Astronomical navigation utilizes natural celestial bodies as navigation targets, offering the advantages of being free from external interference and possessing strong autonomy. This method can effectively address the issue of satellite navigation systems being susceptible to interference, which renders satellite/inertial integrated navigation systems inadequate for meeting the safety and high-precision autonomous navigation requirements of airborne platforms. While some airborne platforms are equipped with astronomical navigation systems based on tracking axis and small-field-view star sensors, these systems are burdened by weight and tracking axis errors that affect accuracy. In contrast, large-field-view star sensors, which do not require a tracking axis system, offer significant advantages in terms of accuracy, size, weight, lifespan, maintainability, reliability, and cost. However, despite these benefits, there have been no practical applications or reports of large-field-view star trackers being used at the altitude range of 10-20 km, where most airborne platforms operate. To meet the autonomous navigation equipment needs of airborne platforms, research is being conducted on daytime star-tracking technology for large-field-view star trackers at an altitude of 10-20 km.Based on a thorough analysis of atmospheric background radiation distribution data, this study aims to optimize the working wavelength band for daytime star measurement. It conducts a comprehensive analysis of the capabilities of airborne large-field-view star trackers for daytime star measurement, considering factors such as optical system design, imaging sensor selection, and star measurement accuracy. To test its findings, an engineering prototype of the star tracker was developed and its performance was evaluated through a daytime star measurement experiment on a flight test vehicle.A large-field-view daytime star tracker optical system has been designed and an engineering prototype has been developed for an airborne application. The prototype weighs less than 1.5 kg and has been successfully tested on a flight test vehicle. At altitudes above 8 km, the engineering prototype is capable of multi-star measurement and accurately outputting attitude, with a star measurement capability of over 1.3 magnitude (H-band) (Fig.4). At an altitude of approximately 20 km, the star tracker can reliably detect more than 10 star targets and output stable attitude measurements. In fact, at this altitude, the engineering prototype has a measurement capability of over 2.7 magnitude (H-band) even during the daytime.According to the requirements of a large field-of-view star tracker for an airborne platform, a 10-20 km airborne large field-of-view daytime star measurement technology has been proposed. The atmospheric background radiation, transmittance, and the daytime star measurement ability of the star tracker at the working altitude of the airborne platform were analyzed, including factors such as the number of electrons for each pixel and the number of sky background electrons at an altitude of 10 km. An engineering prototype was designed and a daytime star measurement experiment was conducted. The experimental data showed that the designed star tracker could achieve continuous and stable output at an altitude of more than 10 kilometers during the daytime. Additionally, for the first time, the daytime large field-of-view star measurement was successfully achieved at altitudes of 10-20 km. The daytime star measurement ability of the star tracker could reach the second-class star in the short-wave infrared H-band. High altitude flight tests have demonstrated that the airborne large field-of-view daytime star measurement technology can detect and identify multiple stars at altitudes of 10-20 km, which is of great significance in improving the autonomous navigation and positioning accuracy of airborne platforms.