Fast computation of the landing footprint of a space-to-ground vehicle is a basic requirement for the deployment of parking orbits, as well as for enabling decision makers to develop real-time programs of transfer tra...Fast computation of the landing footprint of a space-to-ground vehicle is a basic requirement for the deployment of parking orbits, as well as for enabling decision makers to develop real-time programs of transfer trajectories. In order to address the usually slow computational time for the determination of the landing footprint of a space-to-ground vehicle under finite thrust, this work proposes a method that uses polynomial equations to describe the boundaries of the landing footprint and uses back propagation(BP) neural networks to quickly determine the landing footprint of the space-to-ground vehicle. First, given orbital parameters and a manoeuvre moment, the solution model of the landing footprint of a space-to-ground vehicle under finite thrust is established. Second, given arbitrary orbital parameters and an arbitrary manoeuvre moment, a fast computational model for the landing footprint of a space-to-ground vehicle based on BP neural networks is provided.Finally, the simulation results demonstrate that under the premise of ensuring accuracy, the proposed method can quickly determine the landing footprint of a space-to-ground vehicle with arbitrary orbital parameters and arbitrary manoeuvre moments. The proposed fast computational method for determining a landing footprint lays a foundation for the parking-orbit configuration and supports the design of real-time transfer trajectories.展开更多
This paper calculates the land (including water area) requirement for food consumption in both balanced andactual diet in China by ecological footprint analysis. To determine whether logical and actual food demands ar...This paper calculates the land (including water area) requirement for food consumption in both balanced andactual diet in China by ecological footprint analysis. To determine whether logical and actual food demands are withinnatural regenerative ability, carrying capacity (excluding forestry production) is also calculated. Results show that actualdiet patterns were ecologically friendly in the period of 1982-2004 in China, mainly because of the rural moderate dietpatterns. But actual per capita footprint already overran its corresponding logic value of 0.976ha in urban areas in 2002.Productive areas for food production can satisfy the land requirement for actual diet patterns during the researchingperiod in China, nevertheless cannot satisfy that for balanced diet pattern or solve the problem of unbalanced ecologicalfootprint. The continual rising ecological footprint of food consumption in both rural and urban areas indicates that percapita footprint will keep on increasing in China and even may be more than the suggested logic value if no relevantcountermeasures are made to regulate diet patterns. Strictly speaking, China is facing food shortage, both in quality andin quantity.展开更多
基金supported by the National Natural Science Foundation of China (61603398)。
文摘Fast computation of the landing footprint of a space-to-ground vehicle is a basic requirement for the deployment of parking orbits, as well as for enabling decision makers to develop real-time programs of transfer trajectories. In order to address the usually slow computational time for the determination of the landing footprint of a space-to-ground vehicle under finite thrust, this work proposes a method that uses polynomial equations to describe the boundaries of the landing footprint and uses back propagation(BP) neural networks to quickly determine the landing footprint of the space-to-ground vehicle. First, given orbital parameters and a manoeuvre moment, the solution model of the landing footprint of a space-to-ground vehicle under finite thrust is established. Second, given arbitrary orbital parameters and an arbitrary manoeuvre moment, a fast computational model for the landing footprint of a space-to-ground vehicle based on BP neural networks is provided.Finally, the simulation results demonstrate that under the premise of ensuring accuracy, the proposed method can quickly determine the landing footprint of a space-to-ground vehicle with arbitrary orbital parameters and arbitrary manoeuvre moments. The proposed fast computational method for determining a landing footprint lays a foundation for the parking-orbit configuration and supports the design of real-time transfer trajectories.
文摘This paper calculates the land (including water area) requirement for food consumption in both balanced andactual diet in China by ecological footprint analysis. To determine whether logical and actual food demands are withinnatural regenerative ability, carrying capacity (excluding forestry production) is also calculated. Results show that actualdiet patterns were ecologically friendly in the period of 1982-2004 in China, mainly because of the rural moderate dietpatterns. But actual per capita footprint already overran its corresponding logic value of 0.976ha in urban areas in 2002.Productive areas for food production can satisfy the land requirement for actual diet patterns during the researchingperiod in China, nevertheless cannot satisfy that for balanced diet pattern or solve the problem of unbalanced ecologicalfootprint. The continual rising ecological footprint of food consumption in both rural and urban areas indicates that percapita footprint will keep on increasing in China and even may be more than the suggested logic value if no relevantcountermeasures are made to regulate diet patterns. Strictly speaking, China is facing food shortage, both in quality andin quantity.
