Satellite networks have many inherent advantages over terrestrial networks and have become an important part of the global network infrastructure. Routing aimed at satellite networks has become a hot and challenging research topic. Satellite networks, which are special kind of Delay Tolerant Networks (DTN), can also adopt the routing solutions of DTN. Among the many routing proposals, Contact Graph Routing (CGR) is an excellent candidate, since it is designed particularly for use in highly deterministic space networks. The applicability of CGR in satellite networks is evaluated by utilizing the space oriented DTN gateway model based on OPNET(Optimized Network Engineering Tool). Link failures are solved with neighbor discovery mechanism and route recomputation. Earth observation scenario is used in the simulations to investigate CGR’s performance. The results show that the CGR performances are better in terms of effectively utilizing satellite networks resources to calculate continuous route path and alternative route can be successfully calculated under link failures by utilizing fault tolerance scheme. 相似文献
Space Very Long Baseline Interferometry (S-VLBI) is an aperture synthesis technique utilizing an array of radio telescopes including ground telescopes and space orbiting telescopes. It can achieve much higher spatial resolution than that from the ground-only VLBI. In this paper, a new concept of twin spacecraft S-VLBI has been proposed, which utilizes the space-space baselines formed by two satellites to obtain larger and uniform uv coverage without atmospheric influence and hence achieve high quality images with higher angular resolution. The orbit selections of the two satellites are investigated. The imaging performance and actual launch conditions are all taken into account in orbit designing of the twin spacecraft S-VLBI. Three schemes of orbit design using traditional elliptical orbits and circular orbits are presented. These design results can be used for different scientific goals. Furthermore, these designing ideas can provide useful references for the future Chinese millimeter-wave S-VLBI mission. 相似文献
Space satellite observations in an electron phase-space hole (electron hole) have shown that bipolar structures are discovered at the parallel cut of parallel electric field, while unipolar structures spring from the parallel cut of perpendicular electric field. Particle-in-cell (PIC) simulations have demonstrated that the electron bi-stream instability induces several electron holes during its nonlinear evolution. However, how the unipolar structure of the parallel cut of the perpendicular electric field formed in these electron holes is still an unsolved problem, especially in a strongly magnetized plasma (Ωe > ωpe, where Ωe is defined as electron gyrofrequency and ωpe is defined as plasma frequency, respectively). In this paper, with two-dimensional (2D) electrostatic PIC simulations, the evolution of the electron two-stream instability with a finite width in strongly magnetized plasma is investigated. Initially, those conditions lead to monochromatic electrostatic waves, and these waves coalesce with each other during their nonlinear evolution. At last, a solitary electrostatic structure is formed. In such an electron hole, a bipolar structure is formed in the parallel cut of parallel electric field, while a unipolar structure presents in the parallel cut of perpendicular electric field.