## 1 Introduction  
The large cabin of a spacecraft is an important part of space information transmission equipment and core weapons of military defense, as well as a major guarantee for national security and the national economy. Its development level is a concentrated reflection of the manufacturing capability of high-end aerospace equipment. A large spacecraft cabin has the significant characteristics of large size, being lightweight, having a complex structure and so on. At present, existing research outcomes for the large cabin body multi-mounting surface combination milling mostly use large special machine tools or off-line split processing combined with an online repair manufacturing mode. But there are still problems such as unstable and complex process, poor flexibility, long cycle and so on. In recent years, the in-site machining operation mode of mobile robots has emerged with a strong environmental adaptability and high processing efficiency, which has become an effective way to solve the problems of efficient and high precision manufacturing of the large spacecraft cabin [1, 2, 3]. For example, the mobile robot processing system for large aircraft parts studied by the Fraunhofer Association [4], the mobile robot wind turbine blade grinding system proposed by KUKA and the KUKA MRP robot arm movement base oriented towards aircraft skin hole assembly [5], and the mobile processing robot equipment for aircraft fuselage drilling and riveting developed by Zhejiang University [6], etc. In order to meet the requirements of flexibility, machining efficiency and machining accuracy of mobile robot in-site machining operating systems, research on equipment realization, machining mode construction and multi-scale measurement methods of mobile robots have been carried out extensively in recent years. In the field of mobile robot equipment realization, the American Electroimpact (EI) company replaced the KUKA robot control system with the 840 Dsl numerical control system, combined with joint secondary feedback technology to achieve accurate robot control, and launched the accurate robot system secondary feedback using a grating ruler. Their positioning accuracy is better than 0.25 mm. This achievement has been applied to drilling, riveting and milling of large thin-walled components in the aerospace field [7, 8]. Based on EI's program, the German Fraunhofer Association's mobile milling robot provides real-time feedback compensation for T-Mac online measurement results through a Universal Compensation Interface, and the trajectory accuracy reaches 0.27 mm [9]. A NC driven mobile milling robot was developed by Beijing Spacecrafts Manufacturing Co., LTD. Its accuracy was improved by the NC system construction, grating compensation, kinematic parameter calibration, high precision estimation and stiffness compensation [10, 11]. In the field of construction of mobile robot processing modes, the team of [PERSON] of Huazhong University of Science and Technology proposed the \"measurement-operation-processing integration\" scheme of mobile robots in cooperation with Tsinghua University, Beijing Spacecrafts Manufacturing Co., LTD., and realized the variable thickness grinding of aircraft assembly gaskets [12]. For aerospace large carbon fiber composite structure milling, the Fraunhofer Association obtains the reference point coordinates through digital measurement and combines the best fitting method to realize the \"position-finding--machining\" manufacturing process of mobile milling robots [13]. In the field of multi-scale measurement methods for mobile robots, the team of [PERSON] from Dalian University of Technology proposed a combined measurement method with a 3D scanner, laser tracker and industrial robot as positioning devices to realize high-precision measurement, aiming at the contradiction between global measurement and local precision measurement control in 3D digitalization of key local features of large-size parts [14].