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日本也要搞卫星导航,能比得过“北斗”吗?

2017-09-04 09:53:30   中国青年网

据新华社消息,8月下旬,日本利用H2A火箭将导航卫星“引路”3号送入预定轨道,这朝着日本初步构建独立的卫星导航系统“准天顶”又迈进了一步。不过,与我们的“北斗”导航系统相比,“准天顶”能占到便宜吗?以下是文章作者的想法:

8月下旬发射的这颗卫星,是日本准天顶系统(Quasi-Zenith Satellite System)的第三颗卫星。

这是一个区域性的卫星导航系统,所发射的信号与GPS系统的卫星一样,所以它相当于是GPS系统在日本及其海域的一个补充。

三颗卫星分布在43度左右的地球同步轨道上(周期也是24小时),所以它们会一直停留在一个经线附近,也就是日本附近。

图片来自Wikipedia

准天顶地面轨迹图是这样的:

这样做是有一定意义的,因为日本多为山区和森林,城市里高楼林立,容易遮挡GPS信号。如果有更高且额外多出来的辅助卫星(GPS卫星才20000公里高,而准天顶要36000公里高)作为参考,就更容易实现定位,提高定位速度和定位精度。

但显然更多的意义在于日本并不想在卫星导航领域被甩开太远,于是一定要跟上大家脚步,跟着美国的好处在于可以全版学习,毕竟双方是盟国关系。但日本也因此被压制,不可能搞出自己的全球卫星导航系统。

印度也曾经弄过一个类似于准天顶的系统,完全依赖GPS。结果印巴冲突时美国表示公平起见,把双方的GPS信号全关了,于是印度的系统完全瞎掉……所以印度决定不跟美国玩,现在做了自己的独立卫星导航系统(Indian Regional Navigation Satellite System),不过只是针对印度和印度洋。

印度目前的系统

前车之鉴,日本因此也想把这个准天顶系统扩展到7颗,摆脱目前仅仅是个依赖于GPS的区域导航系统的命运。计划在两年内完成这个目标。

然而准天顶真心比起其他国家太弱了。导航卫星最核心的部件就是原子钟,准天顶原计划用铷原子钟过渡到高级的氢原子钟。结果氢原子钟并未研制成功,导致它现在用的钟质量实在太差,比起前辈的GPS卫星铯原子钟都相去甚远。如果完全摆脱GPS系统,估计建成后也是精度很一般的导航系统。

而我国早在2015年发射的第20颗北斗卫星上,就已经使用了最为高大上的氢原子钟,天宫二号还实现了人类历史上首次空间冷原子钟实验。而且我国还是唯一一个采用地球静止、倾斜地球同步和中高轨道结合的卫星导航系统,独一无二。

中美两家的太空PK

日本这颗卫星就和北斗的倾斜地球同步轨道是一个道理,但显然我国要高大上太多了。

目前的全球性卫星导航系统,就只有美国和中国两家在拼,美国由于起步早、技术成熟、在市场化方面占有巨大优势,我国目前进步神速且国内市场巨大未来完全有一拼,但北斗毕竟还没有完全建好。俄罗斯和欧盟在抢第三的位置,俄罗斯在加速恢复格洛纳斯系统,欧盟也在抓紧发射已经被延后了10年多的伽利略系统。

而日本还排在印度后面,但这两个国家都只是地区性的系统而已。

(本文为作者在知乎的回答,观察者网获授权转载)

责任编辑:高宗影 CN060
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