercapacitor, the 3D-graphene/MnO2 composite electrode in the absence of carbon black showed high specific capacitance (333.4 F g−1 at 0.2 A g−1) with excellent cycling stability. This technical approach for fabrication of 3D-graphene/MnO2 composite provides a promising means in the production of energy storage electrode materials for designing high performance supercapacitor devices.

With more and more missions around the Moon, a communication/navigation constellation around the Moon is necessary. Halo orbits, due to their unique geometry, are extensively studied by researchers for this purpose. A dedicated survey is carried out in this work to analyse the coverage ability of halo orbits. It is found that a two-satellite constellation is enough for continuous one-fold coverage of the north or the south polar regions but never both. A three-satellite constellation is enough for continuous one-fold coverage of both north and south polar regions. A four-satellite constellation can cover nearly 100% of the whole lunar surface. In addition, the coverage ability of another special orbit – distant retrograde orbit (DRO) – is analysed for the first time in this study. It is found that three satellites on DROs can cover 99·8% of the lunar surface, with coverage gaps at polar caps. A four-satellite constellation moving on spatial DROs can cover nearly the whole lunar surface. By combining halo orbits and DROs, we design a five-satellite constellation composed of three halo orbit satellites and two DRO satellites. This constellation can provide 100% continuous one-fold coverage of the whole lunar surface.

A comprehensive study on the autonomous orbit determination (AOD) performance of satellite pairs in halo orbits and distant retrograde orbits (DROs) is carried out. A factor called dynamic and geometric dilution of precision (DAGDOP) is proposed to simultaneously incorporate influences from the dynamics and geometry of satellite pairs. Based on the DAGDOP, the effect of different observation arcs on the AOD accuracy is investigated. Next, the AOD accuracy of three different types of satellite pairs-halo+halo, DRO+DRO, and halo+DRO-is systematically analyzed. The hybrid halo+DRO type shows the best overall accuracy. Finally, the AOD performance of the hybrid type is verified in a realistic model. Our studies find that the average AOD accuracy of the halo orbit is about 170 meters, and that of the DRO is about 190 meters. The relative time synchronization error of two satellites is less than 30 nanoseconds.