Interferometric fiber optic gyroscopes (IFOGs) are angular velocity measurement sensors based on the Sagnac effect. With the unique advantages of high performance, high sensitivity, anti-irradiation and high reliability as a solid-state technology with no moving parts, IFOGs have become the significant devices of inertial navigation and orbit and attitude control systems on satellites and spacecrafts.

In recent years, satellite technology has developed rapidly, especially in low-orbit, miniaturized, and high-throughput satellite technology. According to the Union Concerned Scientists (UCS) satellite database, as of January 1, 2022, 4852 satellites were in orbit around the Earth, of which 511 belonged to China. The development of satellite technology has put forward new requirements for IFOGs in space. On the one hand, it is a high-reliability technology. In the satellite fault analysis, the failure rate of the orbit and attitude control subsystems is always at a high level. As the core component of the orbit and attitude control subsystems, in the design process of the IFOGs, ensuring reliability should always be put in the first place. From high-intensity vibration during launch to galactic cosmic radiation, high-energy particles, thermal vacuum, etc. after entering orbit, the complex and harsh space working environments require that IFOGs must be fully prepared in terms of resisting external disturbances and improving environmental adaptability. Especially in the high orbit, high inclination, and deep space operation environment, the energy, dose rate, and cumulative radiation dose of space particles are greatly increased. It is significant to improve the anti-irradiation performance of IFOG components. On the other hand, it is a miniaturization technology. While ensuring lifetime and performance, the device with lower power consumption, lighter weight, and lower cost is always a better choice. Resources will be further limited when applied to small satellites especially. Therefore, research on miniaturization is necessary to enhance the competitiveness of IFOGs in low or medium precision applications.

At present, the IFOG products of industrial sectors in Europe and the US have been applied in the space field in batches. The companies including iXblue in France, Northrop Grumman and Honeywell in the US, and Optolink and Fizoptika in Russia have rich experience in the development and application of spacial IFOGs. With the continuous miniaturization and environmental adaptability improvement, IFOG products are increasingly used in various small spacecrafts. In recent years, with the development of related technology, the level of domestic IFOGs has conjointly been rapidly improved, which play roles in a growing number of space missions, such as Tiangong-1, Shenzhou series spacecrafts, Chang’e series of lunar probes and several in-orbit satellites. After years of research, Beihang University starting from the two routes of high-reliability and miniaturization has successively made breakthroughs in key technologies such as structural configuration optimization, detection technology innovation, functional density improvement, and components upgrading of IFOGs for space. Several spacial IFOGs developed by Beihang University are working stably on more than 60 in-orbit satellites.

This paper reviews several key technologies of IFOGs for space applications developed by Beihang University. The dual-light-source four-axis IFOG solution is first introduced (Fig. 3), and the in-orbit fault diagnosis technology of IFOGs is described (Fig. 4). This is based on the desire for high reliability and downsizing. It has significant advantages over the conventional six-independent-axis redundancy approach in terms of weight, dimension, and power consumption while achieving double backup. The configuration of miniature three-axis IFOGs and the simplest three-axis configuration made possible by time-division multiplexing (TDM) technology are introduced in order to further realize downsizing (Fig. 5). Including source backup, the reliability can be increased. Additionally, an IFOG design based on polarization-maintaining photonic crystal fiber (PM-PCF) is demonstrated to further enhance the anti-irradiation performance. The typical IFOG products for space developed by Beihang University are presented in Table 3.

The IFOGs should be highly reliable due to the hostile space environment. The dual-light-source four-axis arrangement that was presented offers double backup for all of the IFOG components, considerably increasing reliability. The in-orbit fault diagnosis approach is typically applicable to multi-axis IFOGs, which enhances the IFOG’s environmental adaptability while avoiding additional costs associated with all-digital implementation. In order to prevent resource waste brought on by excessive redundancy, a more focused redundant backup is designed for space applications with relatively mild operating environments based on the failure modes and failure rate of components in space. The simplest scheme of the three-axis IFOG could be achieved by the TDM technology. The mass, volume, power consumption, and cost will be significantly decreased, and the device shrinking makes it more appropriate for tiny spacecraft like small satellites. The introduction of the PCF scheme demonstrates an important development trend for IFOGs: improved anti-irradiation properties due to low radiation induced attenuation (RIA) of PCF.