主反射镜的口径大小与结构形式在极大程度上决定了空间望远镜的技术难度与经济成本。为了实现更高的空间分辨率与更强的信息收集能力，各国研制的空间望远镜主反射镜的口径朝着越来越大的趋势发展，从“哈勃空间望远镜”(HST)的24 m，到“新世界观测者空间望远镜”(NWO)的4 m，甚至到“先进技术大口径空间望远镜”(ATLAST)的8 m，无不体现了对超大口径空间观测能力的追求。而单块式主镜凭借其支撑技术的可靠性与经济性，正成为超大口径空间望远镜的首选。通过对国外研制的超大口径空间望远镜的论述与分析，探讨了目前空间望远镜中超大口径主反射镜的关键技术与发展方向。针对目前国内运载能力与光学制造加工能力的极限，提出了建造基于35 m口径主镜的空间望远镜设想。

The aperture and structural configuration extremely determine the technical difficulty and economic cost of a spaceborne telescope. In order to realize higher spatial resolution and capacity of acquisition of information, the aperture of primary mirror of space telescope abroad is getting larger and larger. From the 24 m aperture of the Hubble Space Telescope(HST), to the 4 m aperture of the New World Observer(NWO), up until to the 8-m aperture of the Advanced Technology Large Aperture Space Telescope(ATLAST), all without exception embodies pursuing the high capacity of ultra-large aperture observation. Monolithic primary mirror is becoming the first choice of ultra-large aperture space telescope by right of its technical reliability and economical efficiency. Through analysis and discussion on developing ultra-large aperture space telescopes abroad, the key techniques and trend of development of ultra-large aperture primary mirror are investigated. Then we proposed the assumption to build a 35 m aperture space telescope with a monolithic primary mirror based on the state-of-art capacity of lunching and optical fabrication in China.