The use of innovative ideas and the latest technology have undoubtedly brought down telescope costs substantially. However, there are still ways to further reduce the cost of optical ground-based telescopes and make them affordable to much larger and wide spread astronomical communities. In this and subsequent papers we are presenting our studies carried out towards building affordable mid-size telescopes of 4.0-6.0m in size. In the present era, segmented mirror technology has become the first choice for building moderate to large-size telescopes. In any Segmented Mirror Telescope (SMT) the most important part is its primary mirror control system (M1CS). The conventional M1CS is based on edge sensors and actuators, but such a system introduces many design and implementation complexities. In this paper, we propose to make use of an Off-axis Alignment and Phasing System (OAPS), which is an active mirror kind of control system working in real time to maintain the figure of a segmented primary mirror without the use of edge-sensors. The alignment and phasing system which is an integral part of any segmented telescope can be used in the real time at the off-axis. Through extensive simulations we have explored the feasibility of using an OAPS for co-alignment, co-focusing as well as co-phasing of segmented mirror telescopes. From our simulations we find that the co-alignment and co-focusing of the segments can be achieved with a guide star as faint as 16-18\(^{th}\) magnitude. This implies that seeing limited performance for any segmented telescope can be easily accomplished without use of a complex edge sensor based control system. Whereas, to attain diffraction limited performance, mirror segments need to be co-phased with an accuracy of few tens of nanometers. In our simulations we have used a dispersed fringe sensor based phasing scheme, which can effectively work up to guide stars of 14\(^{th}\) magnitude.

创新理念和最新技术的使用无疑大幅降低了望远镜成本。然而，仍有一些方法可以进一步降低光学地面望远镜的成本，并使规模更大、分布更广的天文学界能够负担得起。在本文和后续论文中，我们将介绍我们为建造经济实惠的 4.0-6.0m 中型望远镜而进行的研究。当今时代，分段镜技术已成为建造中大型望远镜的首选。在任何分段镜面望远镜 (SMT) 中，最重要的部分是其主镜控制系统 (M1CS)。传统的 M1CS 基于边缘传感器和执行器，但这样的系统引入了许多设计和实现的复杂性。在本文中，我们建议使用离轴对准和定相系统（OAPS），这是一种实时工作的主动镜控制系统，可在不使用边缘传感器的情况下保持分段主镜的形状。对准和定相系统是任何分段望远镜的组成部分，可以在离轴处实时使用。通过广泛的模拟，我们探索了使用 OAPS 进行分段镜面望远镜共对准、共聚焦以及共定相的可行性。从我们的模拟中我们发现，可以使用像 16-18 这样微弱的引导星来实现各段的共同对准和共同聚焦 对准和定相系统是任何分段望远镜的组成部分，可以在离轴处实时使用。通过广泛的模拟，我们探索了使用 OAPS 进行分段镜面望远镜共对准、共聚焦以及共定相的可行性。从我们的模拟中我们发现，可以使用像 16-18 这样微弱的引导星来实现各段的共同对准和共同聚焦 对准和定相系统是任何分段望远镜的组成部分，可以在离轴处实时使用。通过广泛的模拟，我们探索了使用 OAPS 进行分段镜面望远镜共对准、共聚焦以及共定相的可行性。从我们的模拟中我们发现，可以使用像 16-18 这样微弱的引导星来实现各段的共同对准和共同聚焦\(^{th}\)幅度。这意味着无需使用复杂的基于边缘传感器的控制系统，就可以轻松实现任何分段望远镜的有限性能观察。然而，为了获得衍射极限性能，镜段需要以几十纳米的精度同相。在我们的模拟中，我们使用了基于分散条纹传感器的定相方案，该方案可以有效地引导 14 \(^{th}\)星等的恒星。