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81.
P. Pergola 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The aim of the work is to design a low-thrust transfer from a Low Earth Orbit to a “useful” periodic orbit in the Earth–Moon Circular Restricted Three Body Model (CR3BP). A useful periodic orbit is here intended as one that moves both in the Earth–Moon plane and out of this plane without any requirements of propellant mass. This is achieved by exploiting a particular class of periodic orbits named Backflip orbits, enabled by the CR3BP. The unique characteristics of this class of periodic solutions allow the design of an almost planar transfer from a geocentric orbit and the use of the Backflip intrinsic characteristics to explore the geospace out of the Earth–Moon plane. The main advantage of this approach is that periodic plane changes can be obtained by performing an almost planar transfer. In order to save propellant mass, so as to increase the scientific payload of the mission, a low-powered transfer is considered. This foresees a thrusting phase to gain energy from a departing circular geocentric orbit and a second thrusting phase to match the state of the target Backflip orbit, separated by an intermediate ballistic phase. This results in a combined application of a low-thrust manoeuvre and of a periodical solution in the CR3BP to realize a new class of missions to explore the Earth–Moon neighbourhoods in a quite inexpensive way. In addition, a low-thrust transit between two different Backflip orbits is analyzed and considered as a possible extension of the proposed mission. Thus, also a Backflip-to-Backflip transfer is addressed where a low-powered probe is able to experience periodic excursions above and below the Earth–Moon plane only performing almost planar and very short transfers. 相似文献
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提出了一种同时提高探针馈电单层圆极化微带天线的增益带宽、阻抗带宽及圆极化轴比带宽的方法,解决了传统单馈点单层微带天线阻抗及圆极化轴比带宽较窄的问题。基于环形贴片行波圆极化辐射原理,通过在辐射贴片上方加载一方环形金属贴片,该贴片内外环与辐射贴片边缘等距设计,可调参数少,增加了天线阻抗及轴比宽带,提高了天线增益,同时实现低剖面应用。基于此方法,设计了一款应用于某型号的UHF频段宽带圆极化天线,并加工实物。实测结果表明:该天线电压驻波比(VSWR)<2的带宽达到17.2%(370 MHz~440 MHz),轴比(AR)小于3 dB的带宽达到8.4%(395 MHz~430 MHz),天线带宽内主辐射增益约7 dB左右。设计方法对提高单馈圆极化微带天线的轻小型化、宽带技术水平具有重大意义,应用前景广阔。 相似文献