Objective The linear motor-driven electromagnetic launch drop tower represents a new generation of microgravity simulation facilities. It overcomes the limitations of free-fall drop towers, such as low microgravity quality and limited experiment cycles, thereby enhancing experimental efficiency and data accumulation. With the increasing demand for longer microgravity durations, it is essential to build taller drop towers has become an inevitable trend. However, engineering implementation faces increasing challenges, including deformation and stability of ultra-tall tower structures and straightness deviations in linear guide rail installation, which can induce vibrations in the drop cabin and adversely affect experimental results. Therefore, establishing high-precision three-dimensional (3D) measuring technology suitable for ultra-tall spatial structures is a fundamental prerequisite to ensure precise guide rail installation and the long-term stable operation of the facility.

Methods Conventional structural measurement techniques, such as plumb lines, surveying robots, and terrestrial laser scanners, typically maintain millimeter-level accuracy, which falls out of the stringent sub-millimeter accuracy requirements. To address it, this paper proposes a multi-station laser tracker measurement method that combines high accuracy with wide spatial coverage. First, the measurement principle of the multi-station laser tracker system is introduced based on the coordinate transformation. Next, taking a 20-meter drop tower project as an example, repeatability tests of the laser tracker in vertical space were conducted to verify its reliability under such actual working space. Simultaneously, a 24-hour monitoring of temperature and 3D coordinates was performed using multiple laser tracker stations and weather stations to analyze the correlation between structural point deformation and ambient temperature. Finally, based on the repeatability error of the measured points mentioned above, the measurement accuracy of the multi-station laser tracker method was simulated within the 3D space of a 150 m high microgravity drop tower.

Results and Discussions The experimental results demonstrated that the laser tracker achieved a repeatability better than ± 0.14 mm in single-station measurements over a 20 m vertical range (Tab.2). Deformation observed at the tower's measurement points was primarily driven by temperature fluctuations, with the top of the tower exhibiting a maximum deformation of up to 0.91 mm (Fig.5). Based on the established correlation between relative deformation displacement and temperature variation, it is recommended the ambient temperature fluctuations are limited to ±0.25 ℃ during high-precision measurement and installation of the drop tower’s precision guide rails (Tab.3). In the simulated multi-station measurement for a 150 m drop tower, the global point error RMS of the common points was 0.11 mm when temperature effects were neglected, while the average and maximum measurement uncertainty were 0.2 mm and 0.56 mm, respectively (Tab.4).

Conclusions To meet the demand of high-precision 3D point measurement in ultra-tall vertical structures such as microgravity drop towers, this paper proposes a multi laser tracker station measurement method. Field measurements conducted on a 20-meter drop tower verified the reliability of laser trackers for vertical space metrology. Pre-engineering multi-station tests were also performed to evaluate actual structural deformation and its constraints on precision alignment. Through the integration of experimental data and simulation, the design scheme is subsequently optimized. The findings demonstrate that the multi-station measurement method is suitable for ultra-tall vertical structures—enabling sub-millimeter level alignment and stability control for drop tower facilities. Moreover, the work provides reliable practical experience for precision surveying and alignment in similar high-precision projects, such as ultra-tall buildings, large-scale scientific installations, and aerospace launch structures. For future research, the deployment scheme will be optimized to address line-of-sight obstructions by integrating site-specific conditions, such as spatial constraints, structural occlusions, and environmental vibrations. Furthermore, a practical and implementable measurement protocol will be developed to realize the optimal measurement strategy for real-world engineering applications.